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Abstract:
Recently, vestibular signals have been shown to contribute to the online control of arm reaching movements. The present experiment had two main goals: (i) measure the latencies of vestibular-evoked arm responses, and (ii) determine whether these responses depend on cognitive processing. Subjects were seated in complete darkness, the right arm raised straight at shoulder level, and were instructed to keep their hand stable in space in spite of unpredictable passive whole body rotations. The EMG latencies of vestibular-evoked arm responses were measured and compared with the EMG latencies of the same muscles when tracking a visual target with the hand. For both tasks, we also tested the influence of pre-cueing on the responses. The main results are: (i) EMG latencies were significantly shorter for vestibular-evoked (162 ms on average) than for visual-based tracking responses (327 ms), and (ii) the influence of pre-cueing on the initial direction of arm responses was very strong in the tracking task (83 of errors in catch trials) and very weak for the vestibular-evoked responses (only 10 of errors in catch trials). These results show that the vestibular control of arm movements has rather short latencies and is virtually independent of cognitive processing.
