Journal of Vision - A multiplicative model for spatial interaction in the human visual cortex, by Zhang, Park, Salant, Thomas, Hirsch, & Hood

Xian Zhang	Department of Psychology, Columbia University, New York, NY, USA
Jason C. Park	Department of Psychology, Columbia University, New York, NY, USA
Jennifer Salant	Department of Psychology, Columbia University, New York, NY, USA
Sonya Thomas	Department of Psychology, Columbia University, New York, NY, USA
Joy Hirsch	Functional MRI center, Department of Radiology, Columbia University, New York, NY, USA
Donald C. Hood	Department of Psychology, Columbia University, New York, NY, USA

Multifocal visual evoked potentials (mfVEP) were recorded simultaneously for both the target and the neighbor stimuli, each varying over 6 levels of contrast: 0%, 4%, 8%, 16%, 32%, and 64%. For most conditions, the relationship between the amplitude of target response and the contrast of the neighbor stimulus, as well as the amplitude of the response to the target stimulus, were described with a simple, normalization model. However, when the neighbor stimulus had a much higher contrast than the target stimulus, the amplitude of the target response was larger than the prediction from the normalization model. These results suggest that spatial interaction observed in the mfVEP requires (1) multiplicative mechanisms, (2) mutual inhibition between neighboring regions, and (3) a mechanism that saturates when the ratio between the contrasts of the target and that of the neighbor is large. A modified multiplicative model that incorporates these elements describes the results.