Chapter 3 Summary

A great deal is now known about how information from photoreceptors is initiated and processed by neurons in the primary visual pathway, including the initial stages of processing in the primary visual cortex (V1).
How neural information is processed in the higher-order regions of the extrastriate visual cortices is less well understood, although a general theme is that activity in the cortex tends to track percepts, whereas neuronal activity in the retina, thalamus, and input layer of V1 is more closely tied to the actual properties of the stimulus.
Another general rule is that visual information important for object recognition projects to the temporal lobes (the ventral stream), whereas information about object location projects to the parietal lobes (the dorsal stream).
A challenge in understanding the basic strategy of visual processing, however, is explaining how inherently uncertain retinal stimuli can give rise to definite percepts and generally successful visually guided behavior. For each of the basic visual qualities—lightness, brightness, color, form, depth, and motion—the perceptual evidence points to a strategy that links images to behavior empirically, gained from both evolutionary and individual experience. How empirical information is expressed in neural circuitry remains to be discovered.
The perceptual recognition of objects depends on associations made during life between these basic qualities elicited by visual stimuli and nonvisual information that defines faces, houses, tools, and other objects.