AREAS PMLS AND 21A OF CAT VISUAL-CORTEX - 2 FUNCTIONALLY DISTINCT AREAS

We have compared the receptive field properties of neurons recorded fr om visuotopically corresponding regions of area 21a and the posteromed ial lateral suprasylvian area (PMLS) of cat visual cortex. In both are as, the great majority of neurons were orientation-selective and binoc ular, and their responses to moving contours were modulated by simulta neous in phase or anti-phase motion of large textured background stimu li ('visual noise'). However, despite the great hodological similarity between the two areas, PMLS neurons had on average significantly high er peak discharge rates, exhibited substantially greater direction sel ectivity indices, and preferred substantially higher stimulus velociti es than area 21a neurons. Furthermore, the majority of binocular neuro ns in the PMLS area and in area 21a were dominated respectively by the contralateral and the ipsilateral eyes. Finally, while 46% of PMLS ne urons were excited by movement of visual noise per se, only 25% of are a 21a neurons could be excited by such stimuli. We argue that the PMLS area, like its presumed primate homologue the middle-temporal (MT) ar ea, is mainly involved in motion analysis. By contrast, area 21a appea rs to he involved in pattern analysis rather than motion analysis. It is likely that phylogenetically area 21a derives from the PMLS area.