An examination of the processing capacity of features in the Thatcher illusion

Detection of the Thatcher illusion (Thompson, Perception, 9:483-484, 1980) is widely upheld as being dependent on configural processing (e.g., Bartlett & Searcy, Cognitive Psychology, 25:281-316, 1993; Boutsen, Humphreys, Praamstra, & Warbrick, NeuroImage, 32:352-367, 2006; Donnelly & Hadwin, Visual Cognition, 10:1001-1017, 2003; Leder & Bruce, Quarterly Journal of Experimental Psychology, 53A:513-536, 2000; Lewis, Perception, 30:769-774, 2001; Maurer, Grand, & Mondloch, Trends in Cognitive Sciences, 6:255-260, 2002; Sturzel & Spillmann, Perception, 29:937-942, 2000). Given that supercapacity processing accompanies configural processing (see Wenger & Townsend, 2001), supercapacity processing should occur in the processing of Thatcherised upright faces. The purpose of this study was to test for evidence that the grotesqueness of upright Thatcherised faces results from supercapacity processing. Two tasks were employed: categorisation of a single face as odd or normal, and a same/different task for sequentially presented faces. The stimuli were typical faces, partially Thatcherised faces (either eyes or mouth inverted) and fully Thatcherised faces. All of the faces were presented upright. The data from both experiments were analysed using mean response times and a number of capacity measures (capacity coefficient, the Miller and Grice inequalities, and the proportional-hazards ratio). The results of both experiments demonstrated some evidence of a redundancy gain for the redundant-target condition over the single-target condition, especially in the response times in Experiment 1. However, there was very limited evidence, in either experiment, that the redundancy gains resulted from supercapacity processing. We concluded that the oddity signalled by inversion of eyes and mouths does not arise from positive interdependencies between these features.