A possible marker of configural processing at the N170: Converging evidence from typical participants and a case of prosopagnosia

Abstract

Both orientation and Thatcherisation are thought to influence configural processing in faces (Boutsen, Humphreys, Praamastra & Warbrick, 2006). We explored the effect of orientation and level of Thatcherisation (typical face, eyes Thatcherised, mouth Thatcherised, or both features Thatcherised) on early ERP components. Participants showed evidence of inversion effects leading to increased amplitude for inverted faces at the N170 and reduced amplitude to inverted faces at the P2. However, the effect of Thatcherisation was only evident in the right hemisphere N170 where there was a reduction in N170 amplitude with level of Thatcherisation. These data suggest two distinct processes (consistent with Towler, Gosling, Duchaine, & Eimer, 2012). In a follow-up study using the same task we tested PHD, an individual with acquired prosopagnosia known to be unable to perceive the Thatcher illusion (Mestry, Donnelly, Menneer & McCarthy, 2012). We did so to explore whether the markers of orientation and Thatcherisation would survive in the ERP in the absence of sensitivity to the Thatcher illusion. PHD did show a significant effect of inversion at both the N170 and P2. However, PHD produced no effect of Thatcherisation at the N170, in contrast to the effect found with typical participants. The results suggest that the effect of Thatcherisation manifest in the right hemisphere N170 underpins the perception of the Thatcher illusion. As the effects of orientation at the N170 and P2 are also found in an individual who does not perceive the illusion, then they cannot reflect the type of configural processing affected by the Thatcher illusion (Donnelly, Cornes and Menner, 2012). In conclusion, the novel N170 Thatcherisation effect is a marker of a kind of configural processing present in typical face processing that is affected by Thatcherisation (Mestry, Menneer, Wenger, & Donnelly, 2012).