Sensation & Perception

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absolute threshold

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minimum stimulus intensity needed to evoke a sensation

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axon

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(part of a neuron) A long, slender projection of a nerve cell or neuron, that typically conducts electrical impulses away from the neuron’s cell body

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bleached/unbleached

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When light comes in and changes the photoreceptors, the rods are bleached out because of too much light. Unbleaching occurs when the light goes away and the rods come back recouperated.

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cell body

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(part of neuron) contains the nucleus. serves as a kind of collection center for information coming in through the dendrites from upstream neurons. If the cell body is excited enough the information it receives from the dendrites, it will pass a signal down the axon.

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center-surround

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shape of receptive field

center-on: responds to an increase in sight levels at center; excited if it hits the center and inhibited if it hits the surround

center-off: responds to a decrease in light levels at center; excited if it hits the surround and inhibited if it hits the center

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convergence

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amount of cells that speak to a particular cell. High level of convergence means a lot more cells, and leads to higher sensitivity

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convex lens

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Focuses light onto a single point in the eye (fovea) where there is a high concentration of cones. The lens is adjustable via surrounding muscles to change its shape and refocus.

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correct rejections

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no signal + no response

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dendrite

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(part of a neuron) receives information from upstream neurons and transmits it to the cell body.

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difference threshold

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minimum amount of stimuli increase/decrease needed to elicit a noticeable change in difference

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dark-adapted

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The process by which our eyes adjust to darkness after being exposed to light; made possible by the dilation of our pupils and changes in the rods and cones of our retinas. Rods detect form and motion, and cones detect color. So in darkness our rods kick into high gear while our cones take a backseat.

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dualism

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idea that mind exists separately from material world of body

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excitation

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increasing the response of the next neuron

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duplex solution

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How we achieve sensitivity and fine resolution. Two kinds of photoreceptor cells (rods and cones), that have different levels of sensitivity to light and different degrees of convergence to ganglion cells. More convergence --> more sensitivity

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eccentricity

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the distance between the retinal image and the fovea

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inhibition

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decreasing the response of the next neuron

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false alarms

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no stimulus w/ response

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focal length

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distance between lens and focusing point

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fovea

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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& serves as the point of fixation

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ganglion cell

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retinal cells that receive visual information from photoreceptors via two immediate neuron types (bipolar cells and amacrine cells) and transmit information to the brain and midbrain.

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hits

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both the stimulus and response are present

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integration

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summing up the inputs to get an output (i.e., a neuron sums up the inhibitory and excitatory synapses and produces an action potential if the threshold is met)

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Just noticeable difference

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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. Unit for intensity

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materialism

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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.

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Method of Adjustment

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person has control over physical stimulus. told to “adjust” the recognizable stimulus until they cannot hear/see it anymore… told to adjust unrecognizable stimulus until they are able to recognize it

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Method of Constant Stimuli

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method that requires creating many stimuli with different intensities to find the tiniest intensity that can be detected. These stimuli are presented multiple times at random. Subject responses are on the lines of hit miss correct rejection or false alarm

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Method of Limits

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Method where experimenter presents stimuli can have stimuli with different intensities as well, however they are presented in either ascending or descending orders of intensity. Note: data from these methods show that there is sometimes an “overshoot” in judgements.

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receptive field

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area of visual field to which the ganglion cell in question responds

donut shaped — called center-surround

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Misses

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stimulus present but no response

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optic nerve

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bundle of last layer of neurons in the retina. conducts impulses from retina to brain; source of blindspot

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Panpsychism

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all matter has consciousness

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perception

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the process of becoming aware of physical objects, phenomena, etc., through the senses; the process of organizing and using information that is received through the sense.

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refraction

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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. Or to measure the degree of refraction in a lens or eye.

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photopigment

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chemically changed by light, in rods and cones, can be bleached or unbleached, reduce electrical current

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photoreceptor

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when waves are turned into light energy; rods, cones, & ganglion cells

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Neuron

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building block cells of our central nervous system. Specialized to transmit information throughout the body.

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psychophysics

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link between physical world & perceptual world

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rate law

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the rate of firing; number of action potentials over a unit of time (called a spike)

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reflection

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

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resolution

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perceiving fine detailed structures; require less convergence, cones

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sensitivity

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ability to perceive object through organs and respond; high response to radiation

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rhodopsin

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the visual pigment found in rods

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transduction

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the change from: external stimuli (em waves, air pressure changes, volatile chemicals) to neural information (that can be used for visual, touch, smell)

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specific nerve energies

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formulated by Muller- says the nature of a sensation depends on which sensory fibers are stimulated, not on how fibers are stimulated

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stimulus

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something that excites and organism to functional activity

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terminal

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(part of a neuron) The point at which a neuron passes information to the neurons with which it contacts.

