Spatial interactions and models of adaptation.

Adaptation mechanisms can be divided into two classes: multiplicative mechanisms which reduce the gain and subtractive mechanisms which discount or filter out the background signal. This paper investigates the neural basis of subtractive adaptation in photopic vision. Specifically, can the spatial interactions revealed by Westheimer's effect be described as subtractive? The evidence presented here shows that they can. That is, small adapting fields raise threshold more than large ones because they produce more response compression, not because they reduce the gain. As the background is enlarged progressively more of the background signal is subtracted off, reducing the response compression at some later non-linear site. These results indicate that retinal center-surround antagonism is one of the mechanisms mediating subtractive adaptation.