Psyc3318 - Perception & Sensation

Front 1

A-beta fiber

Back 1

A wide-diameter, myelinated sensory nerve fiber that transmits signals from mechanical stimulation.

Front 2

A-delta fiber

Back 2

An intermediate-sized, myelinated sensory nerve fiber that transmits pain and temperature signals.

Front 3

abducens (VI) nerves

Back 3

The sixth pair of cranial nerves, which innervate the lateral rectus muscle of the eyeballs.

Front 4

absolute metrical depth cue

Back 4

A depth cue that provides quantifiable information about distance in the third dimension (e.g., his nose sticks out 4 centimeters in front of his face).

Front 5

absolute pitch

Back 5

A rare ability whereby some people are able to very accurately name or produce notes without comparison to other notes.

Front 6

absolute threshold

Back 6

The minimum amount of stimulation necessary for a person to detect a stimulus 50% of the time.

Front 7

absorb

Back 7

To take up something—such as light, noise, or energy—and not transmit it at all.

Front 8

acceleration

Back 8

A change in velocity. Mathematically, acceleration is the derivative of velocity. In words, linear acceleration indicates a change in linear velocity; angular acceleration indicates a change in angular velocity.

Front 9

accessory olfactory bulb (AOB)

Back 9

A smaller neural structure located behind the main olfactory bulb that receives input from the vomeronasal organ.

Front 10

accidental viewpoint

Back 10

A viewing position that produces some regularity in the visual image that is not present in the world (e.g., the sides of two independent objects lining up perfectly).

Front 11

accommodation

Back 11

The process by which the eye changes its focus (in which the lens gets fatter as gaze is directed toward nearer objects).

Front 12

achromatopsia

Back 12

An inability to perceive colors that is caused by damage to the central nervous system.

Front 13

acoustic reflex

Back 13

A reflex that protects the ear from intense sounds, via contraction of the stapedius and tensor tympani muscles.

Front 14

acoustic startle reflex

Back 14

The very rapid motor response to a sudden sound. Very few neurons are involved in the basic startle reflex, which can also be affected by emotional state.

Front 15

active sensing

Back 15

Sensing that includes self-generated probing of the environment. Besides our sense of equilibrium, other active human senses include vision and touch. Animal active sensing includes the use of echoes by whales and bats, the use of electrical signals by some fish, and the use of whiskers/antennae by fish, insects, and nocturnal rodents.

Front 16

acuity

Back 16

The smallest spatial detail that can be resolved at 100% contrast.

Front 17

adaptation

Back 17

A reduction in response caused by prior or continuing stimulation.

Front 18

adapting stimulus

Back 18

A stimulus whose removal produces a change in visual perception or sensitivity.

Front 19

additive color mixture

Back 19

A mixture of lights. If light A and light B are both reflected from a surface to the eye, in the perception of color the effects of those two lights add together.

Front 20

aerial perspective or haze

Back 20

A depth cue based on the implicit understanding that light is scattered by the atmosphere. More light is scattered when we look through more atmosphere. Thus, more distant objects are subject to more scatter and appear fainter, bluer, and less distinct.

Front 21

afferent fiber

Back 21

A neuron that carries sensory information to the central nervous system. Compare efferent fiber.

Front 22

afferent signals

Back 22

Information flowing inward to the central nervous system from sensors in the periphery. Passive sensing would rely exclusively on such sensory inflow, providing a traditional view of sensation. See also afferent fiber.

Front 23

age-related macular degeneration (AMD)

Back 23

A disease associated with aging that affects the macula. AMD gradually destroys sharp central vision, making it difficult to read, drive, and recognize faces. There are two forms of AMD: wet and dry.

Front 24

agnosia

Back 24

A failure to recognize objects in spite of the ability to see them. Agnosia is typically due to brain damage.

Front 25

akinetopsia

Back 25

A rare neuropsychological disorder in which the affected individual has no perception of motion.

Front 26

amacrine cell

Back 26

A retinal cell found in the inner synaptic layer that makes synaptic contacts with bipolar cells, ganglion cells, and other amacrine cells.

Front 27

ambiguous figure

Back 27

A visual stimulus that gives rise to two or more interpretations of its identity or structure.

Front 28

amblyopia

Back 28

A developmental disorder characterized by reduced spatial vision in an otherwise healthy eye, even with proper correction for refractive error. Also known as lazy eye.

Front 29

amplitude or intensity

Back 29

The magnitude of displacement (increase or decrease) of a sound pressure wave. Amplitude is perceived as loudness.

Front 30

amplitude

Back 30

The size (increase or decrease) of a head movement (e.g., angular velocity, linear acceleration, tilt).

Front 31

ampulla

Back 31

An expansion of each semicircular-canal duct that includes that canal’s cupula, crista, and hair cells, where transduction occurs.

Front 32

amygdala-hippocampal complex

Back 32

The conjoined regions of the amygdala and hippocampus, which are key structures in the limbic system. This complex is critically involved in the unique emotional and associative properties of olfactory cognition.

Front 33

analgesia

Back 33

Decreasing pain sensation during conscious experience.

Front 34

anamorphosis or anamorphic projection

Back 34

Use of the rules of linear perspective to create a two-dimensional image so distorted that it looks correct only when viewed from a special angle or with a mirror that counters the distortion.

Front 35

angular acceleration

Back 35

The rate of change of angular velocity. Mathematically, the integral of angular acceleration is angular velocity, and the integral of angular velocity is angular displacement. Angular acceleration, angular velocity, and angular displacement all mathematically represent angular motion.

Front 36

angular motion

Back 36

Rotational motion like the rotation of a spinning top or swinging saloon doors that rotate back and forth.

Front 37

anisometropia

Back 37

A condition in which the two eyes have different refractive errors (e.g., one eye is farsighted and the other not).

Front 38

anomia

Back 38

An inability to name objects in spite of the ability to see and recognize them (as shown by usage). Anomia is typically due to brain damage.

Front 39

anosmia

Back 39

The total inability to smell, most often resulting from sinus illness or head trauma.

Front 40

anterior cingulate cortex (ACC)

Back 40

A region of the brain associated with the perceived unpleasantness of a pain sensation.

Front 41

aperture problem

Back 41

The fact that when a moving object is viewed through an aperture (or a receptive field), the direction of motion of a local feature or part of the object may be ambiguous.

Front 42

aperture

Back 42

An opening that allows only a partial view of an object.

Front 43

apparent motion

Back 43

The illusory impression of smooth motion resulting from the rapid alternation of objects that appear in different locations in rapid succession.

Front 44

aqueous humor

Back 44

The watery fluid in the anterior chamber of the eye.

Front 45

aromatherapy

Back 45

The manipulation of odors to influence, mood, performance, and well-being, as well as the physiological correlates of emotion such as heart rate, blood pressure, and sleep.

Front 46

articulation

Back 46

The act or manner of producing a speech sound using the vocal tract.

Front 47

astigmatism

Back 47

A visual defect caused by the unequal curving of one or more of the refractive surfaces of the eye, usually the cornea.

Front 48

attack

Back 48

The part of a sound during which amplitude increases (onset).

Front 49

attention deficit hyperactivity disorder (ADHD)

Back 49

A quite common childhood disorder that can continue into adulthood. Symptoms include difficulty focusing attention as well as problems controlling behavior.

Front 50

attention

Back 50

Any of the very large set of selective processes in the brain. To deal with the impossibility of handling all inputs at once, the nervous system has evolved mechanisms that are able to bias processing to a subset of things, places, ideas, or moments in time.

Front 51

attentional blink

Back 51

The tendency not to perceive or respond to the second of two different target stimuli amid a rapid stream of distracting stimuli if the observer has responded to the first target stimulus within 200–500 milliseconds before the second stimulus is presented.

Front 52

audibility threshold

Back 52

The lowest sound pressure level that can be reliably detected at a given frequency.

Front 53

auditory nerve

Back 53

A collection of neurons that convey information from hair cells in the cochlea to (afferent) and from (efferent) the brain stem.

Front 54

auditory stream segregation

Back 54

The perceptual organization of a complex acoustic signal into separate auditory events for which each stream is heard as a separate event.

Front 55

autonomic nervous system

Back 55

The part of the nervous system that innervates glands, heart, digestive system, and so on, and that is responsible for regulating many involuntary actions.

Front 56

azimuth

Back 56

The angle of a sound source on the horizontal plane relative to a point in the center of the head between the ears. It is measured in degrees, with 0 degrees being straight ahead. The angle increases clockwise toward the right, with 180 degrees being directly behind.

Front 57

balance system

Back 57

The sensory systems, neural processes, and muscles that contribute to postural control. Specific components include the vestibular organs, kinesthesis, vestibulo-spinal pathways, skeletal bones, and postural control muscles. Because of its crucial contributions to balance, some even informally refer to the vestibular system as the “balance system” and the vestibular organs as the “balance organs.” But the balance system is much more than just the vestibular system, and the vestibular system contributes to more than just balance.

Front 58

balance

Back 58

The neural processes of postural control by which weight is evenly distributed, enabling us to remain upright and stable.

Front 59

basal cell

Back 59

One of the three types of cells in the olfactory epithelium. Basal cells are the precursor cells to olfactory sensory neurons.

Front 60

basic color terms

Back 60

Color words that are monolexemic (single words “blue” not, “sky blue”), used with high frequency, and have meanings that are agreed upon by speakers of a language.

Front 61

basic taste

Back 61

Any of the four taste qualities that are generally agreed to describe human taste experience: sweet, salty, sour, bitter.

Front 62

basilar membrane

Back 62

A plate of fibers that forms the base of the cochlear partition and separates the middle and tympanic canals in the cochlea.

Front 63

Bayesian approach

Back 63

A way of formalizing the idea that our perception is a combination of the current stimulus and our knowledge about the conditions of the world—what is and is not likely to occur. The Bayesian approach is stated mathematically as Bayes’ theorem—P(A|O) = P(A) x P(O|A)/P(O)—which enables us to calculate the probability (P) that the world is in a particular state (A) given a particular observation (O).

Front 64

belt area

Back 64

A region of cortex, directly adjacent to the primary auditory cortex (A1), with inputs from A1, where neurons respond to more complex characteristics of sounds.

Front 65

binaral rivalry

Back 65

Competition between the two nostrils for odor perception. When a different scent is presented to each nostril simultaneously, we perceive each scent to be alternating back and forth with the other, and not a blend of the two scents.

Front 66

binding problem

Back 66

The challenge of tying different attributes of visual stimuli (e.g., color, orientation, motion), which are handled by different brain circuits, to the appropriate object so that we perceive a unified object (e.g., red, vertical, moving right).

Front 67

binocular depth cue

Back 67

A depth cue that relies on information from both eyes. Stereopsis is the primary example in humans, but convergence and the ability of two eyes to see more of an object than one eye sees are also binocular depth cues.

Front 68

binocular disparity

Back 68

The differences between the two retinal images of the same scene. Disparity is the basis for stereopsis, a vivid perception of the three-dimensionality of the world that is not available with monocular vision.

Front 69

binocular rivalry

Back 69

The competition between the two eyes for control of visual perception, which is evident when completely different stimuli are presented to the two eyes.

Front 70

binocular summation

Back 70

The combination (or “summation”) of signals from each eye in ways that make performance on many tasks better with both eyes than with either eye alone.

Front 71

binocular

Back 71

With two eyes.

Front 72

biological motion

Back 72

The pattern of movement of living beings (humans and animals).

Front 73

bipolar cell

Back 73

A retinal cell that synapses with either rods or cones (not both) and with horizontal cells, and then passes the signals on to ganglion cells.

Front 74

bitter

Back 74

One of the four basic tastes; the taste quality, generally considered unpleasant, produced by substances like quinine or caffeine.

