Article Figures & Data
Figures
- Figure 1.
The experimental apparatus and task. A, Subjects grasped the handle of the manipulandum as it was servoed to various positions in the workspace. The green spheres represent targets within the horizontal plane, to which the robot was moved. As subjects were servoed to the targets they were instructed to generate a constant interaction force with the manipulandum. Visual force feedback was provided to subjects throughout the movement. B, The robot moved along a 1 s minimum jerk trajectory during the combined and motion blocks and a slow constant velocity trajectory during the force block.
- Figure 2.
Applied forces for a representative subject performing each experimental block. Force fields represent the mean of three trials in each movement direction for “no-vision” trials before training (first 12 trials) and after training (12 trials after 60 trials of practice with visual feedback).
- Figure 3.
TMS of PPC disrupts the combined task and the control of motion but not the control of force. A, Group mean force error from the target level of force for the no-vision trials. Significant differences were found across before training trials, after training trials, PPC stimulation trials, and control stimulation trials, for each experimental block (combined block, ANOVA, F(3,24) = 5.616, p < 0.005; motion block, ANOVA, F(3,24) = 3.269, p < 0.05; force block, F(3,24) = 3.186, p < 0.05). Error bars denote SEM. Asterisks denote significantly worse performance than that after training (*p < 0.05, **p < 0.01, ***p < 0.001). B, Group force error profiles for performing each experimental block. Blue lines correspond to profiles after training, and red lines are profiles during PPC stimulation. Shaded regions represent the SEM for the profiles. The vertical lines represent time of the TMS pulse.
- Figure 4.
TMS of PPC does not disrupt more complex force control. A, Mean force error for no-vision trials without stimulation and with PPC stimulation. Error bars denote SEM. B, C, Force profiles for a representative subject performing the isometric force tracking task.
- Figure 5.
A linear summation of independent motion and force controllers describes the combined task. Fields of force shown are for a representative subject. Fields generated from trials after training are seen in blue, PPC stimulation fields are seen in red. Force fields generated for trials after training and stimulation for the motion (top left), force (top right), and combined (bottom left) experimental blocks. Vector summation of the FMotion and FForce fields for after training and during PPC stimulation Fields (bottom right) (after training, cMotion = 0.89, cForce = 1.04, R2 = 0.88; PPC stimulation, cMotion = 0.86, cForce = 1.20, R2 = 0.90).
- Figure 6.
Motion and force controllers equally contribute to the combined behavior. A, Summation coefficients for the field combination hypothesis. Field combination is performed on fields before training, after training, during PPC stimulation, and control stimulation. B, Variance accounted for by each controller for each vector summation. C, R2 for each field combination. Error bars denote SEM.
- Figure 7.
Muscle activation is similar for all experiment blocks. Bars denote mean muscle activation across subjects for each experiment block. Error bars denote SEM. BRD, Brachioradials; BI, biceps brachii; TLO, long head of the triceps; TLAT, lateral head of the triceps; AD, anterior deltoid; MD, medial deltoid; PD, posterior deltoid; PC, pectorals major.
Tables
Muscle ANOVA across blocks Brachioradialus F(2,12) = 0.515; p = 0.610 Biceps brachii F(2,12) = 0.540; p = 0.597 Long head of the triceps F(2,12) = 0.115; p = 0.892 Lateral head of the triceps F(2,12) = 0.014; p = 0.986 Anterior deltoid F(2,12) = 0.880; p = 0.440 Medial deltoid F(2,12) = 0.532; p = 0.600 Posterior deltoid F(2,12) = 0.689; p = 0.521 Pectoralis major F(2,12) = 0.072; p = 0.931
