The “Thatcher illusion” refers to a perceptual phenomenon whereby a face whose eyes and mouth have been inverted appears grotesque in an upright orientation, but normal in an inverted position. The normal appearance of inverted thatcherised faces has been attributed to a decrease in configural and an increase in feature-based processing with face inversion. The present study was designed to determine whether the effects of thatcherisation are due, at least in part, to perceived emotion. High density ERPs were recorded from sixteen individuals while they viewed neutral, angry, smiling and thatcherised faces at upright and inverted orientations. The subjects’ task was to determine whether the faces were male or female.
The ERP effects of face type depended on whether the faces were upright or inverted. At upright, five time windows were identified, coinciding with the N170, P250, P360 and a late positive (LP) ERP components. ERPs to angry and thatcherised faces were similar, and differed from those to neutral and happy faces. At inverted orientations, three time windows were identified, coincided with the P1, P250 and the LP ERP components. Here, ERPs to happy and thatcherised faces were similar, and differed from those to angry and neutral faces. These results suggest that ERP effects of upright thatcherised faces are due primarily to perceived negative emotion, while inverted thatcherised faces are perceived as happy. The difference between the effects at the two orientations suggest that the perception of emotional expression may be dependent on configural or featural encoding.