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transducer

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translates one form of energy to another

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Weber's Law

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difference Threshold is a fixed proportion of stimulus intensity. The ratio between intensities stays the same, the difference threshold is proportional to fit a constant ratio between intensities.

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2 types of photoreceptors

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rods & cones

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rod

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perceives form and figure, greys, has high convergence which leads to sensitivity, needs very little light.

only 1 type

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cone

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perceives color, has low convergence which leads to resolution, needs lots of light.

3 subtypes

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3 types of cells in the retina

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ganglion cells

collector cells

photoreceptor cells

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advantages of light

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high resolution, trasmits long distances, interacts with surfaces

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disadvantages of light

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can't be used in the dark, can't see around opague objects

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univariance principle

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you can have several different stimuli that give you the same response; because of the ways that various things work, the strength of the stimulus is the arching — if strength of stimulus is changed, you can change what the response looks like

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quanta

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individual particle of light

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2 types of retinal ganglion cells

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Magnocellular (colorblind + larger, less in retina, more myelinated)

parvocellular (see color + smaller, more in retina, less myelinated)

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dual nature of light

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shows characteristics of both a particle and a wave

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criteria in signal detection task

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criterion set in middle = minimize total error

criterion set to the left = minimize misses, maximizes false alarms

criterion set to the right = minimizes false alarms, maximizes misses

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Fourier analysis

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All sounds, no matter how complex they are, can all be broken down into sine waves at many different frequencies with different amplitudes and wavelengths.

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functions of eye

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1. start image processing

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graded potential

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an electrical potential that can vary continuously in amplitude.

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levels of analysis

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1. Hardware implementation-what is the electronic circuitry/ what are the mechanical parts?

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optics of the eye

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Two parts of the eye focus light onto the fovea: the cornea and the lens. The cornea accounts for roughly 70% of the eye’s focusing power, while the lens accounts for the other 30%. The lens can adjust its focus via the ciliary muscle, allowing us to clearly see farther or closer.

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signal detection theory

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Provides a precise language and graphic notation for analyzing decision making in the presence of uncertainty. 4 kinds of detections - Hit, Miss, False Alarm, and Correct Rejection.

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temporal summation

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one presynaptic neuron fires at high frequency reaching the threshold of the postsynaptic neuron

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Prosopagnosia

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inability to recognize faces; face blind

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Accidental Viewpoint

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A viewing position that produces some regularity in the visual image that is not present in the world e.g. when you stand in a particular position and you happen to see an image that isn’t there. Pictures of people holding up leaning tower of Pisa

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Amodal Completion

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completion of partly- occluded objects, it occurs behind occluding surface. We don’t actually see completed contour and it depends on a variety of cues and top-down processing. This is the normal type of completion!

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Borders

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the physical outline of a figure or object, which is usually (but not always) the same as the contour. Firing rates of Ommatidium in horse-shoe crabs give us borders

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Brightness

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how much light appears to be coming from a given location

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Camouflage

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art of getting your features to group with features of the environment so as to persuade an observer that your features do not form a perceptual group of their own

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Color Constancy

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

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Contralateral

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

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Cortical Magnification

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The amount of cortical area (usually specified in milli­meters) devoted to a specific region (e.g., 1 degree) in the visual field. 80% of V1 cells devoted to central 10 degrees of visual angle

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Disinhibition

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the neighbor of the neighbor inhibits the neighbor which reduces the inhibition of the neighbor on “our” ommatidium. Ganglion cells have this property to preserve contrast

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Figure

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the side of the contour that is object

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Ground

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the side of the contour that is not object

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Figure/Ground Assignment

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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).

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Figure-Ground Assignment is influenced by

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Convexity & symmetry

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Geons

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“geometric ions” [elements], proposed by Bederman, a small set of 3d elements [shapes] you can make up anything out of

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Gestalt Theory

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the whole has a quality that is not captured by local elements; “the whole is more than the sum of the parts”

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illuminance

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amount of light available at reflecting surface

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Illusory Contour

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

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Ipsilateral

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

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Lateral Inhibition

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firing of neighboring ganglion cells; as one goes up, other goes down (neighbor is inhibiting). significance: enhancement of contrast at a boundary (Mach Bands demonstration)

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LGN

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lateral geniculate nucleus. 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. Has 6 layers, & magnocellular and parvocellular cells

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lightness

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how light or dark a surface appears to be intrinsically

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Lightness Constancy

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change in overall illumination —> no change in perception of surface lightness

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Luminance

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illuminance x reflectance; amount of light that comes to the eye from the surface

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Mach Bands

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slightly darker at edge, slightly more intrinsic lightness at one edge, less at another, interpretation that it’s different but we know it’s consistent - there is an illusory ‘bright stripe’ and illusory ‘dark stripe’ = illusions formed by the visual system

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Modal Completion

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Partial camouflage or insufficient image contrast

-occurs in front of ‘uncompleted’ object, and ‘competed’ object appears to be in the front

- see completed contour (white square in the middle of the 4 black circles)

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Monochromat

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only being able to see one light (we are ___________ in dim light)

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Multichannel Model

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different channels devoted to different ranges of frequencies (cycles/degree)

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Mutual Inhibition

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firing rate of A decreases B, and vice versa, both inhibiting each other. This change in the firing rate of A and B is mutual inhibition.

