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Abstract:
Single unit responses in the lower bank of the superior temporal sulcus and inferotemporal cortex show selectivity for faces and objects; however, the degree of selectivity beyond these unimodal visual areas is not well understood. Simultaneous recordings were collected from electrodes placed in multisensory regions of the upper bank of the superior temporal sulcus (uSTS), and in the lateral belt of auditory cortex, which is heavily interconnected with uSTS. The monkey passively viewed three classes of static images: monkey faces, various clip-art objects, and Greebles, an artificial set of homogeneous stimuli. Electrodes in auditory cortex as well as those in uSTS showed local field potential response profiles which differed for faces than for either Greebles or objects. The ‘face’ response in both recorded regions was characterized by a peak negativity around 100ms after stimulus onset. Multiple- and single-unit activity in uSTS revealed a variety of response selectivities to the three stimulus categories, but the most common was an enhanced response for the face stimuli. Discriminatory responses began as early as 50-70ms after stimulus onset. Taken together, these results indicate that 1. faces and objects elicit differentiable neural responses, even outside of unimodal visual areas, 2. Greeble responses are more closely associated with object than with face responses, and 3. category discrimination can occur at early latencies even in multisensory ‘association’ cortex.
