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Kevin Johnston, Brian Timney, Denise Leung, Sarah Khan; Alcohol reduces simultaneous contrast effects in human vision. Journal of Vision 2002;2(7):208. doi: 10.1167/2.7.208.
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Some physiological data suggest that ethanol can reduce inhibitory interactions in the retina (e.g. Backström, 1973; MacNichol & Benolken, 1956). If that is the case, then visual phenomena that rely on lateral inhibition may also be reduced. In a previous study (Johnston et al., 2000) we showed that the apparent contrast of the illusory blobs in the Hermann Grid diminished following alcohol ingestion. In the present study we measured changes in brightness of a target patch using a simultaneous contrast paradigm.
All stimulus generation and data collection were under computer control using a VSG2/3F graphics board. A circular .5° standard patch was superimposed on a circular 2° inducing field. Both were centred 1.5° to the left of a small fixation point. A second .5° comparison patch was located 1.5° to the right of fixation. All stimuli were superimposed on a dark background. Using a double staircase procedure, with a 1s presentation time, subjects adjusted the luminance of the comparison patch to match the brightness of the standard in the presence of the inducer field. Several combinations of inducing and standard luminances were tested.
Participants consumed sufficient ethanol in fruit juice to raise their BACs to 80 mg dl-1. In a second, counterbalanced, session, they received a placebo drink. They were tested when their BACs had reached .06 mg dl-1.
As expected, when the luminance of the inducing field was increased, the perceived luminance of the standard decreased. This simultaneous contrast effect was most pronounced for the lower luminances of the standard, irrespective of consumption condition. Following alcohol ingestion, the brightness reductions were similar when the differences between the inducer and standard were small, but there was a progressively smaller reduction in brightness at the higher inducer luminances.
These data are consistent with an alcohol-induced suppression of inhibitory interactions.
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