Figure 5. