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Lothar Spillmann, Baingio Pinna, John S. Werner; Anomalous darkness induction. Journal of Vision 2004;4(11):84. doi: 10.1167/4.11.84.
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A new effect called anomalous darkness induction is introduced. It is based on a modified Ehrenstein figure in which a light blue annulus on a black background bounds the inner tips of grey radial lines. The central disk enclosed by the annulus appears darker than the background. This effect has been explored as a possible complement to the anomalous brightness induction obtained when the Ehrenstein figure is presented on a white background (Pinna et al., 2003). While anomalous lightness and darkness effects may not be strictly complementary, they do both create anomalous effects with respect to surface quality.
Methods: An array of 4 × 4 Ehrenstein figures as described served as stimuli. The strength of the darkness effect was determined using magnitude estimation. Light blue annuli without radial lines and Ehrenstein figures with grey instead of blue annuli were used as controls. The number, length, width, and contrast of the radial lines as well as the width, contrast, and color of the annuli were varied. Different groups of fourteen observers participated in each condition of the experiment.
Results: The presence of the radial lines was found to be crucial for anomalous darkness. Lines and annuli both affect anomalous blackness in a similar manner to that of anomalous brightness induction, but with reversed polarity. The contribution of simultaneous contrast is much weaker than the intense blackness and brightness induction characteristic of the two illusions.
Conclusion: The results suggest an explanation in terms of brightness and darkness systems involving long-range cortical mechanisms.
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