Front 75

blood oxygen level–dependent (BOLD) signal

Back 75

The ratio of oxygenated to deoxygenated hemoglobin that permits the localization of brain neurons that are most involved in a task.

Front 76

body image

Back 76

The impression of our bodies in space.

Front 77

C fiber

Back 77

A narrow-diameter, unmyelinated sensory nerve fiber that transmits pain and temperature signals.

Front 78

C tactile (CT) afferent

Back 78

A narrow-diameter, unmyelinated sensory nerve fiber that transmits signals from pleasant touch.

Front 79

cataract

Back 79

An opacity of the crystalline lens.

Front 80

categorical perception

Back 80

For speech as well as other complex sounds and images, the phenomenon by which the discrimination of items is no better than the ability to label items.

Front 81

change blindness

Back 81

The failure to notice a change between two scenes. If the gist, or meaning, of the scene is not altered, quite large changes can pass unnoticed.

Front 82

characteristic frequency (CF)

Back 82

The frequency to which a particular auditory nerve fiber is most sensitive.

Front 83

chemosignal

Back 83

Any of various chemicals emitted by humans that are detected by the olfactory system and that may have some effect on the mood, behavior, hormonal status, and/or sexual arousal of other humans.

Front 84

chord

Back 84

A combination of three or more musical notes with different pitches played simultaneously.

Front 85

chorda tympani

Back 85

The branch of cranial nerve VII (the facial nerve) that carries taste information from the anterior, mobile tongue (the part that can be stuck out). The chorda tympani exits the tongue with the lingual branch of the trigeminal nerve (cranial nerve V) and then passes through the middle ear on its way to the brain.

Front 86

chromophore

Back 86

The light-catching part of the visual pigments of the retina.

Front 87

cilium

Back 87

Any of the hairlike protrusions on the dendrites of olfactory sensory neurons. The receptor sites for odorant molecules are on the cilia, which are the first structures involved in olfactory signal transduction.

Front 88

circadian

Back 88

Referring to cells in the magnocellular layers of the lateral geniculate nucleus of the thalamus. Magno from the Greek for “large” referring to the size of the cells.

Front 89

circumvallate papillae

Back 89

Circular structures that form an inverted V on the rear of the tongue (three to five on each side, with the largest in the center). Circumvallate papillae are moundlike structures, each surrounded by a trench (like a moat). These papillae are much larger than fungiform papillae.

Front 90

closure

Back 90

In reference to perception, closure is the name of a Gestalt principle that holds that a closed contour is preferred to an open contour.

Front 91

coarticulation

Back 91

The phenomenon in speech whereby attributes of successive speech units overlap in articulatory or acoustic patterns.

Front 92

cochlea

Back 92

A spiral structure of the inner ear containing the organ of Corti.

Front 93

cochlear nucleus

Back 93

The first brain stem nucleus at which afferent auditory nerve fibers synapse.

Front 94

cochlear partition

Back 94

The combined basilar membrane, tectorial membrane, and organ of Corti, which are together responsible for the transduction of sound waves into neural signals.

Front 95

cognitive habituation

Back 95

The psychological process by which, after long-term exposure to an odor, one no longer has the ability to detect that odor or has very diminished detection ability.

Front 96

cold fiber

Back 96

A sensory nerve fiber that fires when skin temperature decreases.

Front 97

color assimilation

Back 97

A color perception effect in which two colors bleed into each other, each taking on some of the chromatic quality of the other.

Front 98

color constancy

Back 98

The tendency of a surface to appear the same color under a fairly wide range of illuminants.

Front 99

color contrast

Back 99

A color perception effect in which the color of one region induces the opponent color in a neighboring region.

Front 100

color space

Back 100

The three-dimensional space, established because color perception is based on the outputs of three cone types, that describes the set of all colors.

Front 101

color-anomalous

Back 101

A better term for what is usually called “color-blind.” Most “color-blind” individuals can still make discriminations based on wavelength. Those discriminations are different from the norm—that is, anomalous.

Front 102

column

Back 102

A vertical arrangement of neurons. Neurons within a single column tend to have similar receptive fields and similar orientation preferences.

Front 103

comparator

Back 103

An area of the visual system that receives one copy of the command issued by the motor system when the eyes move (the other copy goes to the eye muscles). The comparator compares the image motion signal with the eye motion signal and can compensate for the image changes caused by the eye movement.

Front 104

complex cell

Back 104

A cortical neuron whose receptive field does not have clearly defined excitatory and inhibitory regions.

Front 105

computed tomography (CT)

Back 105

An imaging technology that uses X-rays to create images of slices through volumes of material (e.g., the human body).

Front 106

conductive hearing loss

Back 106

Hearing loss caused by problems with the bones of the middle ear.

Front 107

cone

Back 107

A photoreceptor specialized for daylight vision, fine visual acuity, and color.

Front 108

cone monochromat

Back 108

An individual with only one cone type. Cone monochromats are truly color-blind.

Front 109

cone of confusion

Back 109

A region of positions in space where all sounds produce the same time and level (intensity) differences (ITDs and ILDs).

Front 110

cone-opponent cell

Back 110

A cell type—found in the retina, lateral geniculate nucleus, and visual cortex—that, in effect, subtracts one type of cone input from another.

Front 111

congenital prosopagnosia

Back 111

A form of “face blindness” apparently present from birth, as opposed to “acquired prosopagnosia,” which would typically be the result of an injury to the nervous system.

Front 112

conjunction search

Back 112

Search for a target defined by the presence of two or more attributes (e.g., a red, vertical target among red horizontal and blue vertical distractors).

Front 113

continuity constraint

Back 113

In stereopsis, the observation that, except at the edges of objects, neighboring points in the world lie at similar distances from the viewer. This is one of several constraints that have been proposed as helpful in solving the correspondence problem.

Front 114

contralateral

Back 114

Referring to the opposite side of the body (or brain).

Front 115

contralesional field

Back 115

The visual field on the side opposite a brain lesion. For example, points to the left of fixation are contralesional to damage in the right hemisphere of the brain.

Front 116

contrast sensitivity function (CSF)

Back 116

A function describing how the sensitivity to contrast (defined as the reciprocal of the contrast threshold) depends on the spatial frequency (size) of the stimulus.

Front 117

contrast threshold

Back 117

The smallest amount of contrast required to detect a pattern.

Front 118

contrast

Back 118

The difference in luminance between an object and the background, or between lighter and darker parts of the same object.

Front 119

convergence

Back 119

The ability of the two eyes to turn inward, often used in order to place the two images of a feature in the world on corresponding locations in the two retinal images (typically on the fovea of each eye). Convergence reduces the disparity of that feature to zero (or nearly zero).

Front 120

cornea

Back 120

The transparent “window” into the eyeball.

Front 121

correspondence problem

Back 121

1. In binocular vision, the problem of figuring out which bit of the image in the left eye should be matched with which bit in the right eye. The problem is particularly vexing when the images consist of thousands of similar features, like dots in random dot stereograms. 2.In motion detection, the problem faced by the motion detection system of knowing which feature in frame 2 corresponds to a particular feature in frame 1.

Front 122

corresponding retinal points

Back 122

Two monocular images of an object in the world are said to fall on corresponding points if those points are the same distance from the fovea in both eyes. The two foveas are also corresponding points.

Front 123

cortical magnification

Back 123

The amount of cortical area (usually specified in millimeters) devoted to a specific region (e.g., 1 degree) in the visual field.

Front 124

cranial nerves

Back 124

Twelve pairs of nerves (one for each side of the body) that originate in the brain stem and reach sense organs and muscles through openings in the skull.

Front 125

cribriform plate

Back 125

A bony structure riddled with tiny holes, at the level of the eyebrows, that separates the nose from the brain. The axons from the olfactory sensory neurons pass through the tiny holes of the cribriform plate to enter the brain.

Front 126

crista

Back 126

Any of the specialized detectors of angular motion located in each semicircular canal in a swelling called the ampulla.

Front 127

criterion

Back 127

In signal detection theory, an internal threshold that is set by the observer. If the internal response is above criterion, the observer gives one response (e.g., “yes, I hear that”). Below criterion, the observer gives another response (e.g., “no, I hear nothing”).

Front 128

critical bandwidth

Back 128

The range of frequencies conveyed within a channel in the auditory system.

Front 129

critical period

Back 129

A phase in the life span during which abnormal early experience can alter normal neuronal development. Critical periods are proposed for the development of binocular vision and development of a first human language.

Front 130

cross-adaptation

Back 130

The reduction in detection of one odorant following exposure to another odorant. Cross-adaptation is presumed to occur because the components of the odors (or the odorants) in question share one or more olfactory receptors for their transduction, but the order in which odorants are presented also plays a role.

Front 131

cross-modality matching

Back 131

The ability to match the intensities of sensations that come from different sensory modalities. This ability allows insight into sensory differences. For example, a listener might adjust the brightness of a light until it matches the loudness of a tone.

Front 132

crossed disparity

Back 132

The sign of disparity created by objects in front of the plane of fixation (the horopter). The term crossed is used because images of objects located in front of the horopter appear to be displaced to the left in the right eye, and to the right in the left eye.

Front 133

cue

Back 133

A stimulus that might indicate where (or what) a subsequent stimulus will be. Cues can be valid (giving correct information), invalid (incorrect), or neutral (uninformative).

Front 134

cultural relativism

Back 134

In sensation and perception, the idea that basic perceptual experiences (e.g., color perception) may be determined in part by the cultural environment.

Front 135

cycle

Back 135

For a grating, a pair consisting of one dark bar and one bright bar.

Front 136

cycles per degree

Back 136

The number of pairs of dark and bright bars (cycles of a grating) per degree of visual angle.

Front 137

Cyclopean

Back 137

Referring to stimuli that are defined by binocular disparity alone. Named after the one-eyed Cyclops of Homer’s Odyssey.

Front 138

cytochrome oxidase (CO)

Back 138

An enzyme used to reveal the regular array of “CO blobs,” which are spaced about 0.5 millimeter apart in the primary visual cortex.

Front 139

decay

Back 139

The part of a sound during which amplitude decreases (offset).

Front 140

decibel (dB)

Back 140

A unit of measure for the physical intensity of sound. Decibels define the difference between two sounds as the ratio between two sound pressures. Each 10:1 sound pressure ratio equals 20 dB, and a 100:1 ratio equals 40 dB.

Front 141

dermis

Back 141

The inner of two major layers of skin, consisting of nutritive and connective tissues, within which lie the mechanoreceptors.

Front 142

deuteranope

Back 142

An individual who suffers from color blindness that is due to the absence of M-cones.

Front 143

dichoptic

Back 143

Referring to the presentation of two different stimuli, one to each eye. Different from binocular presentation, which could involve both eyes looking at a single stimulus.

Front 144

diffuse bipolar cell

Back 144

A bipolar retinal cell whose processes are spread out to receive input from multiple cones.

Front 145

diopter (D)

Back 145

A unit of measurement of the optic power of a lens. It is equal to the reciprocal of the focal length, in meters. A 2-diopter lens will bring parallel rays of light into focus at ½ meter (50 cm).

Front 146

diplopia

Back 146

Double vision. If visible in both eyes, stimuli falling outside of Panum’s fusional area will appear diplopic.

Front 147

direction

Back 147

The line one moves along or faces, with reference to the point or region one is moving toward or facing.

Front 148

directional transfer function (DTF)

Back 148

A measure that describes how the pinna, ear canal, head, and torso change the intensity of sounds with different frequencies that arrive at each ear from different locations in space (azimuth and elevation).

Front 149

distractor

Back 149

In visual search, any stimulus other than the target.

