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Abstract

The fast and accurate recognition of face identity is one of the hallmarks of primate visual performance. While numerous studies have revealed face-responsive neurons throughout the monkey brain, particularly in the superior temporal sulcus (STS) and inferotemporal (IT) lobe, the basic encoding strategies for faces remain poorly understood. Recent results using high-level adaptational aftereffects have suggested that the perception of identity involves reference to a stored prototype representation (Leopold et al., Nat. Neuro., 4:1, 2001). In the current study, we investigated the neurophysiological mechanisms underlying face perception in monkeys. We taught a monkey to discriminate between four human faces, and to indicate which face it perceived by pressing one of four buttons. We then measured the responses of IT and STS neurons to morphed faces that were modulated in their identity strength, as determined by their position in a computationally derived face-space. The monkey thus classified caricatures, anti-caricatures and anti-faces as one of the learned faces. Recordings were carried out with an implanted bundle of 64 high impedance Ni-Cr-Al microwire electrodes (Bondar Logothetis, Soc. Neurosci. Abstr., 2000). Individual electrodes were different lengths, and the position of the bundle was adjustable in all directions, allowing for simultaneous measurement of single and multiple units, as well as local field potentials, from various areas in the temporal lobe. We will report on the modulation of temporal neurons to faces morphed along perceptually meaningful trajectories in face space.