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Task-dependent vestibular feedback corrections in reaching

Johannes Keyser, Luc P. J. Selen, and W. Pieter Medendorp

Radboud University Nijmegen, Donders Institute for Brain, Cognition and
Behaviour, Nijmegen, The Netherlands

Theme and topic: E.04.c. Reaching control: Action and sensation, and
D.07.c. Vestibular perception, posture, and spatial orientation

Keywords: Sensorimotor, motor control, optimality

Support: EU FP7 604063 HealthPAC and NWO-VICI 453-11-001.

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When reaching for an object during self-motion, our motor system should
appropriately integrate vestibular signals to compensate for the
intervening motion and its induced inertial forces. We asked whether the
brain processes these vestibular signals automatically with the aim to
preserve hand trajectory in space or more flexibly, correcting
trajectories only in task-relevant spatial dimensions.
Using a robotic manipulandum, we tested subjects (n=24) making reaches
to either a narrow (2 cm) or a wide (60 cm) target in front of them.
Subjects reached to the target without instruction on where to hit it.
In 20% of reaches, subjects received galvanic vestibular stimulation
(GVS) and shutter glasses prevented visual feedback. In GVS trials, the
current was proportional to hand speed, but clipped at 3 mA, with either
positive polarity (cathode left) or negative polarity (cathode right).
We found that the same vestibular stimulation led to smaller trajectory
corrections for the wide target compared to the narrow target. We
interpret this reduced compensation as a task-dependent modulation of
vestibular feedback responses, tuned to minimally interfere with the
task-irrelevant dimension of the reach (Todorov and Jordan, 2002). These
flexible vestibular feedback corrections mimic the sophistication seen
in feedback responses to mechanical (Pruszynski et al., 2008) or visual
(Knill et al., 2011) perturbations of limb position.

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