Digit forces bias sensorimotor transformations underlying control of fingertip position

D. Shibata, A.M.L. Kappers, M. Santello

    Research output: Contribution to JournalArticleAcademicpeer-review

    Abstract

    Humans are able to modulate digit forces as a function of position despite changes in digit placement that might occur from trial to trial or when changing grip type for object manipulation. Although this phenomenon is likely to rely on sensing the position of the digits relative to each other and the object, the underlying mechanisms remain unclear. To address this question, we asked subjects (n = 30) to match perceived vertical distance between the center of pressure (CoP) of the thumb and index finger pads (d<inf>y</inf>) of the right hand ("reference" hand) using the same hand ("test" hand). The digits of reference hand were passively placed collinearly (dy = 0 mm). Subjects were then asked to exert different combinations of normal and tangential digit forces (F<inf>n</inf> and F<inf>tan</inf>, respectively) using the reference hand and then match the memorized d<inf>y</inf> using the test hand. The reference hand exerted F<inf>tan</inf> of thumb and index finger in either same or opposite direction. We hypothesized that, when the tangential forces of the digits are produced in opposite directions, matching error (1) would be biased toward the directions of the tangential forces; and (2) would be greater when the remembered relative contact points are matched with negligible digit force production. For the test hand, digit forces were either negligible (0.5-1 N, 0 ± 0.25 N; Experiment 1) or the same as those exerted by the reference hand (Experiment 2). Matching error was biased towards the direction of digit tangential forces: thumb CoP was placed higher than the index finger CoP when thumb and index finger F<inf>tan</inf> were directed upward and downward, respectively, and vice versa (p < 0.001). However, matching error was not dependent on whether the reference and test hand exerted similar or different forces. We propose that the expected sensory consequence of motor commands for tangential forces in opposite directions overrides estimation of fingertip position through haptic sensory feedback. © 2014 Shibata, Kappers and Santello.
    Original languageEnglish
    Article number564
    JournalFrontiers in Human Neuroscience
    Volume8
    Early online date10 Jul 2014
    DOIs
    Publication statusPublished - 2014

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