Homage to Peter Thompson: The Tony Blair Illusion

In 1980 Peter Thompson published his celebrated paper on the Thatcher illusion, which became one of the most frequently cited papers ever published in Perception. In homage to Peter Thompson, and to mark the quarter-centenary of his efforts, I propose here a Tony Blair illusion (figure 1). We are adept at recognizing faces, but our skills fail when faces are inverted (presented upside down). This failure is thought to be due to disruption of configural processing. Thompson inverted just the eyes and mouth in a portrait of Mrs Thatcher, which produced a grotesque effect. However, when a normal and `thatcherized' face were both inverted, the perceptual differences between them vanished and they both looked fairly normal. Thompson's web page at http://www-users.york.ac.uk/ pt2/ shows his own face, which looks marginally more grotesque when thatcherized. Michael Bach has a Quicktime movie of Mrs Thatcher's face slowly rotating, on his web page at http://www.michaelbach.de/ot/. Thompson's remarkable illusion suggests that decoding of facial expression seems to work best in the same orientation in which faces are seen most of the time. Even 6-month-old babies (Bertin and Bhatt 2004) and autistic children (Rouse et al 2004) are susceptible to the Thatcher illusion. In fact Lewis (2003) found no effect of age among people aged between 6 and 75 years; young children showed the same effects as adults. Similarly, Itier and Taylor (2004) found inversion and contrast-reversal effects in all their child and adult subjects, but these did not increase with age, suggesting no increased reliance on configural processing over the life span. Itier and Taylor (2002) found that negative and inverted faces affected both early (encoding) and late (recognition) stages of face processing, although to different extents. Boutsen and Humphreys (2003) investigated the contribution of local and global processing to the Thatcher illusion in normal observers and concluded that (i) face inversion disrupts local configural processing, but not the processing of image features, and (ii) thatcherization disrupts local configural processing in upright faces. The Thatcher illusion demonstrates that inversion is especially detrimental to the processing of faces. Bartlett and Searcy (1993) attributed this detriment to a loss of holistic or configural processing for inverted faces. Sturzel and Spillmann (2000) suggest that this loss of configural processing occurs suddenly as a face is rotated slowly from upright to inverted, but Lewis (2001) found a gradual loss of configural information during rotation, rather than a rapid switch from one type of processing to another. The fact that inverted faces are so hard to recognize has led to the common assumption that configural cues strongly influence the recognition of upright, but not inverted, faces. However, Sekuler et al (2004) disagree, finding that processing of upright and inverted faces differs quantitatively, not qualitatively; information is extracted more efficiently from upright faces, perhaps as a by-product of orientation-dependent expertise. Faces are also very hard to recognize when they are contrast-reversed (presented in photographic negative). It is known that processing of shading information in face recognition is susceptible to bottom lighting and contrast reversal, an effect that may be due to a disruption of 3-D shape processing. Liu et al (2000) asked whether the disruption can be rectified by 3-D information from shape-from-stereo. They compared identification performance either with or without stereo information using top-lit and Last but not least Perception, 2005, volume 34, pages 1417 ^ 1420