Front 150

divergence

Back 150

The ability of the two eyes to turn outward, often used in order to place the two images of a feature in the world on corresponding locations in the two retinal images (typically on the fovea of each eye). Divergence reduces the disparity of that feature to zero (or nearly zero).

Front 151

dizziness

Back 151

A commonly used lay term that nonspecifically indicates any form of perceived spatial disorientation, with or without instability.

Front 152

doctrine of specific nerve energies

Back 152

A doctrine, formulated by Johannes Müller, stating that the nature of a sensation depends on which sensory fibers are stimulated, not on how fibers are stimulated.

Front 153

dorsal column–medial lemniscal (DCML) pathway

Back 153

The route from the spinal cord to the brain that carries signals from skin, muscles, tendons, and joints.

Front 154

dorsal horn

Back 154

A region at the rear of the spinal cord that receives inputs from receptors in the skin.

Front 155

double dissociation

Back 155

The phenomenon in which one of two functions—such as hearing and sight, or first- and second- order motion—can be damaged without harm to the other, and vice versa.

Front 156

double-opponent cell

Back 156

A cell type, found in the visual cortex, in which one region is excited by one cone type, combination of cones, or color and inhibited by the opponent cones or color (e.g., R+/G–). Another adjacent region would be inhibited by the first input and excited by the second (thus, in this example, R–/G+).

Front 157

dualism

Back 157

The idea that the mind has an existence separate from the material world of the body.

Front 158

duplex

Back 158

In reference to the retina, consisting of two parts: the rods and cones, which operate under different conditions.

Front 159

ear canal

Back 159

The canal that conducts sound vibrations from the pinna to the tympanic membrane and prevents damage to the tympanic membrane.

Front 160

eccentricity

Back 160

The distance between the retinal image and the fovea.

Front 161

efferent commands

Back 161

Information flowing outward from the central nervous system to the periphery. A common example is motor commands that regulate muscle contraction. The copy of such motor commands is often called an “efferent copy.” See also efferent fiber.

Front 162

efferent fiber

Back 162

A neuron that carries information from the central nervous system to the periphery. Compare afferent fiber.

Front 163

egocenter

Back 163

The center of a reference frame used to represent locations relative to the body.

Front 164

electroencephalography (EEG)

Back 164

A technique that, using many electrodes on the scalp, measures electrical activity from populations of many neurons in the brain.

Front 165

emmetropia

Back 165

The condition in which there is no refractive error, because the refractive power of the eye is perfectly matched to the length of the eyeball.

Front 166

end stopping

Back 166

The process by which a cell in the cortex first increases its firing rate as the bar length increases to fill up its receptive field, and then decreases its firing rate as the bar is lengthened further.

Front 167

endogenous cue

Back 167

In directing attention, an endogenous cue is located in (endo) or near the current location of attention

Front 168

endogenous opiate

Back 168

A chemical released by the body that blocks the release or uptake of neurotransmitters necessary to transmit pain sensations to the brain.

Front 169

endogenous spatial attention

Back 169

A form of top-down (knowledge-driven) control of spatial attention in which attention is voluntarily directed toward the site where the observer anticipates a stimulus will occur.

Front 170

ensemble statistics

Back 170

The average and distribution of properties like orientation or color over a set of objects or over a region in a scene.

Front 171

entorhinal cortex

Back 171

A phylogenetically old cortical region that provides the major sensory association input into the hippocampus. The entorhinal cortex also receives direct projections from olfactory regions.

Front 172

entry-level category

Back 172

For an object, the label that comes to mind most quickly when we identify it (e.g., “bird”). At the subordinate level, the object might be more specifically named (e.g., “eagle”); at the superordinate level, it might be more generally named (e.g., “animal”).

Front 173

epidermis

Back 173

The outer of two major layers of skin.

Front 174

equal-loudness curve

Back 174

A graph plotting sound pressure level (dB SPL) against the frequency for which a listener perceives constant loudness.

Front 175

equilibrium

Back 175

In reference to the vestibular system, our vestibular sense comprised of spatial orientation perception—encompassing our perception of linear motion, angular motion, and tilt—combined with reflexive vestibular responses like posture, vestibulo-autonomic reflexes, and vestibulo-ocular reflexes.

Front 176

esotropia

Back 176

Strabismus in which one eye deviates inward.

Front 177

Euclidean

Back 177

Referring to the geometry of the world, so named in honor of Euclid, the ancient Greek geometer of the third century BCE. In Euclidean geometry, parallel lines remain parallel as they are extended in space, objects maintain the same size and shape as they move around in space, the internal angles of a triangle always add to 180 degrees, and so forth.

Front 178

event-related potential (ERP)

Back 178

A measure of electrical activity from a subpopulation of neurons in response to particular stimuli that requires averaging many EEG recordings.

Front 179

exogenous cue

Back 179

In directing attention, an exogenous cue is located out (exo) at the desired final location of attention.

Front 180

exogenous spatial attention

Back 180

A form of bottom-up (stimulus-driven) spatial attention in which attention is reflexively (involuntarily) directed toward the site at which a stimulus has abruptly appeared.

Front 181

exotropia

Back 181

Strabismus in which one eye deviates outward.

Front 182

exploratory procedure

Back 182

A stereotyped hand movement pattern used to touch objects in order to perceive their properties; each procedure is best for determining one (or more) object properties.

Front 183

extinction

Back 183

In visual attention, the inability to perceive a stimulus to one side of the point of fixation (e.g., to the right) in the presence of another stimulus, typically in a comparable position in the other visual field (e.g., on the left side).

Front 184

extrastriate body area (EBA)

Back 184

A region of extrastriate visual cortex in humans that is specifically and reliably activated by images of the body other than the face.

Front 185

extrastriate cortex

Back 185

The region of cortex bordering the primary visual cortex and containing multiple areas involved in visual processing.

Front 186

familiar size

Back 186

A depth cue based on knowledge of the typical size of objects like humans or pennies.

Front 187

feature integration theory

Back 187

Anne Treisman’s theory of visual attention, which holds that a limited set of basic features can be processed in parallel preattentively, but that other properties, including the correct binding of features to objects, require attention.

Front 188

feature search

Back 188

Search for a target defined by a single attribute, such as a salient color or orientation.

Front 189

Fechner’s law

Back 189

A principle describing the relationship between stimulus and resulting sensation that says the magnitude of subjective sensation increases proportionally to the logarithm of the stimulus intensity.

Front 190

feed-forward process

Back 190

A process that carries out a computation (e.g., object recognition) one neural step after another, without need for feedback from a later stage to an earlier stage.

Front 191

figure-ground assignment

Back 191

The process of determining that some regions of an image belong to a foreground object (figure) and other regions are part of the background (ground).

Front 192

filiform papillae

Back 192

Small structures on the tongue that provide most of the bumpy appearance. Filiform papillae have no taste function.

Front 193

filter

Back 193

An acoustic, electrical, electronic, or optic device, instrument, computer program, or neuron that allows the passage of some range of parameters (e.g., orientations, frequencies) and blocks the passage of others.

Front 194

first-order motion

Back 194

The motion of an object that is defined by changes in luminance.

Front 195

flavor

Back 195

The combination of true taste (sweet, salty, sour, bitter) and retronasal olfaction.

Front 196

focus of expansion

Back 196

The point in the center of the horizon from which, when we’re in motion (e.g., driving on the highway), all points in the perspective image seem to emanate. The focus of expansion is one aspect of optic flow.

Front 197

foliate papillae

Back 197

Folds of tissue containing taste buds. Foliate papillae are located on the rear of the tongue lateral to the circumvallate papillae, where the tongue attaches to the mouth.

Front 198

formant

Back 198

A resonance of the vocal tract. Formants are specified by their center frequency and are denoted by integers that increase with relative frequency.

Front 199

Fourier analysis

Back 199

A mathematical procedure by which any signal can be separated into component sine waves at different frequencies. Combining these sine waves will reproduce the original signal.

Front 200

fovea

Back 200

A small pit, near the center of the macula, that contains the highest concentration of cones, and no rods. It is the portion of the retina that produces the highest visual acuity and serves as the point of fixation.

Front 201

frame of reference

Back 201

The coordinate system used to define locations in space.

Front 202

free fusion

Back 202

The technique of converging (crossing) or diverging the eyes in order to view a stereogram without a stereoscope.

Front 203

frequency

Back 203

For sound, the number of times per second that a pattern of pressure change repeats. Frequency is perceived as pitch.

Front 204

functional magnetic resonance imaging (fMRI)

Back 204

A variant of magnetic resonance imaging that makes it possible to measure localized patterns of activity in the brain. Activated neurons provoke increased blood flow, which can be quantified by measuring changes in the response of oxygenated and deoxygenated blood to strong magnetic fields.

Front 205

fundamental frequency

Back 205

The lowest-frequency component of a complex periodic sound.

Front 206

fundus

Back 206

The back layer of the retina—what the eye doctor sees through an ophthalmoscope.

Front 207

fungiform papillae

Back 207

Mushroom-shaped structures (maximum diameter 1 millimeter) that are distributed most densely on the edges of the tongue, especially the tip. Taste buds (an average of six per papilla) are buried in the surface.

Front 208

fusiform face area (FFA)

Back 208

A region of extrastriate visual cortex in humans that is specifically and reliably activated by human faces.

Front 209

G protein–coupled receptor (GPCR)

Back 209

Any of the class of receptors that are present on the surface of olfactory sensory neurons. All GPCRs are characterized by a common structural feature of seven membrane-spanning α-helices.

Front 210

ganglion cell

Back 210

A retinal cell that receives visual information from photoreceptors via two intermediate neuron types (bipolar cells and amacrine cells) and transmits information to the brain and midbrain.

Front 211

gate control theory

Back 211

A description of the pain-transmitting system that incorporates modulating signals from the brain.

Front 212

geon

Back 212

In Biederman’s recognition-by-components model, any of the “geometric ions” out of which perceptual objects are built.

Front 213

Gestalt grouping rules

Back 213

A set of rules describing which elements in an image will appear to group together. The original list was assembled by members of the Gestalt school of thought.

Front 214

Gestalt

Back 214

In German, literally “form.” In reference to perception, a school of thought stressing that the perceptual whole could be greater than the apparent sum of the parts.

Front 215

gestation

Back 215

Fetal development during pregnancy.

Front 216

glabrous

Back 216

In reference to skin, lacking hair.

Front 217

global superiority effect

Back 217

The finding in various experiments that the properties of the whole object take precedence over the properties of parts of the object.

Front 218

glomerulus

Back 218

Any of the spherical conglomerates containing the incoming axons of the olfactory sensory neurons. Each OSN converges onto two glomeruli (one medial, one lateral).

Front 219

good continuation

Back 219

A Gestalt grouping rule stating that two elements will tend to group together if they seem to lie on the same contour.

Front 220

graded potential

Back 220

An electrical potential that can vary continuously in amplitude.

Front 221

granule cells

Back 221

Like mitral cells, granule cells are at the deepest level of the olfactory bulb. They comprise an extensive network of inhibitory neurons, integrate input from all the earlier projections, and are thought to be the basis of specific odorant identification.

Front 222

gravity

Back 222

A force that attracts a body toward the center of the Earth.

Front 223

guided search

Back 223

Search in which attention can be restricted to a subset of possible items on the basis of information about the target item’s basic features (e.g., its color).

Front 224

gustation

Back 224

The sense of taste.

Front 225

hair cell

Back 225

Any cell that has stereocilia for transducing mechanical movement in the inner ear into neural activity sent to the brain; some hair cells also receive inputs from the brain.

Front 226

haptic perception

Back 226

Knowledge of the world that is derived from sensory receptors in skin, muscles, tendons, and joints, usually involving active exploration.

