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Impact Factor:0.917 | Ranking:Psychology 64 out of 76 | Psychology, Experimental 80 out of 85
Source:2016 Release of Journal Citation Reports, Source: 2015 Web of Science Data

The Hollow-Face Illusion: Object-Specific Knowledge, General Assumptions or Properties of the Stimulus?

  1. Harold Hill
    1. Human Information Science Laboratories, ATRi, Keihanna Science City, 2-2-2 Hikaridai, Seika-cho, Soraku-gun, Kyoto 619 0288, Japan
  2. Alan Johnston
    1. Department of Psychology, University College London, Gower Street, London WC1E 6BT, UK
  1. e-mail: hill{at}atr.jp


The hollow-face illusion, in which a mask appears as a convex face, is a powerful example of binocular depth inversion occurring with a real object under a wide range of viewing conditions. Explanations of the illusion are reviewed and six experiments reported. In experiment 1 the detrimental effect of figural inversion, evidence for the importance of familiarity, was found for other oriented objects. The inversion effect held for masks lit from the side (experiment 2). The illusion was stronger for a mask rotated by 908 lit from its forehead than from its chin, suggesting that familiar patterns of shading enhance the illusion (experiment 2). There were no effects of light source visibility or any left/right asymmetry (experiment 3). In experiments 4 – 6 we used a ‘virtual’ hollow face, with illusion strength quantified by the proportion of noise texture needed to eliminate the illusion. Adding characteristic surface colour enhanced the illusion, consistent with the familiar face pigmentation outweighing additional bottom - up cues (experiment 4). There was no difference between perspective and orthographic projection. Photographic negation reduced, but did not eliminate, the illusion, suggesting shading is important but not essential (experiment 5). Absolute depth was not critical, although a shallower mask was given less extreme convexity ratings (experiment 6). We argue that the illusion arises owing to a convexity preference when the raw data have ambiguous interpretations. However, using a familiar object with typical orientation, shading, and pigmentation greatly enhances the effect.

  • Received September 23, 2005.
  • Revision received March 22, 2006.
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