Abstract
Standard models of perceptual decision-making postulate that a response is triggered in reaction to stimulus presentation when the accumulated stimulus evidence reaches a decision threshold. This framework excludes however the possibility that informed responses are generated proactively at a time independent of stimulus. Here, we find that, in a free reaction time auditory task in rats, reactive and proactive responses coexist, suggesting that choice selection and motor initiation, commonly viewed as serial processes, are decoupled in general. We capture this behavior by a novel model in which proactive and reactive responses are triggered whenever either of two competing processes, respectively Action Initiation or Evidence Accumulation, reaches a bound. In both types of response, the choice is ultimately informed by the Evidence Accumulation process. The Action Initiation process readily explains premature responses, contributes to urgency effects at long reaction times and mediates the slowing of the responses as animals get satiated and tired during sessions. Moreover, it successfully predicts reaction time distributions when the stimulus was either delayed, advanced or omitted. Overall, these results fundamentally extend standard models of evidence accumulation in decision making by showing that proactive and reactive processes compete for the generation of responses.
Highlights
Standard models of perceptual decision-making postulate that a response is triggered in reaction to stimulus presentation when the accumulated stimulus evidence reaches a decision threshold
In addition to reactive responses triggered by sensory evidence accumulation, animals exhibit informed proactive responses whose timing is independent of the stimulus
An acoustic stimulus was played after a 300 ms fixation period at the center port, and interrupted once the animal withdrew from the center port to make a response by poking at one of the two side ports
Summary
Standard models of perceptual decision-making postulate that a response is triggered in reaction to stimulus presentation when the accumulated stimulus evidence reaches a decision threshold. We find that, in a free reaction time auditory task in rats, reactive and proactive responses coexist, suggesting that choice selection and motor initiation, commonly viewed as serial processes, are decoupled in general We capture this behavior by a novel model in which proactive and reactive responses are triggered whenever either of two competing processes, respectively Action Initiation or Evidence Accumulation, reaches a bound. In addition to reactive responses triggered by sensory evidence accumulation, animals exhibit informed proactive responses whose timing is independent of the stimulus This coexistence was captured by a perceptual decision-making model where responses can be triggered by either of two parallel dynamical processes: Action Initiation, yielding proactive responses; or Evidence Accumulation, yielding reactive responses. The results obtained in this condition held for expectation-biased trials (see below)
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