The missing-fundamental illusion at isoluminance.
The missing-fundamental illusion describes how a square wave with its fundamental Fourier component removed appears as a square wave. This illusion is normally explained with reference to the bandpass nature of the luminance-contrast-sensitivity function, together with a 'default-to-square-wave' rule. Since the chromatic-contrast-sensitivity function is low-pass, we should not expect a missing-fundamental illusion at isoluminance. Using a simultaneous-detection-and-identification paradigm to eliminate contrast as a cue to discrimination, we nevertheless found that chromatic missing fundamentals and square waves could not be separately identified at detection threshold: just under twice the contrast required to detect the stimuli was needed to identify them. To test whether this was due to insufficiently narrow chromatic-channel bandwidths, we measured detection and identification thresholds for chromatic F and 3F sine-wave gratings. In this case identification was possible almost at detection threshold, suggesting that channel bandwidth limitations were not the critical factor. It is suggested that the weak missing-fundamental illusion observed at isoluminance probably reflects the operation of mechanisms similar to those that are responsible for the chromatic Craik-Cornsweet illusion.
Kingdom
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McGill Vision Research, Department of Ophthalmology, McGill University, Montréal, Québec, Canada. fred@jiffy.vision.mcgill.ca
Simmons
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D003118:Color Perception; D003196:Computer Graphics; D015350:Contrast Sensitivity; D006801:Humans; D009903:Optical Illusions; D010466:Perceptual Closure; D010775:Photic Stimulation; D011581:Psychological Tests