תפיסה (מושגים מהספר) - סמסטר ב - אוניברסיטת חיפה

Front 1

Absolute threshold

Back 1

The minimum stimulus energy necessary for an observer to detect a stimulus.

Front 2

Action

Back 2

Motor activities such as moving the head or eyes and locomoting through the environment. Action is one of the major outcomes of the perceptual process.

Front 3

Bottom-up processing

Back 3

Processing that is based on the information on the receptors. Also called data-based processing.

Front 4

Classical psychophysical methods

Back 4

The methods of limits adjustment and constant stimuli described by Fechner that are used for measuring thresholds.

Front 5

Cognitive influences on perception

Back 5

How the knowledge memories and expectations that a person brings to a situation influence his or her perception.

Front 6

Difference threshold

Back 6

The minimal detectable difference between two stimuli.

Front 7

Environmental stimulus

Back 7

The stimulus “out there” in the external environment.

Front 8

Frontal lobe

Back 8

Receiving signals from all of the senses the frontal lobe plays an important role in perceptions that involve the coordination of information received through two or more senses. It also serves functions such as language thought memory and motor functioning.

Front 9

Knowledge

Back 9

Any information that the perceiver brings to a situation. See also Top-down processing.

Front 10

Magnitude estimation

Back 10

A psychophysical method in which the subject assigns numbers to a stimulus that are proportional to the subjective magnitude of the stimulus.

Front 11

Method of adjustment

Back 11

A psychophysical method in which the experimenter or the observer adjusts the stimulus intensity in a continuous manner until the observer detects the stimulus.

Front 12

Method of constant stimuli

Back 12

A psychophysical method in which a number of stimuli with different intensities are presented repeatedly in a random order.

Front 13

Method of limits

Back 13

A psychophysical method for measuring threshold in which the experimenter presents sequences of stimuli in ascending and descending order.

Front 14

Neural processing

Back 14

Operations that transform electrical signals within a network of neurons or that transform the response of individual neurons.

Front 15

Oblique effect

Back 15

Enhanced sensitivity to vertically and horizontally oriented visual stimuli compared to obliquely oriented (slanted) stimuli. This effect has been demonstrated by measuring both perception and neural responding.

Front 16

Occipital lobe

Back 16

A lobe at the back of the cortex that is the site of the cortical receiving area for vision.

Front 17

Parietal lobe

Back 17

A lobe at the top of the cortex that is the site of the cortical receiving area for touch and is the termination point of the dorsal (where or how) stream for visual processing.

Front 18

Perceived magnitude

Back 18

A perceptual measure of stimuli such as light or sound that indicates the magnitude of experience.

Front 19

Perception

Back 19

Conscious sensory experience.

Front 20

Perceptual process

Back 20

A sequence of steps leading from the environment to perception of a stimulus recognition of the stimulus and action with regard to the stimulus.

Front 21

Phenomenological method

Back 21

Method of determining the relationship between stimuli and perception in which the observer describes what he or she perceives.

Front 22

Physiological approach to perception

Back 22

Analyzing perception by determining how a person’s perception is related to physiological processes that are occurring within the person. This approach focuses on determining the relationship between stimuli and physiological responding and between physiological responding and perception.

Front 23

Power function

Back 23

A mathematical function of the form P=KSn where P is perceived magnitude K is a constant S is the stimulus intensity and n is an exponent.

Front 24

Primary receiving areas

Back 24

Areas of the cerebral cortex that first receive most of the signals initiated by a sense’s receptors. For example the occipital cortex is the site of the primary receiving area for vision and the temporal lobe is the site of the primary receiving area for hearing.

Front 25

Principle of representation

Back 25

A principle of perception that everything a person perceives is based not on direct contact with stimuli but on representations of stimuli on the receptors and in the person’s nervous system.

Front 26

Principle of transformation

Back 26

A principle of perception that stimuli and responses created by stimuli are transformed or changed between the environmental stimulus and perception.

Front 27

Psychophysical approach to perception

Back 27

Analyzing perception by determining how a person’s perception is related to stimuli in the environment. This approach focuses on determining the relationship between stimuli in the environment and perceptual responding.

Front 28

Psychophysics

Back 28

Traditionally the term psychophysics refers to quantitative methods for measuring the relationship between properties of the stimulus and the subject’s experience. In this book all methods that are used to determine the relationship between stimuli and perception will be broadly referred to as pychophysical methods.

Front 29

Rat-man demonstration

Back 29

The demonstration in which presentation of a “ratlike’’ or “manlike’’ picture influences an observer’s perception of a second picture which can be interpreted either as a rat or as a man. This demonstration illustrates an effect of top-down processing on perception.

Front 30

Reaction time

Back 30

The time between presentation of a stimulus and an observer's or listener's response to the stimulus. Reaction time is often used in experiments as a measure of speed of processing.

Front 31

Recognition

Back 31

The ability to place an object in a category that gives it meaning—for example recognizing a particular red object as a tomato.

Front 32

Response compression

Back 32

The result when doubling the physical intensity of a stimulus less than doubles the subjective magnitude of the stimulus.

Front 33

Response criterion

Back 33

In a signal detection experiment the subjective magnitude of a stimulus above which the participant will indicate that the stimulus is present.

Front 34

Response expansion

Back 34

The result when doubling the physical intensity of a stimulus more than doubles the subjective magnitude of the stimulus.

Front 35

Sensory receptors

Back 35

Cells specialized to respond to environmental energy with each sensory system’s receptors specialized to respond to a specific type of energy.

Front 36

Signal detection theory

Back 36

A theory stating that the detection of a stimulus depends both on the participant's sensitivity to the stimulus and on the participant’s response criterion.

Front 37

Steven's power law

Back 37

A law concerning the relationship between the physical intensity of a stimulus and the perception of the subjective magnitude of the stimulus. The law states that P=KSn where P is perceived magnitude K is a constant S is the stimulus intensity and n is an exponent.

Front 38

Temporal lobe

Back 38

A lobe on the side of the cortex that is the site of the cortical receiving area for hearing and the termination point for the ventral or what stream for visual processing. A number of areas in the temporal lobe such as the fusiform face area and the extrastriate body area serve functions related to perceiving and recognizing objects.

Front 39

Top-down processing

Back 39

Processing that starts with the analysis of high-level information such as the knowledge a person brings to a situation. Also called knowledge-based processing. Distinguished from bottom-up or data-based processing which is based on incoming data.

Front 40

Transduction

Back 40

In the senses the transformation of environmental energy into electrical energy. For example the retinal receptors transduce light energy into electrical energy.

Front 41

Visual form agnosia

Back 41

The inability to recognize objects.

Front 42

Visual pigment

Back 42

A light-sensitive molecule contained in the rod and cone outer segments. The reaction of this molecule to light results in the generation of an electrical response in the receptors.

Front 43

Visual search

Back 43

A procedure in which a person's task is to find a particular element in a display that contains a number of elements.

Front 44

Weber fraction

Back 44

The ratio of the difference threshold to the value of the standard stimulus in Weber’s law.

Front 45

Weber's law

Back 45

A law stating that the ratio of the difference threshold (DL) to the value of the stimulus (S) is constant. According to this relationship doubling the value of a stimulus will cause a doubling of the difference threshold. The ratio DL/S is called the Weber fraction.

Front 46

Absorption spectrum

Back 46

A plot of the amount of light absorbed by a visual pigment versus the wavelength of light.

Front 47

Accommodation

Back 47

In vision bringing objects located at different distances into focus by changing the shape of the lens.

Front 48

Action potential

Back 48

Rapid increase in positive charge in a nerve fiber that travels down the fiber. Also called the nerve impulse.

Front 49

Amacrine cell

Back 49

A neuron that transmits signals laterally in the retina. Amacrine cells synapse with bipolar cells and ganglion cells.

Front 50

Axial myopia

Back 50

Myopia (nearsightedness) in which the eyeball is too long. See also refractive myopia.

Front 51

Axon

Back 51

The part of the neuron that conducts nerve impulses over distances. Also called the nerve fiber.

Front 52

Bipolar cell

Back 52

A retinal neuron that receives inputs from the visual receptors and sends signals to the retinal ganglion cells.

