Table 1.
Definitions and descriptions of key terms.
Fig 1.
Illustration of the instrumented objects.
Nano 17 force sensors recorded digit forces. A motion capture system tracked the positions of four reflective markers fixed to each object.
Fig 2.
Participants held the objects in pinch grasps and positioned them above the reference point. Targets and cursors were displayed on the computer screen placed on the table.
Fig 3.
Targets and cursors feedback on the computer screen.
(A) position of cursors and objects at the start of a trial, (B) objects positioned in the frontal plane such that the spring is stretched to bring both cursors within the targets, (C) target tracking with right object while left object is stabilized, and (D) score displayed at the end of the trial.
Fig 4.
Target profiles and tracking performance by each hand.
(A) Regular (triangular) movement and (B) Irregular (fBm) movement. Data shown are across trial mean and standard error for a representative participant.
Fig 5.
Grip and load forces for both hands.
(A) moving left and static right hand during regular and irregular movements with the left hand, (B) moving right and static left hand during regular and irregular movements with the right hand. Data shown are across trial mean and standard error for a representative participant. The plots use different Y axes for grip and load forces.
Fig 6.
Cross-recurrence plots for a representative subject.
(A) Regular movement with left hand, (B) regular movement with right hand, (C) irregular movement with left hand, and (D) irregular movement with right hand. Normalized grip and load forces are shown below each cross recurrence plot. Note that the grip-load coupling analysis was done during object movement by each hand. Therefore, the plots shown are for each hand during their respective movement tasks.
Table 2.
Summary of participant performance scores for each hand × task difficulty block. The values computed are across participant average ± S.E. within each block.
Fig 7.
(A) Moving hand, and (B) Static hand. ‘*’ indicates significant differences (p < 0.05). Data are mean ± standard error.
Fig 8.
Mean (A) and variance (B) of the load on the moving object. Mean (C) and variance (D) of the load on the stabilized object. ‘*’ indicates significant differences (p < 0.05). Data are mean ± standard error.
Fig 9.
RMSE (A) vertical and (B) mediolateral during object movement. (C) standard deviation and (D) compliance during object stabilization. ‘*’ indicates significant differences (p < 0.05). Data are mean ± standard error.
Fig 10.
Measures quantifying grip-load force coupling during object movement (A) Correlation at zero lag, and (B) trapping time. (C) Mean grip force during object stabilization. ‘*’ indicates significant differences (p < 0.05). Data are mean ± standard error.