Chapter Summary

One important property of vertebrate retinas is that the feature extractions that they perform are designed to lead to the survival of the host animal. Thus, in birds, there are many DS units, no doubt to permit visual flight stabilization and obstacle avoidance. In rabbits, the DS units are organized so that their preferred directions lie grouped around three and four major axes, depending on the DS unit type. Such grouping of preferred directions may be associated with the control of eye movements. (Rabbits sit still to avoid detection by predators, and so must move their eyes to track moving objects.)

Certain frog feature extraction operations appear to be associated with detecting flies (food) moving into the visual field. Frogs sit still when they hunt, and wait until prey approaches before striking. Unlike rabbits, frogs cannot move their eyeballs to track their prey. Thus, the entire retina must participate in tracking a moving spot.

The vertebrate retina does not fulfill a function similar to the ganglia in the optic lobes. The retina works in concert with the visual tectum and the optical cortex of the brain. The arthropod optic lobes are far older in an evolutionary sense, and have been specialized for the visually mediated survival of their host animal. The retina can be viewed (no pun intended) as a pre-processing network that supplies information to plastic neural networks that can perform learned, cognitive tasks. That feature extraction occurs in both the arthropod optic lobe and in the vertebrate retina argues for the importance of the preprocessing of visual information. Clearly, it has survival value.

Theoretical Models of Information Processing and Feature Extraction in Visual Sensory Arrays

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