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Adaptation Reveals Multichannel-Coded Cells Tuned to Body Orientation in Humans.
Vision Sciences Society Meeting - Florida 2008
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Neurophysiological research has revealed superior temporal sulcus (STS) cells in macaques that respond selectively to different directions of seen body orientation in the absence of head or face based cues (Perrett et al, 1992). Here we use adaptation to investigate, for the first time, the functional organization of social direction perception from seen body orientation, with masked heads, in humans. In Experiment 1 we found that adaptation to left (or right) facing bodies increased participants tendency to perceive subsequently viewed left (or right) facing bodies as facing directly towards them – evidence for direction selective coding of seen body orientation in humans. In Experiment 2 we sought to investigate whether the visual representation of body orientation is coded by an opponent-coding system, recently implicated in facial identity perception (Jiang, Blanz, & O'Toole, 2006; Leopold, Bondar, & Giese, 2006; Leopold, O'Toole, Vetter, & Blanz, 2001; Rhodes et al., 2005) or a multichannel system, which has been shown underlie the visual representation of seen gaze (Calder, Jenkins, Cassel & Clifford, in press). We tested predictions that arise from the underlying assumptions of these two models and found that, consistent with multichannel coding, simultaneous adaptation to left and right facing bodies resulted in an increased tendency to perceive subsequently seen left and right body orientations as direct. Conversely, but also consistent with a multichannel system, adapting to direct facing bodies increased accuracy in perception of subsequently seen left and right body directions. In each case an opponent-coding model would predict no effect of adaptation. Together, our findings provide the first evidence for selective neural representations of different body directions within the context of multichannel coding. These findings extend pervious adaptation research showing separable coding of seen gaze (Jenkins, Beaver & Calder, 2006) and head direction (Fang & He, 2005).