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Knut Drewing, Julia Trommershaeuser; Detection and costs of force perturbations during visually-guided pointing movements. Journal of Vision 2005;5(8):625. doi: 10.1167/5.8.625.
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The successful execution of movements not only requires directing the movement towards the selected goal, but also detecting and compensating for perturbations interfering with the goal of the movement. Here we asked if participants are able to detect external force perturbations, how the executed movement is affected by the perturbation and, how the perturbation interferes with the goal of the task. Participants were instructed to rapidly hit a visual target, which was presented within a three-dimensional visuo-haptic virtual environment. Late responses and failures to hit the target were penalized. Participants were presented with a force pulse, which was applied to their right finger tip during the initial phase of the pointing movement. Force perturbations were applied orthogonally to the movement direction. We determined detection thresholds for perturbations from six different directions (up, down, upper right/left; lower right/left) using a two-interval forced choice paradigm. 5 participants completed the experiment. Surprisingly, detection thresholds for the applied perturbations (threshold about .10 N) were just slightly higher than tactile-kinesthetic detection in a single-task context (about .05N, Lederman & Klatzky, 1999). Detection performance did not depend on the direction of the perturbation, but was better for short perturbations (30 ms presentation time) compared to longer perturbations (50 ms presentation time). Shorter perturbations differed from longer perturbations by a steeper increase in force amplitude (10% of the duration). Locally, perturbations (> about 0.07 N) affected the movement kinematics significantly as compared to trajectories without perturbation. However, the distribution of movement end points at the location of the visual target did not correlate with the direction of the perturbation. These results are a first hint that the brain is able to detect force perturbations during visually guided pointing movements without extra costs.
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