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Seiichiro Naito, Masafumi Kaite; Does the luminance condition for test figures change the illusion?. Journal of Vision 2008;8(6):727. doi: 10.1167/8.6.727.
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© ARVO (1962-2015); The Authors (2016-present)
The general illusion theory tells that at the equiluminant condition (EQ) the magnitude of the illusion would reduce. We confirmed (VSS2007), however, that Plasmid illusion (PL) and Gravity lens illusion (GL) kept their illusory effect at EQ. It might be promising if we could make a taxonomy of illusions based on whether the illusion follows or does not follow the EQ reduction theory with some accountable reasons. The EQ generally implies that the whole figure elements are equiluminant. Since the luminance of the test figures (TF) can be varied independently of the inducing figures (IF) and the background (BG) luminance, we investigated how much the illusory effects still held when the TF luminance was different from the IF and BG while they were red-green equiluminant. We found that the illusory effect of GL reduced to 60% of the EQ case, when TF were black or white. For PL the magnitude reduced similarly, though the amount of reduction was smaller. We might be able to assign every illusion to one of the typical patterns. A few classical illusions such as Ebbinghaus, Mueller-Lyer, and Orbison were investigated with the method. We found Ebbinhaus was similar to GL or PL. MuellerLyer was less clear whether the illusion held or varied. Orbison is the classical example that the illusory effects would disappear at EQ. It might give an insight for the illusion theory to realize the fact that IF of GL are filled circles and IF of PL are thick ring segments, while Mueller-Lyer and Orbison are composed of line segments. If the thickness of the lines is too thin, it will be actually difficult to observe the figures at EQ. The Mueller-Lyer was observed with varied line thickness. The appropriate conditions for Mueller-Lyer gave the similar results as PL.
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