Evoked Potential Studies of Face and Object Processing

Abstract

Very little is known about how faces or other objects are analysed by human brain. In this paper I try to show that valuable information about some of the physiological processes involved can be derived from scalp-recorded, visual evoked potentials. The response properties of a distinct scalp potential, the “vertex positive peak” (VPP), are described, which suggest that there is a low-level, stimulusrelated stage of processing, probably located in the inferotemporal cortex, which is designed to detect very rapidly the suddenly fixated images of single faces or objects. The underlying cortical mechanisms: (1) respond to any two-dimensional patterned image consistent with the basic structure of a face; (2) respond more strongly and more quickly to faces than to objects; and (3) respond fastest of all to the most commonly experienced views of complete faces. Preliminary evidence further suggests that different neuronal populations in the same cortical areas are involved in the generation of face- and object-evoked VPP responses. The functional implications of these evoked potential findings are discussed, also their relationship to the results of other electrophysiological and psychological studies in humans and of neurobiological studies in monkeys. Some ways of further enhancing the information derived from such experiments are also suggested.