Grasp Orientation in Ambiguous Settings is Sensitive to Prior Object Motion

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Grasp Orientation in Ambiguous Settings is Sensitive to Prior Object Motion


Maffitt, N. J.; Soteropoulos, D. S.; Kraskov, A.


The wrist posture chosen to grasp an object is normally consistent, determined by the optimal, most efficient strategy learnt from previous experience. Yet in certain settings, despite object properties remaining constant and intention the same, the action chosen by an individual can vary with a lack of clear preference for one posture over another. This is referred to as motor ambiguity. Here, we investigate the influence of preceding dynamically changing visual information on participants\' choice between two possible wrist postures when grasping an object at various orientations. We found that the decision is influenced by the participant observing rapid object rotation. Surprisingly, rather than being biased to choose the grasp that would have been appropriate for the initial position before object rotation, participants become more likely to use the alternate wrist posture. When object rotation is blocked from view, the bias effect is abolished. Furthermore, the bias strength was found to be independent of the motion magnitude, and persists even when greater decision time is allowed. We suggest that the influence of motion on ambiguous grasping could be attributed to participants overestimating the object\'s final position when its motion is observed, preparing them to use the grasp appropriate for the upcoming region of certainty. The overestimation may be due to miscalculations in the cerebellar internal model or the gain computation induced by the pairing of rapid motion with the uncertainty of the ambiguous context.

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