Perceptual decisions result from the continuous accumulation of memory and sensory evidence

Abstract

How do we combine memories with sensory input to make decisions? Previous research has shown that perceptual decisions can be made on the basis of prior expectations combined with sensory input. To date, these expectations have been treated as static, received quantities, fixed across decisions of the same type. Here, we tested the hypothesis that expectations can themselves be inferred using dynamic evidence accumulation, in a process continuous with that of sensory inference. In two experiments using a novel cue-guided perceptual decision task that independently varied memory and sensory evidence, we tested the degree to which decisions reflected accumulation of both kinds of information. In Experiment 1, we found that participants' response times and choices matched the qualitative and quantitative predictions of a two-stage evidence accumulation model. In Experiment 2, participants performed the same task while being scanned using fMRI. Using neural pattern analysis, we measured the expectations that participants formed in advance of a noisy visual stimulus on each trial, and found that these trial-specific expectations reliably predicted the speed of subsequent responses. These results demonstrate that perceptual decisions rely on a continuous process of evidence accumulation, that begins by dynamically inferring possible responses even before sensory information is available.