Fig. 2.

EMG and kinematic data from a typical subject who trained for three sets (each set, 192 movements) at Left in fieldB₃ and was then tested at Right in joint space translation of that field, named B₄.A, EMG data from biceps during movements in the null field (solid line) and in the force fieldB₃ (dashed line). Data are aligned to the initiation of movement. The arm is in the Left work space. Each subfigure indicates EMG activity for a movement toward a target at one of the eight directions. Thesolid line is for the null field, and the dashed line is for the last set of training in fieldB₃. The center figure is the spatial tuning function for this muscle in the null and force fields. The EMG from time −50 to 100 msec for each movement is averaged, and the mean ± SD over all movements toward each of eight directions is shown. The preferred direction vector is the sum of the eight vectors. The means ± SD of the vector's angle and the length are noted by the gray region. Training in the field is coincident with a −38° rotation in the preferred direction vector.B, Magnitude of the hand velocity vector perpendicular to the direction of the target, averaged for each target set. Theblack lines are for training inB₃ at Left (3 target sets). The gray line is for the test of generalization at Right inB₄ (1 target set). Movementnumbers are indicated. C, Magnitude of the parallel velocity vector toward targets. Little change is observed.D, Maximum displacement perpendicular (Perp.) to the direction of the target. The bin size is 16 movements. Connected lines indicate a target set (192 movements). E, Spatial EMG function for biceps in the Right work space. Field B₄ at Right required a rotation of −31° in the biceps' preferred direction, similar to the rotation that field B₃ required at Left. Coincident with this, performance measures indicated generalization.L, Left; R, Right.