Visible flicker from invisible patterns

• Published in: Nature (London) Vol. 361; no. 6409; pp. 256 - 258
• Main Authors: MacLeod, Donald I. A, He, Sheng
• Format: Journal Article
• Language: English
• Published: London Nature Publishing 21.01.1993; Nature Publishing Group
• Subjects: Biological and medical sciences; Contrast Sensitivity; Flicker Fusion; Fundamental and applied biological sciences. Psychology; Humans; Interferometry - methods; Lasers; Light intensity; Pattern Recognition, Visual; Perception; Photic Stimulation; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Retina; Retina - physiology; Social research; Vision; Human; Cone; Interference; Photoreceptor; Stimulus intensity; Contrast; Flicker; Stimulus luminance; Visual system; Spatial frequency; Temporal frequency; Modulation; Vision; Perception
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/361256a0

Using a laser interferometer we can create grating patterns of high optical contrast (interference fringes) directly on the retina. With coarse fringe patterns, the alternating light and dark bars of the pattern can be seen, but the bars of the finest fringes are not subjectively resolved. We report here that when we rapidly modulate the contrast of a fine fringe pattern (keeping overall luminance constant), observers experience flicker, even if the fringes are too finely spaced to be perceived as a grating. For this flicker to be seen, the pattern needs to be resolvable by the photoreceptors themselves, but not necessarily by later stages of visual processing. It can be explained if, in man, signals associated with individual cone receptors do not depend linearly on light intensity, but instead are scaled by a fast sensitivity-regulating or light-adaptation mechanism. Contrast-modulation flicker is not demonstrable in rod vision; rod vision therefore lacks such a local adaptation process.