Motor adaptation under visual feedback uncertainty
by Virginia Casasnovas Orus
Date of Examination:2024-11-12
Date of issue:2025-03-07
Advisor:Prof. Dr. Alexander Gail
Referee:Prof. Dr. Alexander Gail
Referee:Prof. Dr. Hansjörg Scherberger
Persistent Address:
http://dx.doi.org/10.53846/goediss-11125
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Abstract
English
Our motor system continuously receives sensory feedback from our limbs to control movement. This feedback is crucial for compensating for perturbations that disrupt proper control, a process known as motor adaptation. However, sensory feedback can be uncertain due to limitations in our sensory systems or environmental conditions, which may hinder adaptation. This thesis explores the behavioral and neural consequences of having uncertain visual feedback of hand position during reaching, with a particular focus on motor adaptation. In a first study, we investigated visuomotor adaptation behavior in human participants. We found that adaptation to large reach errors was diminished when visual feedback was uncertain. Given that adaptation is not a unitary process, we also dissociated the implicit and explicit contributions and observed that both were attenuated by visual feedback uncertainty. These findings build on previous work testing small reach errors, suggesting that reach errors drive adaptation based on their level of uncertainty. To explore the neural consequences of visual feedback uncertainty, we conducted a second study in which we recorded motor cortex activity of rhesus monkeys during reaching. Monkeys performed center-out reaches either manually or via a brain-computer interface (BCI), with which visual feedback is directly controlled by neural activity. We employed a BCI because it turns somatosensory feedback irrelevant to perform the task, making visual feedback the only source of information about movement control. Focusing on the planning process, neural representations of the motor goal were not affected by visual feedback uncertainty during manual reaching. In contrast, these representations were impaired around movement initiation for BCI reaching. This suggests that visual feedback uncertainty affects motor goal encoding as it becomes critical for movement control. We also found that irrespective of its effect on motor goal representations, visual feedback uncertainty was represented in motor cortex activity for both manual and BCI reaches. This study highlights the liability that conditions of visual feedback uncertainty can pose to BCI users, showcasing the need for additional sources of feedback to ensure proper control. Altogether, we conclude that visual feedback uncertainty is reflected at the behavioral and neural level when it becomes critical for movement control.
Keywords: Visual feedback uncertainty; Motor adaptation; Motor cortex; Non-human primates; Reach planning
