This chapter examines the neuroanatomy and feature extraction properties of various vertebrate retinas. It begins by reviewing the function(s) of each of the interneurons that make up the retina. The retinal photoreceptors, the rods and cones, are different from arthropod retinula cells in that they hyperpolarize in response to absorbed light energy. Rods and cones do not spike; they are essentially analog transducers, like retinula cells.
The early work on feature extraction was done on the retinas of frogs. Workers generally recorded from ganglion cell (optic nerve) axons. The classic paper on retinal feature extraction, described in Section 6.2, was published by Lettvin et al., (1959). One of the author's Ph.D. students (Reddy, 1977) recorded from directionally sensitive units in the frog's brain. Some of his results are described in Section 6.2.2.
Finally, feature extraction operations are described in the retinas of pigeons and rabbits in Section 6.3. Again, many of the ganglion cell types found in frogs appear in these animals. Only when cats and primates are considered is it found that certain retinal feature extraction operations are missing, as they are presumably performed more efficiently in the visual cortex.
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