Abstract
A model of the retina based on biological data is developed to study the processing of images by the retina as a model for an adaptive receptor. The direct visual pathway (photoreceptors, bipolar and ganglion cells) and the horizontal units and their gap-junctions, as well as the dopaminergic interplexiform cells and dopamine release are modeled. A small network of 12 units is first simulated in order to study the behavior of the different components involved, and the role played by lateral inhibition is analyzed. A 64×64 photoreceptors model, containing 16,448 units, is then simulated. The following properties were found for stimuli that remain constant in time: (i) The difference between the time constants of the photoreceptors and the horizontal units lead to both the formation of a transient output image that contains pertinent features of the input, and the formation of a reverse after-image when the stimulus is removed. (ii) Global modifications of lateral inhibition strength allow either contrast rendering or contour enhancement. Local modifications of lateral inhibition strength bring about adaptation to local input characteristics.
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