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Occlusion

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partial view —> fragmented images on retinas

visual completion from fragmented images

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Perceptual Grouping

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a set of rules describing which elements in an image will appear to group together

similar things group into units

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Receptive Field

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

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Reflectance

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the percentage of light hitting a surface that is reflected and not absorbed into the surface (given as a function of wavelength)

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Retinotopic Mapping

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the order in which things fall on the retina is preserved and the spatial arrangement on the retina.

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Sinusoid Features

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higher spatial frequencies difficult to see at a distance thus making it difficult to see sine waves at a distance; physical measure of contrast across display

amplitude = maximum - minimum

contrast = (maximum intensity - minimum intensity) / mean

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Sinusoidal Waveform

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sine wave

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Size Aftereffect

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You get used to a size of a certain object. You are presented with the same object but smaller in size, but you perceive it as larger than it is.

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Subordinate Category

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object more specifically named

ex: fox sparrow

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Superordinate Category

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object more generally named

ex: animal

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Spatial Scale

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increase in distance = decrease in objects apparent size, but not the intrinsic size

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Bottom-Up Processing

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perception is entirely made up from things in the world around you. Just pure stimulus and breakdown of the stimulus influence perception. Driven by input. Lightness and brightness illusions are driven by bottom-up processing

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Top-Down Processing

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perception is entirely constructed by evolutionary standpoint. All info and experience you’ve collected over the years influences your perception. Driven by cognitive understanding

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Contour Integration

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the aggregation of a sequence of visual items into a “virtual curve.”

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Contrast Sensitivity

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refers to the ability of the visual system to distinguish between an object and its background

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Fourier's Theorem

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breaking down a square wave into sine waves and vise versa. Various amplitudes, frequencies, and phase shifts of sine waves can be added together to create any mathematical curve.

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Early Visual Stream

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Eye, visual chiasm, LGN, V1

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6 Laws of Perceptual Organization

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Law of Similarity

Law of Symmetry

Common Fate

Law of Proximity

Law of Continuity

Law of Closure

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Wallach's Ratio Rule

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When ratios of light intensities agree, objects will appear to have the same lightness

ratio of light intensity is preserved across changes in illumination. Ratio between stimulus and stimulus surround. ratios of dark and light are constant, by turning off the light, we know that the ratio is still the same,

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Helm Holtz

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This guy proposed there were 3 nerves; each produces a different color sensation
- L nerve: red
- M nerve: green
- S nerve: blue
His theory supports trichromatic theory.

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Trichromat

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Use three colors to see a whole bunch of colors. Most people are this.

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Thomas Young

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This person had 3 prisms reflect red, green and blue light. They combined to get white.
Supports trichromatic theory.

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Opponent Process Theory

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This theory has two systems: the "red-green" system and the "blue-yellow" system.
According to this theory, red + green = grey

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Parvocellular

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This type of cell:
(1) is color sensitive
(2) has small receptive fields, resulting in high resolution and low sensitivity
(3) has slower responses

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Magnocellular

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This type of cell:
(1) is not color sensitive
(2) has larger receptive fields, resulting in low resolution and high sensitivity
(3) has quick responses to signal motion

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Simple Cells

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This type of V1 cell displays orientation selectivity; this type of cell is most responsive to vertical and horizontal orientation.
This type of cell can also be categorized as a cortical cell; "cortical" comes from cortex.
Clear on/off regions (exact positioning).

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Orientation Selectivity

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A new feature we learned about when studying the simple cells of V1. Each cell responds to a certain object/light orientation.

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Complex Cells

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Edges and bars.
On/off regions not clear (exact positioning not necessary due to large receptive field). A type of cell in V1; a cortical cell.
"End-stopped" - sharp corners and high curvature.

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End Stopping

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This is a property of simple and complex cells of V1. This property says that V1 cells respond best to a bar of specific length, corners, and sharp turns.

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Perceptual Grouping

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A feature of perceptual organization. It pertains to the grouping of similar things into units.
A set of rules describing which elements in an image will appear to group together.

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View Based Recognition

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A theory of object recognition proposed by Bulch. The idea is that if you look a long enough time you can recognize an object.

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L Cone

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This type of cone is most sensitive and is particularly useful for passing on information about red light.

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M Cone

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This type of cone is most sensitive and is particularly useful for passing on information about green light.

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S Cone

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This type of cone is most sensitive and is particular useful for passing on information about blue light.

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Naive Template Theory

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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.