Front 227

haptic virtual environment

Back 227

A synthetic world that may be experienced haptically by operation of an electromechanical device that delivers forces to the hand of the user.

Front 228

harmonic spectrum

Back 228

The spectrum of a complex sound in which energy is at integer multiples of the fundamental frequency.

Front 229

helicotrema

Back 229

The opening that connects the tympanic and vestibular canals at the apex of the cochlea.

Front 230

hertz (Hz)

Back 230

A unit of measure for frequency. One hertz equals one cycle per second.

Front 231

heterodimer

Back 231

A chain of two molecules that are different from each other.

Front 232

heuristic

Back 232

A mental shortcut.

Front 233

high-spontaneous fiber

Back 233

An auditory nerve fiber that has a high rate (more than 30 spikes per second) of spontaneous firing; high-spontaneous fibers increase their firing rate in response to relatively low levels of sound.

Front 234

homologous regions

Back 234

Brain regions that appear to have the same function in different species.

Front 235

homunculus

Back 235

A maplike representation of regions of the body in the brain.

Front 236

horizontal cell

Back 236

A specialized retinal cell that contacts both photoreceptor and bipolar cells.

Front 237

horopter

Back 237

The location of objects whose images lie on corresponding points. The surface of zero disparity.

Front 238

hyperalgesia

Back 238

An increased or heightened response to a normally painful stimulus.

Front 239

hypercolumn

Back 239

A 1-millimeter block of striate cortex containing two sets of columns, each covering every possible orientation (0–180 degrees), with one set preferring input from the left eye and one set preferring input from the right eye.

Front 240

hyperopia

Back 240

Farsightedness, a common condition in which light entering the eye is focused behind the retina and accommodation is required in order to see near objects clearly.

Front 241

hyperpolarization

Back 241

An increase in membrane potential such that the inner membrane surface becomes more negative than the outer membrane surface.

Front 242

illuminant

Back 242

The light that illuminates a surface.

Front 243

illusory conjunction

Back 243

An erroneous combination of two features in a visual scene—for example, seeing a red X when the display contains red letters and Xs but no red Xs.

Front 244

illusory contour

Back 244

A contour that is perceived even though nothing changes from one side of it to the other in an image.

Front 245

image

Back 245

A picture or likeness.

Front 246

imbalance

Back 246

Lack of balance; unsteadiness; nearly falling over.

Front 247

inattentional blindness

Back 247

A failure to notice—or at least to report—a stimulus that would be easily reportable if it were attended.

Front 248

incus

Back 248

The middle of the three ossicles, connecting the malleus and the stapes.

Front 249

inferior colliculus

Back 249

A midbrain nucleus in the auditory pathway.

Front 250

inferotemporal (IT) cortex

Back 250

Part of the cerebral cortex in the lower portion of the temporal lobe, important in object recognition.

Front 251

inhibition of return

Back 251

The relative difficulty in getting attention (or the eyes) to move back to a recently attended (or fixated) location.

Front 252

inner ear

Back 252

A hollow cavity in the temporal bone of the skull, and the structures within this cavity: the cochlea and the semicircular canals of the vestibular system canals.

Front 253

inner segment

Back 253

The part of a photoreceptor that lies between the outer segment and the cell nucleus.

Front 254

insular cortex

Back 254

The primary cortical processing area for taste—the part of the cortex that first receives taste information. Also called insula or gustatory cortex.

Front 255

interaural level difference (ILD)

Back 255

The difference in level (intensity) between a sound arriving at one ear versus the other.

Front 256

interaural time difference (ITD)

Back 256

The difference in time between a sound arriving at one ear versus the other.

Front 257

interocular transfer

Back 257

The transfer of an effect (such as adaptation) from one eye to the other.

Front 258

inverse-square law

Back 258

A principle stating that as distance from a source increases, intensity decreases faster such that decrease in intensity is equal to the distance squared. This general law also applies to optics and other forms of energy.

Front 259

ipsilateral

Back 259

Referring to the same side of the body (or brain).

Front 260

ipsilesional field

Back 260

The visual field on the same side as a brain lesion.

Front 261

iris

Back 261

The colored part of the eye, consisting of a muscular diaphragm surrounding the pupil and regulating the light entering the eye by expanding and contracting the pupil.

Front 262

isointensity curve

Back 262

A map plotting the firing rate of an auditory nerve fiber against varying frequencies at varying intensities.

Front 263

just noticeable difference (JND) or difference threshold

Back 263

The smallest detectable difference between two stimuli, or the minimum change in a stimulus that enables it to be correctly judged as different from a reference stimulus.

Front 264

juxtaglomerular neurons

Back 264

The first layer of cells surrounding the glomeruli. They are a mixture of excitatory and inhibitory cells and respond to a wide range of odorants. The selectivity of neurons to specific odorants increases in a gradient from the surface of the olfactory bulb to the deeper layers.

Front 265

kinesthesia

Back 265

Perception of the position and movement of our limbs in space.

Front 266

kinesthetic

Back 266

Referring to perception involving sensory mechanoreceptors in muscles, tendons, and joints.

Front 267

koniocellular cell

Back 267

A neuron located between the magnocellular and parvocellular layers of the lateral geniculate nucleus. This layer is known as the koniocellular layer.

Front 268

koniocellular

Back 268

Referring to cells in the koniocellular layer of the lateral geniculate nucleus of the thalamus. Konio from the Greek for “dust” referring to the appearance of the cells.

Front 269

L-cone

Back 269

A cone that is preferentially sensitive to long wavelengths; colloquially (but not entirely accurately) known as a “red cone.”

Front 270

labeled lines

Back 270

A theory of sensory coding in which each nerve fiber carries a particular stimulus quality.

Front 271

lateral geniculate nucleus (LGN)

Back 271

A structure in the thalamus, part of the midbrain, that receives input from the retinal ganglion cells and has input and output connections to the visual cortex.

Front 272

lateral inhibition

Back 272

Antagonistic neural interaction between adjacent regions of the retina.

Front 273

lateral superior olive (LSO)

Back 273

A relay station in the brain stem where inputs from both ears contribute to detection of the interaural level difference.

Front 274

learned taste aversion

Back 274

The avoidance of a novel flavor after it has been paired with gastric illness. The smell, not the taste, of the substance is key for the learned aversion response in humans.

Front 275

lens

Back 275

The lens inside the eye that enables the changing of focus.

Front 276

lesion

Back 276

In reference to neurophysiology,1. (n) A region of damaged brain. 2. (v) To destroy a section of the brain.

Front 277

limbic system

Back 277

The encompassing group of neural structures that includes the olfactory cortex, the amygdala, the hippocampus, the piriform cortex, and the entorhinal cortex. It is involved in many aspects of emotion and memory. Olfaction is unique among the senses for its direct connection to it.

Front 278

linear acceleration

Back 278

The rate of change of linear velocity. Mathematically, the integral of linear acceleration is linear velocity, and the integral of linear velocity is linear displacement, which is also referred to as “translation.” Linear acceleration, linear velocity, and linear displacement all mathematically represent linear motion.

Front 279

linear motion

Back 279

Translational motion like the predominant movement of a train car or bobblehead doll.

Front 280

linear perspective

Back 280

A depth cue based on the fact that lines that are parallel in the three-dimensional world will appear to converge in a two-dimensional image.

Front 281

lordosis

Back 281

The position that females of some species (e.g., pigs and rats) need to assume in order to be impregnated. It involves the inward curving of the spinal column and exposure of the genitals.

Front 282

loudness

Back 282

The psychological aspect of sound related to perceived intensity (amplitude).

Front 283

low-spontaneous fiber

Back 283

An auditory nerve fiber that has a low rate (less than 10 spikes per second) of spontaneous firing; low-spontaneous fibers require relatively intense sound before they will fire at higher rates.

Front 284

luminance-defined object

Back 284

An object that is delineated by differences in reflected light.

Front 285

M ganglion cell

Back 285

A ganglion cell resembling a little umbrella that receives excitatory input from diffuse bipolar cells and feeds the magnocellular layer of the lateral geniculate nucleus.

Front 286

M-cone

Back 286

A cone that is preferentially sensitive to middle wavelengths; colloquially (but not entirely accurately) known as a “green cone.”

Front 287

macula

Back 287

In reference to vision, the central part of the retina that has a high concentration of cones. In reference to the vestibular system, any of the specialized detectors of linear acceleration and gravity found in each otolith organ.

Front 288

magnetic resonance imaging (MRI)

Back 288

An imaging technology that uses the responses of atoms to strong magnetic fields to form images of structures like the brain. The method can be adapted to measure activity in the brain, as well (see functional magnetic resonance imaging).

Front 289

magnetoencephalography (MEG)

Back 289

A technique, similar to electroencephalography, that measures changes in magnetic activity across populations of many neurons in the brain.

Front 290

magnitude estimation

Back 290

A psychophysical method in which the participant assigns values according to perceived magnitudes of the stimuli.

Front 291

magnocellular layer

Back 291

Either of the bottom two neuron-containing layers of the lateral geniculate nucleus, the cells of which are physically larger than those in the top four layers.

Front 292

main olfactory bulb (MOB)

Back 292

The olfactory bulb; the blueberry-sized extension of the brain just above the nose; the first region of the brain where smells are processed. In humans we refer simply to “olfactory bulb(s)”; in animals with accessory olfactory bulbs, we distinguish between “main” and “accessory.”

Front 293

malleus

Back 293

One of the three ossicles. The malleus receives vibration from the tympanic membrane and is attached to the incus.

Front 294

masking

Back 294

Using a second sound, frequently noise, to make the detection of another sound more difficult.

Front 295

materialism

Back 295

The idea that the only thing that exists is matter, and that all things, including the mind and consciousness, are the results of interaction between bits of matter.

Front 296

mathematical integration

Back 296

Computing an integral—one of the two main operations in calculus (the other, the inverse operation, is differentiation). Velocity is the integral of acceleration. Change of position is the integral of velocity.

Front 297

mechanoreceptor

Back 297

A sensory receptor that responds to mechanical stimulation (pressure, vibration, or movement).

Front 298

medial geniculate nucleus

Back 298

The part of the thalamus that relays auditory signals to the temporal cortex and receives input from the auditory cortex.

Front 299

medial superior olive (MSO)

Back 299

A relay station in the brain stem where inputs from both ears contribute to detection of the interaural time difference.

Front 300

Meissner corpuscle

Back 300

A specialized nerve ending associated with fast-adapting (FA I) fibers that have small receptive fields.

Front 301

melanopsin

Back 301

A photopigment, found in a class of photoreceptive retinal ganglion cells, that is sensitive to ambient light.

Front 302

melody

Back 302

A sequence of notes or chords perceived as a single coherent structure.

Front 303

Merkel cell neurite complex

Back 303

A specialized nerve ending associated with slowly adapting (SA I) fibers that have small receptive fields.

Front 304

metamers

Back 304

Different mixtures of wavelengths that look identical. More generally, any pair of stimuli that are perceived as identical in spite of physical differences.

Front 305

method of adjustment

Back 305

A method of limits in which the subject controls the change in the stimulus.

Front 306

method of constant stimuli

Back 306

A psychophysical method in which many stimuli, ranging from rarely to almost always perceivable (or rarely to almost always perceivably different from a reference stimulus), are presented one at a time. Participants respond to each presentation: “yes/no,” “same/different,” and so on.

Front 307

method of limits

Back 307

A psychophysical method in which the particular dimension of a stimulus, or the difference between two stimuli, is varied incrementally until the participant responds differently.

Front 308

metrical depth cue

Back 308

A depth cue that provides quantitative information about distance in the third dimension.

Front 309

microsaccade

Back 309

An involuntary, small, jerklike eye movement.

