Test 3 Psych-2600 Sensation and Perception

Cerebral achromatopsia

A loss of colour vision caused by damage to the cortex

Chromatic colours

Colour with hue (blue, yellow, red, green)

Selective reflection

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

Achromatic colours

Colour without hue (White, black, grey)

Selective transmission

When some wavelengths pass through visually transparent objects of substances and others do not (associated with chromatic colour perception)

Subtractive colour mixture

The creation of colours that occurs when paints of different colours are mixed together (Blue+yellow=green)

Additive colour mixture

Creation of colours that occurs when lights of different colours are superimposed (Blue+yellow=white)

Spectral colours

Colours that appear in the visible spectrum (ROYGBIV)

Nonspectral colours

Colours that do not appear in the spectrum because they are mixtures of other colours

Hues

Experience of a chromatic colour, or combination of these colours

Saturation

The relative amount of whiteness in a chromatic colour (less whiteness=more saturated)

Value

The light-to-dark dimension of colour

Colour solid (HSV colour solid)

A solid in which colours are arranged in an orderly way based on their hue, saturation and value

Trichromatic theory of vision (Young-Helmholtz theory)

Perception of colour is determined by the ratio of activity in three receptor mechanisms with different spectral sensitivities

Metamerism

Two physically different stimuli are perceptually identical (Two lights with different wavelength distributions are perceived as having the same colour)

Metamers

Two lights that have different wavelength distributions but are perceptually identical

Principle of Univariance

Once a photon of light is absorbed by a visual pigment molecule, the identity of the light's wavelength is lost (the receptor doesn't know the wavelength of light that is absorbed, only the totally amount of light absorbed)

Monochromat

Person who is completely colour-blind, can match any wavelength in the spectrum by adjusting the intensity of any other wavelength, usually one functioning receptor type (rods)

Dichromats

Person with a colour deficiency. Can match any wavelength in the spectrum by mixing two other wavelengths

Trichromats

A person with normal colour vision, can match any wavelength in the spectrum by mixing three other wavelengths in various proportions

Opponent-process theory of colour vision

Hering; Perception of colour is determined by blue-yellow and red-green output mechanisms. The mechanisms oppose each other, one is excitatory and one is inhibitory. Black-white mechanism is concerned with brightness perception

Hering's primary colours

Red, yellow, green and blue in the colour circle

Complementary afterimages

An afterimage that is on the opposite side of the colour circle from the inducing colour

Hue cancellation

Hurvich and Jameson; Subject is shown a monochromatic reference light and asked to remove/cancel one of the colours in the reference light by adding a second wavelength

Opponent neurons

In retina and LGN, neurons that have excitatory response to wavelengths in one part of the spectrum and an inhibitory response to wavelengths in the other part of the spectrum

Single-opponent neurons

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

Double-opponent neurons

Neurons that have receptive fields in which stimulation in one part causes an excitatory response to wavelengths in one area of the spectrum and inhibitory response to wavelengths in another area, and stimulation of an adjacentt part of the receptive field causes the opposite response

Monochromatism

Rare form of colour blindness In which the absence of cones receptors results in perception only of shades of lightness, with no chromatic colour present

Ishihara plates

Display of coloured dots used to test for the presence of colour deficiency, designed so trichromats can perceive numbers, but people with colour deficiencies cannot perceive these numbers or perceive different colours than trichromats

Colour constancy

The perception of an object's hue remains constant even when the wavelength distribution of the illumination has changed

Chromatic adaptation

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

Partial colour constancy

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

Memory colour

An object's characteristic colour influences our perception of that object's colour

Lightness constancy

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

Reflectance

The % of light reflected from a surface

Ratio principle

Two areas that reflect different amounts of light will have the same perceived lightness if the ratios of their intestines to the intensities of their surroundings are the same

Reflectance edge

The edge between two areas where the reflectance of two surfaces changes

Illumination edge

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

Penumbra

The fuzzy border at the edge of a shadow

Short wavelength colour

Blue

Medium wavelength colour

Green

Long and medium wavelength colour

Yellow

Long wavelength colour

Red

Short, medium and long wavelength colour

White

Cue approach to depth perception

Focuses on identifying info in the retinal image that correlates to depth in the scene (overlap, relative height, relative size, atmospheric perspective, convergence, accommodation)

Occlusion

Depth cue in which one object hides or partially hides another object, causing the hidden object to be perceived as further away (monocular depth cue)

Oculomotor cues

Depth cue that depends on our ability to sense the position of the eyes and tension of eye muscles (Accommodation and convergence)

Monocular cues

Depth cue that can work when we use only one eye (overlap, relative size, relative height, familiar size, linear perspective, movement parallax, accommodation)

Pictorial cues

Monocular depth cue that can be depicted in pictures (overlap, relative height, relative size)

Relative height

Objects that have bases below the horizon appear to be further away when they are higher in the field and vice versa (monocular depth cue)

Familiar size

Judgement of distance is based on knowledge of sizes of objects (Epstein's coin)

