主题：Spatial and temporal ensemble coding in face adaptation
报告人：Dr. Hong Xu, Assistant Professor, UTU
How do we perceive a group of faces? What info do we extract from a group of people approaching us? We investigate these questions from temporal and spatial manipulations of the faces. We use visual adaptation to investigate this automatic and passive process. We first adapted subjects to faces in a rapid serial visual presentation (RSVP) sequence and asked them to judge subsequently presented face’s emotions. We found that subjects biased their judgement toward the opposite of the ensemble face of the RSVP sequence. It thus suggests the existence of automatic ensemble coding during adaptation. We then adapted subjects to a group of faces presented at different locations. It has been reported that the average face appears more attractive than individual faces, and the target face becomes more attractive in a group, the so called “cheerleader effect”. We would expect the ensemble average of the adapting face group to generate the same aftereffect as the face group. Surprisingly, in addition to that, we observed a comparison between the target and surround faces during adaptation. It thus suggests that spatial ensemble coding may activate two processing mechanisms: a social positive effect as indicated by cheerleader effect, and a comparison between the target and its surround. Therefore, spatial ensemble coding may activate multiple levels of face analysis. Comparing these studies, we propose two distinct processes: ‘gist’ averaging for spatial ensemble coding, and ‘computational’ averaging for temporal ensemble coding. These findings imply that distinct visual pathways and subcortical structures may be activated during facial processing.