Figure 5.

Model components used to fit the data shown in Figures 6 and 7. The putative neural signal underlying the BOLD response was modeled as a linear combination of (1) a local luminance-brightness response (only present in the section of cortex representing a physically changing part of the stimulus), (2) narrow and wide edge responses, and (3) a surround-induced (brightness) response in the center region (note that during central disk modulation, it is impossible to separate out luminance and brightness responses). The combined neural signal was convolved with a Gaussian to impose the low-pass characteristics of the BOLD response (FWHM, 3.5 mm) ((Engel et al., 1997).