Topic 4 - Visual Illusions Flashcards
Oculomotor cues
based on sensing the position of the eyes and muscle tension
- Ocular convergence
- Accommodation
Ocular convergence
inward movement of the eyes when we focus on nearby objects
Accommodation
change in the shape of the lens when we focus on objects at different distances
Monocular depth cues
Only come from one eye
Pictorial cues and motion-produced cues
Pictorial Cues
sources of depth information that come from 2-D images, such as pictures
Includes: Occlusion Relative height Relative size Familiar Size Perspective convergence Atmospheric perspective Texture gradient Shadows
Occlusion
When one object partially covers another
Relative height
objects below the horizon that are higher in the field of vision are more distant
Relative size
when objects are equal size, the closer one will take up more of your visual field
Familiar size
distance information based on our knowledge of object size
Perspective convergence
parallel lines appear to come together in the distance
Atmospheric perspective
distance objects are fuzzy and have a blue tint (on a clear day)
Texture gradient
equally spaced elements are more closely packed as distance increases
Shadows
indicate where objects are located
Motion parallax
close objects in direction of movement glide rapidly past but objects in the distance appear to move slowly
Deletion and accretion
objects are covered or uncovered as we move relative to them
Binocular depth cues
Two eyes cues
Includes binocular disparity and stereopsis
Stereoscopic depth perception
depth perception created by input form both eyes
Strabismus
misalignment of the eyes
Binocular disparity
difference in the images on the left and right retinas
- Corresponding retinal points - points on retina that would overlap - a surface called the horopter
- Noncorresponding points - images that are not on the horopter
- Absolute disparity - angle between noncorresponding points, angle of disparity
- Crossed disparity - eyes see object on the opposite side of visual field to side eye is on
- Uncrossed disparity - eyes see object on same side of visual field to side eye is on
- Relative disparity - difference between absolute disparity of two objects
Steropsis
depth information provided by binocular disparity (perceptual)
Stereoscope uses two pictures from slightly different viewpoints (one to each eye)
- Random-dot stereogram - has two identical patterns with one shifted in position
Correspondence problem
How does the visual system match images from the two eyes? – Matches may be made by specific features of objects
This may not work for objects like random-dot stereograms, A satisfactory answer has not yet been proposed
Depth perception in other species
Animals use same cues
Frontal eyes needed for binocular disparity
Lateral eyes provide a wider view
Experiment by Tsutsui et al.
binocular depth perception
- Monkeys matched texture gradients that were 2-D pictures and 3-D stereograms.
- Recordings from a neuron in the parietal lobe showed: >Cell responded to 2D pictorial cues, Cell also responded to 3D binocular disparity
Binocular depth cells, disparity selective cells
These cells respond best to a specific degree of absolute disparity between images on the right and left retinas (have a tuning curve)