Front 53

Blind spot

Back 53

The small area where the optic nerve leaves the back of the eye. There are no visual receptors in this area so small images falling directly on the blind spot cannot be seen.

Front 54

Cell body

Back 54

The part of a neuron that contains the neuron's metabolic machinery and that receives stimulation from other neurons.

Front 55

Cone

Back 55

Cone-shaped receptors in the retina that are primarily responsible for vision in high levels of illumination and for color vision and detail vision.

Front 56

Cone spectral sensitivity curve

Back 56

A plot of visual sensitivity versus wavelength for cone vision. Often measured by presenting a small spot of light to the fovea which contains only cones. Can also be measured when the eye is light adapted so cones are the most sensitive receptors.

Front 57

Convergence (neural)

Back 57

When many neurons synapse onto a single neuron.

Front 58

Cornea

Back 58

The transparent focusing element of the eye that is the first structure through which light passes as it enters the eye. The cornea is the eye's major focusing element.

Front 59

Dark adaptation

Back 59

Visual adaptation that occurs in the dark during which the sensitivity to light increases. This increase in sensitivity is associated with regeneration of the rod and cone visual pigments.

Front 60

Dark adaptation curve

Back 60

The function that traces the time course of the increase in visual sensitivity that occurs during dark adaptation.

Front 61

Dark-adapted sensitivity

Back 61

The sensitivity of the eye after it has completely adapted to the dark.

Front 62

Dendrites

Back 62

Nerve processes on the cell body that receive stimulation from other neurons.

Front 63

Depolarization

Back 63

When the inside of a neuron becomes more positive as occurs during the initial phases of the action potential. Depolarization is often associated with the action of excitatory neurotransmitters.

Front 64

Detached retina

Back 64

A condition in which the retina is detached from the back of the eye.

Front 65

Electromagnetic spectrum

Back 65

Continuum of electromagnetic energy that extends from very-short-wavelength gamma rays to longwavelength radio waves. Visible light is a narrow band within this spectrum.

Front 66

Excitatory response

Back 66

The response of a nerve fiber in which the firing rate increases.

Front 67

Eye

Back 67

The eyeball and its contents which include focusing elements the retina and supporting structures.

Front 68

Falling phase of the action potential

Back 68

In the axon or nerve fiber the increase in negativity from +40 mV back to –70 mV (the resting potential level) that occurs during the action potential. This increase in negativity is associated with the flow of positively charged potassium ions (K+) out of the axon.

Front 69

Far point

Back 69

As a light is moved toward the eye the distance at which the light becomes focused on the retina.

Front 70

Farsightedness

Back 70

A condition causing poor vision in which people can see objects that are far away but do not see near objects clearly. Also called hyperopia.

Front 71

Fovea

Back 71

A small area in the human retina that contains only cone receptors. The fovea is located on the line of sight so that when a person looks at an object the center of its image falls on the fovea.

Front 72

Ganglion cell

Back 72

A neuron in the retina that receives inputs from bipolar and amacrine cells. The axons of the ganglion cells are the nerve fibers that travel out of the eye in the optic nerve.

Front 73

Horizontal cell

Back 73

A neuron that transmits signals laterally across the retina. Horizontal cells synapse with receptors and bipolar cells.

Front 74

Hyperopia

Back 74

A condition causing poor vision in which people can see objects that are far away but do not see near objects clearly. Also called farsightedness.

Front 75

Hyperpolarization

Back 75

When the inside of a neuron becomes more negative. Hyperpolarization is often associated with the action of inhibitory neurotransmitters.

Front 76

Inhibitory response

Back 76

Occurs when a neuron's firing rate decreases due to inhibition from another neuron.

Front 77

Ions

Back 77

Charged molecules. Sodium (Na+) potassium (K+) and chlorine (Cl–) are the main ions found within nerve fibers and in the liquid that surrounds nerve fibers.

Front 78

Isomerization

Back 78

Change in shape of the retinal part of the visual pigment molecule that occurs when the molecule absorbs a quantum of light. Isomerization triggers the enzyme cascade that results in transduction from light energy to electrical energy in the retinal receptors.

Front 79

Laser-assisted in situ keratomileusis (LASIK)

Back 79

A process in which the cornea is sculpted with a laser in order to achieve clear vision by adjusting the focusing power of the cornea so it focuses light onto the retina.

Front 80

Lens

Back 80

The transparent focusing element of the eye through which light passes after passing through the cornea and the aqueous humor. The lens's change in shape to focus at different distances is called accommodation.

Front 81

Light-adapted sensitivity

Back 81

The sensitivity of the eye when in the light-adapted state. Usually taken as the starting point for the dark adaptation curve because it is the sensitivity of the eye just before the lights are turned off.

Front 82

Macular degeneration

Back 82

A clinical condition that causes degeneration of the macula an area of the retina that includes the fovea and a small surrounding area.

Front 83

Monochromatic light

Back 83

Light that contains only a single wavelength.

Front 84

Myopia

Back 84

An inability to see distant objects clearly. Also called nearsightedness.

Front 85

Near point

Back 85

The distance at which the lens can no longer accommodate enough to bring close objects into focus. Objects nearer than the near point can be brought into focus only by corrective lenses.

Front 86

Nearsightedness

Back 86

An inability to see distant objects clearly. Also called myopia.

Front 87

Nerve fiber

Back 87

In most sensory neurons the long part of the neuron that transmits electrical impulses from one point to another. Also called the axon.

Front 88

Neural circuit

Back 88

A number of neurons that are connected by synapses.

Front 89

Neural convergence

Back 89

Synapsing of a number of neurons onto one neuron.

Front 90

Neuron

Back 90

The structure that transmits electrical signals in the body. Key components of neurons are the cell body dendrites and the axon or nerve fiber.

Front 91

Neurotransmitter

Back 91

A chemical stored in synaptic vesicles that is released in response to a nerve impulse and has an excitatory or inhibitory effect on another neuron.

Front 92

Optic nerve

Back 92

Bundle of nerve fibers that carry impulses from the retina to the lateral geniculate nucleus and other structures. Each optic nerve contains about 1 million ganglion cell fibers.

Front 93

Outer segment

Back 93

Part of the rod and cone visual receptors that contain the light-sensitive visual pigment molecules.

Front 94

Peripheral retina

Back 94

The area of retina outside the fovea.

Front 95

Permeability

Back 95

A property of a membrane that refers to the ability of molecules to pass through it. If the permeability to a molecule is high the molecule can easily pass through the membrane.

Front 96

Preferential looking (PL) technique

Back 96

A technique used to measure perception in infants. Two stimuli are presented and the infant’s looking behavior is monitored for the amount of time the infant spends viewing each stimulus.

Front 97

Presbyopia

Back 97

The inability of the eye to accommodate due to a hardening of the lens and a weakening of the ciliary muscles. It occurs as people get older.

Front 98

Propagated response

Back 98

A response such as a nerve impulse that travels all the way down the nerve fiber without decreasing in amplitude.

Front 99

Pupil

Back 99

The opening through which light reflected from objects in the environment enters the eye.

Front 100

Purkinje shift

Back 100

The shift from cone spectral sensitivity to rod spectral sensitivity that takes place during dark adaptation. See also spectral sensitivity.

Front 101

Receptor site

Back 101

Small area on the postsynaptic neuron that is sensitive to specific neurotransmitters.

Front 102

Refractive myopia

Back 102

Myopia (nearsightedness) in which the cornea and/or the lens bends the light too much. See also axial myopia.

Front 103

Refractory period

Back 103

The time period of about 1/1000th of a second that a nerve fiber needs to recover from conducting a nerve impulse. No new nerve impulses can be generated in the fiber until the refractory period is over.

Front 104

Resting potential

Back 104

The difference in charge between the inside and the outside of the nerve fiber when the fi ber is not conducting electrical signals. Most nerve fi bers have resting potentials of about 70 mV which means the inside of the fiber is negative relative to the outside.

Front 105

Retina

Back 105

A complex network of cells that covers the inside back of the eye. These cells include the receptors which generate an electrical signal in response to light as well as the horizontal bipolar amacrine and ganglion cells.

