Reaction times reveal the contribution of the different receptor components in luminance perception

Piéron (1914, 1920, 1952) demonstrated that simple reaction time decays as a hyperbolic function of luminance. Similarities between cell latencies and reaction time (RT) to luminance suggest that this relationship may be determined by retinal processes. If the exponent of the Piéron function is specific to a given sensory modality, as assumed by some authors (e.g., Bonnet, 1992a, 1992b; Norwich, 1987), it should reflect receptor activities. Consequently, functions with different exponents should fit data for different luminance ranges. In a contrast-discrimination experiment, we investigated this question with a large range of luminance levels in a two-alternative spatial forced-choice task. The results of the experiment show that three functions with different exponents fit RT to the three luminance ranges (scotopic, mesopic, and photopic). The exponent decreases with increasing luminance. The findings indicate that the exponent and the asymptotic latency of the RT function reflect receptor activities of the visual system.