21 research outputs found
Objects Secure Grip During Manipulation of Hand-Held Importance of Cutaneous Feedback in Maintaining a The Effects of Digital Anesthesia on Force Control Using a Precision Grip Human Ability to Scale and Discriminate Forces Typical of Those Occurring duri
Eye-Hand Coordination: Dexterous Object Manipulation in New Gravity Fields
The stabilisation of an object manipulated with the hand depends on applying a sufficiently strong force with each finger such that sufficient friction is generated to resist the load force acting tangentially to the contact surfaces. Gravity normally provides a constant force acting on the object (depending on its weight) which is adequately taken into account by an appropriate level of grip force.Variations in inertial forces caused by the subject's own arm movements over a range of accelerations also produce synchronous changes in grip forces that rise and fall with the changes in the tangential load forces on the fingers.That is, grip force reflects an anticipatory adjustment to the fluctuations in inertial forces.The modulation of grip force in anticipation of load force implies that the nervous system has access to information concerning the object's weight, mass and the kinematics of the forthcoming movement, since changes in any of these require a different grip force.This suggests that the internal models used to predict load forces and generate appropriate grip forces are pretty good. It remains to be proved, however, whether the entire control process of grip-force compensation is based on feedforward, model-based control, or if some components of the required grip responses are generated through reflex actions. Microgravity presents a significant challenge to dexterous object manipulation for a number of reasons. Owing to all the potential deviations from the expected characteristics of the load forces, planning movement under microgravity conditions might involve a greater reliance on visual, tactile and/or memory cues to an object's mass. In addition, there might be over- gripping to reduce the consequence of an erroneous estimate of mass. Alternatively, the hand might initially be moved more slowly than normal to allow more time for feedback-based adjustments to grip force. In this regard, a series of experiments has been designed in order to study the effects of a change in gravity on the dynamics of prehension, on the kinematics of upper limb movements and on eye-hand coordination. This report describes the results of some experiments already performed and the scientific objectives of the experiments that will be carried out in the coming years