Week 9: Space Perception and Binocular Vision Definitions

pictoral depth cues

cues to distance/depth used by artists to depict 3D depth in 2D pictures

monocular depth cue

a depth cue that is available even when the world is viewed with one eye alone

binocular depth cue

a depth cue that relies on information from both eyes

stereopsis

a vivid perception of the three-dimensionality of the world that is not available with monocular vision

probability summation

increased detection probably based on the statistical advantage of having two (or more) detectors rather than one

binocular summation

combination of signals from both eyes in ways that make performance on many tasks better than with either eye alone

oculomotor depth cues

cues that are based on feedback from the oculomotor muscles controlling the shape of the lens and the position of the eyes

accommodation

the process by which the eye changes its focus (lens changes its shape)

convergence

the ability of the two eyes to turn inward, often used to focus on nearer objects

divergence

the ability of the two eyes to turn outward, often used to focus on farther objects

static monocular depth cues

cues that provide information about depth on the basis of position, size, and effects of lighting of objects in the retinal image, size

occlusion

a cue to relative depth order in which one object partially obstructs the view of another object

nonmetrical depth cue

provides info about the depth order (relative depth) but not depth magnitude (e.g., his nose is in front of his face)

metrical depth cue

provides quantitative info about distance in the 3rd dimension

relative height/proximity to horizon

objects touching the ground (higher = farther) and objects in the sky (lower = farther)

size-distance relation

the farther away an object is from the observer, the smaller is its retinal image

relative size

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

projective geometry

describes how the world is projected onto a surface

familiar size

a cue based on knowledge of the typical size of objects

relative metrical depth cue

can specify that object A is 2x as far as object B without providing information about the absolute distance to either A or B

absolute metrical depth cue

provides quantifiable information about distance in the 3rd dimension (e.g., nose sticks out 4cm in front of his face)

texture gradient

a depth cue based on the geometric fact that items of the same size form smaller, closer spaced images the farther away they get

aerial (or atmospheric) perspective

a depth cue based on the implicit understanding that light is scattered by the atmosphere

linear perspective

lines that are parallel in the 3D world will appear to converge in a 2D image as they extend into the distance

vanishing point

the apparent point at which parallel lines receding in depth converge

anamorphosis

use of the rules of linear perspective to create a 2D image so distorted that it looks correct only when viewed from a specific angle or with a mirror that counters the distortion

dynamic monocular depth cues

cues that provide information about depth on the basis of motion

triangulation cues

triangle formed by the 2 eyes and the point on which they fixate in the 3D world. The angles of that triangle are related to the location of the fixated point in depth

motion parallax

images closer to the observer move faster across the visual field than images farther away

optic flow

the changing angular position of points in a perspective image that we experience as we move through the world

deletion

the gradual hiding (occlusion) of an object as it passes behind another one

accretion

the gradual revealing (“de-occlusion”) of an object as it emerges from behind another one

binocular disparity

the differences between the two retinal images of the same scene

corresponding points

a point on the left retina and a point on the right retina that would coincide if the two retinas were superimposed (e.g., the foveas of the two eyes)

non-corresponding points

a point on the left retina and a point on the right retina that would not coincide if the two retinas were superimposed (e.g., the fovea of one eye and a point 4mm to the right of the fovea in the other eye)

absolute disparity

the difference in the angular distance of the images of an object from the foveas of the 2 eyes

relative disparity

the difference in the absolute disparities of 2 objects

diplopia

double vision, if visible in both eyes, stimuli falling outside of panum’s fusional area will appear diplopic

panum’s fusional area

the region in space in front of and behind the horopter within which binocular single vision is possible

horopter

the location of objects whose images lie on the corresponding points in the two retinas

crossed disparity

the sign of disparity created by objects in front of the plane of the horopter

uncrossed disparity

the sign of disparity created by objects behind the plane of the horopter

correspondence problem

in binocular vision, the problem of figuring out which bit of the image in the left eye should be matched with which bit in the right eye

stereoscope

a device for presenting one image to one eye and another image to the other eye

random dot stereogram (RDS)

a stereogram made of a large number of randomly placed dots

free fusion

the technique of converging (crossing) or diverging (uncrossing) the eyes in order to view a stereogram without a stereoscope

uniqueness constraint

the observation that a feature in the world is represented exactly once in each retinal image

continuity constraint

the observation that, except at the edges of objects, neighbouring points in the world lie at similar distances from the viewer

strabismus

a misalignment of the two eyes such that a single object in space is imaged on the fovea of one eye, and on the nonfoveal area of the other (turned) eye

amblyopia

a developmental disorder characterized by reduced spatial vision in an otherwise healthy eye (lazy eye)

suppression

inhibition of an unwanted image; occurs frequently in people with strabismus

esotropia

strabismus in which one eye deviates inward

exotropia

strabismus in which one eye deviates outward

stereoblindness

an inability to make use of binocular disparity as a depth cue

binocular rivalry

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

size constancy

the perception of an object as having a constant size even though our sensation of the object changes

shape constancy

the relative constancy of the perceived shape of an object despite variations in its orientation