Midterm 2 terms

monochromatic colour

single component of colour that cannot be refracted into different colours

problem of univariance

an infinite set of different wavelength-intensity combinations can elicit the same response from a single type of photoreceptor

one type of photoreceptor cannot discriminate colour based on wavelength

scotopic

dim light

rods are sensitive

rhodopsin

photopigment in rods

Young-Helmholtz-Maxwell theory

colour vision is based on 3 photoreceptors sensitive to a particular ranges of wavelengths

trichromatic colour vision

Maxwell’s colour-matching technique

three colors can mix in different proportion to make other colours

additive explanation

s cones

420 nm “blue”

m cones

534nm “green”

l cones

565nm “red”

fovea

the _____ only has red and green cones

metamers

pair of stimuli that are perceived as identical though they are physically different

different mixtures of wavelengths can look identical

additive colour mixture

if lights are reflected, in perception they are added together

subtractive colour mixture

if pigments mix and light shines on them, what remains contributes to colour perception

hue

chromatic aspect of colour

saturation

chromatic strength of hue

brightness

distance from black in colour space

non spectral hues

don’t exist as pure light, only as mixtures of wavelengths

opponent colour theory

colour perception is based on red-green, blue-yellow, and black-white ratios

LGN has neurons that code differences between sets of cones

V1 colour system

blobs

V2 colour system

thin stripes

V4

colour area

achomatopsia

inability to perceive colours due to damage in CNS

ishiahara test

tests colour blindness

8% of males and 0.5% of females are colour blind

cone monochromat

only one type of cone

true colour blindness

rod monochromat

no cones at all

true colour blindness

visual impairment in bright light

deuteranope

colour anomalous people with no m-cones

protanope

colour anomalous people with no l-cones

tritanope

colour anomalous people with no s-cones

cultural relativism

different cultures describe colour differently and may perceive colours differently

unrelated colour

colour that can only be experienced in isolation

related colour

colour that can only be seen relative to other colours

example - brown & grey

colour constancy

tendency for surface to appear the same colour under a wide range on lumination

example - bees & goldfish

sensation equation

sensation = illuminant x reflectance

\[what we see\] = \[what we don’t and don’t care\] x \[what we don’t know and care about\]

12 = a\*b

illuminant

what we don’t know and aren’t interested in

assumptions: 1 light source that is broadband, surface reflects broadband and has mutual reflections

reflectance

what we don’t know but want to know

dichromats

two photoreceptors

example - dogs

tetrachromat

four colour receptors

example - chickens

motion aftereffect (MAE)

illusion of motion of a stationary motion after prolonged exposure to a moving object

due to imbalance in medial temporal

example - waterfall illusion, falls of Foyers

reichardt detector

motion perception is discrete

delay causes motion perception in bugs

apparent motion

illusionary impression of smooth motion resulting from the rapid alteration of objects that appear in different locations in rapid succession

correspondence problem

how do motion detection system know which feature is frame 2 corresponds to frame 1

aperture problem

the direction of motion is ambiguous when through a receptive field, the

partial view of object

global motion detector

integrates local motion information

magnocellular layers

lesions in _____________ __________ of LGN impair perception of large, rapidly moving objects

complex V1 cells

occipital neurons sensitve to motion

middle temporal lobe

brain region important for motion perception

medial temporal / MT / V5 / hMT

brain region that are selective for motion in a particular direction

global motion task

used to study motion perception in MT

normal monkeys can determine correct direct with 2-3% of cues being targets

lesioned monkeys need 10x more target cues to determine direction

interocular transfer

adaption from one eye to the other after LGN

first order motion

motion of an object that is defined by change in luminance

second order motion

motion of an object is defined by contrast or texture

double dissociation

first and second order motion are independent which was discovered using _________ __________

optic flow

changing angular position of points as you move

biological movement

movement of living things

akinetopsia

individual has no perception of motion

medial temporal lesion

Akiyoshi Kitaoki’s rollers illusion

pinna illusion

6

3

there are __ muscles attached to each eye paired into __ groups

superior/inferior oblique

inferior/superior/lateral/medial rectus

3

eye muscles are controlled by ___ cranial nerves

superior colliculus

initiates and guides eye movement

smooth pursuit

eyes move smoothly to follow moving object

keep target stable and in fovea

saccade

saccadic eye movement

rapid eye movement when fixation changes from one object/location to another

move fovea to target as quickly as possible to reduce travel time

vergence eye movements

two eyes move in opposite direction

looking at objects in depth so retinal images converge

fixational eye movement

microsaccades

spatial constancy

ability to the perceive the world as stable and continuous despite eye movement

allows us to discriminant movement from eye vs object movement

compensation theory

perceptual system receives information about eye movement and discounts changes in retinal images that result from it

efference copy

corollary discharge

copy of motor command that was sent to eyes gets sent to visual system / comparator

comparator

area of the visual system that compensates for changes due to eye movement inhibiting other visual areas to perceive it as motion

saccadic suppression

reduction of visual sensitivity when moving eyes in saccade

eliminates smear during eye movement

Euclidian geometry

parallel lines remain parallel as they extend into space

parallax

placement of observer causes changes in POV

result of two retinal images in a 3D world

binocular disparity

differences between the two retinal images due to parallax

basis of stereopsis

stereopsis

vivid perception of 3D world not available with monocular vision

“popping out in depth’

binocular cues

convergence, stereopsis, ability to see more of an object

monocular cues

occlusion, relative size, position cues, familiar size, aerial perceptive, linear perceptive, motion cues

occlusion

cue relative to depth order, one object obstructs the view of another

nonmetrical depth cue

provides information about depth order but not magnitude

metrical depth cue

provides quantitative information about distance

ex - meters, yards

relative size

comparison of size between items without knowing the absolute size of either

texture gradient

depth cue based on fact that items appear smaller the farther away they are

relative height

objects at different distances from the viewer on the ground plane will form images at different heights in retinal image

natural scene statistics

statistical properties and regularities in natural environment

common distribution and relationship between features of an image

familiar size

depth cue based on knowledge of typical size of an object

ex - size of a quarter, a hand, a book, etc.

aerial perspective

depth cue based on fact that light is scattered by atmosphere

objects farter away appear bluer

ex - haze

linear perspective

depth cue based on fact that parallel lines in 3D converge in 2D

vanishing point

apparent point in which parallel lines converge

foreshortening

visual effect where an object appears shorter because it is angled towards screen/retina/plane

anamorphism

distorted projection or perspective requiring the viewer to use a special device or vantage point to reconstitute the image

motion parallax

objects moving at constant speed across retina will appear to move faster the closer they are to the observer

convergence

turn eyes inward to focus on something close

divergence

turn eyes outward to focus on something far

corresponding retinal points

zero binocular disparity

points of retinal images that have the same distance from the fovea

horopter

location of objects in space whose images lie on corresponding points

surface of zero disparity

panum’s fusion area

region of space in front and behind horopter where binocular single vision is possible

diplopia

double vision for points outside Panum’s fusion area

absolute disparity

difference in actual retinal coordinates in both eyes of the feature in the visual scene

relative disparity

difference in absolute disparities of two elements in the visual scene

free fusion

technique of converging or diverging the eyes

crossing you eyes

stereoblindness

inability to make use of binocular disparity as depth cues