The Influence of Visual Feedback on the Mechanical Efficiency of Reaches

In the past few decades, reaching movements have become a common platform to study the motor system. It is known that visual feedback has a strong influence on reaches, often favoring the hand to move on a straight line between the starting and ending positions. Given the fact that straight reaches are costly for many definitions of mechanical effort, the reason behind this high tendency for straight reaches is unclear. This dissertation presents a study of how visual feedback can affect human reaching movements. To investigate this matter, we conducted several experimental studies where visual feedback was distinguished or altered during the movement. We found that by removing visual feedback, reaches become variable, whereas on average reaches were not different with and without visual feedback. We looked at reaches made with visual feedback of the limb and found that limb-feedback leads to significant increase in hand curvature. Our results provide evidence that the typical cursor feedback induces straight reaches. We also looked at perturbed reaches with visual feedback of the limb coupled to the feedback of the perturbation. We found that in such condition, subjects are more likely to ignore the feedback of the limb and optimize their movement with respect to the dynamics of the perturbation. In general, despite finding conditions where reaches are not straight, we were not able to explain these curved movements in the context of minimizing the effort of movement. Our results benefit future experimental studies by reducing potential visual biases as well as the neuroscience field. In long term, this thesis has the potential to impact rehabilitation and clinical practices.