Old wine in new bottles? Some thoughts on Logvinenko's "Lightness induction revisited".

One of the most compelling visual phenomena is simultaneous lightness contrast (SLC). The observation that grey looks darker when set against white than when set against black has intrigued philosophers and scientists for two millennia (see Wade 1996), yet there is still no consensus as to exactly why it happens. In a renaissance of interest in the effects of context on surface colour appearance (eg see the recent special issues of Perception 1997, volume 26, numbers 4 and 7) SLC is currently the focus of a controversy which first occupied Hering and Helmholtz in the 19th century. They disagreed over whether SLC was based on peripheral sensory processes sensitive to contrast, or central influences involving assumptions about the configuration of the display as a whole. Logvinenko's article ``Lightness induction revisited'', published in the preceding issue of Perception, is a good example of how opinion on this question has changed in recent years. Thirty years ago the dominant view was that contrast-sensitive mechanisms were intimately involved with SLC, a view sustained through the studies of Hurvich and Jameson (eg Hurvich and Jameson 1966), whose own ideas were strongly influenced by Hering (eg Hering 1874/1964). Recently, however, the pendulum has swung the other way, and Logvinenko's article typifies the newly found emphasis on perceptual interpretation in SLC. The seminal study by Gilchrist (1977) is in my view the watershed that precipitated this change in opinion. Using a conventional display consisting of two grey patches on a different surround, Gilchrist observed that the magnitude of SLC was enhanced when the grey patches, normally seen as surrounded by materials of different reflectances, were instead seen as being under different illuminations. Since the luminance contrasts between the patches and their surrounds were kept the same under both configurations, the enhancement of SLC could not be due to the effects of local contrast. Instead, it must have been because of the way the subjects interpreted the display as a whole. Since Gilchrist's study, the dramatic improvement in computer graphics has been used to produce ever more compelling effects on a similar theme (eg Knill and Kersten 1991; Adelson 1993; Anderson 1997; Logvinenko 1999). Complex geometric arrangements evoking vivid impressions of shadows, transparency, shading, and occlusion have replaced the conventional SLC display. The results have been by-and-large impressive. So much so that for many protagonists the question is now no longer whether SLC is due to the effects of contrast or perceptual interpretation, but exactly what rules of perceptual interpretation underly SLC. Logvinenko believes the answer lies with the notion of `lightness ^ shadow' invariance. As I understand his use of the term, lightness ^ shadow invariance is where the lightness (perceived reflectance) of an object remains unchanged when the object is cast in shadowöa form of lightness constancy that takes into account local perturbations in illumination rather than changes in the ambient level (and see Arend 1994). Logvinenko develops his case for lightness ^ shadow invariance through an examination (with supportive data) of a number of variants of Adelson's (1993) tile pattern, which is shown here in figure 1 (also Logvinenko's figure 1). The difference in lightness, or brightness (perceived luminance), between the equal-in-luminance diamonds labelled 1 and 2 is for most observers greater in figure 1a than 1b. Logvinenko, like Adelson, argues that the enhanced SLC in figure 1a cannot be explained by the effects of local contrast, as the contrasts between the diamonds and their surrounds are similar Guest editorial Perception, 1999, volume 28, pages 929 ^ 934