Specialized face processing and hemispheric asymmetry in man and monkey: evidence from single unit and reaction time studies.

Experimental and clinical studies have generally shown that the neural mechanisms for face processing in man are (1) designed to deal with the configuration of upright faces and (2) located predominantly in the right cerebral hemisphere. Monkeys would seem to process faces in a different manner to humans since they appear to show no hemispheric asymmetry and to treat upright and inverted faces equivalently. We re-examine these claims. Our reaction time studies reveal that monkeys do behave like human subjects since they process facial configuration faster when stimuli are presented upright as compared with horizontal or inverted. Single unit studies in the monkey reveal patches of neurones responsive to faces in the upper bank and fundus of the left superior temporal sulcus (STS). Recording from the right hemisphere also reveals cells responsive to faces but in this hemisphere such cells appear less numerous. These cells process upright faces faster than inverted faces. Face processing in monkeys and man appears to utilize qualitatively similar mechanisms, but the extent and/or direction of cerebral asymmetry in these mechanisms may not be similar.

Visual analysis of body movements by neurones in the temporal cortex of the macaque monkey: a preliminary report.

Movement provides biologically important information about the nature (and intent) of animate objects. We have studied cells in the superior temporal sulcus of the macaque monkey which seem to process such visual information. We found that the majority of cells in this brain region were selective for type of movement and for stimulus form, most cells responding only to particular movements of the body or some part of it. A variety of cell types emerged, including cells sensitive to: translation of bodies in view, movements into view (appearance) or out of view (disappearance) and the articulation and rotation of the body/head. Directional selectivity for cells sensitive to translation tended to lie along one of 3 orthogonal Cartesian axes centred on the monkey (towards/away, left/right and up/down). One type of rotation sensitive cell was tuned to rotation about one or more of these axes, a second type was sensitive to different head rotations which brought the face to confront the monkey or turned the face away. Reconstructions of cell positions indicated that cells of the same type were clumped anatomically both across the surface of the cortex and perpendicular to the surface.