Abstract
Most perceptual decisions require comparisons between current input and an internal template. Classic studies propose that templates are encoded in sustained activity of sensory neurons. However, stimulus encoding is itself dynamic, tracing a complex trajectory through activity space. Which part of this trajectory is pre-activated to reflect the template? Here we recorded magneto- and electroencephalography during a visual target-detection task, and used pattern analyses to decode template, stimulus, and decision-variable representation. Our findings ran counter to the dominant model of sustained pre-activation. Instead, template information emerged transiently around stimulus onset and quickly subsided. Cross-generalization between stimulus and template coding, indicating a shared neural representation, occurred only briefly. Our results are compatible with the proposal that template representation relies on a matched filter, transforming input into task-appropriate output. This proposal was consistent with a signed difference response at the perceptual decision stage, which can be explained by a simple neural model.
Highlights
Human perception is flexible: the dimensions guiding perceptual decisions can be updated rapidly as a function of the current task
When decisions are based on perceptual analysis, task goals influence behaviour by creating an internal template: incoming sensory information is matched against it
Singlecell neurophysiology (Chelazzi et al, 1993; Luck et al, 1997; Chelazzi et al, 1998) and human functional magnetic resonance imaging have demonstrated that template representation and stimulus processing can occur in overlapping neural populations in the visual cortex
Summary
Human perception is flexible: the dimensions guiding perceptual decisions can be updated rapidly as a function of the current task. Singlecell neurophysiology (Chelazzi et al, 1993; Luck et al, 1997; Chelazzi et al, 1998) and human functional magnetic resonance imaging (fMRI; Chawla et al, 1999; Kastner and Ungerleider, 2000; Silver et al, 2007; Kastner et al, 2009; Reddy et al, 2009) have demonstrated that template representation and stimulus processing can occur in overlapping neural populations in the visual cortex. In the simplest case, increasing baseline activity of a stimulus-specific representation could boost target processing (Sylvester et al, 2009) This boost could facilitate target selection and reduce distractor competition for downstream processing resources (Bundesen et al, 2005; Maunsell and Treue, 2006)
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