OBJECT SHAPE PROCESSING IN THE VISUAL-SYSTEM EVALUATED USING FUNCTIONAL MRI

We used functional MRI (fMRI) to determine the cortical regions activa ted during processing of visual object shape in humans in six men and three women, using a paradigm with a baseline condition of simple shap e detection and an activated condition of object/nonobject shape discr imination. Eight of the nine subjects studied showed significant signa l changes. Seven of eight showed changes in the occipital lobes (five bilateral, two right only, one left only), All eight subjects with sig nal changes exhibited changes in the parietal lobes bilaterally. In th e occipitotemporal gyri, there were signal changes bilaterally in seve n subjects and unilaterally, on the right;, in one. Activation-related fMRI signal increases were also present in the posterior superior and middle temporal gyri in seven of the subjects, with four showing bila teral signal changes, two showing signal changes on the left only, and one only on the right. The data strongly suggest that processing of o bject shape information in humans activates both the ventral and dorsa l visual processing pathways (''what'' and ''where'' pathways), descri bed previously both in humans and in nonhuman primates.