Chapter 6 Summary
1. Reconstructing a three-dimensional world from two non-Euclidean, curved,
-dimensional retinal images is one basic problem faced by the brain.
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2. A number of
cues provide information about three-dimensional space. These include occlusion, various size and position cues, aerial perspective, linear perspective, motion cues, accommodation, and convergence.
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3. Having two eyes is an advantage for a number of reasons, some of which have to do with depth perception. It is important to remember, however, that it is possible to reconstruct the three-dimensional world from a single two-dimensional image. Two eyes have other advantages over just one: expanding the visual
,
permitting binocular summation, and providing redundancy if one eye is damaged.
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4. Having two laterally separated eyes connected to a single brain also provides us with important information about depth through the geometry of the small differences between the images in each eye. These differences, known as binocular
,
give rise to stereoscopic depth perception.
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5. Random-dot stereograms show that we
to know what we’re seeing before we see it in stereoscopic depth. Binocular disparity alone can support shape perception.
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6. Stereopsis has been exploited to add, literally, depth to entertainment—from nineteenth-century photos to twenty-first-century movies. It has also served to enhance the perception of information in military and medical settings.
7. The difficulty of matching an image element in one eye with the correct element in the other eye is known as the correspondence problem. The brain uses several strategies to solve the problem. For example, it reduces the initial complexity of the problem by matching large “blobs” in the
-spatial-frequency information before trying to match every
-frequency detail.
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8. Single neurons in the primary visual cortex and beyond have
,
fields that cover a region in three-dimensional space, not just the two-dimensional image plane. Some neurons seem to be concerned with a crude in-front/behind judgment. Other neurons are concerned with more precise, metrical depth perception.
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9. When the stimuli on corresponding loci in the two eyes are different, we experience a continual perceptual competition between the two eyes known as binocular
.
is part of the effort to make the best guess about the current state of the world based on the current state of the input.
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10. All of the various monocular and binocular depth cues are combined (unconsciously) according to what prior knowledge tells us about the probability of the current event. Making the wrong guess about the cause of visual input can lead to
.
Bayes’ theorem is the basis of one type of formal understanding of the rules of combination.
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11. Stereopsis emerges suddenly at about
of age in humans, and it can be disrupted through abnormal visual experience during a critical period early in life.
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