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Sascha Serwe, Knut Drewing, Julia Trommershäuser; Integration of multi-sensory directional information during goal-directed pointing. Journal of Vision 2007;7(9):307. doi: 10.1167/7.9.307.
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We studied multi-sensory integration of directional information during the execution of goal-directed pointing movements. Subjects pointed at a visual target of 6 cm diameter, presented at 35 cm from the starting position of the arm movement. Subjects performed the pointing movement under open loop conditions, i.e. visual feedback about finger and target position was removed during the movement. Proprioceptive directional information was provided by applying a small force pulse (amplitude 1 N, pulse duration 50 ms) orthogonal to the movement direction early in the movement. In some trials, a noisy visual directional cue was presented. Time and spatial location of presentation of the visual cue were matched to the force pulse. The direction of the visual cue was either consistent with the force pulse direction or differed by 30°, either clockwise or counterclockwise. Subjects were instructed to hit the target within 1200 ms following target presentation. We measured perceived direction of the proprioceptive cue when both cues were provided and perceived direction for each cue alone. In conditions in which both cues were presented simultaneously, we compared subjects' responses to the predictions of an ideal observer model. The model combines visual and proprioceptive direction estimates measured in single-cue conditions by weighted averaging. The weights depend on the reliability of each cue. In accordance with the predictions of the ideal observer model we find that subjects' responses were less variable when both visual and proprioceptive cues were available. In conditions in which the mean direction of proprioceptive cue and visual cue differed, subjects' responses exhibited a bias towards the direction of the visual cue. This bias was larger for more reliable visual cues and smaller for more reliable force pulse directions. These results are consistent with the idea of a reliability weighted combination of both cues.
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