Psyc 367 (UAlberta- Farley) Ch. 10 Perceiving Depth and Size

Monocular Cues

Sound localization cue that involves one ear/eye

information that can be based on the image from a single eye

Absolute Disparity (Angle of Disparity)

The visual angle between the images of an object on the two retinas.

When images of an object fall on corresponding points, the angle is zero. When images fall on non-corresponding points, the angle indicates the degree of non-correspondence.

Accretion

A cue that provides information about the relative depth of 2 surfaces.

Occurs when the farther object is uncovered by the nearer object due to sideways movement of an observer relative to the objects.

Ames Room

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.

Angular Size Contrast Theory

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 is. 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.

Apparent Distance Theory

An explanation of the moon illusion that is based on the idea that the horizon moon is surrounded by depth cues but the moon higher in the sky has none

emphasizes how the brain uses contextual distance cues to interpret an object’s size

Atmosphere Perspective

A depth cue.

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

Binocular Depth Cells/disparity selective cells

A neuron in the visual cortex (+ dorsal and ventral streams) that responds best to stimuli that fall on points separated by a specific degree of disparity on the two retinas.

Binocular Disparity

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

Binocularly Fixate

Directing the two foveas to exactly the same spot.

Conflicting Cues Theory

A theory of visual illusions proposed by R. H. Day, which states that our perception of line length depends on:

• the actual line length (objective cues)

• the overall figure length. (contextual cues)

When different visual cues provide conflicting information, our brain combines them into a single perception

Correspondence Problem

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.

How does the visual system match up the images in the two eyes?

Corresponding Retinal Points

The points on each retina that would overlap if one retina were slid on top of the other (superimposed).

Receptors at corresponding points send their signals to the same location in the brain.

Crossed Disparity

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

used by the brain to judge the relative depth of nearby objects, particularly those closer than the point of focus

Cue Approach to Depth Perception

focuses on identifying information in the retinal image correlated with the scene's depth.

Some of the depth cues that have been identified are overlap, relative height, relative size, atmospheric perspective, convergence, and accommodation.

Deletion

A cue that provides information about the relative depth of two surfaces.

Occurs when a farther object is covered by a nearer object due to sideways movement of an observer relative to the object.

Disparity Tuning Curve

A plot of neuron's response vs the degree of disparity of a visual stimulus.

essential concept in understanding how the brain processes depth information to achieve stereopsis (3D depth)

Emmert's Law

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.

Familiar Size

A depth cue in which judgement of ditance 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 influences perception of the coins' distances.

Horopter

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.

Misapplied Size Constance Scaling

A principle, proposed by Richard Gregory, that when mechanisms that help maintain size constancy in the 3D world are applied to 2D pictures

when the brain uses depth cues to figure out how big something should be, but misinterprets the depth cues, leading to a size illusion (an object looks larger or smaller than it really is).

Moon Illusion

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

Motion Parallax

A motion produced depth cue.

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

Muller-Lyer Illusion

An illusion in which 2 lines of equal length appear to be different lengths because of the addition of "fins" to the end of the lines.

Non-corresponding Points

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

objects that aren’t on the horopter fall on these points

Occlusion

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.

Oculomotor Cues

Depth cue that depends on our ability to sense the position of our eyes and the tension in our eye muscles.

Accomodation and convergence are cues.

Perspective Convergence

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

Pictorial Cues

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

Ponzo Illusion

An illusion of size in which 2 objects of equal size that are positioned between 2 converging lines appear to be different in size.

Random-Dot Stereogram

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.

Relative Disparity

The difference between two objects' absolute disparities.

Relative Height

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.

Relative Size

A monocular 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.

Size Constancy

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

S = R x D

object moves farther away, we perceive it to remain a constant size; retinal size gets smaller our perception of the distance increases

Size-Distance Scaling

A hypothesized mechanisms 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, by the object's perceived distance.

Stereopsis

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.

Stereoscope

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.

Stereoscopic Depth Perception

The perception of depth that is created by input from both eyes.

• basis for how 3D glasses typically work; presenting different images to each eye

Strabismus

Misalignment of the eyes, such as crossed eyes or wall-eyes (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.

Texture Gradient

how the texture or pattern of a surface appears to change as it extends into the distance

closer objects: The texture appears larger, more distinct, and more detailed.

Farther objects: he texture becomes smaller, more compact, and less distinct

Uncrossed Disparity

Disparity that occurs when one object is being fixated, and therefore on the horoptor, and another object is located behind the horoptor, father from the observer.

helps the brain judge the relative depth of objects that are farther away than the point of focus.

Visual Angle

The angle of an object relative to an observer's eyes.

always determined relative to an observer

as things get closer = visual angle increases

as things get farther away = visual angle decreases

convergence

inward movement of the eyes when we focus on nearby objects

accommodation

the shape of the lens changes when we focus on objects at different distances

shadows

helps enhance depth by indicatinf where objects/features are located

disparate images

slightly different visual input each eye receives due to their horizontal separation on the face

Dual pathway for emotion

thalamus sends sensory input along 2 independent neural pathways:

1. one directly to amygdala: processing of input before cortex = faster responses to imminent threats

2. One to cerebral cortex: conscious interpretation, feedback processes, flexibility for response

Possible solution to correspondence problem

visual system to rely on the specific features of objects to help “keep track” of what is creating an image where

Possible explanation for ponzo illusion

size-constancy scaling

same retinal image formed, yet perceived to be at different distances, will be perceived as being different from actual sizes

Possible explanation for ames room

size-distance scaling + relative size

frontal eyes

allows for fields that significantly overlap, which affords good stereoscopic depth perception

lateral eyes

results in poor stereoscopic depth perception, but gains a more panoramic view