Front 310

microvilli

Back 310

Slender projections of the cell membrane on the tips of some taste bud cells that extend into the taste pore.

Front 311

mid-spontaneous fiber

Back 311

An auditory nerve fiber that has a medium rate (10–30 spikes per second) of spontaneous firing. The characteristics of mid-spontaneous fibers are intermediate between low- and high-spontaneous fibers.

Front 312

middle (midlevel) vision

Back 312

A loosely defined stage of visual processing that comes after basic features have been extracted from the image (low-level, or early, vision) and before object recognition and scene understanding (high-level vision).

Front 313

middle canal

Back 313

One of three fluid-filled passages in the cochlea. The middle canal is sandwiched between the tympanic and vestibular canals and contains the cochlear partition. Also called scala media.

Front 314

middle ear

Back 314

An air-filled chamber containing the middle bones, or ossicles. The middle ear conveys and amplifies vibration from the tympanic membrane to the oval window.

Front 315

middle temporal area (MT)

Back 315

An area of the brain thought to be important in the perception of motion.

Front 316

midget bipolar cell

Back 316

A small bipolar cell in the central retina that receives input from a single cone.

Front 317

mitral cell

Back 317

The deepest layer of neurons in the olfactory bulb. Each mitral cell responds only to a few specific odorants.

Front 318

monocular depth cue

Back 318

A depth cue that is available even when the world is viewed with one eye alone.

Front 319

monocular

Back 319

With one eye.

Front 320

monosodium glutamate (MSG)

Back 320

The sodium salt of glutamic acid (an amino acid).

Front 321

motion aftereffect (MAE)

Back 321

The illusion of motion of a stationary object that occurs after prolonged exposure to a moving object.

Front 322

motion parallax

Back 322

An important depth cue that is based on head movement. The geometric information obtained from an eye in two different positions at two different times is similar to the information from two eyes in different positions in the head at the same time.

Front 323

muscle spindle

Back 323

A sensory receptor located in a muscle that senses its tension.

Front 324

myopia

Back 324

Nearsightedness, a common condition in which light entering the eye is focused in front of the retina and distant objects cannot be seen sharply.

Front 325

naïve template theory

Back 325

The proposal that the visual system recognizes objects by matching the neural representation of the image with a stored representation of the same “shape” in the brain.

Front 326

nasal dominance

Back 326

The asymmetry characterizing the intake of air by the two nostrils, which corresponds to differing sensitivity to odorants between the two nostrils. Nasal dominance alternates nostrils throughout the day, but there is no predictability about when the nostrils alternate.

Front 327

Necker cube

Back 327

An outline that is perceptually bi-stable. Unlike the situation with most stimuli, two interpretations continually battle for perceptual dominance.

Front 328

negative afterimage

Back 328

An afterimage whose polarity is the opposite of the original stimulus. Light stimuli produce dark negative afterimages. Colors are complementary; for example, red produces green, and yellow produces blue.

Front 329

neglect

Back 329

As a neurological symptom, in visual attention: (1) The inability to attend or respond to stimuli in the contralesional visual field (typically, the left field after right parietal damage). (2) Ignoring half of the body or half of an object.

Front 330

neural plasticity

Back 330

The ability of neural circuits to undergo changes in function or organization as a result of previous activity.

Front 331

neuroimaging

Back 331

A set of methods that generate images of the structure and/or function of the brain. In many cases, these methods allow us to examine the brain in living, behaving humans.

Front 332

neurotransmitter

Back 332

A chemical substance used in neuronal communication at synapses.

Front 333

neutral point

Back 333

The point at which an opponent color mechanism is generating no signal. If red-green and blue-yellow mechanisms are at their neutral points, a stimulus will appear achromatic. (The black-white process has no neutral point.)

Front 334

nociceptor

Back 334

A sensory receptor that responds to painful input, such as extreme heat or pressure.

Front 335

nonaccidental feature

Back 335

A feature of an object that is not dependent on the exact (or accidental) viewing position of the observer.

Front 336

nonmetrical depth cue

Back 336

A depth cue that provides information about the depth order (relative depth) but not depth magnitude (e.g., his nose is in front of his face).

Front 337

nontaster (of PTC/PROP)

Back 337

An individual born with two recessive alleles for the TAS2R38 gene and unable to taste the compounds phenylthiocarbamide and propylthiouracil.

Front 338

occlusion

Back 338

A cue to relative depth order in which, for example, one object obstructs the view of part of another object.

Front 339

octave

Back 339

The interval between two sound frequencies having a ratio of 2:1.

Front 340

ocular dominance

Back 340

The property of the receptive fields of striate cortex neurons by which they demonstrate a preference, responding somewhat more rapidly when a stimulus is presented in one eye than when it is presented in the other.

Front 341

oculomotor (III) nerves

Back 341

The third pair of cranial nerves, which innervate all the extrinsic muscles of the eye except the lateral rectus and the superior oblique muscles, and which innervate the elevator muscle of the upper eyelid, the ciliary muscle, and the sphincter muscle of the pupil.

Front 342

odor hedonics

Back 342

The liking dimension of odor perception, typically measured by ratings of an odors’s perceived pleasantness, familiarity, and intensity.

Front 343

odor

Back 343

The translation of a chemical stimulus into a smell sensation.

Front 344

odorant receptor (OR)

Back 344

The region on the cilia of olfactory sensory neurons where odorant molecules bind.

Front 345

odorant

Back 345

A molecule that is defined by its physicochemical characteristics, which is capable of being translated by the nervous system into the perception of a smell. For example, “You were given the odorant methyl salicylate to smell, which has the odor of wintergreen mint.”

Front 346

OFF bipolar cell

Back 346

A bipolar cell that responds to a decrease in light captured by the cones.

Front 347

OFF-center cell

Back 347

A cell that depolarizes in response to a decrease in light intensity in its receptive-field center.

Front 348

olfaction

Back 348

The sense of smell.

Front 349

olfactory (I) nerves

Back 349

The first pair of cranial nerves. The axons of the olfactory sensory neurons bundle together after passing through the cribriform plate to form the olfactory nerve, which conducts impulses from the olfactory epithelia in the nose to the olfactory bulb.

Front 350

olfactory bulb

Back 350

A blueberry-sized extension of the brain just above the nose, where olfactory information is first processed. There are two olfactory bulbs, one in each brain hemisphere, corresponding to the right and left nostrils.

Front 351

olfactory cleft

Back 351

A narrow space at the back of the nose into which air flows and where the olfactory epithelium is located.

Front 352

olfactory epithelium

Back 352

A secretory mucous membrane in the human nose whose primary function is to detect odorants in inhaled air. Located on both sides of the upper portion of the nasal cavity and the olfactory clefts, the olfactory epithelium contains three types of cells: olfactory sensory neurons, basal cells, and supporting cells.

Front 353

olfactory sensory neuron (OSN)

Back 353

One of three cell types—the main one—in the olfactory epithelium. OSNs are small neurons located beneath a mucous layer in the epithelium. The cilia on the OSN dendrites contain the receptor sites for odorant molecules.

Front 354

olfactory tract

Back 354

The bundle of axons of the mitral and tufted cells within the olfactory bulb that sends odor information to the primary olfactory cortex.

Front 355

olfactory white

Back 355

The olfactory equivalent of “white noise” or the color white. When at least 30 odorants of equal intensity that span olfactory physiochemical and psychological (perceptual) space are mixed, they produce a resultant odor percept that is the same as every other mixture of 30 odorants meeting the span and equivalent intensity criteria, even though the various mixtures do not share any common odorants.

Front 356

ON bipolar cell

Back 356

A bipolar cell that responds to an increase in light captured by the cones.

Front 357

ON-center cell

Back 357

A cell that depolarizes in response to an increase in light intensity in its receptive-field center.

Front 358

opponent color theory

Back 358

The theory that perception of color is based on the output of three mechanisms, each of them resulting from an opponency between two colors: red-green, blue-yellow, and black-white.

Front 359

optic (II) nerves

Back 359

The second pair of cranial nerves, which arise from the retina and carry visual information to the thalamus and other parts of the brain.

Front 360

optic array

Back 360

The collection of light rays that interact with objects in the world that are in front of a viewer. Term coined by J. J. Gibson.

Front 361

optic flow

Back 361

The pattern of apparent motion of objects in a visual scene produced by the relative motion between the observer and the scene.

Front 362

optokinetic nystagmus (OKN)

Back 362

A reflexive eye movement in which the eyes will involuntarily track a continually moving object.

Front 363

orbitofrontal cortex (OFC)

Back 363

The part of the frontal lobe of the cortex that lies behind the bone (orbit) containing the eyes. The OFC is responsible for the conscious experience of olfaction, as well as the integration of pleasure and displeasure from food; and it has been referred to as the secondary olfactory cortex and the secondary taste cortex. The OFC is also involved in many other functions, and it is critical for assigning affective value to stimuli—in other words, determining hedonic meaning.

Front 364

organ of Corti

Back 364

A structure on the basilar membrane of the cochlea that is composed of hair cells and dendrites of auditory nerve fibers.

Front 365

orientation tuning

Back 365

The tendency of neurons in striate cortex to respond optimally to certain orientations and less to others.

Front 366

orthonasal olfaction

Back 366

Sniffing in and perceiving odors through our nostrils, which occurs when we are smelling something that is outside of us.

Front 367

oscillatory

Back 367

Referring to back-and-forth movement that has a constant rhythm.

Front 368

ossicle

Back 368

Any of three tiny bones of the middle ear: malleus, incus, and stapes.

Front 369

otitis media

Back 369

Inflammation of the middle ear, commonly in children as a result of infection.

Front 370

otoconia

Back 370

Tiny calcium carbonate stones in the ear that provide inertial mass for the otolith organs, enabling them to sense gravity and linear acceleration.

Front 371

otolith organ

Back 371

Either of two mechanical structures (utricle and saccule) in the vestibular system that sense both linear acceleration and gravity.

Front 372

otosclerosis

Back 372

Abnormal growth of the middle-ear bones that causes hearing loss.

Front 373

ototoxic

Back 373

Producing adverse effects on cochlear or vestibular organs or nerves.

Front 374

outer ear

Back 374

The external sound-gathering portion of the ear, consisting of the pinna and the ear canal.

Front 375

outer segment

Back 375

The part of a photoreceptor that contains photopigment molecules.

Front 376

oval window

Back 376

The flexible opening to the cochlea through which the stapes transmits vibration to the fluid inside.

Front 377

P ganglion cell

Back 377

A small ganglion cell that receives excitatory input from single midget bipolar cells in the central retina and feeds the parvocellular layer of the lateral geniculate nucleus.

Front 378

Pacinian corpuscle

Back 378

A specialized nerve ending associated with fast-adapting (FA II) fibers that have large receptive fields.

Front 379

panpsychism

Back 379

The idea that the mind exists as a property of all matter—that is, that all matter has consciousness.

Front 380

Panum’s fusional area

Back 380

The region of space, in front of and behind the horopter, within which binocular single vision is possible.

Front 381

papilla

Back 381

Any of multiple structures that give the tongue its bumpy appearance. From smallest to largest, the papilla types that contain taste buds are fungiform, foliate, and circumvallate; filiform papillae, which do not contain taste buds, are the smallest and most numerous.

Front 382

parabelt area

Back 382

A region of cortex, lateral and adjacent to the belt area, where neurons respond to more complex characteristics of sounds, as well as to input from other senses.

Front 383

parahippocampal place area (PPA)

Back 383

A region of extrastriate visual cortex in humans that is specifically and reliably activated more by images of places than by other stimuli.

Front 384

parallel search

Back 384

A search in which multiple stimuli are processed at the same time.

