Functional Electronic Model of the Frog Retina

Based on some earlier concepts, a functional electronic model of the frog retina has been designed and constructed. This system duplicates functionally the four image-feature-abstraction process found by Lettvin and co-workers in the frog retina. From the input image, the model abstracts 1) edges, 2) moving convexities, 3) contrast changes, and 4) net dimming. Information presented to the receptors flows in a parallel mode through successive separate processing layers of the model; this information is preserved as it flows as a transformed "map" of the input image. Finally, the processed information is displayed as a spatial map of the four abstracted features of the input image, similar to the "mapping" performed in the brain of the frog. The model was constructed using neon-lamp/photoconductive (Ne-Pc) circuits on separate processing layers. These two elements serve the dual purpose of being principal circuit components as well as providing the interconnections between processing planes. In this manner, the inputs to a processing plane are photoconductive cells and and the outputs are neon lamps. This fabrication technique provides the advantages of easy access to individual components, rapid visual inspection of the operation of individual layers, and the simplicity of modifying the system by inserting or removing a particular layer.