The Impacts of Inversion and Thatcherisation on Face Processing: Mapping between ERP and GRT

Abstract

Prior work on the Thatcher illusion (Cornes et al., 2011; Mestry et al., 2012) has indicated both perceptual and decisional components of the illusion. We provide evidence of neural correlates associated with independent influences of inversion and level of feature manipulation (Thatcherisation) in the Thatcher illusion. We also provide an account of how ERP results can be interpreted within the configural processing framework defined by general recognition theory (GRT). We conducted a study examining inversion and the level of Thatcherisation (typical face, eyes Thatcherised, mouth Thatcherised, or both features Thatcherised) on a set of event-related components (the P1, N170, P2 and P3b) that have previously been considered in relation to the Thatcher illusion. Results reveal three independent effects: (1) inversion effects leading to increased amplitude for inverted faces at the N170 and P2 in the occipito-parietal area; (2) a reduction in N170 amplitude with level of Thatcherisation in the right hemisphere; and (3) inversion effects leading to increased amplitude for inverted faces at P3b in the centro-parietal area. This study reveals effects of Thatcherisation that are independent from effects of inversion in the ERP data. These effects can also be mapped to perceptual and decisional measures of configurality revealed in behavioural data using GRT (Mestry et al., 2012). We suggest the Thatcherisation effect at N170 may relate to violations of perceptual independence, the inversion effect across N170 and P2 may relate to violations of perceptual separability, and the inversion effect at P3b may relate to violations of decisional separability. Thus, we suggest a possible role for ERP data in providing a source of converging evidence for inferences regarding the role of perceptual and decisional factors in configurality.