Evidence for a decision variable in the human motor system.

Editor's Note: These short, critical reviews of recent papers in the Journal, written exclusively by graduate students or postdoctoral fellows, are intended to summarize the important findings of the paper and provide additional insight and commentary. For more information on the format and purpose of the Journal Club, please see Review of Selen et al. Many traditional information-processing models assume that the processes underlying decision formation are neatly separable from, and causally antecedent to, those involved in action generation. According to these models, centralized cog-nitive processing results in the formation of a decision that is subsequently passed along to the motor system to be transformed into the desired action. Because the motor system is recruited only after the decision outcome is complete, these models leave little room for the motor system to play an ongoing role in the decision process itself. Recent work on embodied cognition in cognitive science and robotics directly challenges these sequential models, suggesting instead that material properties of the body and aspects of motor behavior may be engaged in an ongoing fashion to augment and shape cognitive processing Neuroscientists have also begun to uncover specific evidence that neural systems supporting action are more closely related to those supporting cognition than previously thought. For instance, signals that reflect accruing sensory evidence relevant to making perceptual decisions have been identified within the same oculomotor circuits that govern the planning of eye movements, indicating that decision formation and motor preparation may engage common neural systems (Gold and Shadlen, 2000, 2007). A recent paper by Selen et al. (2012), published in The Journal of Neuroscience, builds upon this emerging body of work. This study provides novel behavioral evidence for decision-related signals in the human motor system and advances the current state of the field in two major ways. First, one lingering criticism of earlier studies of perceptual decision making in nonhuman primates has been that the results might merely reflect the fact that monkeys were heavily trained to map perceptual decisions onto motor outputs. If true, discovering that accumulating sensory information is reflected in the oculo-motor signals responsible for generating saccadic eye movements in an overtrained task would be an unsurprising and uninteresting result. Confirming the presence of similar effects in normal, untrained human subjects is therefore a critical step forward. Second, in moving from invasive recording and microstimulation paradigms involving monkeys (Gold and Shadlen, 2000, 2007) to human studies, …