Biomedical subjects

Gabriel Baud-Bovy

Publications and source records attributed to Gabriel Baud-Bovy.

3 recordsLinked to original sources

PubMed2006

The haptic reproduction of orientations in three-dimensional space.

This research studied the haptic perception of orientations in space rather than in a plane. It aimed at identifying the nature of the system of coordinate used to represent an orientation in space, when two parameters are necessary to code an orientation. Blindfolded participants inserted the tip of the index finger in a thimble mounted at the extremity of a haptic interface, explored the orientation of a "virtual rod" with to-and-fro movements and, after a short delay, reproduced the same orientation with the same fingertip in the absence of the virtual rod. Globally, the haptic reproduction of orientations was anisotropic. When the reproduction of orientations was carried out in the frontal plane, a classical oblique effect (lower performance for the diagonal orientations than for the vertical and horizontal orientations) occurred. When the reproduction of orientations was carried out in space, orientations seemed to be coded in a coordinate system based on the sagittal plane.

Adult↗

PubMed2004

Amplitude and direction errors in kinesthetic pointing.

We investigated the accuracy with which, in the absence of vision, one can reach again a 2D target location that had been previously identified by a guided movement. A robotic arm guided the participant's hand to a target (locating motion) and away from it (homing motion). Then, the participant pointed freely toward the remembered target position. Two experiments manipulated separately the kinematics of the locating and homing motions. Some robot motions followed a straight path with the bell-shaped velocity profile that is typical of natural movements. Other motions followed curved paths, or had strong acceleration and deceleration peaks. Current motor theories of perception suggest that pointing should be more accurate when the homing and locating motion mimics natural movements. This expectation was not borne out by the results, because amplitude and direction errors were almost independent of the kinematics of the locating and homing phases. In both experiments, participants tended to overshoot the target positions along the lateral directions. In addition, pointing movements towards oblique targets were attracted by the closest diagonal (oblique effect). This error pattern was robust not only with respect to the manner in which participants located the target position (perceptual equivalence), but also with respect to the manner in which they executed the pointing movements (motor equivalence). Because of the similarity of the results with those of previous studies on visual pointing, it is argued that the observed error pattern is basically determined by the idiosyncratic properties of the mechanisms whereby space is represented internally.

Adult↗

PubMed2002

Factors influencing variability in load forces in a tripod grasp.

The aim of this investigation was to determine the factors that influence the variability in the load force during a precision grip. Subjects grasped an object with three coarse contact surfaces using a tripod grasp of the thumb, index and middle fingers. The orientations of the contact surfaces and their locations relative to the object's center of mass were varied. Forces and torques exerted by each of the three digits were measured or computed from the equilibrium conditions and analyzed during the static hold phase. The static load force depends on the object's weight, but also on the precise location of the center of pressure of each digit, as well as on the magnitude of the tangential torque and horizontal grip force. Variations in these parameters caused deviations in the load forces by as much as 20% or more from their nominal values. For the thumb, the largest source of variability was the vertical location of the center of pressure. For the two fingers, variations in the locations of the centers of pressure (along the horizontal and vertical) and in the magnitudes of the tangential torques had effects that were about equal in magnitude. Since many of the sources of variability in load force are unpredictable, these results point to the importance of online feedback regulation of grip force.

Afferent Pathways↗