Front 106

Retinitis pigmentosa

Back 106

A retinal disease that causes a gradual loss of vision beginning in the peripheral retina.

Front 107

Rising phase of the action potential

Back 107

In the axon or nerve fiber the decrease in negativity from –70 mV to +40 mV (the peak action potential level) that occurs during the action potential. This increase is caused by an inflow of Na+ ions into the axon.

Front 108

Rod

Back 108

A cylinder-shaped receptor in the retina that is responsible for vision at low levels of illumination.

Front 109

Rod monochromat

Back 109

A person who has a retina in which the only functioning receptors are rods.

Front 110

Rod spectral sensitivity curve

Back 110

The curve plotting visual sensitivity versus wavelength for rod vision. This function is typically measured when the eye is dark adapted by a test light presented to the peripheral retina.

Front 111

Rod-cone break

Back 111

The point on the dark adaptation curve at which vision shifts from cone vision to rod vision.

Front 112

Sensory receptors

Back 112

Cells specialized to respond to environmental energy with each sensory system's receptors specialized to respond to a specific type of energy.

Front 113

Spectral sensitivity

Back 113

The sensitivity of visual receptors to different parts of the visible spectrum. See also spectral sensitivity curve.

Front 114

Spectral sensitivity curve

Back 114

The function relating a subject’s sensitivity to light to the wavelength of the light. The spectral sensitivity curves for rod and cone vision indicate that the rods and cones are maximally sensitive at 500 nm and 560 nm respectively. See also Purkinje shift.

Front 115

Spontaneous activity

Back 115

Nerve firing that occurs in the absence of environmental stimulation.

Front 116

Synapse

Back 116

A small space between the end of one neuron (the presynaptic neuron) and the cell body of another neuron (the postsynaptic neuron).

Front 117

Transduction

Back 117

In the senses the transformation of environmental energy into electrical energy. For example the retinal receptors transduce light energy into electrical energy.

Front 118

Visible light

Back 118

The band of electromagnetic energy that activates the visual system and that therefore can be perceived. For humans visible light has wavelengths between 400 and 700 nanometers.

Front 119

Visual acuity

Back 119

The ability to resolve small details.

Front 120

Visual evoked potential (VEP)

Back 120

An electrical response to visual stimulation recorded by the placement of disk electrodes on the back of the head. This potential reflects the activity of a large population of neurons in the visual cortex.

Front 121

Visual pigment

Back 121

A light-sensitive molecule contained in the rod and cone outer segments. The reaction of this molecule to light results in the generation of an electrical response in the receptors.

Front 122

Visual pigment bleaching

Back 122

The change in the color of a visual pigment that occurs when visual pigment molecules are isomerized by exposure to light.

Front 123

Visual pigment regeneration

Back 123

Occurs after the visual pigment’s two components—opsin and retinal—have become separated due to the action of light. Regeneration which occurs in the dark involves a rejoining of these two components to reform the visual pigment molecule. This process depends on enzymes located in the pigment epithelium.

Front 124

Wavelength

Back 124

For light energy the distance between one peak of a light wave and the next peak.

Front 125

Area V1

Back 125

The visual receiving area of the brain called area V1 to indicate that it is the first visual area in the cortex. Also called striate cortex.

Front 126

Belongingness

Back 126

The hypothesis that an area’s appearance is influenced by the part of the surroundings that the area appears to belong to. This principle has been used to explain the perception of lightness in the Benary cross and White’s illusion.

Front 127

Center-surround antagonism

Back 127

the competition between the center and surround regions of a center-surround receptive field caused by the fact that one is excitatory and the other is inhibitory. Stimulating center and surround areas simultaneously decreases responding of the neuron compared to stimulating the excitatory area alone

Front 128

Center-surround organization

Back 128

Arrangement of a neuron’s receptive fields in which one area is surrounded by another area like the hole in a donut (corresponding to the center) and the donut (the surround). Stimulation of the center and surround causes opposite responses. See also Excitatory-center inhibitory-surround receptive field; Inhibitory-center excitatory-surround receptive field.

Front 129

Center-surround receptive field

Back 129

A receptive field that has a center-surround organization.

Front 130

Cerebral cortex

Back 130

The 2-mm-thick layer that covers the surface of the brain and contains the machinery for creating perception as well as for other functions such as language memory and thinking.

Front 131

Complex cell

Back 131

A neuron in the visual cortex that responds best to moving bars with a particular orientation.

Front 132

Contrast threshold

Back 132

The intensity difference that can just barely be seen between two areas. For vision this is often measured using gratings with alternating light and dark bars.

Front 133

Distributed coding

Back 133

Type of neural code in which different perceptual qualities are signaled by the pattern of activity across many neurons. This contrasts with specificity coding in which qualities are signaled by activity in a specific type of neuron.

Front 134

Easy problem of consciousness

Back 134

The problem of determining the relationship between physiological processes like nerve firing and perceptual experience. Note that this involves determining a relationship not a cause. See also hard problem of consciousness.

Front 135

End-stopped cell

Back 135

A cortical neuron that responds best to lines of a specific length that are moving in a particular direction.

Front 136

Excitatory area

Back 136

Area of a receptive field that is associated with excitation. Stimulation of this area causes an increase in the rate of nerve firing.

Front 137

Excitatory-center

Back 137

inhibitory-surround receptive field "A center-surround receptive field in which stimulation of the center area causes an excitatory response and stimulation of the surround causes an inhibitory response.

Front 138

Experience-dependent plasticity

Back 138

A process by which neurons adapt to the specific environment within which a person or animal lives. This is achieved when neurons change their response properties so they become tuned to respond best to stimuli that have been repeatedly experienced in the environment. See also neural plasticity; selective rearing.

Front 139

Feature detector

Back 139

A neuron that responds selectively to a specific feature of the stimulus such as orientation or direction of motion.

Front 140

Fusiform face area (FFA)

Back 140

An area in the human inferotemporal (IT) cortex that contains neurons that are specialized to respond to faces.

Front 141

Grandmother cell

Back 141

A hypothesized type of neuron that responds only to a very specific stimulus such as a person’s grandmother. See also specificity coding.

Front 142

Hard problem of consciousness

Back 142

The problem of determining how physiological processes such as ion flow across nerve membranes cause different perceptual experiences. See also mind-body problem.

Front 143

Hermann grid

Back 143

A display that results in the illusion of dark areas at the intersection of two white “corridors.” This perception can be explained by lateral inhibition.

Front 144

Inferotemporal (IT) cortex

Back 144

An area of the brain outside Area V1 (the striate cortex) involved in object perception and facial recognition.

Front 145

Inhibitory area

Back 145

Area of a receptive field that is associated with inhibition. Stimulation of this area causes a decrease in the rate of nerve firing.

Front 146

Inhibitory-center

Back 146

excitatory-surround receptive fieldA center-surround receptive field in which stimulation of the center causes an inhibitory response and stimulation of the surround causes an excitatory response.

Front 147

Lateral geniculate nucleus (LGN)

Back 147

The nucleus in the thalamus that receives inputs from the optic nerve and in turn communicates with the cortical receiving area for vision.

Front 148

Lateral inhibition

Back 148

Inhibition that is transmitted laterally across a nerve circuit. In the retina lateral inhibition is transmitted by the horizontal and amacrine cells.

Front 149

Lightness

Back 149

The perception of shades ranging from white to grey to black.

Front 150

Mind-body problem

Back 150

One of the most famous problems in science: How do physical processes such as nerve impulses or sodium and potassium molecules flowing across membranes (the body part of the problem) become transformed into the richness of perceptual experience (the mind part of the problem)? See also hard problem of consciousness.

Front 151

Neural correlate of consciousness (NCC)

Back 151

Connections between the firing of neurons and perceptual experience. See also easy problem of consciousness.

Front 152

Neural plasticity

Back 152

The capacity of the nervous system to change in response to experience. Examples are how early visual experience can change the orientation selectivity of neurons in the visual cortex and how tactile experience can change the sizes of areas in the cortex that represent different parts of the body. See also experience-dependent plasticity; selective rearing.

