The role of early retinal lateral inhibition: More than maximizing luminance information

Lateral inhibition is one of the first and most important stages of visual processing. There are at least four theories related to information theory in the literature for the role of early retinal lateral inhibition. They ar e based on the spatial redundancy in natural images and the advantage of re moving this redundancy from the visual code. Here, we contrast these theori es with data from the retina's outer plexiform layer. The horizontal cells' lateral-inhibition extent displays a bell-shape behavior as function of ba ckground luminance, whereas all the theories show a fall as luminance incre ases,It is remarkable that different theories predict the same luminance be havior, explaining "half" of the biological data. We argue that the main re ason is how these theories deal with photon-absorption noise. At dim light levels, for which this noise is relatively large, large receptive fields wo uld increase the signal-to-noise ratio through averaging. Unfortunately, su ch an increase at low luminance levels may smooth out basic visual informat ion of natural images. To explain the biological behavior, we describe an a lternate hypothesis, which proposes that the role of early visual lateral i nhibition is to deal with noise without missing relevant clues from the vis ual world, most prominently, the occlusion boundaries between objects.