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Inci Ayhan, Aurelio Bruno, Shin'ya Nishida, Alan Johnston; The effect of luminance signal on adaptation-based duration compression. Journal of Vision 2010;10(7):1412. doi: 10.1167/10.7.1412.
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Adapting to high temporal frequency luminance-modulated gratings reduces the apparent duration of a subsequently presented sub-second dynamic stimulus (Johnston, Arnold & Nishida, 2006, Current Biology, 16(5):472-9). Here we investigate the effect of the luminance signal on the strength of this temporal aftereffect using stimuli defined along the equiluminant S-constant axis and elevated with respect to the equiluminance plane of the DKL space (Derrington, Krauskopf & Lennie, 1984, Journal of Physiology, 357:241-65). We first found the individual equiluminance points using the minimum motion technique (Cavanagh, MacLeod & Anstis, 1987, Journal of the Optical Society of America A, 4(8):1428-38) for different temporal frequencies and contrasts. We then eliminated the effect of adaptation on the perceived speed (of a 7Hz test) by using interleaved 5Hz and 10Hz adaptors for different luminance levels (equiluminance and an intermediate (65cd/m2) luminance difference between the magenta and cyan grating phases), separately. Finally, we used these individual ratios, at which no change occurred in the perceived speed of a 7Hz test pattern, in our duration experiments. A standard grating (600ms, 7Hz, 0.5cpd) was always displayed at the adapted location (in half of the trials 5° above, in half of the trials 5° below the fixation point) and a comparison (7Hz, 0.5cpd), presented at the unadapted side, was varied over trials (300ms – 1200ms) to generate a psychometric function. The PSE provided a measure of perceived duration. Both test and adaptor were either isoluminant, or luminance modulated with a 45cd/m2 and 90cd/m2 luminance difference between the magenta and cyan phases of the chromatic gratings (magenta being darker). We found an apparent temporal compression of the luminance modulated gratings which decreased with a reduction in luminance contrast and was no longer significantly different from zero at equiluminance. This provides further evidence for the involvement of the magnocellular system in adaptation-based compression.
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