Chapter 10 Flashcards
(12 cards)
Oculomotor cues
Oculomotor cues are based on sensing the position of the eyes and muscle tension.
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.
Monocular Cues
Focuses on image info that is correlated with depth in the scene
We learn the connection through repeated exposure.
Occlusion, relative height, atmospheric perspective, texture gradient and shadows.
Motion produced cues
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.
Covering an object: deletion
Uncovering an object is accretion
Relative vs absolute depth
refer to pics
Binocular Depth perception
Binocular disparity: difference in images from two eyes
Difference can be described by examining corresponding points on the two retinas.
The horopter: imaginary sphere that passes through the point of focus
Objects on the horopter fall on corresponding points on the two retinas.
Objects that do not fall on the horopter fall on noncorresponding points
These points make disparate images.
The angle between these points is the absolute disparity.
The amount of disparity indicates how far an object is from the horopter.
Relative disparity is the difference between the absolute disparity of two objects.
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.
Physiology of depth perception
Neurons have been found that respond best to binocular disparity.
These are called binocular depth cells or disparity selective cells.
They respond best to a specific degree of absolute disparity between images on the right and left retinas.
Disparity tuning curve – like the tuning curves you learned about before (e.g., orientation)
Experiment by Blake and Hirsch
Cats were reared by alternating vision between two eyes.
Results showed that they had few binocular neurons and were unable to use binocular disparity to perceive depth
Experiment by DeAngelis et al
A monkey was trained to indicate depth from disparate images.
Disparity-selective neurons were activated by this process.
Experimenter used microstimulation to activate different disparity-selective neurons.
The monkey shifted judgment to the artificially stimulated disparity.
Holway and Boring
Participants adjust comparison light circle
Test circles can be from 20-120 feet away
2 conditions – 1 dark, 1 with depth cues
Moon Illusion explanations…
One possible explanation:
Apparent-distance theory: horizon moon is surrounded by depth cues while the moon higher in the sky has none.
The horizon is perceived as further away than the sky, and called “flattened heavens”.
Another possible explanation:
Angular size-contrast theory: the moon appears smaller when surrounded by larger objects.
Thus, the large expanse of the sky makes it appear smaller.
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Size and depth – size constancy
Perception of an object’s size remains relatively constant.
This effect remains even if the size of the retinal image changes.
Size-distance scaling equation
S = K (R X D) (changes in distance and retinal size balance each other)
Emmert’s law
