Divisive and Subtractive Mask Effects: Linking Psychophysics and Biophysics

Abstract

We describe an analogy between psychophysically measured effects in contrast masking, and the behavior of a simple integrate-and(cid:173) fire neuron that receives time-modulated inhibition. In the psy(cid:173) chophysical experiments, we tested observers ability to discriminate contrasts of peripheral Gabor patches in the presence of collinear Gabor flankers. The data reveal a complex interaction pattern that we account for by assuming that flankers provide divisive inhibi(cid:173) tion to the target unit for low target contrasts, but provide sub(cid:173) tractive inhibition to the target unit for higher target contrasts. A similar switch from divisive to subtractive inhibition is observed in an integrate-and-fire unit that receives inhibition modulated in time such that the cell spends part of the time in a high-inhibition state and part of the time in a low-inhibition state. The simi(cid:173) larity between the effects suggests that one may cause the other. The biophysical model makes testable predictions for physiological single-cell recordings.