Asymmetric switch-costs and ERPs reveal facial identity dominance over expression.

Previous studies on face processing have revealed an asymmetric overlap between identity and expression, as identity is processed irrespective of expression while expression processing partly depends on identity. To investigate whether this relative interaction is caused by dominance of identity over expression, participants performed familiarity and expression judgments during task switching. This paradigm reveals task-set dominance with a paradoxical asymmetric switch-cost (i.e., greater difference between switch and repeat trials when switching toward the dominant task). Event-related potentials (ERPs) were recorded to find the neural signature of the asymmetric cost. As expected, greater switch-cost was shown in the familiarity task with respect to response times, indicating its dominance over the expression task. Moreover, a left-sided ERP correlate of this effect was observed at the level of the frontal N2 component, interpreted as an index of modulations in endogenous executive control. Altogether, these results confirm the overlap between identity and expression during face processing and further indicate their relative dominance.

Perceptual interactions between visual processing of facial familiarity and emotional expression: an event-related potentials study during task-switching.

Models of face processing suggest that facial familiarity and expression processes involve independent visual systems. But under some conditions, the two processes interact, as when selective attention is solicited, and/or when a link is established between consecutive stimuli. To assess these assumptions during perceptual face processing, event-related potentials (ERPs) were used while subjects discriminated either familiarity or expression in a task-switching paradigm. Switched trials were designed with competitor priming, the unattended dimension being previously attended. The results indicate interactions appearing in the right hemisphere during the perceptual encoding stage (N170) when subjects processed either familiarity or expression during switched trials. These interactions gain both hemispheres during memory retrieval (P2) and in terms of accuracy. Altogether, these results confirm the critical role of the right hemisphere in perceiving faces and their expressions. Moreover, they suggest that familiarity and expression can interact in both directions.