Front 385

parallelism

Back 385

A rule for figure-ground assignment stating that parallel contours are likely to belong to the same figure.

Front 386

parietal lobe

Back 386

In each cerebral hemisphere, a lobe that lies toward the top of the brain between the frontal and occipital lobes.

Front 387

parvocellular layer

Back 387

Any of the top four neuron-containing layers of the lateral geniculate nucleus, the cells of which are physically smaller than those in the bottom two layers.

Front 388

parvocellular

Back 388

Referring to cells in the parvocellular layers of the lateral geniculate nucleus of the thalamus. Parvo from the Greek for “small” referring to the size of the cells.

Front 389

perception

Back 389

The act of giving meaning to a detected sensation.

Front 390

period

Back 390

For hearing, the time required for a full wavelength of an acoustic sine wave to pass by a point in space.

Front 391

phantom limb

Back 391

Sensation perceived from a physically amputated limb of the body.

Front 392

phase locking

Back 392

Firing of a single neuron at one distinct point in the period (cycle) of a sound wave at a given frequency. (The neuron need not fire on every cycle, but each firing will occur at the same point in the cycle.)

Front 393

phase

Back 393

A fraction of the cycle of the sine wave described in degrees (0° to 360°) or radians (0π to 2π). In hearing, phase can be used to describe fractions of a period that relate to time.

Front 394

phase

Back 394

The relative position of a grating.

Front 395

pheromone

Back 395

A chemical emitted by one member of a species that triggers a physiological or behavioral response in another member of the same species. Pheromones are signals for chemical communication and do not need to have any smell.

Front 396

phonation

Back 396

The process through which vocal folds are made to vibrate when air pushes out of the lungs.

Front 397

photoactivation

Back 397

Activation by light.

Front 398

photon

Back 398

A quantum of visible light or other form of electromagnetic radiation demonstrating both particle and wave properties.

Front 399

photopic

Back 399

Referring to light intensities that are bright enough to stimulate the cone receptors and bright enough to “saturate” the rod receptors (that is, drive them to their maximum responses).

Front 400

photoreceptor

Back 400

A light-sensitive receptor in the retina.

Front 401

pictorial depth cue

Back 401

A cue to distance or depth used by artists to depict three-dimensional depth in two-dimensional pictures.

Front 402

pinna

Back 402

The outer, funnel-like part of the ear.

Front 403

pitch

Back 403

The psychological aspect of sound related mainly on the frequency of vibration.

Front 404

place code

Back 404

Tuning of different parts of the cochlea to different frequencies, in which information about the particular frequency of an incoming sound wave is coded by the place along the cochlear partition that has the greatest mechanical displacement.

Front 405

placebo effect

Back 405

Decreasing pain sensation when people think they’re taking an analgesic drug but actually are not.

Front 406

polysensory

Back 406

Referring to blending multiple sensory systems.

Front 407

positivism

Back 407

A philosophical position arguing that all we really have to go on is the evidence of the senses, so the world might be nothing more than an elaborate hallucination.

Front 408

positron emission tomography (PET)

Back 408

An imaging technology that enables us to define locations in the brain where neurons are especially active by measuring the metabolism of brain cells using safe radioactive isotopes.

Front 409

preattentive stage

Back 409

The processing of a stimulus that occurs before selective attention is deployed to that stimulus.

Front 410

prefrontal cortex

Back 410

A region of the brain concerned with cognition and executive control.

Front 411

presbyopia

Back 411

Literally “old sight.” The age-related loss of accommodation, which makes it difficult to focus on near objects.

Front 412

primary auditory cortex (A1)

Back 412

The first area within the temporal lobes of the brain responsible for processing acoustic information.

Front 413

primary olfactory cortex or piriform cortex

Back 413

The neural area where olfactory information is first processed. It comprises the amygdala, parahippocampal gyrus, and interconnected areas; and it interacts closely with the entorhinal cortex.

Front 414

primary visual cortex (V1), area 17, or striate cortex

Back 414

The area of the cerebral cortex of the brain that receives direct inputs from the lateral geniculate nucleus, as well as feedback from other brain areas.

Front 415

primer pheromone

Back 415

A pheromone that triggers a physiological (often hormonal) change among conspecifics. This effect usually involves prolonged pheromone exposure.

Front 416

principle of univariance

Back 416

The fact that an infinite set of different wavelength-intensity combinations can elicit exactly the same response from a single type of photoreceptor. One photoreceptor type cannot make color discriminations based on wavelength.

Front 417

probability summation

Back 417

The increased detection probability based on the statistical advantage of having two (or more) detectors rather than one.

Front 418

projective geometry

Back 418

For purposes of studying perception of the three-dimensional world, the geometry that describes the transformations that occur when the three-dimensional world is projected onto a two-dimensional surface. For example, parallel lines do not converge in the real world, but they do in the two-dimensional projection of that world.

Front 419

proprioception

Back 419

Perception mediated by kinesthetic and internal receptors.

Front 420

prosopagnosia

Back 420

An inability to recognize faces.

Front 421

protanope

Back 421

An individual who suffers from color blindness that is due to the absence of L-cones.

Front 422

proximity

Back 422

A Gestalt grouping rule stating that the tendency of two features to group together will increase as the distance between them decreases.

Front 423

psychoacoustics

Back 423

The study of the psychological correlates of the physical dimensions of acoustics; a branch of psychophysics.

Front 424

psychophysics

Back 424

The science of defining quantitative relationships between physical and psychological (subjective) events.

Front 425

pupil

Back 425

The dark, circular opening at the center of the iris in the eye, where light enters the eye.

Front 426

qualia (sing. quale)

Back 426

In philosophy, private conscious experiences of sensation or perception.

Front 427

random dot stereogram (RDS)

Back 427

A stereogram made of a large number (often in the thousands) of randomly placed dots. Random dot stereograms contain no monocular cues to depth. Stimuli visible stereoscopically in random dot stereograms are Cyclopean stimuli.

Front 428

rapid serial visual presentation (RSVP)

Back 428

An experimental procedure in which stimuli appear in a stream at one location (typically the point of fixation) at a rapid rate (typically about eight per second).

Front 429

rate saturation

Back 429

The point at which a nerve fiber is firing as rapidly as possible and further stimulation is incapable of increasing the firing rate.

Front 430

rate-intensity function

Back 430

A graph plotting the firing rate of an auditory nerve fiber in response to a sound of constant frequency at increasing intensities.

Front 431

reaction time (RT)

Back 431

A measure of the time from the onset of a stimulus to a response.

Front 432

realism

Back 432

A philosophical position arguing that there is a real world to sense.

Front 433

receiver operating characteristic (ROC) curve

Back 433

In studies of signal detection, the graphical plot of the hit rate as a function of the false-alarm rate. If these are the same, points fall on the diagonal, indicating that the observer cannot tell the difference between the presence and absence of the signal. As the observer’s sensitivity increases, the curve bows upward toward the upper left corner. That point represents a perfect ability to distinguish signal from noise (100% hits, 0% false alarms).

Front 434

receptive field

Back 434

The region on the retina in which visual stimuli influence a neuron’s firing rate.

Front 435

receptor adaptation

Back 435

The biochemical phenomenon, occurring after continual exposure to an odorant, whereby receptors stop responding to an odorant and detection ceases.

Front 436

receptor potential

Back 436

A change in voltage across the membrane of a sensory receptor cell (in the vestibular system, a hair cell) in response to stimulation.

Front 437

recognition-by-components model

Back 437

Biederman’s model of object recognition, which holds that objects are recognized by the identities and relationships of their component parts.

Front 438

reflect

Back 438

To redirect something that strikes a surface—especially light, sound, or heat—usually back toward its point of origin.

Front 439

reflectance

Back 439

The percentage of light hitting a surface that is reflected and not absorbed into the surface. Typically reflectance is given as a function of wavelength.

Front 440

reflexive eye movement

Back 440

A movement of the eye that is automatic and involuntary.

Front 441

refract

Back 441

1. To alter the course of a wave of energy that passes into something from another medium, as water does to light entering it from the air. 2. To measure the degree of refraction in a lens or eye.

Front 442

Reissner’s membrane

Back 442

A thin sheath of tissue separating the vestibular and middle canals in the cochlea.

Front 443

relatability

Back 443

The degree to which two line segments appear to be part of the same contour.

Front 444

related color

Back 444

A color, such as brown or gray, that is seen only in relation to other colors. For example, a “gray” patch in complete darkness appears white.

Front 445

relative height

Back 445

As a depth cue, the observation that objects at different distances from the viewer on the ground plane will form images at different heights in the retinal image. Objects farther away will be seen as higher in the image.

Front 446

relative metrical depth cue

Back 446

A depth cue that could specify, for example, that object A is twice as far away as object B without providing information about the absolute distance to either A or B.

Front 447

relative size

Back 447

A comparison of size between items without knowing the absolute size of either one.

Front 448

releaser pheromone

Back 448

A pheromone that triggers an immediate behavioral response among conspecifics.

Front 449

response enhancement

Back 449

An effect of attention on the response of a neuron in which the neuron responding to an attended stimulus gives a bigger response.

Front 450

retina

Back 450

A light-sensitive membrane in the back of the eye that contains rods and cones, which receive an image from the lens and send it to the brain through the optic nerve.

Front 451

retinitis pigmentosa (RP)

Back 451

A progressive degeneration of the retina that affects night vision and peripheral vision. RP commonly runs in families and can be caused by defects in a number of different genes that have recently been identified.

Front 452

retronasal olfaction

Back 452

Perceiving odors through your mouth while breathing and chewing. This occurs when we are smelling something that is inside our mouth and is what gives us the experience of flavor.

Front 453

retronasal olfactory sensation

Back 453

The sensation of an odor that is perceived when chewing and swallowing force an odorant in the mouth up behind the palate into the nose. Such odor sensations are perceived as originating from the mouth, even though the actual contact of odorant and receptor occurs at the olfactory mucosa.

Front 454

rhodopsin

Back 454

The visual pigment found in rods.

Front 455

rod monochromat

Back 455

An individual with no cones of any type. In addition to being truly color-blind, rod monochromats are badly visually impaired in bright light.

Front 456

rod

Back 456

A photoreceptor specialized for night vision.

Front 457

round window

Back 457

A soft area of tissue at the base of the tympanic canal that releases excess pressure remaining from extremely intense sounds.

Front 458

Ruffini ending

Back 458

A specialized nerve ending associated with slowly adapting (SA II) fibers that have large receptive fields.

Front 459

S-cone

Back 459

A cone that is preferentially sensitive to short wavelengths; colloquially (but not entirely accurately) known as a “blue cone.”

Front 460

saccade

Back 460

A type of eye movement, made both voluntarily and involuntarily, in which the eyes rapidly change fixation from one object or location to another.

Front 461

saccadic suppression

Back 461

The reduction of visual sensitivity that occurs when we make saccadic eye movements. Saccadic suppression eliminates the smear from retinal image motion during an eye movement.

Front 462

saccule

Back 462

One of the two otolith organs. A saclike structure that contains the saccular macula. Also called sacculus.

Front 463

salience

Back 463

The vividness of a stimulus relative to its neighbors.

Front 464

salty

Back 464

One of the four basic tastes; the taste quality produced by the cations of salts (e.g., the sodium in sodium chloride produces the salty taste). Some cations also produce other taste qualities (e.g., potassium tastes bitter as well as salty). The purest salty taste is produced by sodium chloride (NaCl), common table salt.

Front 465

scatter

Back 465

To disperse something—such as light—in an irregular fashion.

Front 466

scene-based guidance

Back 466

Information in our understanding of scenes that helps us find specific objects in scenes (e.g., objects do not float in air, faucets are near sinks).

