Bloch’s law and a temporal integration model for simple reaction time to light

Abstract

In a series of experiments designed to determine whether Bloch’s law holds for simple RT to low-energy visual stimuli, mean RTs were found to agree with Bloch’s law to a close approximation only when a narrow range of stimulus intensities is used. However, they could be accounted for more generally by (1) assuming that detection depends on a “visual response function” (VRF) initiated and maintained by the light stimulus (when the time integral of the VRF reaches a criterion, S detects the light and initiates a response): and (2) the fact that VRF generated by a square-wave flash rises quickly to its maximum, remains at this value for the duration of the flash, and then decays exponentially to zero after flash offset. S continues to integrate the VRF throughout its lifetime, and consequently for a brief stimulus, detection will occur during the exponentially decaying portion of the response-the portion corresponding to “visual persistence.” Finally. when luminances used vary by more than a factor of four. Bloch’s law fails to hold, while the model succeeds, implying that the temporal integration model more generally accounts for RTs.