Directional Uncertainty in Visually Guided Pointing

Abstract

Studies of the relationship between stimulus-response uncertainty and reaction times indicate three qualitatively different functions: Hick's law, simple-choice step function, or flat curve (no effect at all). The extent of stimulus-response (S-R) compatibility appears to interact with the effects of uncertainty on response times. One possible hypothesis regarding these various S-R uncertainty functions is that uncertainty will have an effect whenever the stimuli and their associated responses are not within the same egocentric spatial coordinates. We tested this hypothesis in 5 undergraduate participants (2 men, M age 18.7 yr., range 18–20) by investigating the time-course of pointing to peripherally located visual targets under four different levels of uncertainty (1, 2, 4, or 8 possible locations). Surprisingly, the resulting response function does not match any of those previously reported. Visually guided pointing produced a quadratic reaction time function as S-R uncertainty increases in log₂ steps from 1 to 8.