Front 153

Neural processing

Back 153

Operations that transform electrical signals within a network of neurons or that transform the response of individual neurons.

Front 154

Occipital lobe

Back 154

A lobe at the back of the cortex that is the site of the cortical receiving area for vision.

Front 155

Ommatidium

Back 155

A structure in the eye of the Limulus that contains a small lens located directly over a visual receptor. The Limulus eye is made up of hundreds of these ommatidia. The Limulus eye has been used for research on lateral inhibition because its receptors are large enough so that stimulation can be applied to individual receptors.

Front 156

Orientation tuning curve

Back 156

A function relating the firing rate of a neuron to the orientation of the stimulus.

Front 157

Prosopagnosia

Back 157

A form of visual agnosia in which the person can’t recognize faces.

Front 158

Receptive field

Back 158

A neuron’s receptive field is the area on the receptor surface (the retina for vision; the skin for touch) that when stimulated affects the firing of that neuron.

Front 159

Selective adaptation

Back 159

A procedure in which a person or animal is selectively exposed to one stimulus and then the effect of this exposure is assessed by testing with a wide range of stimuli. Typically sensitivity to the exposed stimulus is decreased.

Front 160

Selective rearing

Back 160

A procedure in which animals are reared in special environments. An example of selective rearing is the experiment in which kittens were reared in an environment of vertical stripes to determine the effect on orientation selectivity of cortical neurons.

Front 161

Simple cortical cells

Back 161

A neuron in the visual cortex that responds best to bars of a particular orientation.

Front 162

Simultaneous contrast

Back 162

The effect that occurs when surrounding one color with another changes the appearance of the surrounded color. Occurs for chromatic and achromatic stimuli.

Front 163

Sparse coding

Back 163

The idea that a particular object is represented by the firing of a relatively small number of neurons.

Front 164

Specifity coding

Back 164

Type of neural code in which different perceptions are signaled by activity in specific neurons. See also distributed coding.

Front 165

Striate cortex

Back 165

The visual receiving area of the cortex located in the occipital lobe.

Front 166

Superior colliculus

Back 166

An area in the brain that is involved in controlling eye movements and other visual behaviors. This area receives about 10 percent of the ganglion cell fibers that leave the eye in the optic nerve.

Front 167

Visual receiving area

Back 167

The area of the occipital lobe where signals from the retina and LGN first reach the cortex.

Front 168

White's illusion

Back 168

A display in which two rectangles are perceived as differing in lightness even though they both reflect the same amount of light and even though the rectangle that is perceived as lighter receives more lateral inhibition than the one perceived as darker.

Front 169

Ablation

Back 169

Removal of an area of the brain. This is usually done in experiments on animals to determine the function of a particular area. Also called lesioning.

Front 170

Action pathway

Back 170

Pathway that conducts signals from the striate cortex to the parietal lobe. See also dorsal pathway.

Front 171

Brain imaging

Back 171

Procedures that make it possible to visualize areas of the human brain that are activated by different types of stimuli tasks or behaviors. The two most common techniques used in perception research are positron emission tomography (PET) and functional magnetic resonance imaging (fMRI).

Front 172

Cortical magnification

Back 172

Occurs when a disproportionately large area on the cortex is activated by stimulation of a small area on the receptor surface. One example of cortical magnification is the relatively large area of visual cortex that is activated by stimulation of the fovea. An example in the somatosensory system is the large area of somatosensory cortex activated by stimulation of the lips and fingers.

Front 173

Dorsal pathway

Back 173

Pathway that conducts signals from the striate cortex to the parietal lobe. The dorsal pathway has also been called the where the how or the action pathway by different investigators.

Front 174

Double dissociation

Back 174

In brain damage when function A is present and function B is absent in one person and function A is absent and function B is present in another. Presence of a double dissociation means that the two functions involve different mechanisms and operate independently of one another.

Front 175

Expertise hypothesis

Back 175

The idea that human proficiency in perceiving certain things can be explained by changes in the brain caused by long exposure practice or training.

Front 176

Extrastriate body area (EBA)

Back 176

An area of the temporal lobe that is activated by pictures of bodies and parts of bodies.

Front 177

Functional magnetic resonance imaging (fMRI)

Back 177

A brain imaging technique that indicates brain activity in awake behaving organisms. The fMRI response occurs when the response to a magnetic field changes in response to changes in blood flow in the brain.

Front 178

Fusiform face area (FFA)

Back 178

An area in the human inferotemporal (IT) cortex that contains neurons that are specialized to respond to faces.

Front 179

How pathway

Back 179

Pathway that conducts signals from the striate cortex to the parietal lobe. See also dorsal pathway.

Front 180

Hypercolumn

Back 180

In the striate cortex unit proposed by Hubel and Wiesel that combines location orientation and ocular dominance columns that serve a specific area on the retina.

Front 181

Landmark discrimination problem

Back 181

The behavioral task used in Ungerleider and Mishkin’s experiment in which they provided evidence for the dorsal or where visual processing stream. Monkeys were required to respond to a previously indicated location.

Front 182

Location column

Back 182

A column in the visual cortex that contains neurons with the same receptive field locations on the retina.

Front 183

Module

Back 183

A structure that processes information about a specific behavior or perceptual quality. Often identified as a structure that contains a large proportion of neurons that respond selectively to a particular quality such as the fusiform face area which contains many neurons that respond selectively to faces.

Front 184

Neuropsychology

Back 184

The study of the behavioral effects of brain damage in humans.

Front 185

Object discrimination problem

Back 185

The behavioral task used in Ungerleider and Mishkin’s experiment in which they provided evidence for the ventral or what visual processing stream. Monkeys were required to respond to an object with a particular shape.

Front 186

Ocular dominance

Back 186

The degree to which a neuron is influenced by stimulation of each eye. A neuron has a large amount of ocular dominance if it responds only to stimulation of one eye. There is no ocular dominance if the neuron responds equally to stimulation of both eyes.

Front 187

Ocular dominance column

Back 187

A column in the visual cortex that contains neurons that respond best to stimulation of the same eye.

Front 188

Orientation column

Back 188

A column in the visual cortex that contains neurons with the same orientation preference.

Front 189

Parahippocampal place area (PPA)

Back 189

An area in the temporal lobe that is activated by indoor and outdoor scenes.

Front 190

Positron emission tomography (PET)

Back 190

A brain mapping technique that is used in awake human subjects to determine which brain areas are activated by various tasks.

Front 191

Retinotopic map

Back 191

A map on a structure in the visual system such as the lateral geniculate nucleus or the cortex that indicates locations on the structure that correspond to locations on the retina. In retinotopic maps locations adjacent to each other on the retina are usually represented by locations that are adjacent to each other on the structure.

Front 192

Spatial organization

Back 192

How different locations in the environment and on the receptors are represented in the brain.

Front 193

Tiling

Back 193

The adjacent (and often overlapping) location columns working together to cover the entire visual field (similar to covering a floor with tiles).

Front 194

Ventral pathway

Back 194

Pathway that conducts signals from the striate cortex to the temporal lobe. Also called the what pathway because it is involved in recognizing objects.

Front 195

What pathway

Back 195

Pathway that conducts signals from the striate cortex to the temporal lobe. Called the what pathway because it is involved in recognizing objects. See also ventral pathway.

Front 196

Where pathway

Back 196

Pathway that conducts signals from the striate cortex to the parietal lobe. See also dorsal pathway.

Front 197

Apparent movement

Back 197

An illusion of movement that occurs when two objects separated in space are presented rapidly one after another separated by a brief time interval.

Front 198

Bayesian inference

Back 198

A statistical approach to perception in which perception is determined by taking probabilities into account. These probabilities are based on past experiences in perceiving properties of objects and scenes.

Front 199

Binocular rivalry

Back 199

A situation in which one image is presented to the left eye and a different image is presented to the right eye and perception alternates back and forth between the two images.

Front 200

Border ownership

Back 200

When two areas share a border as occurs in figure–ground displays the border is usually perceived as belonging to the figure.

Front 201

Figure

Back 201

When an object is seen as separate from the background (the “ground”) it is called a figure. See also figure–ground segregation.

Front 202

Figure-ground segregation

Back 202

The perceptual separation of an object from its background.

