A Two-Stage Cascade Model of BOLD Responses in Human Visual Cortex
(A) Size parameter (σ). The top panel shows the estimated σ value at 2° eccentricity for each visual field map. To quantify receptive field size, we compute model responses to small white spots (0.25°×0.25°) and fit 2D Gaussians to the results. The bottom panel shows contours at ±2 s.d. of the fitted Gaussians. (B) Exponent parameter (n). The top panel shows the median n value for each visual field map. To demonstrate the effect of n, we compute model responses to full-field noise patterns varying in contrast (same patterns used for the spatial stimuli). The bottom panel shows the resulting contrast response functions, normalized such that the maximum response is 1. (C) Second-order parameter (c). The top panel shows the median c value for each visual field map. To interpret the effect of c, we compute model responses to a 20%-contrast plaid pattern covering the entire receptive field and the same plaid pattern covering half of the receptive field. The bottom panel shows responses to the full and half plaids, normalized such that the response to the full plaid is 1. For reference we also show results obtained when c is set to 0.