Spatiotemporal frequency and direction sensitivities of human visual areasmeasured using fMRI

Using functional magnetic resonance imaging (fMRI) we have studied the vari ation in response magnitude, in each visual area (V1-V5), as a function of spatial frequency (SF), temporal frequency (TF) and unidirectional motion v ersus counterphase flicker. Each visual area was identified in each subject using a combination of retinotopic mapping fMRI and cortical flattening te chniques. A drifting (or counterphasing) sinusoidal grating was used as the stimulus in a study in which we parametrically varied SF between 0.4 and 7 cycles/degree and TF between 0 and 18 Hz. For each experiment we construct ed fMRI amplitude tuning curves, averaged across subjects, for each visual area. The tuning curves that resulted are consistent with the known physiol ogical properties of cells in the corresponding macaque visual areas, previ ous functional imaging studies, and in the case of V1, the psychophysically determined contrast sensitivity functions for spatial and temporal frequen cy. In the case of V3A, the SF tuning functions obtained were more similar to those found in single cell studies of macaque V3 rather than macaque V3A All areas showed at least a moderate preference for directed versus counte rphasing motion with V5 showing the largest preference. Visual areas V1, V2 , V3, and V3A showed more direction sensitivity at law spatial frequencies, while VP, V4, and V5 had the highest drifting versus counterphasing ratios for higher spatial frequencies. (C) 2000 Academic Press.