A Two-Stage Cascade Model of BOLD Responses in Human Visual Cortex
Figure 4
Compressive nonlinearity accounts for spatial tolerance.
We measured responses to noise patterns covering different portions of the visual field. Responses of an example voxel are shown (subject 2, area V2, voxel 38512). The DN model underestimates responses to stimuli covering a small portion of the receptive field and overestimates responses to stimuli covering a large portion of the receptive field. To improve performance, we incorporated a compressive static nonlinearity into the model. The compressive nonlinearity is applied after spatial summation and provides increased tolerance for changes in the position and size of a stimulus [11]. The compressive spatial summation (CSS) model fits the data accurately.