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K. Hoddinott, G. B. Henning, N. J. Hill; Masking produced by mach bands. Journal of Vision 2001;1(3):436. doi: 10.1167/1.3.436.
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The detectability of narrow target or signal bars perturbing a stimulus that produces Mach bands is difficult to measure in the vicinity of either dark or bright Mach bands because the targets affect the shape of the bands. An incremental signal makes the dark Mach band shallower and wider and a decremental signal makes the dark Mach band narrower and deeper; the converse occurs in the bright Mach bands. Signals in, but not centred on, either band make the bands asymmetric (Henning, Millar & Hill, 2000). To prevent observers using such cues, we randomized the polarity of the signals on each trial. We used a two-alternative forced-choice experiment in which each trial comprised two 400-msec observation intervals separated by a 600-msec pause. A Mach-band stimulus was presented in both intervals with the narrow target on any trial presented with equal probability in only one of the two observation intervals. Further, on any given trial, the target was randomly chosen to be an increment or a decrement. The psychometric functions relating the percentage of correct responses to the logarithm of the signal luminance were parallel, and the “thresholds” indicate that both dark and bright Mach bands make detection difficult. Separation of the results into those produced by increments and those produced by decrements reveal oscillations in detectability at about 5 cycles per degree of visual angle. The oscillations observed with increments are 180° out-of-phase with those observed with decrements.
HenningG. BMillarR. W.HillN. J.(2000). “Detection of incremental and decremental bars at different locations across Mach bands and related stimuli,” J. Opt. Soc. Am., A 17, 1147– 1159.
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