PREDICTIVE FEEDFORWARD SENSORY CONTROL DURING GRASPING AND MANIPULATION IN MAN

During dexterous manipulation the basal relationships expressed in the employed fundamental muscle synergies are tuned precisely not only to the manipulative intent, but also to the physical properties of the o bject. Recent findings indicate that the sensorimotor mechanisms invol ved depend largely on predictive rather than servo-control mechanisms: The CNS monitors specific, more-or-less expected, peripheral sensory events and use these to directly apply control signals that are approp riate for the current task and its phase. On a fast time scale, discre te mechanical events encoded in populations of somatosensory afferents trigger compensatory actions to task perturbations, and allow task pr ogress to be monitored for timing the release of motor commands relate d to the serial manipulative phases. This type of predictive feed-forw ard sensory control is termed 'sensory discrete-event driven control'. On an extended time scale, previous experience with the object at han d or similar objects is used to adjust the motor commands parametrical ly in advance of the movement, eg. for the object's weight and surface friction. Through vision, for instance, common objects can be identif ied in terms of the grip and lifting forces necessary for a successful lift. This ability to directly parameterize the default motor command s is termed 'anticipatory parameter control'.