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On the square root intensity coding at the level of cone photoreceptors
1Faculty of Computer Science and Systems Engineering, Kyushu Institute of Technology, Iizuka, Japan.
Abstract:
In psychophysics as well as in sensory physiology, the response amplitude R is often a power function of the stimulus intensity S over a wide range of S (i.e. R = aSk; a = constant). In vision, there is a recent report that such a power relationship ("square root intensity coding" if k = 0.5) may arise as early as at the cone photoreceptor level if the stimulus is a narrow slit of light. A simple model is presented here to account for this finding: strong electrical coupling with several neighboring cones can act to expand the dynamic range of the impaled cone in such a way as to produce a square root coding region for the responses to fine visual objects such as small spots and narrow slits.