Biomedical subjects

John F Soechting

Publications and source records attributed to John F Soechting.

21 records · Page 2Linked to original sources

PubMed2002

Patterns of hand motion during grasping and the influence of sensory guidance.

This study was aimed at describing temporal synergies of hand movement and determining the influence of sensory cues on the control of these synergies. Subjects were asked to reach to and grasp various objects under three experimental conditions: (1) memory-guided movements, in which the object was not in view during the movement; (2) virtual object, in which a virtual image of the object was in view but the object was not physically present; and (3) real object, in which the object was in view and physically present. Motion of the arm and of 15 degrees of freedom of the hand was recorded. A principal components analysis was developed to provide a concise description of the spatiotemporal patterns underlying the motion. Vision of the object during the reaching movement had no influence on the kinematics, and the effect of the physical presence of the object became manifest primarily after the fingers had contacted the object. Two principal components accounted for >75% of the variance. For both components, there was a strong positive correlation in the rotations of metacarpophalangeal and proximal interphalangeal joints of the fingers. The first principal component exhibited a pattern of finger extension reversing to flexion, whereas the second principal component became important only in the second half of the reaching movement.

Arm↗

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↗

PubMedDate not supplied

Effect of compliance on haptic perception of curvature.

The haptic sense of geometric properties such as the curvature of a contour is derived from somatosensory cues about the motions and forces experienced during exploratory actions. This study addressed the question of whether compliance, the relationship between force and displacement, influences haptic perception of curvature. Subjects traced a curved 30 cm long compliant contour by grasping the handle of a manipulandum and reported whether the contour curved towards or away from them. The contour at which there was equal probability of responding either way was taken to represent one that was sensed as being straight. The compliance of the contour was varied, being constant, greatest in the middle or greatest at the ends. Subjects exhibited a bias in what they sensed to be a straight edge. However, the actual handpath that was judged to be straight did not vary across the three compliance profiles. Our results rule out a hypothetical strategy in which an intended motion is planned and the actual trajectory is then inferred by sensing force feedback. Another strategy in which the force against the contour is controlled and the handpath is inferred from proprioceptive feedback is more consistent with the observations.

Adult↗