Problem 6 Flashcards
Occlusion
Pictorial cue
Occurs when one object partially hides another from view
–> partially hidden object is perceived to be more distant
Oculomotor cues
Created by
- CONVERGENCE
- -> inward movement of the eyes that occurs when we look at nearby objects - ACCOMMODATION
- -> the change in the shape of the lens, when focusing on objects
=> cues based on our ability to sense the position of our eyes
Monocular cues
Cues that work with one eye
a) accommodation
b) pictorial cues
c) motion produced cues
Pictorial cues
Sources of depth information that can be depicted in a two dimensional picture
–> cues are stationary/fixed
Relative size
Pictorial cue
When 2 objects are of equal size, the one farther away will take up less of our view than the one closer
–> cue depends on a persons knowledge of physical sizes
Familiar size
Pictorial cue
Cues used when judging the distance based on prior knowledge of the size of objects
Texture gradient
Pictorial cue
Elements equally spaced in a scene appear to be more closely packed as distance increases
Relative height
Pictorial cue
Objects with their bases closer to the horizon are usually seen as being more distant
Perspective convergence
Pictorial cue
Cue experienced when looking down parallel lines that appear to converge in distance
Atmospheric perspective
Pictorial cue
Occurs when distant objects appear less sharp than nearer objects, with a slight blue tint
–> works above 30 m
Shadows
Pictorial cue
Decreases in light intensity caused by a blockage of light that provide info about the location of objects
Motion produced cues
Cues that emerge when we start moving, that enhance our perception of depth
–> works at close + medium ranges
Motion parallax
Motion-produced cue
Occurs when nearby objects appear to glide rapidly past us, but more distant objects appear to move more slowly
ex.: moving nearby cars seem to speed away in a blur, whereas those farther away seem to be moving slowly
Deletion + Accretion
As one moves sideways, some things become covered (=deletion) and some become uncovered (= accretion)
Stereoscopic vision
Ability to use disparity between 2 eyes as a cue to depth
Binocular disparity
Describes the differences between two retinal images of the same scene
–> basis for stereopsis
Corresponding retinal points
Points on the retina that overlap if the eyes are superimposed on each other
Horopter
Imaginary circle that passes through the point of focus
–> the surface has 0 disparity
Non-corresponding points
Images of objects that are not on the horopter fall on non-corresponding points
Absolute disparity
The degree to which these objects deviate from falling on corresponding points
–> determined by measuring the angle between where the CP would be located and where it is actually located
Angle of disparity
Amount of absolute disparity
–> provides info about the objects distance from the horopter
Crossed disparity
Sign of disparity produced by objects in front of the horopter
- You would need to “cross” your eyes to fixate on the object in front of you
- Objects appear to be displaced to the right in the left eye and vice versa
Uncrossed disparity
Sign of disparity produced by objects behind the horopter
–> objects seem to be displaced to the right in right eye + same for left eye
Relative disparity
The difference in absolute disparities of objects in a scene remains the same as an observer looks around the scene
–> helps indicate where objects are located relative to others
Random dot stereogram
Stereogram made of a large number of randomly placed dots, that contains no monocular cues to depth
–> shows that disparity alone can result in depth perception
Correspondence problem
Refers to the question of how the visual system matches the parts of the images in the left and right eyes that correspond to one another?
Binocular depth cells
Disparity selective cells
Respond best when stimuli presented to either eye create a specific degree of absolute disparity
Which cortical areas are involved in depth perception ?
Depth perception starts in primary visual area and extends into different areas in the ventral + dorsal streams
Selective rearing
If an animal is reared in an environment that contains only certain types of stimuli, neurons that respond to these stimuli will become more prevalent
–> explains why we respond predominantly to vertical + horizontal lines
Size constancy
Refers to the fact that our perception of an objects size is relatively constant, even when we view the object from different distances
Size distance scaling
To perceive the actual size of an object the observer combines the information of
a) the retinal size of the object
b) the objects distance
Equation for size distance scaling
S = K ( R x D )
S –> objects perceived size
K –> constant
R –> size of retinal image
D –> Perceived distance of object
Müller - Lyer illusion
Illusion in which two lines of equal length appear unequal depending on whether angular lines forming arrowheads at each end point toward or away from each other
–> because our perception depends on the overall length of the figure
Which constraints help us solve the correspondence problem ?
- Uniqueness
–> a feature in the world will be represented exactly once in each retinal image
- Continuity
–> except at the edges of objects, neighboring points in the world lie at similar distances from the viewer
