Figure 1.

Bilateral arm reaching test setup, target locations, and protocol. A: setup. The circles on the bottom and the middle of the touch screen show the home position and a target, respectively. At each trial, participants were instructed to reach to the target using either right or left index finger (depending on conditions) as quickly and accurately as possible. Magnetic sensors were attached to the index finger tips of both hands to record the choice of hand and kinematics. B: 35 targets displayed in the workspace (plus the home target, shown surrounded by a square). Gray shading shows the time constraint for each target in the fast condition. C: experimental protocol common for the stroke group. On day 1, the forced choice blocks (PA and NA) were always presented before the spontaneous choice blocks (SC) for familiarization purpose. On days 2 and 3, reminder sessions (R) were presented before the spontaneous choice blocks, followed by the forced choice blocks (PA) for the medium and fast conditions (see materials and methods). The spontaneous choice blocks used for the analysis of the paretic arm choice are shaded in gray. D: examples of velocity profile of a single reaching movements for one subject poststroke illustrating the computation of movement time. E: example of estimated joint angle. An inverse kinematics model was used to estimate shoulder and elbow joint angles from hand trajectories. F: example of shoulder and elbow joint torques estimated by an inverse dynamics model of the arm in 2 dimensions. Fast, fast-time constraint condition; Medium, medium-time constraint condition; NA, nonparetic arm only block; No-time, no-time constraint condition; PA, paretic arm only block; R, reminder block; SC, spontaneous choice block.