Seminar Details
2011-12-13 (14.00) : Adaptive control of grip force to compensate for static and dynamic torques during object manipulation
At Euler building
Organized by Mathematical Engineering
Speaker :
Giard, Thibault
Abstract :
Manipulating a cup by the handle requires compensating for the torque
induced by the moment of the mass of the cup relative to the location
of the handle. In the present study, we investigated the control
strategy of subjects asked to perform grip-lift movements with an
object with center of mass located away from the grip
axis. Participants were asked to lift the manipulandum with a
two-fingers precision grip and stabilize it in front of a visual
target. Subjects showed a gradual and slow adaptation of the grip
force scaling across trials: the grip force tended to decrease slowly
and the temporal coordination between grip force and load torque rates
displayed gradually better-coordinated patterns. Importantly, this
adaptation was much slower than the stabilization of the same
parameters measured either when no torque came into play or after
previous adaptation to the presence of a torque. In contrast, the
maximum rotation induced by the torque was efficiently controlled
after only few trials, and an unexpected decrease in the tangential
torque produced significant overcompensation. An unexpected increase
in torque produced a consistent opposite effect. This shows that the
compensation for the dynamic torque was based on an anticipatory
dynamic counter-torque produced by the arm and wrist motor
commands. The comparatively slow stabilization of grip force control
suggests a specific adaptation process engaged by the presence of the
torque. This paradigm including tangential torques clearly constitutes
a powerful tool to extract the adaptive component of grip control
during object manipulation.