Ch 6 - Space Perception & Binocular Vision

realism

a philosophical position arguing that there is a real world to sense

positivism

a philosophical position arguing that all we really have to go on is the evidence of the senses, so the world might be nothing more than an elaborate hallucination

binocular

referring to two eyes

probability summation

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

binocular summation

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

binocular disparity

the differences between the two retinal images of the same scene

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

monocular

referring to one eye

stereopsis

the ability to use binocular disparity as a cue to depth

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 is the primary example in humans, but convergence and the ability of two eyes to see more of an object than one eye sees are also binocular depth cues

pictorial depth cues

a cue to distance or depth used by artists to depict 3D depth in 2D pictures

occlusion

a cue to relative depth order in which, for example, one object obstructs the view of part of another object

nonmetrical depth cue

a depth cue that provides information about the depth order (relative depth) but not depth magnitude

metrical depth cue

a depth cue that provides quantitative information about distance in the third dimension

projective geometry

for purposes of studying perception of the three-dimensional world, the geometry that describes the transformations that occur when the three-dimensional world is projected onto a two-dimensional surface

texture gradient

a depth cue based on the geometric fact that items of the same size form smaller images when they are farther away

an array of items that change in size smoothly across the image will appear to form a surface tilted in depth

relative height

as a depth cue, the observation that objects at different distances from the viewer on the ground plane will form images at different heights in the retinal image

objects farther away will be seen as higher in the image

relative size

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

familiar size

a depth cue based on knowledge of the typical sizes of objects, such as humans or pennies

relative metrical depth cue

a depth cue that could specify that object A is twice as far away as object B without providing information about the absolute distance to either A or B

absolute metrical depth cue

a depth cue that provides quantifiable information about distance in the third dimension

aerial perspective (haze)

a depth cue based on the implicit understanding that light is scattered when we look through more atmosphere

more distant objects are subject to more scatter and appear fainter, bluer, and less distinct

linear perspective

a depth cue based on the fact that liens that are parallel in the three-dimensional world

vanishing point

the apparent point at which parallel lines receding in depth converge

anamorphosis (anamorphic projection)

use of the rules of linear perspective to create a two-dimensional image so distorted that it looks correct only when viewed from a special angle or with a mirror that counters the distortion

triangulation

refers to the triangle formed by the two 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

depth cue based on head movement

geometric information obtained from an eye in two different positions at two different times is similar to the information from two eyes in different positions in the head at the same time

optic flow

the pattern of apparent motion of objects in a visual scene produced by the relative motion between the observer and the scene

accommodation

the process by which the eye changes its focus

lens gets fatter as gaze is directed toward nearer objects

convergence

ability of the two eyes to turn inward, often used in order to place the two images of a feature in the world on corresponding locations in the two retinal images (typically the fovea)

reduces the disparity of that feature to zero

divergence

ability of the two eyes to turn outward, often used in order to place the two images of a feature in the world on corresponding locations in the two retinal images (fovea)

reduces the disparity of that feature to zero

vergence angle

the angle formed by lines from each eye to the current object of fixation

the larger it is, implies a closer object

absolute disparity

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

relative disparity

the difference in the absolute disparities of two objects

corresponding retinal points

two monocular images of an object in the world are said to fall on corresponding points if those points are the same distance from the fovea

the two foveas are these

horopter (vieth-muller circle)

the location of objects whose images lie on corresponding points

the surface of zero binocular disparity

diplopia

double vision

if visible in both eyes, stimuli falling outside of panum’s fusional area will appear this way

panum’s fusional area

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

crossed disparity

the sign of disparity created by objects in front of the plane of fixation (horopter)

images of objects located in front of the horopter appear to be displaced to the left in the right eye and to the right in the left eye

uncrossed disparity

the sign of disparity created by objects behind the plane of fixation (horopter)

used because images of objects located behind the horopter will appear to be displaced to the right in the right eye and to the left in the left eye

stereoscope

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

free fusion

the technique of converging or diverging the eyes in order to view a stereogram without a stereoscope

stereoblindness

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

typically used to describe individuals with vision loss in both eyes

random dot stereogram (RDS)

a stereogram made of a large number of randomly placed dots

contain no monocular cues to depth

look like barcodes

cyclopean

referring to stimuli that are defined by binocular disparity alone

correspondence problem

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

uniqueness constraint

in reference to stereopsis, the observation that a feature in the world is represented exactly once in each retinal image

simplifies the correspondence problem

continuity constraint

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

helpful in solving the correspondence problem

the bayesian approach

a way of formalizing the idea that our perception is a combination of the current stimulus and our knowledge about the conditions of the world

what is and is not likely to occur

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

stereoacuity

a measure of the smallest binocular disparity that can generate a sensation of depth

dichoptic

referring to the presentation of two different stimuli, one to each eye

different from binocular presentation, which could involve both eyes looking at a single stimulus

critical period

a period of time during development when the organism is particularly susceptible to developmental changes

strabismus

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

esotropia

strabismus in which one eye deviates inward

exotropia

strabismus in which one eye deviates outward

tilt aftereffect

the perceptual illusion of tilt, produced by adaptation to a pattern of given orientation

suppression

the inhibition of an unwanted image

occurs frequently in people with strabismus