Article Figures & Data
Figures
- Fig. 1.
A, Top view of the experimental setup. Subjects grasp a manipulandum attached to two force-served linear motors mounted at right angles to give motion in the horizontal plane. B, Side view of the manipulandum instrumented with force sensors to measure grip force normal to the contact surface and load forces tangential to the surface.
- Fig. 2.
Single kinematic and force records from one subject under the three load conditions. Shaded regionsindicate the horizontal load force (HF) resisting the movement and the primary kinematic variable on which this component of the load depended. Under all three load conditions, grip force (GF) is adjusted in parallel with fluctuations in load force (LF), the resultant load tangential to the grasp surface. All calibration bars start at zero. Dashed vertical lines indicate movement onset.
- Fig. 3.
Overlaid kinematic and kinetic records taken from the last 20 trials under the inertial load condition (after adaptation to the load). Five push and five pull trials are shown for two subjects. Calibration values for bars are given in the bottom left panel. All bars start at zero.
- Fig. 4.
Overlaid kinematic and kinetic records taken from the last 20 trials under the viscous load condition (after adaptation to the load). Five push and five pull trials are shown for two subjects. Calibration values for bars are given in the bottom left panel. All bars start at zero.
- Fig. 5.
Overlaid kinematic and kinetic records taken from the last 20 trials under the composite load condition (after adaptation to the load). Five push and five pull trials are shown for two subjects. Calibrations for bars are given in the bottom left panel. All bars start at zero.
- Fig. 6.
Five hand velocity profiles from the last 10 pull trials in each of the three load conditions for four subjects. Velocity profiles were normalized with respect to area and peak velocity and aligned with respect to peak velocity. Whereas one-half of the subjects produced profiles that were invariant across loads (illustrated byS8 and S6), the others did not (illustrated by S10 and S3).
Tables
- Table 1.
Inertial load Viscous load Composite load Pushes Pulls Pushes Pulls Pushes Pulls Movement time (MT) (sec) 0.72 0.72 0.82 0.78 0.87 0.84 (0.05) (0.06) (0.08) (0.13) (0.08) (0.09) Peak velocity (cm/sec) 71.6 71.4 68.5 66.7 56.6 55.6 (7.4) (8.8) (9.1) (10.3) (7.0) (8.7) Time to peak velocity (% MT) 46.1 46.9 42.6 44.0 45.6 46.2 (4.2) (3.3) (6.6) (8.3) (5.7) (4.3) Peak load force (LF) (N) 7.1 7.1 13.4 13.8 9.79 9.14 (2.1) (1.2) (3.1) (2.4) (2.4) (1.1) Peak grip force (GF) (N) 15.7 18.1 23.6 28.8 20.6 21.9 (5.4) (4.7) (5.7) (4.7) (3.9) (4.7) Time to peak LF (% MT) 28.3 26.0 38.5 38.0 (6.3) (3.7) (6.3) (9.4) Time to peak GF (% MT) 27.3 26.1 36.6 35.1 (5.3) (4.3) (9.7) (9.6) Median force ratio 2.95 3.07 2.25 2.63 2.41 2.76 (1.05) (0.58) (0.46) (0.55) (0.83) (0.95) Means and SD (in parentheses) of the mean scores of 10 subjects. Subject means were based on the last 30 trials in each load condition.