Front 467

scotoma

Back 467

The blind spot in the middle of the visual field.

Front 468

scotopic

Back 468

Referring to light intensities that are bright enough to stimulate the rod receptors but too dim to stimulate the cone receptors.

Front 469

second-order motion

Back 469

The motion of an object that is defined by changes in contrast or texture, but not by luminance.

Front 470

selective attention

Back 470

The form of attention involved when processing is restricted to a subset of the possible stimuli.

Front 471

semicircular canal

Back 471

Any of three toroidal tubes in the vestibular system that sense angular motion.

Front 472

sensation

Back 472

The ability to detect a stimulus and, perhaps, to turn that detection into a private experience.

Front 473

sense of angular motion

Back 473

The perceptual modality that senses rotation.

Front 474

sense of linear motion

Back 474

The perceptual modality that senses translation.

Front 475

sense of tilt

Back 475

The perceptual modality that senses head inclination with respect to gravity.

Front 476

sensitivity

Back 476

1. The ability to respond to transmitted signals. 2. In signal detection theory, a value that defines the ease with which an observer can tell the difference between the presence and absence of a stimulus or the difference between stimulus 1 and stimulus 2.

Front 477

sensorineural hearing loss

Back 477

Hearing loss due to defects in the cochlea or auditory nerve.

Front 478

sensory exafference

Back 478

Change in afference caused by external stimuli. For the vestibular system, vestibular afference evoked by passive head motion would yield sensory exafference. Compare sensory reafference.

Front 479

sensory integration

Back 479

The process of combining different sensory signals. Typically, combining several signals yields more accurate and/or more precise information than can be obtained from individual sensory signals. This is not the mathematical process of integration learned in calculus (e.g., the integral of acceleration is velocity).

Front 480

sensory reafference

Back 480

Change in afference caused by self-generated activity. For the vestibular system, vestibular afference evoked by an active self-generated head motion would yield sensory reafference. Compare sensory exafference.

Front 481

serial self-terminating search

Back 481

A search from item to item, ending when a target is found.

Front 482

set size

Back 482

The number of items in a visual display.

Front 483

shape-pattern theory

Back 483

The current dominant biochemical theory for how chemicals come to be perceived as specific odors. Shape-pattern theory contends that different scents—as a function of the fit between odorant shape to OR shape—activate different arrays of olfactory receptors in the olfactory epithelia. These various arrays produce specific firing patterns of neurons in the olfactory bulb, which then determine the particular scent we perceive.

Front 484

sharper tuning

Back 484

An effect of attention on the response of a neuron in which the neuron responding to an attended stimulus responds more precisely. For example, a neuron that responds to lines with orientations from –20 degrees to +20 degrees might come to respond to ±10-degree lines.

Front 485

signal detection theory

Back 485

A psychophysical theory that quantifies the response of an observer to the presentation of a signal in the presence of noise. Measures obtained from a series of presentations are sensitivity (d′) and criterion of the observer.

Front 486

similarity

Back 486

A Gestalt grouping rule stating that the tendency of two features to group together will increase as the similarity between them increases.

Front 487

simple cell

Back 487

A cortical neuron whose receptive field has clearly defined excitatory and inhibitory regions.

Front 488

simultagnosia

Back 488

An inability to perceive more than one object at a time. Simultagnosia is a consequence of bilateral damage to the parietal lobes (Balint syndrome).

Front 489

sine wave

Back 489

A simple, smoothly changing oscillation that repeats across space. Higher frequency sine waves have more oscillations and lower frequencies have fewer oscillations over a given distance. 1. In hearing, a waveform for which variation as a function of time is a sine function. Also called pure tone. 2. In vision, a pattern for which variation in a property like brightness or color as a function of space is a sine function.

Front 490

sine wave or pure tone

Back 490

The waveform for which variation as a function of time is a sine function.

Front 491

sine wave grating

Back 491

A grating with a sinusoidal luminance profile as shown in Figure 3.4b.

Front 492

single-opponent cell

Back 492

Another way to refer to cone-opponent cells, in order to differentiate them from double-opponent cells.

Front 493

sinusoidal

Back 493

Referring to any oscillation, such as a sound wave or rotational motion, whose waveform is that of a sine curve. The period of a sinusoidal oscillation is the time that it takes for one full back-and-forth cycle of the motion to occur. The frequency of a sinusoidal oscillation is defined as the numeral 1 divided by the period.

Front 494

smooth pursuit

Back 494

A type of voluntary eye movement in which the eyes move smoothly to follow a moving object.

Front 495

somatosensation

Back 495

Collectively, sensory signals from the skin, muscles, tendons, joints, and internal receptors.

Front 496

somatosensory area 1 (S1)

Back 496

The primary receiving area for touch in the cortex.

Front 497

somatosensory area 2 (S2)

Back 497

The secondary receiving area for touch in the cortex.

Front 498

somatotopic

Back 498

Spatially mapped in the somatosensory cortex in correspondence to spatial events on the skin.

Front 499

somatotypical

Back 499

Having normal somatosensation.

Front 500

sour

Back 500

One of the four basic tastes; the taste quality produced by the hydrogen ion in acids.

Front 501

source segregation or auditory scene analysis

Back 501

Processing an auditory scene consisting of multiple sound sources into separate sound images.

Front 502

spatial disorientation

Back 502

Any impairment of spatial orientation. More specifically, any impairment of our sense of linear motion, angular motion, or tilt.

Front 503

spatial frequency

Back 503

The number of cycles of a grating (e.g., dark and bright bars) per unit of visual angle (usually specified in cycles per degree).

Front 504

spatial layout

Back 504

The description of the structure of a scene (e.g., enclosed, open, rough, smooth) without reference to the identity of specific objects in the scene.

Front 505

spatial orientation

Back 505

A sense consisting of three interacting modalities: perception of linear motion, angular motion, and tilt.

Front 506

spatial-frequency channel

Back 506

A pattern analyzer, implemented by an ensemble of cortical neurons, in which each set of neurons is tuned to a limited range of spatial frequencies.

Front 507

specific anosmia

Back 507

The inability to smell one specific compound amid otherwise normal smell perception.

Front 508

specific hungers theory

Back 508

The idea that deficiency of a given nutrient produces craving (a specific hunger) for that nutrient. Curt Richter first proposed this theory and demonstrated that cravings for salty or for sweet are associated with deficiencies in those substances. However, the idea proved wrong for other nutrients (e.g., vitamins).

Front 509

spectral power distribution

Back 509

The physical energy in a light as a function of wavelength.

Front 510

spectral reflectance function

Back 510

The percentage of a particular wavelength that is reflected from a surface.

Front 511

spectral sensitivity

Back 511

Refering to the sensitivity of a cell or a device to different wavelengths on the electromagnetic spectrum.

Front 512

spectrogram

Back 512

In sound analysis, a three-dimensional display that plots time on the horizontal axis, frequency on the vertical axis, and amplitude (intensity) on a color or gray scale.

Front 513

spectrum

Back 513

A representation of the relative energy (intensity) present at each frequency.

Front 514

spinothalamic pathway

Back 514

The route from the spinal cord to the brain that carries most of the information about skin temperature and pain.

Front 515

staircase method

Back 515

A psychophysical method for determining the concentration of a stimulus required for detection at the threshold level. The staircase method is an example of a method of limits. A stimulus (e.g., odorant) is presented in an ascending concentration sequence until detection is indicated, and then the concentration is shifted to a descending sequence until the response changes to “no detection.” This ascending and descending sequence is typically repeated several times, and the concentrations at which reversals occur are averaged to determine the threshold detection level of that odorant for a given individual. Also called reverse staircase method.

Front 516

stapedius

Back 516

The muscle attached to the stapes; tensing the stapedius decreases vibration.

Front 517

stapes

Back 517

One of the three ossicles. Connected to the incus on one end, the stapes presses against the oval window of the cochlea on the other end.

Front 518

stereoacuity

Back 518

A measure of the smallest binocular disparity that can generate a sensation of depth.

Front 519

stereoblindness

Back 519

An inability to make use of binocular disparity as a depth cue. This term is typically used to describe individuals with vision in both eyes. Someone who has lost one (or both) eyes is not typically described as “stereoblind.”

Front 520

stereocilium

Back 520

Any of the hairlike extensions on the tips of hair cells in the cochlea that, when flexed, initiate the release of neurotransmitters.

Front 521

stereoisomers

Back 521

Isomers (molecules that can exist in different structural forms) in which the spatial arrangements of the atoms are mirror-image rotations of one another, like a right and left hand.

Front 522

stereopsis

Back 522

The ability to use binocular disparity as a cue to depth.

Front 523

stereoscope

Back 523

A device for simultaneously presenting one image to one eye and another image to the other eye. Stereoscopes can be used to present dichoptic stimuli for stereopsis and binocular rivalry.

Front 524

Stevens’ power law

Back 524

A principle describing the relationship between stimulus and resulting sensation that says the magnitude of subjective sensation is proportional to the stimulus magnitude raised to an exponent.

Front 525

stimulus onset asynchrony (SOA)

Back 525

The time between the onset of one stimulus and the onset of another.

Front 526

strabismus

Back 526

A misalignment of the two eyes such that a single object in space is imaged on the fovea of one eye and on a nonfoveal area of the other (turned) eye.

Front 527

structural description

Back 527

A description of an object in terms of the nature of its constituent parts and the relationships between those parts.

Front 528

structuralism

Back 528

A school of thought believing that complex objects or perceptions could be understood by analysis of the components.

Front 529

substantia gelatinosa

Back 529

A jellylike region of interconnecting neurons in the dorsal horn of the spinal cord.

Front 530

subtraction method

Back 530

In function magnetic imaging, brain activity is measured in two conditions: one with and one without the involvement of the mental process of interest. Subtracting the two conditions shows regions of brain specifically activated by that process.

Front 531

subtractive color mixture

Back 531

A mixture of pigments. If pigments A and B mix, some of the light shining on the surface will be subtracted by A, and some by B. Only the remainder contributes to the perception of color.

Front 532

superior colliculus

Back 532

A structure in the midbrain that is important in initiating and guiding eye movements.

Front 533

superior olive

Back 533

An early brain stem region in the auditory pathway where inputs from both ears converge.

Front 534

supertaster

Back 534

Supertasters are those individuals who experience the most intense taste sensations; for some stimuli, they are dramatically more intense than for medium tasters or nontasters. Supertasters also tend to experience more intense oral burn and oral touch sensations. A variety of factors may contribute to this heightened perception, among the most important is the density of fungiform papillae.

Front 535

supporting cell

Back 535

One of the three types of cells in the olfactory epithelium. Supporting cells provide metabolic and physical support for the olfactory sensory neurons.

Front 536

suppression

Back 536

In vision, the inhibition of an unwanted image. Suppression occurs frequently in people with strabismus.

Front 537

surroundedness

Back 537

A rule for figure-ground assignment stating that if one region is entirely surrounded by another, it is likely that the surrounded region is the figure.

Front 538

sweet

Back 538

One of the four basic tastes; the taste quality produced by some sugars, such as glucose, fructose, and sucrose. These three sugars are particularly biologically useful to us, and our sweet receptors are tuned to them. Some other compounds (e.g., saccharin, aspartame) are also sweet.

Front 539

symmetry

Back 539

A rule for figure-ground assignment stating that symmetrical regions are more likely to be seen as figure.

Front 540

synapse

Back 540

The junction between neurons that permits information transfer.

Front 541

synaptic terminal

Back 541

The location where axons terminate at the synapse for transmission of information by the release of a chemical transmitter.

Front 542

syncopation

Back 542

Any deviation from a regular rhythm.

Front 543

tactile agnosia

Back 543

The inability to identify objects by touch.

