Fig. 1.

Design of experiments. A, General concept, taking conditions I and IV in B as examples. The subject is required to make slow (blue arrow) and fast (red arrow) reaching movements to a target without prisms inEpoch 1. Then the visual field is displaced to theleft by prisms in Epoch 2, during which the subject is required to make the fast reaching movements. The subject initially reaches to the position of the virtual image of the target (gray cross) but, after practice, reaches to the position of the real target (solid cross, Adaptation). InEpoch 3-1, when the prisms are removed, the subject is required to execute the fast reaching movements in one condition (I) and the slow reaching movements in another (IV). B, Eight conditions (I–VIII) of four reaching movements (Fast, Semifast, Semislow, and Slow) that required movement durations of <300, ∼800, ∼2000, and ∼5000 msec, respectively. One experiment consisted of 90 trials: 15, 15, 30, 15, and 15 trials for Epoch 1-1, 1-2, 2, 3-1, and 3-2, respectively. In Epoch 2, the visual field was displaced to the left or to the right by 15-diopter wedge prisms. The prisms were removed for the last Epochs (No Prism). C, Intermanual transfer of adaptation acquired with fast (I) and slow (II) reaching movements of the ipsilateral arm (Ipsi) to the contralateral arm (Contra). D, Time sequence of one trial. Each column schematically shows the status of the visual field (oval shape) and the position of the hand relative to the button and the screen. Shutters opened at 0(Start), when the subject pressed the button. A target appeared after beeps at a random location in a square area (40 mm × 40 mm) on the screen (1, Target On). Vision was blocked from 2 (Release) to 3(Touch) and allowed again for 100 msec immediately after the touch.