TY - JOUR
T1 - Force synergies for multifingered grasping
T2 - Effect of predictability in object center of mass and handedness
AU - Rearick, Matthew P.
AU - Santello, Marco
PY - 2002
Y1 - 2002
N2 - To grasp with five digits of the hand requires an efficient parceling of contact forces in order to maintain static equilibrium as an object is lifted and held. In a previous study, subjects were asked to reach, grasp and lift a five-digit grip apparatus whose center of mass (CM) location was changed for each block of trials. Despite a modulation of force sharing patterns among the digits as a function of center of mass location, consistent in-phase and out-of-phase relationships between normal forces were found in the frequency domain. In the present study, we have used the same task to assess the effect of (a) predictability of an object's CM location (random vs blocked presentation) and (b) handedness (dominant vs non-dominant hand). Contrary to our original expectations, we found a similar modulation of normal forces to CM location during the hold phase across all conditions. Specifically, the force sharing pattern, i.e., the rank order of force contributed by each digit, emerged very early in the grasp sequence, remaining relatively stable throughout the duration of the lift and hold. Nevertheless, the extent to which force sharing patterns could be discriminated as a function of CM location was lower in the random than in the blocked conditions. Lastly, normal forces exerted by pairs of digits tended to be synchronized, both in-phase (thumb and fingers) and out-of-phase (pairs of digits) across a large proportion of the functional frequency range (up to 10 Hz) in all conditions. The composite of these findings suggests that the central nervous system uses stereotyped control strategies for coordinating multiple grip forces during grasping. Specific aspects of these schemes appear to be affected by predictability of object CM location, but not by hand dominance.
AB - To grasp with five digits of the hand requires an efficient parceling of contact forces in order to maintain static equilibrium as an object is lifted and held. In a previous study, subjects were asked to reach, grasp and lift a five-digit grip apparatus whose center of mass (CM) location was changed for each block of trials. Despite a modulation of force sharing patterns among the digits as a function of center of mass location, consistent in-phase and out-of-phase relationships between normal forces were found in the frequency domain. In the present study, we have used the same task to assess the effect of (a) predictability of an object's CM location (random vs blocked presentation) and (b) handedness (dominant vs non-dominant hand). Contrary to our original expectations, we found a similar modulation of normal forces to CM location during the hold phase across all conditions. Specifically, the force sharing pattern, i.e., the rank order of force contributed by each digit, emerged very early in the grasp sequence, remaining relatively stable throughout the duration of the lift and hold. Nevertheless, the extent to which force sharing patterns could be discriminated as a function of CM location was lower in the random than in the blocked conditions. Lastly, normal forces exerted by pairs of digits tended to be synchronized, both in-phase (thumb and fingers) and out-of-phase (pairs of digits) across a large proportion of the functional frequency range (up to 10 Hz) in all conditions. The composite of these findings suggests that the central nervous system uses stereotyped control strategies for coordinating multiple grip forces during grasping. Specific aspects of these schemes appear to be affected by predictability of object CM location, but not by hand dominance.
KW - Finger force synergies
KW - Force control
KW - Grasping
KW - Human hand
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U2 - 10.1007/s00221-002-1024-x
DO - 10.1007/s00221-002-1024-x
M3 - Article
C2 - 11976758
AN - SCOPUS:0036236517
SN - 0014-4819
VL - 144
SP - 38
EP - 49
JO - Experimental Brain Research
JF - Experimental Brain Research
IS - 1
ER -