Front 544

target

Back 544

The goal of a visual search.

Front 545

tastant

Back 545

Any stimulus that can be tasted.

Front 546

taste

Back 546

Sensations evoked by solutions in the mouth that contact receptors on the tongue and the roof of the mouth that then connect to axons in cranial nerves VII, IX, and X.

Front 547

taste bud

Back 547

A globular cluster of cells that has the function of creating neural signals conveyed to the brain by the taste nerves. Some of the cells in a taste bud have specialized sites on their apical projections that interact with taste stimuli. Some of the cells form synapses with taste nerve fibers.

Front 548

taste receptor cell

Back 548

A cell within the taste bud that contains sites on its apical projection that can interact with taste stimuli. These sites fall into two major categories: those interacting with charged particles (e.g., sodium and hydrogen ions), and those interacting with specific chemical structures.

Front 549

taster (of PTC/PROP)

Back 549

An individual born with one or both dominant alleles for the TAS2R38 gene and able to taste the compounds phenylthiocarbamide and propylthiouracil. PTC/PROP tasters who also have a high density of fungiform papillae are PROP supertasters.

Front 550

tau (τ)

Back 550

Information in the optic flow that could signal time to collision (TTC) without the necessity of estimating either absolute distances or rates. The ratio of the retinal image size at any moment to the rate at which the image is expanding is tau, and TTC is proportional to tau.

Front 551

tectorial membrane

Back 551

A gelatinous structure, attached on one end, that extends into the middle canal of the ear, floating above inner hair cells and touching outer hair cells.

Front 552

tempo

Back 552

The perceived speed of the presentation of sounds.

Front 553

temporal code

Back 553

Tuning of different parts of the cochlea to different frequencies, in which information about the particular frequency of an incoming sound wave is coded by the timing of neural firing as it relates to the period of the sound.

Front 554

temporal integration

Back 554

The process by which a sound at a constant level is perceived as being louder when it is of greater duration. The term also applies to perceived brightness, which depends on the duration of light.

Front 555

tensor tympani

Back 555

The muscle attached to the malleus; tensing the tensor tympani decreases vibration.

Front 556

texture gradient

Back 556

A depth cue based on the geometric fact that items of the same size form smaller images when they are farther away. An array of items that change in size smoothly across the image will appear to form a surface tilted in depth.

Front 557

texture segmentation

Back 557

Carving an image into regions of common texture properties.

Front 558

texture-defined object or contrast-defined object

Back 558

An object that is defined by differences in contrast, or texture, but not by luminance.

Front 559

thermoreceptor

Back 559

A sensory receptor that signals information about changes in skin temperature.

Front 560

threshold tuning curve

Back 560

A graph plotting the thresholds of a neuron or fiber in response to sine waves with varying frequencies at the lowest intensity that will give rise to a response.

Front 561

tilt aftereffect

Back 561

The perceptual illusion of tilt, produced by adaptation to a pattern of a given orientation.

Front 562

tilt

Back 562

To attain a sloped position like that of the Leaning Tower of Pisa.

Front 563

timbre

Back 563

The psychological sensation by which a listener can judge that two sounds with the same loudness and pitch are dissimilar. Timbre quality is conveyed by harmonics and other high frequencies.

Front 564

time to collision (TTC)

Back 564

The time required for a moving object (such as a cricket ball) to hit a stationary object (such as a batsman’s head). TTC = distance/rate.

Front 565

tip link

Back 565

A tiny filament that stretches from the tip of a stereocilium to the side of its neighbor.

Front 566

tip-of-the-nose phenomenon

Back 566

The inability to name an odor, even though it is very familiar. Contrary to the tip-of-the-tongue phenomenon, one has no lexical access to the name of the odor, such as first letter, rhyme, number of syllables, and so on, when in the tip-of-the-nose state. This is an example of how language and olfactory perception are deeply disconnected.

Front 567

tone chroma

Back 567

A sound quality shared by tones that have the same octave interval.

Front 568

tone height

Back 568

A sound quality corresponding to the level of pitch. Tone height is monotonically related to frequency.

Front 569

tonotopic organization

Back 569

An arrangement in which neurons that respond to different frequencies are organized anatomically in order of frequency.

Front 570

topographical mapping

Back 570

The orderly mapping of the world in the lateral geniculate nucleus and the visual cortex.

Front 571

transduce

Back 571

To convert from one form of energy to another (e.g., from light to neural electrical energy, or from mechanical movement to neural electrical energy).

Front 572

transmit

Back 572

To convey something (e.g., light) from one place or thing to another.

Front 573

transparent

Back 573

Allowing light to pass through with no interruption, so that objects on the other side can be clearly seen.

Front 574

triangle test

Back 574

A test in which a participant is given three odorants to smell, of which two are the same and one is different. The participant is required to state which is the odd odor out. Typically, the order in which the three odorants are given (e.g., same, same, different; different, same, same; same, different, same) is manipulated and the test is re-peated several times for greater accuracy.

Front 575

trichromatic theory of color vision or trichromacy

Back 575

The theory that the color of any light is defined in our visual system by the relationships of three numbers—the outputs of three receptor types now known to be the three cones. Also called the Young-Helmholtz theory.

Front 576

trigeminal (V) nerve

Back 576

The fifth cranial nerve, which transmits information about the “feel” of an odorant (e.g., mint feels cool, cinnamon feels warm), as well as pain and irritation sensations (e.g., ammonia feels burning).

Front 577

tritanope

Back 577

An individual who suffers from color blindness that is due to the absence of S-cones.

Front 578

trochlear (IV) nerves

Back 578

The fourth pair of cranial nerves, which innervate the superior oblique muscles of the eyeballs.

Front 579

tufted cell

Back 579

The next layer of cells after the juxtaglomerular neurons. They repond to fewer odorants than the juxtaglomerular cells, but more than neurons at the deepest layer of cells.

Front 580

two-point touch threshold

Back 580

The minimum distance at which two stimuli (e.g., two simultaneous touches) are just perceptible as separate.

Front 581

two-tone suppression

Back 581

A decrease in the firing rate of one auditory nerve fiber due to one tone, when a second tone is presented at the same time.

Front 582

tympanic canal

Back 582

One of three fluid-filled passages in the cochlea. The tympanic canal extends from the round window at the base of the cochlea to the helicotrema at the apex. Also called scala tympani.

Front 583

tympanic membrane

Back 583

The eardrum; a thin sheet of skin at the end of the outer ear canal. The tympanic membrane vibrates in response to sound.

Front 584

umami

Back 584

The taste sensation produced by monosodium glutamate.

Front 585

uncrossed disparity

Back 585

The sign of disparity created by objects behind the plane of fixation (the horopter). The term uncrossed is used because images of objects located behind the horopter will appear to be displaced to the right in the right eye, and to the left in the left eye.

Front 586

unique hue

Back 586

Any of four colors that can be described with only a single color term: red, yellow, green, blue. Other colors (e.g., purple or orange) can be described as compounds (reddish blue, reddish yellow).

Front 587

uniqueness constraint

Back 587

In stereopsis, the observation that a feature in the world is represented exactly once in each retinal image. This constraint simplifies the correspondence problem.

Front 588

unrelated color

Back 588

A color that can be experienced in isolation.

Front 589

utricle

Back 589

One of the two otolith organs. A saclike structure that contains the utricular macula. Also called utriculus.

Front 590

vanishing point

Back 590

The apparent point at which parallel lines receding in depth converge.

Front 591

vection

Back 591

An illusory sense of self-motion caused by moving visual cues when one is not, in fact, actually moving.

Front 592

velocity

Back 592

The speed and direction in which something moves. Mathematically, velocity is the integral of acceleration. In words, linear velocity is distance divided by time to traverse that distance; angular velocity is rotation angle divided by time to traverse that angle.

Front 593

vergence

Back 593

A type of eye movement in which the two eyes move in opposite directions; for example, both eyes turn toward the nose (convergence) or away from the nose (divergence).

Front 594

vertigo

Back 594

A sensation of rotation or spinning. The term is often used more generally to mean any form of dizziness.

Front 595

vestibular canal

Back 595

One of three fluid-filled passages in the cochlea. The vestibular canal extends from the oval window at the base of the cochlea to the helicotrema at the apex. Also called scala vestibuli.

Front 596

vestibular organs

Back 596

The set of five sense organs—three semicircular canals and two otolith organs—located in each inner ear that sense head motion and head orientation with respect to gravity. See also vestibular system.

Front 597

vestibular system

Back 597

The set of five sense organs—three semicircular canals and two otolith organs—located in each inner ear that sense head motion and head orientation with respect to gravity and the neural pathways directly associated with these sense organs. See also vestibular organs.

Front 598

vestibulo-ocular reflex (VOR)

Back 598

A short-latency reflex that helps stabilize vision by counterrotating the eyes when the vestibular system senses head movement.

Front 599

vestibulocochlear (VIII) nerves

Back 599

The eighth pair of cranial nerves, which connect the inner ear with the brain, transmitting impulses concerned with hearing and spatial orientation. The vestibulocochlear nerve is composed of the cochlear nerve branch and the vestibular nerve branch.

Front 600

vibration theory

Back 600

An alternative to shape-pattern theory for describing how olfaction works. Vibration theory proposes that every odorant has a different vibrational frequency, and that molecules that produce the same vibrational frequencies will smell the same.

Front 601

Vieth-Müller circle

Back 601

The location of objects whose images fall on geometrically corresponding points in the two retinas. If life were simple, this circle would be the horopter, but life is not simple.

Front 602

viewpoint invariance

Back 602

1. A property of an object that does not change when observer viewpoint changes. 2. A class of theories of object recognition that proposes representations of objects that do not change when viewpoint changes.

Front 603

visual acuity

Back 603

A measure of the finest detail that can be resolved by the eyes.

Front 604

visual angle

Back 604

The angle subtended by an object at the retina.

Front 605

visual crowding

Back 605

The deleterious effect of clutter on peripheral object recognition.

Front 606

visual search

Back 606

Search for a target in a display containing distracting elements.

Front 607

visual-field defect

Back 607

A portion of the visual field with no vision or with abnormal vision, typically resulting from damage to the visual nervous system.

Front 608

vitalism

Back 608

The idea that there is a force in life that is distinct from physical entities.

Front 609

vitreous humor

Back 609

The transparent fluid that fills the vitreous chamber in the posterior part of the eye.

Front 610

vocal tract

Back 610

The airway above the larynx used for the production of speech. The vocal tract includes the oral tract and nasal tract.

Front 611

volley principle

Back 611

The idea that multiple neurons can provide a temporal code for frequency if each neuron fires at a distinct point in the period of a sound wave but does not fire on every period.

Front 612

vomeronasal organ (VNO)

Back 612

A chemical sensing organ at the base of the nasal cavity with a curved tubular shape. The VNO evolved to detect chemicals that cannot be processed by ORs, such as large and/or aqueous molecules, the types of molecules that constitute pheromones. Also called Jacobson’s organ.

Front 613

warmth fiber

Back 613

A sensory nerve fiber that fires when skin temperature increases.

Front 614

wave

Back 614

An oscillation that travels through a medium by transferring energy from one particle or point to another without causing any permanent displacement of the medium.

Front 615

wavelength

Back 615

The distance required for one full cycle of oscillation for a sine wave.

Front 616

Weber fraction

Back 616

The constant of proportionality in Weber’s law.

Front 617

Weber’s law

Back 617

The principle describing the relationship between stimulus and resulting sensation that says the just noticeable difference (JND) is a constant fraction of the comparison stimulus.

Front 618

white noise

Back 618

Noise consisting of all audible frequencies in equal amounts. White noise in hearing is analogous to white light in vision, for which all wavelengths are present.