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Xian Zhang, Jason C. Park, Jennifer Salant, Sonya Thomas, Joy Hirsch, Donald C. Hood; Multiplicative model for spatial interaction in the human visual cortex. Journal of Vision 2007;7(9):238. doi: 10.1167/7.9.238.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To understand the neural mechanism underlying spatial interaction, the multifocal visual evoked potential (mfVEP)[1,2] for both the target and neighbor stimuli were recorded simultaneously. A normalization model  and a new multiplicative model were fitted to the data.
Methods: The display was a one ring, 24-sector checkerboard display, subtending 44.5°. Each sector consisted of 2 (in angle) by 6 (in eccentricity) checks. The check size was scaled according to cortical magnification. The 1st,…,23rd sectors and the 2nd,…,24th sectors made up two sets of sectors, mutually being the target and the neighbor to each other. Both the target and neighbor varied in 6 levels of contrasts: 0,4,8,6,32,64%.
Results: For most conditions, the relationship between the amplitude of target response and the contrast of the neighbor, as well as the relationship between the amplitude of target response and the contrast of the target, 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 that predicted by the normalization model. A multiplicative model was developed to describe these data.
Conclusion: To account for these spatial interaction results requires: 1) a multiplicative mechanism, 2) mutual interaction between neighboring regions, and 3) a mechanism that saturates when the ratio in contrasts between target and neighbor is large. A multiplicative model with these characteristics described the results well.
References:  Sutter, E. E. and D. Tran (1992);  Hood, D. C., Q. Ghadiali, et al. (2006);  Heeger, D. J. (1993)
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