Simultaneous lightness contrast is a textbook illusion, which demonstrates that the lightness of an object may depend on its immediate surround. There are two classical explanations of this illusion — a low level (physiological) one descending from Hering’s ideas of inhibitory processes in the visual system (Hering,
1874/1964; Cornsweet,
1970), and a high-level (psychological) one enunciated by Helmholtz (1867), who believed that simultaneous lightness contrast is a result of “misjudgement of illumination.” Hering’s approach has evolved into a number of low-level models (e.g., Kingdom & Moulden,
1992; Blakeslee & McCourt,
1999; Ross & Pessoa,
2000), which give an account of simultaneous lightness contrast and related illusions such as grating induction (McCourt,
1982). At the same time, a variety of impressive modifications of simultaneous lightness contrast have been presented over the last two decades — the tile and snake illusions (Adelson,
1993,
2000) to mention two — that challenge the low-level explanation and lend themselves to Helmholtzian explanation (Adelson & Pentland,
1996; Kingdom,
1997,
1999; Logvinenko,
1999,
2002a,
2000b). Eventually, a general opinion has been established that there are two different mechanisms — Hering-type and Helmholtz-type — and they both contribute into simultaneous lightness contrast (e.g., Kingdom,
2003a). Furthermore, it is widely believed that Hering-type mechanisms mainly contribute into classical simultaneous lightness contrast, grating induction, and some other related lightness illusions (such as Mach bands, Herman grid, and the like), whereas Helmholtz-type mechanisms are mostly responsible for illusions such as Adelson’s tile and snake lightness illusions.
In this report, we raise the following question. Being very different in their nature, do Hering- and Helmholtz-type mechanisms cooperate to create the same lightness illusion or do they produce different illusions? In other words, are, say, grating induction, on the one hand, and Adelson’s tile and snake illusions, on the other, particular cases of the same lightness illusion (simultaneous lightness contrast), or are they different lightness phenomena? Below we present some evidence that these may be different phenomena.
As shown recently, the tile illusion disappears when the wall of blocks depicted in the tile pattern is implemented as a real 3D object despite that the retinal image of this 3D wall of blocks is practically the same as that of the tile pattern (Logvinenko, Kane, & Ross,
2002). On the other hand, grating induction can be observed when the inducing patterns (cylinders) are presented stereoscopically (Kingdom,
2003b). We decided to ascertain whether grating induction can be produced by real 3D cylinders, illuminated to form a sinusoidal illuminance distribution on the retina, which usually invokes grating induction.