Front 203

Gestalt psychology

Back 203

An approach to psychology that developed as a reaction to structuralism. The Gestalt approach proposes principles of perceptual organization and figure–ground segregation and states that “the whole is different than the sum of its parts.”

Front 204

Gist of a scene

Back 204

General description of a scene. People can identify most scenes after viewing them for only a fraction of a second as when they flip rapidly from one TV channel to another. It takes longer to identify the details within the scene.

Front 205

Global image features

Back 205

Information that may enable observers to rapidly perceive the gist of a scene. Features associated with specific types of scenes include degree of naturalness degree of openness degree of roughness degree of expansion and color.

Front 206

Ground

Back 206

In object perception the background is called the ground. See also figure.

Front 207

Grouping

Back 207

In perceptual organization the process by which visual events are “put together” into units or objects.

Front 208

Illusory contour

Back 208

Contour that is perceived even though it is not present in the physical stimulus.

Front 209

Inverse projection problem

Back 209

The idea that a particular image on the retina could have been caused by an infinite number of different objects. This means that the retinal image does not unambiguously specify a stimulus.

Front 210

Light-from-above assumption

Back 210

The assumption that light usually comes from above which influences our perception of form in some situations.

Front 211

Likelihood principle

Back 211

The idea proposed by Helmholtz that we perceive the object that is most likely to have caused the pattern of stimuli we have received.

Front 212

Organizing principles

Back 212

In Gestalt psychology the rules that determine how elements in a scene become grouped together.

Front 213

Perceptual organization

Back 213

The process by which small elements become perceptually grouped into larger objects.

Front 214

Perceptual segregation

Back 214

Perceptual organization in which one object is seen as separate from other objects.

Front 215

Persistence of vision

Back 215

A phenomenon in which perception of any stimulus persists for about 250 ms after the stimulus is physically terminated.

Front 216

Physical regularities

Back 216

Regularly occurring physical properties of the environment. For example there are more vertical and horizontal orientations in the environment than oblique (angled) orientations.

Front 217

Principle of common fate

Back 217

A Gestalt principle of perceptual organization that states that things that are moving in the same direction appear to be grouped together.

Front 218

Principle of common region

Back 218

A modern Gestalt principle that states that elements that are within the same region of space appear to be grouped together.

Front 219

Principle of good continuation

Back 219

A Gestalt principle of perceptual organization that states that points that when connected result in straight or smoothly curving lines are seen as belonging together and that lines tend to be seen in such a way as to follow the smoothest path.

Front 220

Principle of good figure

Back 220

A Gestalt principle of perceptual organization that states that every stimulus pattern is seen in such a way that the resulting structure is as simple as possible. Also called the principle of pragnanz or the principle of simplicity.

Front 221

Principle of pragnanz

Back 221

A Gestalt principle of perceptual organization that states that every stimulus pattern is seen in such a way that the resulting structure is as simple as possible. Also called the principle of good figure or the principle of simplicity.

Front 222

Principle of proximity

Back 222

A Gestalt principle of perceptual organization that states that things that are near to each other appear to be grouped together. Also called the law of nearness.

Front 223

Principle of similarity

Back 223

A Gestalt principle stating that similar things appear to be grouped together.

Front 224

Principle of simplicity

Back 224

A Gestalt principle of perceptual organization that states that every stimulus pattern is seen in such a way that the resulting structure is as simple as possible. Also called the principle of good figure or the principle of pragnanz.

Front 225

Principle of uniform connectedness

Back 225

A modern Gestalt principle that states that connected regions of a visual stimulus are perceived as a single unit.

Front 226

Regularities in the environment

Back 226

Characteristics of the environment that occur regularly and in many different situations.

Front 227

Reversible figure-ground

Back 227

A figure–ground pattern that perceptually reverses as it is viewed so that the figure becomes the ground and the ground becomes the figure. The best-known reversible figure–ground pattern is Rubin’s vase–face pattern.

Front 228

Scene

Back 228

A view of a real-world environment that contains (a) background elements and (b) multiple objects that are organized in a meaningful way relative to each other and the background.

Front 229

Segregation

Back 229

The process of separating one area or object from another. See also figure–ground segregation.

Front 230

Semantic encoding

Back 230

A method for analyzing the patterns of voxel activation recorded from visual areas of an observer’s brain based on the relationship between voxel activation and the meaning or category of a scene.

Front 231

Semantic regularities

Back 231

Characteristics associated with the functions associated with different types of scenes. These characteristics are learned from experience. For example most people are aware of the kinds of activities and objects that are usually associated with kitchens.

Front 232

Sensations

Back 232

Elementary elements that according to the structuralists combine to create perceptions.

Front 233

Structural encoding

Back 233

A method for analyzing the patterns of voxel activation recorded from visual areas of an observer’s brain based on the relationship between voxel activation and structural characteristics of a scene such as lines contrasts shapes and textures.

Front 234

Structuralism

Back 234

The approach to psychology prominent in the late 19th and early 20th centuries that postulated that perceptions result from the summation of many elementary sensations. The Gestalt approach to perception was in part a reaction to structuralism.

Front 235

Theory of unconscious inference

Back 235

The idea proposed by Helmholtz that some of our perceptions are the result of unconscious assumptions that we make about the environment. See also likelihood principle.

Front 236

Viewpoint invariance

Back 236

The condition in which object properties don’t change when viewed from different angles. Responsible for our ability to recognize objects when viewed from different angles.

Front 237

Visual masking stimulus

Back 237

A visual pattern that when presented immediately after a visual stimulus decreases a person’s ability to perceive the stimulus. This stops the persistence of vision and therefore limits the effective duration of the stimulus.

Front 238

Attention

Back 238

The process of focusing on some objects while ignoring others. Attention can enhance the processing of the attended object.

Front 239

Attentional capture

Back 239

Occurs when stimulus salience causes an involuntary shift of attention. For example attention can be captured by movement.

Front 240

Autism

Back 240

A serious developmental disorder in which one of the major symptoms is the withdrawal of contact from other people. People with autism typically do not make eye contact with others and have difficulty telling what emotions others are experiencing in social situations.

Front 241

Balint's syndrome

Back 241

A condition resulting from damage to a person’s parietal lobe. One characteristic of this syndrome is an inability to focus attention on individual objects.

Front 242

Binding

Back 242

The process by which features such as color form motion and location are combined to create our perception of a coherent object. Binding can also occur across senses as when sound and vision are associated with the same object.

Front 243

Binding problem

Back 243

The problem of how neural activity in many separated areas in the brain is combined to create a perception of a coherent object.

Front 244

Change blindness

Back 244

Difficulty in detecting differences between two visual stimuli that are presented one after another often with a short blank stimulus interposed between them. Also occurs when part of a stimulus is changed very slowly.

Front 245

Conjunction search

Back 245

A visual search task in which it is necessary to search for a combination (or conjunction) of two or more features on the same stimulus to find the target. An example of a conjunction search would be looking for a horizontal green line among vertical green lines and horizontal red lines.

Front 246

Covert attention

Back 246

Attention without looking. Seeing something “out of the corner of your eye” is an example of covert attention.

Front 247

Dishabituation

Back 247

An increase in looking time that occurs when a stimulus is changed. This response is used in testing infants to see whether they can differentiate two stimuli.

Front 248

Dual-task procedure

Back 248

An experimental procedure in which subjects are required to carry out simultaneously a central task that demands attention and a peripheral task that involves making a decision about the contents of a scene.

Front 249

Feature integration theory

Back 249

A theory proposed by Treisman to explain how an object is broken down into features and how these features are recombined to result in a perception of the object.

Front 250

Feature search

Back 250

A visual search task in which a person can find a target by searching for only one feature. An example would be looking for a horizontal green line among vertical green lines.

Front 251

Fixation

Back 251

The brief pause of the eye that occurs between eye movements as a person scans a scene.

Front 252

Focused attention stage (of perceptual processing)

Back 252

The stage of processing in feature integration theory in which the features are combined. According to Treisman this stage requires focused attention.

Front 253

Habituation

Back 253

Paying less attention to the same stimulus that is presented repeatedly. For example infants look at a stimulus less and less on each successive trial. See also dishabituation.

