Seeing, fast and slow: the effects of processing time on perceptual bias

Fast and slow decisions exhibit distinct behavioral properties, such as the presence of decision bias in faster but not slower responses. This dichotomy is currently explained by assuming that distinct cognitive processes map to separate brain mechanisms. Here, we suggest an alternative, single-process account based on the stochastic properties of decision processes. Our experimental results show perceptual biases in a variety of tasks (specifically: learned priors, tilt illusion, and tilt aftereffect) that were much reduced with increasing reaction time. To account for this, we consider a simple yet general explanation: prior and noisy decision-related evidence are integrated serially, with evidence and noise accumulating over time (as in the standard drift diffusion model). With time, owing to noise accumulation, the prior effect is predicted to diminish. This illustrates that a clear behavioral separation - presence vs. absence of bias - may reflect a simple stochastic mechanism. HighlightsO_LIPerceptual and decisional biases are reduced in slower decisions. C_LIO_LISimple mechanistic single-process account for slow bias-free decisions. C_LIO_LISignal detection theory criterion is ~zero in decision times>median. C_LI