Biology subjects

Parvin, D.

Publications and source records attributed to Parvin, D..

5 recordsLinked to original sources

bioRxiv2019

Distinct Processing of Selection and Execution Errors in Neural Signatures of Outcome Monitoring

Losing a point in tennis could result from poor shot selection or faulty stroke execution. To explore how the brain responds to these different types of errors, we examined feedback-locked EEG activity while participants completed a modified version of a standard three-armed bandit probabilistic reward task. Our task framed unrewarded outcomes as either the result of errors of selection or errors of execution. We examined whether amplitude of a medial frontal negativity (the Feedback-Related Negativity; FRN) was sensitive to the different forms of error attribution. Consistent with previous reports, selection errors elicited a large FRN relative to rewards and amplitude of this signal correlated behavioral adjustment following these errors. A different pattern was observed in response to execution errors. These outcomes produced a larger FRN, a frontocentral attenuation in activity preceding this component, and a subsequent enhanced error positivity in parietal sites. Notably, the only correlations with behavioral adjustment were with the early frontocentral attenuation and amplitude of the parietal signal; FRN differences between execution errors and rewarded trials did not correlate with subsequent changes in behavior. Our findings highlight distinct neural correlates of selection and execution error processing, providing insight into how the brain responds to the different classes of error that determine future action.

neuroscience↗

bioRxiv2019

Exploring Contextual Interference in Implicit and Explicit Motor Learning

The classic advice given to anyone learning a new skill is \"practice makes perfect.\" While this provides a good general rule to follow, it lacks any detail on what form of practice will efficiently maximize learning. So when faced with the task of acquiring multiple skills, what is the optimal way to learn? Would it be more beneficial to master each skill separately or learn them all at once in an interleaved fashion? A concept known as contextual interference suggests that using a random practice schedule leads to better retention than a blocked one. There are some motor learning studies that are consistent with this hypothesis and some that are not. In order to explore these conflicting results, we applied contextual interference to a simple reaching task that could allow us to observe its effects to various components of motor learning. We had participants learn three different visuomotor rotations and manipulated interference by placing them in groups characterized by how training targets are ordered (blocked vs. random). Using reaction time and hand angle as our measures of performance, we found that participants who experienced a random practice schedule had significant improvements in their ability to retain information, which was manifest as higher levels of implicit adaptation and faster reaction times. However, this did not necessarily mean the information was executed accurately since hand angles did not differ between groups. These findings suggest contextual interference will be most advantageous in situations that require fast explicit recall of a motor plan to use rather than those that emphasize accuracy.

neuroscience↗

bioRxiv2018

Neural Signatures of Prediction Errors in a Decision-making Task are Modulated by Action Execution Failures

Decisions must be implemented through actions, and actions are prone to error. As such, when an expected outcome is not obtained, an individual should not only be sensitive to whether the choice itself was suboptimal, but also whether the action required to indicate that choice was executed successfully. The intelligent assignment of credit to action execution versus action selection has clear ecological utility for the learner. To explore this scenario, we used a modified version of a classic reinforcement learning task in which feedback indicated if negative prediction errors were, or were not, associated with execution errors. Using fMRI, we asked if prediction error computations in the human striatum, a key substrate in reinforcement learning and decision making, are modulated when a failure in action execution results in the negative outcome. Participants were more tolerant of non-rewarded outcomes when these resulted from execution errors versus when execution was successful but the reward was withheld. Consistent with this behavior, a model-driven analysis of neural activity revealed an attenuation of the signal associated with negative reward prediction error in the striatum following execution failures. These results converge with other lines of evidence suggesting that prediction errors in the mesostriatal dopamine system integrate high-level information during the evaluation of instantaneous reward outcomes.

neuroscience↗

bioRxiv2018

Intrinsic rewards modulate sensorimotor adaptation

Recent studies have demonstrated that task success signals can modulate behavioral changes during sensorimotor adaptation tasks, primarily through the engagement of explicit processes. In a series of reaching experiments with human participants, we explore a potential interaction between reward-based learning and implicit adaptation, using a method in which feedback is not contingent on task performance. We varied the size of the target to compare conditions in which visual feedback indicated an invariant angular error that either hit or missed the target. Hitting the target attenuated the behavioral changes from adaptation, an effect we attribute to the generation of an intrinsic reward signal. We evaluated two models, one in which reward and adaptation systems operate in parallel, and a second in which reward acts directly on the adaptation system. The results favor the latter, consistent with evidence showing communication, and possible overlap, between neural substrates underlying reward-based learning and sensorimotor adaptation.

neuroscience↗

bioRxiv2017

Invariant errors reveal limitations in motor correction rather than constraints on error sensitivity

Implicit sensorimotor adaptation is traditionally described as a process of error reduction, whereby a fraction of the error is corrected for with each movement. Here, in our study of healthy human participants, we characterize two constraints on this learning process: the size of adaptive corrections is only related to error size when errors are smaller than 6{degrees}, and learning functions converge to a similar level of asymptotic learning over a wide range of error sizes. These findings are problematic for current models of sensorimotor adaptation, and point to a new theoretical perspective in which learning is constrained by the size of the error correction, rather than sensitivity to error.

neuroscience↗