Relative size

When two objects are of equal size, the one that is further away will take up less of the field of view

Perspective convergence

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

Atmospheric perspective

Objects that are further away look more blurred and bluer than objects that are closer because we look through more air and particles to see them

Texture gradient

The visual pattern formed by a regularly texted surface that extends away from the observer. Elements appear smaller as distance from the observer increases

Motion Parallax

As the observer moves, nearby objects appear to move rapidly across the visual field whereas far objects appear to move more slowly

Deletion

Father object is covered by a nearer object due to sideways movement of an observer relative to the objects

Accretion

Farther object is uncovered by the nearer object due to sideways movement of an observer relative to the objects

Stereoscopic depth perception

Perception of depth that is created by input from both eyes

Strabismus

Misalignment of the eyes (Crossed eyes or walleyes), visual system suppresses vision in one eye to avoid double vision, so the person sees the world with only one eye at a time

Binocular disparity

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

Corresponding retinal points

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

Horopter

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

Noncorresponding points

Two points, one on each retina, that would not overlap if the retinas were slid onto each other (disparate points)

Absolute disparity (angle of disparity)

The visual angle between the images of an object on the two retinas. When images fall on corresponding points, the angle is 0, when images fall on noncorresponding points, the angle indicates the degree of noncorrespondence

Crossed disparity

Disparity that occurs when one object is being fixated, and is therefore on the horopter, and another object is located in front of the horopter, closer to the observer

Uncrossed disparity

Disparity that occurs when one object is being fixated, and is therefore on the horopter, and another object is located behind the horopter, farther from the observer

Relative disparity

The difference between two objects' absolute disparities

Stereopsis

Impression of depth from binocular disparity (difference in position of images of the same objects on OS and OD retinas)

Random-dot stereogram

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/below the rest of the pattern when viewed in a stereoscope

Stereoscope

A device that presents pictures to OS and OD so binocular disparity a person would experience when viewing an actual scene is duplicated (causes convincing illusion of depth)

Correspondence problem

Visual system must determine which parts of the images in OS and OD correspond to one another. (How does the visual system match up images OU?)

Binocular depth cells (disparity-selective cells)

Neuron in visual cortex that responds to stimuli that fall on points separated by a specific degree of disparity on the two retinas

Visual Angle

Angle of an object relative to an observer's eye. Always determines relative to the observer, and changes as distance between the object and observer change

Size constancy

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

Size-distance scaling

A hypothesized mechanism that helps maintain size constancy by considering the objects perceived distance. (Size = retinal image x perceived distance)

Emmert's law

The size of an afterimage depends on the distance of the surface against which the afterimage is viewed (farther away the surface, large the afterimage appears)

Muller-Lyer illusion

Two lines of equal length appear to be of different lengths because of the addition of "fins" to the ends of the lines

Ponzo illusion

Two objects of equal size that are positioned between two converging lines appear to be different in size (aka railroad track illusion)

Ames room

Adelbert Ames; a distorted room that creates an incorrect perception of sizes of people in the room

Moon illusion

The moon appears to be larger when it is on or near the horizon than when it is high in the skin

Apparent distance theory

In response to the moon illusion, the horizon moon and zenith (sky) moon have the same visual angle but are perceived to be at different distances, the farther appearing horizon moon should be larger.

Angular size contrast theory

In response to the moon illusion, perceived size of the moon is determined by the sizes of the objects that surround it

Frontal eyes

Eyes on front of the head, so the views of two eyes overlap

Lateral eyes

Eyes on opposite sides of the head, so the views of two eyes don't overlap or overlap slightly

Binocularly fixate

Directing the two foveas to exactly the same spot

Sound - Physical definition

Pressure changes in air or other medium

Sound - Perceptual definition

The experience we have when we hear

Sound wave

Pattern of pressure changes in a medium

Pure tone

A tone with pressure changes that can be described by a single sine wave

Frequency

The # of times per second that pressure changes of a sound stimulus repeat (Hertz = 1 cycle/second)

Amplitude

In repeating sound waves, represents the pressure difference between atmospheric pressure and the maximum pressure of the wave

Decibel (dB)

A unit that indicates the pressure of a sound stimulus relative to a reference pressure

Loudness

Quality of sound that ranges from soft to loud. For a tone of a particular frequency, loudness usually increases with increasing decibels

Audibility curve

A curve that indicates the sound pressure level (SPL) at threshold for frequencies across the audible spectrum

Auditory response area

The psychophysically measured area that defines the frequencies and sound pressure levels over which hearing functions (located between the audibility curve and threshold of feeling curve)

Equal loudness curve

A curve that indicates the sound pressure levels that result in a perception of the same loudness at frequencies across the audible spectrum

Pitch

The quality of sound, ranging from low to high, that is most closely associated with the frequency of a tone

Timbre

Quality that distinguishes between two tones that sound different even though they have the same loudness, pitch, and duration

Outer ear components

Pinnae, auditory canal