Fig. 2.

Spatial summation is subadditive throughout visual cortex. A: example tests of spatial summation. The black bars indicate the responses of an example V1 voxel and V3 voxel to the apertures shown below. In both cases, the response to the full aperture is less than the linear prediction (horizontal line). The summation ratio, defined as the response to the full aperture divided by the linear prediction, is 0.78 for the V1 voxel and 0.59 for the V3 voxel. B: median summation ratio in different visual field maps. We calculated the median summation ratio across aperture pairs located within 0.5-pRF sizes from the pRF center. (If an aperture pair is distant from a pRF, 1 aperture would have no influence on the response, and linear summation would hold trivially; see Supporting Fig. C for details; all supporting tables and figures are located at http://kendrickkay.net/; also see endnote.) Responses are subadditive in all visual field maps and especially so in extrastriate maps.