In theoretical accounts of perceptual decision-making, a decision variable integrates noisy sensory evidence and determines action through a boundary-crossing criterion. Signals bearing these very properties have been characterized in single neurons in monkeys, but have yet to be directly identified in humans. Using a gradual target detection task, we isolated a freely evolving decision variable signal in human subjects that exhibited every aspect of the dynamics observed in its single-neuron counterparts. This signal could be continuously tracked in parallel with fully dissociable sensory encoding and motor preparation signals, and could be systematically perturbed mid-flight during decision formation. Furthermore, we found that the signal was completely domain general: it exhibited the same decision-predictive dynamics regardless of sensory modality and stimulus features and tracked cumulative evidence even in the absence of overt action. These findings provide a uniquely clear view on the neural determinants of simple perceptual decisions in humans.
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The authors thank S. Hillyard, I. Robertson, M. Bellgrove, E. Lalor and J. Balsters for helpful comments, and P. Collins, E. Lacey, C. Devine and D. Allen for their assistance with data collection. This work was supported by an Irish Research Council for Science Engineering and Technology EMPOWER fellowship (R.G.O.).
The authors declare no competing financial interests.
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O'Connell, R., Dockree, P. & Kelly, S. A supramodal accumulation-to-bound signal that determines perceptual decisions in humans. Nat Neurosci 15, 1729–1735 (2012). https://doi.org/10.1038/nn.3248
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