The structure of motor programming: evidence from reaction times and lateralized readiness potentials

Ready for action! When the brain learns, yet memory-biased action does not follow

Does memory prepare us to act? Long-term memory can facilitate signal detection, though the degree of benefit varies and can even be absent. To dissociate between learning and behavioral expression of learning, we used high-density electroencephalography (EEG) to assess memory retrieval and response processing. At learning, participants heard everyday sounds. Half of these sound clips were paired with an above-threshold lateralized tone, such that it was possible to form incidental associations between the sound clip and the location of the tone. Importantly, attention was directed to either the sound clip (Experiment 1) or the tone (Experiment 2). Participants then completed a novel detection task that separated cued retrieval from response processing. At retrieval, we observed a striking brain-behavior dissociation. Learning was observed neurally in both experiments. Behaviorally, however, signal detection was only facilitated in Experiment 2, for which there was an accompanying explicit memory for tone presence. Further, implicit neural memory for tone location correlated with the degree of response preparation, but not response execution. Together, the findings suggest 1) that attention at learning affects memory-biased action and 2) that memory prepared action via both explicit and implicit associative memory, with the latter triggering response preparation.

Layers of latent effects in cognitive control: An EEG investigation

Recent research demonstrates that two components of reaching behavior - initiation time (the time elapsed from stimulus presentation to movement initiation) and reach curvature (the degree to which a reach movement deviates from a direct path to the selected response) - exhibit distinct cross-trial dynamics in cognitive control tasks, indicating that these components of behavior reflect two dissociable processes underlying cognitive control: a threshold adjustment process involving the inhibition of motor output and a controlled selection process involving the recruitment of top-down resources to support goal-relevant behavior. The current study investigates the extent to which the cross-trial dynamics previously observed in reaching behavior in the Eriksen flanker task are reflected in event-related potentials during standard button-press responses. Candidate EEG measures of the threshold adjustment process (N2 and Pre-LRP amplitudes) failed to reveal the cross-trial dynamics previously observed in initiation times. Slow wave amplitudes exhibited a close correspondence to the cross-trial dynamics observed in reach curvatures, indicating that the measure is sensitive to some functions of the controlled selection process. Further, LRP slopes presented a close correspondence to the cross-trial dynamics observed in response times, indicating that this measure reflects the combined output of the threshold adjustment process and controlled selection process. The implications of these findings for future research examining the links among behavioral and neural dynamics are discussed.

Neurophysiological Correlates of Visual Dominance: A Lateralized Readiness Potential Investigation

When multisensory information concurrently arrives at our receptors, visual information often receives preferential processing and eventually dominates awareness and behavior. Previous research suggested that the visual dominance effect implicated the prioritizing of visual information into the motor system. In order to further reveal the underpinning neurophysiological mechanism of how visual information is prioritized into the motor system when vision dominates audition, the present study examined the time course of a particular motor activation ERP component, the lateralized readiness potential (LRP), during multisensory competition. The onsets of both stimulus-locked LRP (S-LRP) and response-locked LRP (R-LRP) were measured. Results showed that, the R-LRP onset to the auditory target was delayed about 91 ms when it was paired with a simultaneous presented visual target, compared to that when it was presented by itself. For the visual target, however, the R-LRP onset was comparable irrespective of whether it was paired with an auditory target or not. No significant difference was obtained for the onset of S-LRP. Taken together, the time courses of LRPs indicated that visual information was preferentially processed within the motor system, which coincides with the previous finding that the dorsal visual stream prioritizes the flow of visual information into the motor system.