Abstract
A key question within systems neuroscience is how the brain translates physical stimulation into a behavioral response: perceptual decision making. To answer this question, it is important to dissociate the neural activity underlying the encoding of sensory information from the activity underlying the subsequent temporal integration into a decision variable. Here, we adopted a decoding approach to empirically assess this dissociation in human magnetoencephalography recordings. We used a functional localizer to identify the neural signature that reflects sensory-specific processes, and subsequently traced this signature while subjects were engaged in a perceptual decision making task. Our results revealed a temporal dissociation in which sensory processing was limited to an early time window and consistent with occipital areas, whereas decision-related processing became increasingly pronounced over time, and involved parietal and frontal areas. We found that the sensory processing accurately reflected the physical stimulus, irrespective of the eventual decision. Moreover, the sensory representation was stable and maintained over time when it was required for a subsequent decision, but unstable and variable over time when it was task-irrelevant. In contrast, decision-related activity displayed long-lasting sustained components. Together, our approach dissects neuro-anatomically and functionally distinct contributions to perceptual decisions.
Highlights
A key question within systems neuroscience is how the brain translates physical stimulation into a behavioral response: perceptual decision making
In the present study we sought to dissociate sensory processing from decision-related processing during perceptual decision making. We accomplished this using a novel approach where we employed a functional localizer task to identify the neural signature specific to sensory processing, and used this to trace the temporal trajectory of sensory encoding during perceptual decision making
We found that that sensory information was encoded in neural signals during a relative early time window that extended from 130 to approximately 350 ms post stimulus, and that this encoded sensory information correctly reflected the physical stimulus even in the case of an incorrect decision
Summary
A key question within systems neuroscience is how the brain translates physical stimulation into a behavioral response: perceptual decision making To answer this question, it is important to dissociate the neural activity underlying the encoding of sensory information from the activity underlying the subsequent temporal integration into a decision variable. We focus on the simplest of perceptual decision making tasks, stimulus detection, in which subjects are required to report the presence or absence of a stimulus in noise, and aimed to dissociate the neural activity underlying the sensory process from that underlying the decision process. By contrasting categories that differ on one dimension only (stimulus presence or behavioral report), one would expect to obtain the neural activity underlying the process that corresponds to that factor (e.g. refs 12–16) This approach suffers from at least two conceptual problems. It is often unclear how to interpret differential neural activity revealed by this factor
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