Front 254

High-load task

Back 254

Task that involves more processing resources and that therefore uses more of a person’s perceptual capacity.

Front 255

Illusory conjunction

Back 255

Illusory combination of features that are perceived when stimuli containing a number of features are presented briefly and under conditions in which focused attention is difficult. For example presenting a red square and a blue triangle could potentially create the perception of a red triangle.

Front 256

Inattentional blindness

Back 256

A situation in which a stimulus that is not attended is not perceived even though the person is looking directly at it.

Front 257

Load theory of attention

Back 257

Lavie’s proposal that the amount of perceptual capacity that remains as a person is carrying out a task determines how well the person can avoid being distracted by task-irrelevant stimuli. If a person’s perceptual load is close to perceptual capacity the person is less likely to be distracted by task-irrelevant stimuli. See also high-load tasks; low-load tasks; perceptual capacity; perceptual load.

Front 258

Low-load task

Back 258

A task that uses only a small amount of the person’s perceptual capacity.

Front 259

Overt attention

Back 259

Attention that involves looking directly at the attended object.

Front 260

Perceptual capacity

Back 260

The resources a person has for carrying out perceptual tasks.

Front 261

Perceptual completion

Back 261

The perception of an object as extending behind occluding objects.

Front 262

Perceptual load

Back 262

The amount of a person’s perceptual capacity needed to carry out a particular perceptual task.

Front 263

Preattentive stage (of perceptual processing)

Back 263

An automatic and rapid stage of processing proposed by Treisman’s feature integration theory during which a stimulus is decomposed into individual features.

Front 264

Precueing

Back 264

A procedure in which a cue stimulus is presented to direct an observer’s attention to a specific location where a test stimulus is likely to be presented. This procedure was used by Posner to show that attention enhances the processing of a stimulus presented at the cued location.

Front 265

Saccadic eye movement

Back 265

Rapid eye movement between fixations that occurs when scanning a scene.

Front 266

Saliency map

Back 266

A “map” of a visual display that takes into account characteristics of the display such as color contrast and orientation that are associated with capturing attention.

Front 267

Same-object advantage

Back 267

The faster responding that occurs when enhancement spreads within an object. Faster reaction times occur when a target is located within the object that is receiving the subject’s attention even if the subject is looking at another place within the object.

Front 268

Scene schema

Back 268

An observer’s knowledge about what is contained in typical scenes. An observer’s attention is affected by knowledge of what is usually found in the scene.

Front 269

Scene statistics

Back 269

The probability of various things occurring in the environment.

Front 270

Spatial attention

Back 270

Attention to a specific location.

Front 271

Stimulus salience

Back 271

Characteristics such as bright colors high contrast and highly visible orientations that cause stimuli to stand out and therefore attract attention.

Front 272

Task-irrelevant stimuli

Back 272

Stimuli that do not provide information relevant to the task at hand.

Front 273

Visual scanning

Back 273

Moving the eyes to focus attention on different locations on objects or in scenes.

Front 274

Visual search

Back 274

A procedure in which a person’s task is to find a particular element in a display that contains a number of elements.

Front 275

Akinetopsia

Back 275

A condition in which damage to an area of the cortex involved in motion perception causes blindness to motion.

Front 276

Aperture problem

Back 276

Occurs when only a portion of a moving stimulus can be seen as when the stimulus is viewed through a narrow aperture. This can result in misleading information about the direction in which the stimulus is moving.

Front 277

Apparent motion

Back 277

An illusion of movement that occurs when two objects separated in space are presented rapidly one after another separated by a brief time interval.

Front 278

Attentional capture

Back 278

Occurs when stimulus salience causes an involuntary shift of attention. For example attention can be captured by movement.

Front 279

Biological motion

Back 279

Motion produced by biological organisms. Most of the experiments on biological motion have used walking humans with lights attached to their joints and limbs as stimuli. See also point-light walker.

Front 280

Coherence

Back 280

In research on movement perception in which arrays of moving dots are used as stimuli the degree of correlation between the direction of the moving dots. Zero percent coherence means all of the dots are moving independently; 100 percent coherence means all of the dots are moving in the same direction.

Front 281

Comparator

Back 281

A structure hypothesized by the corollary discharge theory of movement perception. The corollary discharge signal and the sensory movement signal meet at the comparator to determine whether movement will be perceived.

Front 282

Corollary discharge signal (CDS)

Back 282

A copy of the motor signal that is sent to the eye muscles to cause movement of the eye. The copy is sent to the hypothetical comparator of corollary discharge theory.

Front 283

Corollary discharge theory

Back 283

The theory that explains motion perception as being determined both by movement of the image on the retina and by signals that indicate movement of the eyes. See also corollary discharge signal.

Front 284

Event

Back 284

A segment of time at a particular location that is perceived by observers to have a beginning and an ending.

Front 285

Event boundary

Back 285

The point in time when one event ends and another begins.

Front 286

Global optic flow

Back 286

Information for movement that occurs when all elements in a scene move. The perception of global optic flow indicates that it is the observer that is moving and not the scene.

Front 287

Illusory motion

Back 287

Perception of motion when there actually is none. See also apparent motion.

Front 288

Image displacement signal (IDS)

Back 288

In corollary discharge theory the signal that occurs when an image moves across the visual receptors.

Front 289

Implied motion

Back 289

When a still picture depicts an action that involves motion so that an observer could potentially extend the action depicted in the picture in his or her mind based on what will most likely happen next.

Front 290

Induced motion

Back 290

The illusory movement of one object that is caused by the movement of another object that is nearby.

Front 291

Local disturbance in the optic array

Back 291

Occurs when one object moves relative to the environment so that the stationary background is covered and uncovered by the moving object. This local disturbance indicates that the object is moving relative to the environment.

Front 292

Microstimulation

Back 292

A procedure in which a small electrode is inserted into the cortex and an electrical current passed through the electrode activates neurons near the tip of the electrode. This procedure has been used to determine how activating specific groups of neurons affects perception.

Front 293

Motion aftereffect

Back 293

An illusion that occurs after a person views a moving stimulus and then sees movement in the opposite direction when viewing a stationary stimulus immediately afterward. See also waterfall illusion.

Front 294

Motor signal (MS)

Back 294

In corollary discharge theory the signal that is sent to the eye muscles when the observer moves or tries to move his or her eyes.

Front 295

Optic array

Back 295

The structured pattern of light created by the presence of objects surfaces and textures in the environment.

Front 296

Point-light walker

Back 296

A biological motion stimulus created by placing lights at a number of places on a person’s body and having an observer view the moving-light stimulus that results as the person moves in the dark.

Front 297

Real motion

Back 297

The physical movement of a stimulus. Contrasts with apparent motion.

Front 298

Real-motion neuron

Back 298

Neuron in the monkey’s cortex that responds when movement of an image across the retina is caused by movement of a stimulus but does not respond when movement across the retina is caused by movement of the eyes.

Front 299

Reichardt detector

Back 299

A neural circuit that results in neurons firing to movement in one direction. Excitation and inhibition are arranged so that movement in one direction creates inhibition that reduces or eliminates neural responding whereas movement in the opposite direction creates excitation that enhances neural responding.

Front 300

Representational momentum

Back 300

Occurs when motion depicted in a still picture continues in an observer’s mind.

Front 301

Shortest path constraint

Back 301

In the perception of apparent motion the principle that apparent movement tends to occur along the shortest path between two stimuli.

Front 302

Waterfall illusion

Back 302

An aftereffect of movement that occurs after viewing a stimulus moving in one direction such as a waterfall. Viewing the waterfall makes other objects appear to move in the opposite direction. See also movement aftereffect.

Front 303

Achromatic color

Back 303

Color without hue. White black and all the grays between these two extremes are achromatic colors.

Front 304

Additive color mixture

Back 304

The creation of colors that occurs when lights of different colors are superimposed.

Front 305

Anomalous trichromat

Back 305

A person who needs to mix a minimum of three wavelengths to match any other wavelength in the spectrum but mixes these wavelengths in different proportions from a trichromat.

