The present study examines whether visual information indicating the center of mass (CM) of an object can be used for the
appropriate scaling of fingertip forces at each digit during precision grip. In separate experiments subjects lifted an object
with various types of visual cues concerning the CM location several times and then rotated and lifted it again to determine
whether the visual cues signaling the new location of the CM could be used to appropriately scale the fingertip forces. Specifically,
subjects had either no visual cues, visual instructional cues (i.e., an indicator) or visual geometric cues where the longer
axis of the object indicated the CM. When no visual cues were provided, subjects were unable to appropriately scale the load
forces at each digit following rotation despite their knowledge of the new weight distribution. When visual cues regarding
the CM location were provided, the nature of the visual cues determined their effectiveness in retrieval of internal representations
underlying the anticipatory scaling of fingertip forces. Specifically, when subjects were provided with visual instructional
information, they were unable to appropriately scale the forces. More appropriate scaling of the load forces occurred when
the visual cues were ecologically meaningful, i.e., when the shape of the object indicated the CM location. We suggest that
visual instructional cues do not have access to the implicit processes underlying dynamic force control, whereas visual geometric
cues can be used for the retrieval of the internal representation related to CM for appropriate partitioning of the forces
in each digit.
Anticipatory control Visual information Internal representation Center of mass Human precision grip Isometric fingertip force
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