Neural basis of stereo dkpth perceffion measured with fMRI

Purpose: To measure \isual cortical r -sponses invoUed in stère* depth peiception. Background: Disparity tuned neuron-, arc widespread in several \isual cortical areas, but il is not clear which ol these neurons are involved m steieo depth perception per se For stereo-defined corrugated surface , depth can he perceived over a \\idcr range of disparities when tht surface depth mcdulales at a lower spatial liequency. For visual aieas that are directly involved in sten-o vision, f'MRl responses to disparities that aie too large should lesemble responses tt> binocularly uneorrelated slereojiranis. Methods: Stimuli were (square-wav.-] corrugated surfaces delined b\ disparity in currelated, dyn.innc. random-dot stei'fugrams. \\ith various disparities and spatial frequencies (i.e., Iront/back panel width; ). These target stereogranis alternated e\ery \X seconds with binocularly uncorrelaled random-dot slereogranis. 1MRI resjionsc (using a \'2* weighted spiral acquisition) wa> quantified as the ampliuuieot modulation uf ihe i 36 see period) sinusoid that best lit eajh pixel's time-seiies Responses were averaged o\er each of several regions of intcres . Results: ( 1 ) Strong bilateral fMRI le-iponse modulations \\ere found in area X I and in an area on the ventral surface of th.- occipital lobe near the fusiform gyrus. (2} Responses were small and inconsistent in other \isual areas, including putali\e MT (3) Responses were larger (by about a factor of 2i in the fusiform area than in VI (4) Disparity tuning curves in both .ireas depended on the spatial frequency ol the depth corrugations in a manner that u as consistent with the percept, i.e., the response modulation fell to /ero at about the -ame disparities foi which the subject could mi iongei see deplh. Conclusions: We propose that VI ard an area near the hisitnrm g\ rus nie the lirsi 1 \isual areas in the pathway mediating stereo vision.