Biology subjects

Smeets, J.

Publications and source records attributed to Smeets, J..

4 recordsLinked to original sources

bioRxiv2023

The influence of movement speed on reward-based motor learning

Human movement is inevitably variable. This variability can be seen as a constraint to overcome, but it may also be a feature: being variable may result in the discovery of better movement solutions. Especially when feedback is limited to binary information on movement success or failure, variability is key for discovering which movements lead to success. Since moving faster increases variability, we aimed to answer the question whether movement speed can be harnessed to improve such reward-based motor learning. Subjects performed a stepping task in a slow and a fast session. They had to learn the gain between their step lengths and visual target distances on screen based on binary reward feedback. We successfully manipulated movement speed between sessions and participants could learn the gain in both sessions. We found no difference in learning between speed sessions, despite the fact that variability in gain increased in the fast relative to the slow session. To distinguish between different sources of variability, we estimated inevitable motor noise from the variability following successful trials. We estimated exploration as the additional variability following non-successful trials relative to following successful trials. We found no relation between variability sources and learning. In conclusion, reward-based motor learning is possible in a gain-learning task. In this task, moving faster did not lead to higher learning. Since the role of variability may differ between experimental tasks, whether movement speed can be harnessed to improve motor learning needs to be tested in other experimental tasks.

neuroscience↗

bioRxiv2023

Implicit reward-based motor learning

Binary feedback, providing information solely about task success or failure, can be sufficient to drive motor learning. While binary feedback can induce explicit adjustments in movement strategy, it remains unclear if this type of feedback also induce implicit learning. We examined this question in a center-out reaching task by gradually moving an invisible reward zone away from a visual target to a final rotation of 7.5{degrees} or 25{degrees} in a between-group design. Participants received binary feedback, indicating if the movement intersected the reward zone. By the end of the training, both groups modified their reach angle by about 95% of the rotation. We quantified implicit learning by measuring performance in a subsequent no-feedback aftereffect phase, in which participants were told to forgo any adopted movement strategies and reach directly to the visual target. The results showed a small, but robust (2-3{degrees}) aftereffect in both groups, highlighting that binary feedback elicits implicit learning. Notably, for both groups, reaches to two flanking generalization targets were biased in the same direction as the aftereffect. This pattern is at odds with the hypothesis that implicit learning is a form of use-dependent learning. Rather, the results suggest that binary feedback can be sufficient to recalibrate a sensorimotor map.

neuroscience↗

bioRxiv2019

Why some size illusions affect grip aperture

There is an extensive literature debating whether perceived size is used to guide grasping. A possible reason for not using judged size is that using judged positions might lead to more precise movements. As this argument does not hold for small objects, and all studies showing an effect of the Ebbinghaus illusion on grasping used small objects, we hypothesized that size information is used for small objects but not for large ones. Using a modified diagonal illusion, we obtained an effect of about 10% on perceptual judgements, without an effect on grasping, irrespective of object size. We therefore reject our precision hypothesis. We discuss the results in the framework of grasping as moving digits to positions on an object. We conclude that the reported disagreement on the effect of illusions is because the Ebbinghaus illusion not only affects size, but -unlike most size illusions- also affects perceived positions.

neuroscience↗

bioRxiv2019

Practicing one thing at a time: the secret to reward-based learning?

Binary reward feedback on movement success is sufficient for learning in some simple reaching tasks, but not in some more complex ones. It is unclear what the critical conditions for learning are. Here, we ask how reward-based sensorimotor learning depends on the number of factors that are task-relevant. In a task that involves two factors, we test whether learning improves by giving feedback on each factor in a separate phase of the learning. Participants learned to perform a 3D trajectory matching task on the basis of binary reward-feedback in three phases. In the first and second phase, the reward could be based on the produced slant, the produced length or the combination of the two. In the third phase, the feedback was always based on the combination of the two factors. The results showed that reward-based learning did not depend on the number of factors that were task-relevant. Consistently, providing feedback on a single factor in the first two phases did not improve motor learning in the third phase.

neuroscience↗