Disentangling signal from noise in visual contrast discrimination.
Human ability to detect stimulus changes (Delta C) decreases with increasing reference level (C). Because detection performance reflects the signal-to-noise ratio within the relevant sensory brain module, this behavior can be accounted for in two extreme ways: first, the internal response change Delta R evoked by a constant Delta C decreases with C (that is, the transducer R = f(C) displays a compressive nonlinearity), whereas the internal noise is independent of R; second, Delta R is constant with C but the noise level increases with R. A newly discovered constraint on human decision-making helps solve this century-old problem: in a detection task where multiple changes occur with equal probabilities, observers use a unique response criterion to decide whether a change has occurred. For contrast discrimination, our results supported the first account above: human performance was limited by the contrast transducer nonlinearity and an almost constant noise.
Gorea
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Laboratoire de Psychologie Expérimentale, Centre National de la Recherche Scientifique (CNRS) and René Descartes University, 71 Avenue Edouard Vaillant, 92774 Boulogne-Billancourt, France. gorea@psycho.univ-paris5.fr
Sagi
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D015350:Contrast Sensitivity / Q000502:physiology*; D006801:Humans; D008433:Mathematics; D017603:Signal Detection, Psychological / Q000502:physiology*