Spatial frequency tuning in human retinotopic visual areas.

Human medial occipital cortex comprises multiple visual areas, each with a distinct retinotopic representation of visual environment. We measured spatial frequency (SF) tuning curves with functional magnetic resonance imaging (fMRI) and found consistent differences between these areas. Areas V1, V2, VP, V3, V4v, and V3A were all band-pass tuned, with progressively lower SF optima in V1, V2, and V3A. In VP and V3, the SF optima were similar to optima in V2, whereas V4v showed more individual variation and scattered SF representations on the cortical surface. Area V5+ showed low-pass SF tuning. In each area, the SF optimum declined with increasing eccentricity. After accounting for the cortical magnification, the cortical extent of the optimal spatial wavelengths was approximately constant across eccentricity in V1, which suggests an anatomical constraint for the optimal SF, and this extent is actually comparable to the extent of horizontal connections within primate V1. The optimal spatial wavelengths in the visual field are also of similar extent to the spatial summation fields of macaque V1. The progressive decline in the SF tuning from V1 to V2 and V3A is compatible with the view that these areas represent visual information at different spatial scales.