A Two-Stage Cascade Model of BOLD Responses in Human Visual Cortex
(A) Simulation results. Stimuli consisted of a horizontal grating presented within circles of different sizes. Using the typical parameter values found in V2 (see Figure 9), we simulated the response of an array of model units tiling the visual field. Responses are strongest for units positioned at the edge of the grating since responses are driven primarily by variation in contrast-energy. (B) Responses of one unit (marked by a white dot in panel A). With increasing stimulus size, the response rises and then falls, consistent with surround-suppression effects found in electrophysiology [e.g. 20], .