Seminar Details
2005-11-29 (14.00 pm) : Grip force control during active collisions in different gravitational fields
At Auditoire Euler
Organized by Mathematical Engineering
Speaker :
White, Olivier
Abstract :
Studies have shown that grip force, normal to each finger-object
contact surface is adjusted in anticipation of load forces, acting
tangentially to the contact surface when lifting and moving hand-held objects.
Prediction may not be correct and in many cases, predictive feedforward control
may be supplemented by feedback control. A problem is then to dissociate the two
forms of control in the behavioural record. One method is to study self-produced
collisions in which the time period over which the load is applied is too short to
allow a feedback loop to operate.
Changes in gravity present a significant challenge to dexterous
object manipulation. The aim of the present study was to analyse
grip force control in repetitive collisions during parabolic flight
to determine the role played by gravity in prediction of collision load
forces.
Seven subjects participated in the study. Each subject was secured by
a seat belt on a chair with an instrumented manipulandum grasped between
the thumb and the index finger of the right hand. Subjects performed a
targeted tapping task with the manipulandum while dynamics of precision
grip and kinematics of the upper limb were recorded. Subjects briefly
tapped the manipulandum randomly on surfaces placed above and below the
hands neutral position.
In normal gravity, subjects were able to produce similar impact forces in
both directions but they produced larger forces downwards in micro- and
hypergravity. In contrast, they applied more grip force upwards than downwards,
leading to an inefficient grip-to-load force ratio.
During the transport of the object towards the target, the acceleration
contributed either positively or negatively to the inertial forces felt by
the fingers and grip force was adequately adjusted. However, while acceleration
contributed equivalently for both directions in microgravity, grip force was
still higher upwards. In contrast to previous studies, the grip-load force
modulation disappeared and was not learned at the term if the experiment.
We suggest that a continuous internal model of altered gravity field and
collisions is under building in the central nervous system.