sens and percep chapter 6

Advantages of binocular vision

We can lose one eye and still see, extends the visual field (190∘190∘ compared to 110∘110∘), enables binocular summation, and allows stereopsis.

Binocular summation

combining signals from both eyes improves performance on tasks such as visual search. This includes probability summation, a statistical advantage of two detectors

Binocular Disparity

The horizontal difference between the projections of an image on the two retinas, providing the primary geometric cue for depth.

Stereopsis

The perceptual impression of three-dimensional depth extracted from horizontal retinal disparity.

Horopter

The location of objects whose images fall on corresponding points, the surface of zero disparity

Occlusion

a near object blocks part of a farther one

Relative height

more distant objects form retinal images that are higher and smaller

Relative size

comparing the sizes of two items without knowing the absolute size of either, farther objects look smaller

Familiar size

Uses knowledge of an object’s typical size

Linear perspective

Parallel lines in the world converge toward a vanishing point

Texture gradient

same-sized items form smaller images when farther, a smooth size change makes a surface look tilted in depth

Haze (aerial or atmospheric perspective)

The atmosphere scatters light, so distant objects look fainter and less distinct

Motion parallax

A monocular cue from head movement, information from one eye at two places and times resembles information from two eyes at once

Deletion

A father object is covered uo by head movement

Accretion

A farther object is uncovered by head movement

Accomodation

The lens changes shape to focus. Distant gaze gives a flat lens, near gaze gives a fat lens

Vergence

A binocular triangulation cue from the eyes turning inward or outward, which place the image of a feature on corresponding retinal points and reduce its disparity to zero

Convergence

A binocular triangulation cue from the eyes turning inward

Divergence

A binocular triangulation cue from the eyes turning outward

Corresponding retinal points

Two images fall on corresponding points if both are the same distance from the fovea in each eye

Noncorresponding (disparate) points

Images fall at different distances from the fovea in the two eyes, so there is binocular disparity 

Absolute disparity

How far an object’s image deviates from corresponding pointsR

Relative Disparity

The difference between absolute disparities of two objectsC

Crossed disparity

Created by objects in front of the horopterU

Uncrossed disparity

Created by objects behind the horopter

Panum’s fusional area

The zone in front of an behind the horopter within which binocular single vision is possible without double vision

Correspondence problem

Deciding which part of the left image matches which part of the right, uniqueness constraint and continuity constraints help

Physiology of stereopsis

A disparity-selective neuron is a binocular cortical cell tuned to a particular disparity

Blake and Hirsch

Alternating monocular deprivation of kittens during the critical period sharply reduced binocular neurons in visual cortex eliminated the cats’ use of disparity for depth 

DeAngelis et al.

Microstimulating near-tuned disparity neurons in macaque area MT shifted the monkey’s depth judgments toward nearer

Bayesian Approach

Perception combines the current stimulus with knowledge of what is and is not likely in the world

Visual angle

The angle that an object subtends on the retina

Size Constancy

Perceived size stays about the same across viewing distances even though retinal image size changes

Ponzo Illusion

Linear perspective cues suggest one line is farther away, so by S = R x D it looks bigger

Muller-Lyer Illusion

Misapplied size constancy scaling, depth mechanisms applied to 2D pictures. A line seen as farther must be bigger; one seen as nearer must be smaller

Ames room illusion

Explanation 1: size-distance scaling, both people seem the same distance away, so the ones whose image is much smaller looks tiny

Explanation 2: relative size

Moon

Apparent-distance theory: the horizon moon sits against terrain with depth cues, so it looks father, and with constant R a larger D gives a larger S

Angular size-contrast theory: the moon looks small when surrounded by large things like a big sky

Interocular disparities

Differences between the two retinal images due to the presentation of two different stimuli, one to each eye 

Binocular rivalry

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

Suppression

The inhibition of an image so that it is not consciously perceived

Strabismus

Misaligned eyes, so one object lands on the fovea of one eye and a nonfoveal spot in the other

Esotropia

One eye turns inward

Exotropia

One eye turns outward

Critical-period point

A defined early developmental window during which normal, aligned visual input to both eyes is required to wire binocular cortical circuits and establish stereopsis

Ambylopia

A developmental reduction of visual acuity in an anatomically healthy eye, caused by abnormal visual experience such as uncorrected strabismus during early life