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Hector Rieiro, Susana Martinez-Conde, Jose Luis Pardo-Vazquez, Nishit Srivastava, Stephen L. Macknik; Apparent contrast peaks, rather than plateaus, as a function of stimulus duration. Journal of Vision 2010;10(7):1402. doi: https://doi.org/10.1167/10.7.1402.
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The apparent contrast of a visual stimulus varies as a function of duration, a phenomenon known as temporal integration. There are two accepted principles to explain the role of stimulus duration in perceived contrast. Bloch's law states that below a critical duration, apparent contrast is a function of both stimulus intensity and duration. Above this critical duration, apparent contrast plateaus. Contrary to Bloch Law's predictions, Broca and Sulzer proposed that apparent contrast is maximized for specific stimulus durations, and that smaller or greater durations result in lesser apparent contrast. Contradictory results have been published; some support Bloch's Law and some support the Broca-Sulzer effect. We hypothesize that the source of this discrepancy may be that previous studies were conducted on experienced subjects who knew the proposed hypotheses (i.e. previous studies used the authors as subjects), and that no previous study properly controlled for subject criterion. To address these concerns, we designed a 2-AFC task that counterbalanced stimulus dynamics and controlled for subject criterion. Nine human subjects were presented with Gabor patches of different contrasts and durations over a 50% grey background and were asked to report which of them had higher contrast. Our results show that when the stimulus duration had a value between 67-100 ms, subjects experienced significantly higher apparent contrast, peaking at approximately 7% greater perceived contrast than very long durations of the same stimulus. This result more-or-less matches the Broca-Sulzer finding, but provides the appropriate controls for the first time. The existence of this peak has important implications for the design of power-efficient lighting and visual display equipment.
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