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Abstract:
People can adjust their reaching-to-grasp movements online to sudden changes in spatial properties of a target, such as its position or size. We investigated whether they can also do this when a non-spatial property -- weight -- suddenly changes. Guiding your movement by using visual cues about an object's weight is less direct than using visual cues about its position. The former depends heavily on experience and is expected to be processed by the (slow) ventral stream instead of the (fast) dorsal stream. We asked participants to reach out and lift an object. Sometimes a weight was visibly added to, or removed from, the object after the participants had started their movement. The delay between the grasp and the lift, and the lifting speed, depended only on the final weight of the object, irrespective of whether the object had changed weight. Thus, participants can adjust online to a visually indicated change in weight. Most participants used more time to move to a changed object than an unchanged object. However, a lack of correlation between this increase in time and the amount of adjustment suggests that this time was not used for reprogramming the movement, but was an involuntary reaction to the change.