Front 306

Cerebral achromatopsia

Back 306

A loss of color vision caused by damage to the cortex.

Front 307

Chromatic adaptation

Back 307

Exposure to light in a specific part of the visible spectrum. This adaptation can cause a decrease in sensitivity to light from the area of the spectrum that was presented during adaptation.

Front 308

Chromatic color

Back 308

Color with hue such as blue yellow red or green.

Front 309

Color blindness

Back 309

A condition in which a person perceives no chromatic color. This can be caused by absent or malfunctioning cone receptors or by cortical damage.

Front 310

Color constancy

Back 310

The effect in which the perception of an object’s hue remains constant even when the wavelength distribution of the illumination is changed. Partial color constancy occurs when our perception of hue changes a little when the illumination changes though not as much as we might expect from the change in the wavelengths of light reaching the eye.

Front 311

Color deficiency

Back 311

People with this condition (sometimes incorrectly called color blindness) see fewer colors than people with normal color vision and need to mix fewer wavelengths to match any other wavelength in the spectrum.

Front 312

Color-matching experiment

Back 312

A procedure in which observers are asked to match the color in one field by mixing two or more lights in another field.

Front 313

Desaturated

Back 313

Low saturation in chromatic colors as would occur when white is added to a color. For example pink is not as saturated as red.

Front 314

Deuteranopia

Back 314

A form of red–green color dichromatism caused by lack of the middle-wavelength cone pigment.

Front 315

Dichromat

Back 315

A person who has a form of color deficiency. Dichromats can match any wavelength in the spectrum by mixing two other wavelengths. Deuteranopes protanopes and tritanopes are all dichromats.

Front 316

Double-opponent neurons

Back 316

Neurons that have receptive fields in which stimulation of one part of the receptive field causes an excitatory response to wavelengths in one area of the spectrum and an inhibitory response to wavelengths in another area of the spectrum and stimulation of an adjacent part of the receptive field causes the opposite response. An example of double-opponent responding is when the response of one part of a receptive field is L+ M- and the response of an adjacent part is L- M+.

Front 317

Hue

Back 317

The experience of a chromatic color such as red green yellow or blue or combinations of these colors.

Front 318

Illumination edge

Back 318

The border between two areas created by different light intensities in the two areas.

Front 319

Ishihara plate

Back 319

A display of colored dots used to test for the presence of color deficiency. The dots are colored so that people with normal (trichromatic) color vision can perceive numbers in the plate but people with color deficiency cannot perceive these numbers or perceive different numbers than someone with trichromatic vision.

Front 320

Lightness

Back 320

The perception of shades ranging from white to grey to black.

Front 321

Lightness constancy

Back 321

The constancy of our perception of an object’s lightness under different intensities of illumination.

Front 322

Memory color

Back 322

The idea that an object’s characteristic color influences our perception of that object’s color.

Front 323

Metamerism

Back 323

The situation in which two physically different stimuli are perceptually identical. In vision this refers to two lights with different wavelength distributions that are perceived as having the same color.

Front 324

Metamers

Back 324

Two lights that have different wavelength distributions but are perceptually identical.

Front 325

Monochromat

Back 325

A person who is completely color-blind and therefore sees everything as black white or shades of gray. A monochromat can match any wavelength in the spectrum by adjusting the intensity of any other wavelength. Monochromats generally have only one type of functioning receptors usually rods.

Front 326

Neutral point

Back 326

The wavelength at which a dichromat perceives gray.

Front 327

Opponent neuron

Back 327

A neuron that has an excitatory response to wavelengths in one part of the spectrum and an inhibitory response to wavelengths in the other part of the spectrum.

Front 328

Opponent-process theory of color vision

Back 328

A theory originally proposed by Hering which claimed that our perception of color is determined by the activity of two opponent mechanisms: a blue–yellow mechanism and a red–green mechanism. The responses to the two colors in each mechanism oppose each other one being an excitatory response and the other an inhibitory response. In addition this theory also includes a black–white mechanism which is concerned with the perception of brightness. See also opponent neuron.

Front 329

Partial color constancy

Back 329

A type of color constancy that occurs when changing an object’s illumination causes a change in perception of the object’s hue but less change than would be expected based on the change in the wavelengths of light reaching the eye. Note that in complete color constancy changing an object’s illumination causes no change in the object’s hue.

Front 330

Penumbra

Back 330

The fuzzy border at the edge of a shadow.

Front 331

Protanopia

Back 331

A form of red–green dichromatism caused by a lack of the long-wavelength cone pigment.

Front 332

Ratio principle

Back 332

A principle stating that two areas that reflect different amounts of light will have the same perceived lightness if the ratios of their intensities to the intensities of their surroundings are the same.

Front 333

Reflectance

Back 333

The percentage of light reflected from a surface.

Front 334

Reflectance curve

Back 334

A plot showing the percentage of light reflected from an object versus wavelength.

Front 335

Reflectance edge

Back 335

An edge between two areas where the reflectance of two surfaces changes.

Front 336

Saturation (color)

Back 336

The relative amount of whiteness in a chromatic color. The less whiteness a color contains the more saturated it is.

Front 337

Selective reflection

Back 337

When an object reflects some wavelengths of the spectrum more than others.

Front 338

Selective transmission

Back 338

When some wavelengths pass through visually transparent objects or substances and others do not. Selective transmission is associated with the perception of chromatic color. See also selective reflection.

Front 339

Simultaneous color contrast

Back 339

The effect that occurs when surrounding one color with another changes the appearance of the surrounded color. Occurs for chromatic and achromatic stimuli.

Front 340

Single-opponent neuron

Back 340

Neurons that increase firing to long wavelengths presented to the center of the receptive field and decrease firing to short wavelengths presented to the surround (or vice versa).

Front 341

Subtractive color mixture

Back 341

The creation of colors that occurs when paints of different colors are mixed together.

Front 342

Trichromat

Back 342

A person with normal color vision. Trichromats can match any wavelength in the spectrum by mixing three other wavelengths in various proportions.

Front 343

Trichromatic theory of color vision

Back 343

A theory proposing that our perception of color is determined by the ratio of activity in three receptor mechanisms with different spectral sensitivities. See also Young-Helmholtz theory of color vision.

Front 344

Tritanopia

Back 344

A form of dichromatism thought to be caused by a lack of the short-wavelength cone pigment.

Front 345

Unilateral dichromat

Back 345

A person who has dichromatic vision in one eye and trichromatic vision in the other eye. People with this condition (which is extremely rare) have been tested to determine what colors a dichromats perceive by asking them to compare the perceptions they experience with their dichromatic eye and their trichromatic eye.

Front 346

Young-Helmholtz theory of color vision

Back 346

A theory proposing that our perception of color is determined by the ratio of activity in three receptor mechanisms with different spectral sensitivities. See also trochromatic theory of color vision.

Front 347

Absolute disparity

Back 347

The visual angle between the images of an object on the two retinas. When images of an object fall on corresponding points the angle of disparity is zero. When images fall on noncorresponding points the angle of disparity indicates the degree of noncorrespondence.

Front 348

Accretion

Back 348

A cue that provides information about the relative depth of two surfaces. Occurs when the farther object is uncovered by the nearer object due to sideways movement of an observer relative to the objects. See also deletion.

Front 349

Active method (3-D TV)

Back 349

A method used to create 3-D television images. The active method alternates the left-eye and right-eye images on the screen 30 or more times a second. This method is called active because the viewing glasses have a shutter system that is synchronized with the alternating images on the TV screen.

Front 350

Ames room

Back 350

A distorted room first built by Adelbert Ames that creates an erroneous perception of the sizes of people in the room. The room is constructed so that two people at the far wall of the room appear to stand at the same distance from an observer. In actuality one of the people is much farther away than the other.

Front 351

Angle of disparity

Back 351

The visual angle between the images of an object on the two retinas. When images of an object fall on corresponding points the angle of disparity is zero. When images fall on noncorresponding points the angle of disparity indicates the degree of noncorrespondence.

Front 352

Angular size contrast theory

Back 352

An explanation of the moon illusion that states that the perceived size of the moon is determined by the sizes of the objects that surround it. According to this idea the moon appears small when it is surrounded by large objects such as the expanse of the sky when the moon is overhead.

Front 353

Apparent distance theory

Back 353

An explanation of the moon illusion that is based on the idea that the horizon moon which is viewed across the filled space of the terrain should appear farther away than the zenith moon which is viewed through the empty space of the sky. This theory states that because the horizon and zenith moons have the same visual angle but are perceived to be at different distances the farther appearing horizon moon should appear larger.

Front 354

Atmospheric perspective

Back 354

A depth cue. Objects that are farther away look more blurred and bluer than objects that are closer because we must look through more air and particles to see them.

Front 355

Binocular depth cell

Back 355

A neuron in the visual cortex that responds best to stimuli that fall on points separated by a specific degree of disparity on the two retinas. Also called a disparity-selective cell.

Front 356

Binocular disparity

Back 356

Occurs when the retinal images of an object fall on disparate points on the two retinas.

Front 357

Binocularly fixate

Back 357

Directing the two foveas to exactly the same spot.

Front 358

Conflicting cues theory

Back 358

A theory of visual illusions proposed by R. H. Day which states that our perception of line length depends on an integration of the actual line length and the overall figure length.

Front 359

Correspondence problem

Back 359

The problem faced by the visual system which must determine which parts of the images in the left and right eyes correspond to one another. Another way of stating the problem is: How does the visual system match up the images in the two eyes? This matching of the images is involved in determining depth perception using the cue of binocular disparity.

Front 360

Corresponding retinal points

Back 360

The points on each retina that would overlap if one retina were slid on top of the other. Receptors at corresponding points send their signals to the same location in the brain.

Front 361

Cue approach to depth perception

Back 361

The approach to explaining depth perception that identifies information in the retinal image and also information provided by aiming and focusing the eyes on an object that is correlated with depth in the scene. Some of the depth cues that have been identified are overlap relative height relative size atmospheric perspective convergence and accommodation.

Front 362

Deletion

Back 362

A cue that provides information about the relative depth of two surfaces. Deletion occurs when a farther object is covered by a nearer object due to sideways movement of an observer relative to the objects. See also accretion.

Front 363

Disparity tuning curve

Back 363

A plot of a neuron’s response versus the degree of disparity of a visual stimulus. The disparity to which a neuron responds best is an important property of disparity-selective cells which are also called binocular depth cells.

Front 364

Disparity-selective cell

Back 364

A neuron in the visual cortex that responds best to stimuli that fall on points separated by a specific degree of disparity on the two retinas. Also called a binocular depth cell.

Front 365

Echolocation

Back 365

Locating objects by sending out high-frequency pulses and sensing the echo created when these pulses are reflected from objects in the environment. Echolocation is used by bats and dolphins.

Front 366

Emmert's law

Back 366

A law stating that the size of an afterimage depends on the distance of the surface against which the afterimage is viewed. The farther away the surface the larger the afterimage appears.

Front 367

Familiar size

Back 367

A depth cue in which judgment of distance is based on knowledge of the sizes of objects. Epstein’s coin experiment illustrated the operation of the cue of familiar size by showing that the relative sizes of the coins infl uenced perception of the coins’ distances.

Front 368

Frontal eyes

Back 368

Eyes located in front of the head so the views of the two eyes overlap.

Front 369

Horopter

Back 369

An imaginary surface that passes through the point of fixation. Images caused by a visual stimulus on this surface fall on corresponding points on the two retinas.

Front 370

Lateral eyes

Back 370

Eyes located on opposite sides of an animal’s head so the views of the two eyes do not overlap or overlap only slightly as in the pigeon and rabbit.

Front 371

Lenticular projection

Back 371

A method used to create 3-D television images. The screen is coated with a film containing two sets of lenses which results in different images reaching the left and right eyes.

Front 372

Müller-Lyer illusion

Back 372

An illusion in which two lines of equal length appear to be of different lengths because of the addition of “fins’’ to the ends of the lines.

Front 373

Misapplied size constancy scaling

Back 373

A principle proposed by Richard Gregory that when mechanisms that help maintain size constancy in the three-dimensional world are applied to two-dimensional pictures an illusion of size sometimes results.

Front 374

Monocular cue

Back 374

Depth cue—such as overlap relative size relative height familiar size linear perspective movement parallax and accommodation—that can work when we use only one eye.

Front 375

Moon illusion

Back 375

An illusion in which the moon appears to be larger when it is on or near the horizon than when it is high in the sky.

Front 376

Motion parallax

Back 376

A depth cue. As an observer moves nearby objects appear to move rapidly across the visual field whereas far objects appear to move more slowly.

Front 377

Noncorresponding points

Back 377

Two points one on each retina that would not overlap if the retinas were slid onto each other. Also called disparate points.

Front 378

Occlusion

Back 378

Depth cue in which one object hides or partially hides another object from view causing the hidden object to be perceived as being farther away. A monocular depth cue.

Front 379

Oculomotor cue

Back 379

Depth cue that depends on our ability to sense the position of our eyes and the tension in our eye muscles. Accommodation and convergence are oculomotor cues.

Front 380

Passive method (3-D TV)

Back 380

A method used to create 3-D television images. Polarized light is used to create left and right images—one image is polarized so its vibration is vertical and the other is polarized so its vibration is horizontal. The TV is viewed through polarizing lenses which let vertically polarized light into one eye and horizontally polarized light into the other eye creating the disparity that results in three-dimensional perception.

Front 381

Perspective convergence

Back 381

The perception that parallel lines in the distance converge as distance increases.

Front 382

Pictorial cue

Back 382

Monocular depth cue such as overlap relative height and relative size that can be depicted in pictures.

Front 383

Ponzo illusion

Back 383

An illusion of size in which two objects of equal size that are positioned between two converging lines appear to be different in size. Also called the railroad track illusion.

Front 384

Random-dot stereogram

Back 384

A pair of stereoscopic images made up of random dots. When one section of this pattern is shifted slightly in one direction the resulting disparity causes the shifted section to appear above or below the rest of the pattern when the patterns are viewed in a stereoscope.

Front 385

Relative disparity

Back 385

The difference between two objects’ absolute disparities.

Front 386

Relative height

Back 386

A monocular depth cue. Objects that have bases below the horizon appear to be farther away when they are higher in the field of view. Objects that have bases above the horizon appear to be farther away when they are lower in the field of view.

Front 387

Relative size

Back 387

A cue for depth perception. When two objects are of equal size the one that is farther away will take up less of the field of view.

Front 388

Size constancy

Back 388

Occurs when the size of an object is perceived to remain the same even when it is viewed from different distances.

Front 389

Size-distance scaling

Back 389

A hypothesized mechanism that helps maintain size constancy by taking an object’s perceived distance into account. According to this mechanism an object’s perceived size S is determined by multiplying the size of the retinal image R times the object’s perceived distance D.

Front 390

Stereopsis

Back 390

The impression of depth that results from binocular disparity—the difference in the position of images of the same object on the retinas of the two eyes.

Front 391

Stereoscope

Back 391

A device that presents pictures to the left and the right eyes so that the binocular disparity a person would experience when viewing an actual scene is duplicated. The result is a convincing illusion of depth.

Front 392

Stereoscopic depth perception

Back 392

The perception of depth that is created by input from both eyes. See also binocular disparity.

Front 393

Stereoscopic vision

Back 393

Two-eyed depth perception involving mechanisms that take into account differences in the images formed on the left and right eyes.

Front 394

Strabismus

Back 394

Misalignment of the eyes such as crossed-eyes or walleyes (outward looking eyes) in which the visual system suppresses vision in one of the eyes to avoid double vision so the person sees the world with only one eye at a time.

Front 395

Texture gradient

Back 395

The visual pattern formed by a regularly textured surface that extends away from the observer. This pattern provides information for distance because the elements in a texture gradient appear smaller as distance from the observer increases.

Front 396

Visual angle

Back 396

The angle of an object relative to an observer’s eyes. This angle can be determined by extending two lines from the eye—one to one end of an object and the other to the other end of the object. Because an object’s visual angle is always determined relative to an observer its visual angle changes as the distance between the object and the observer changes.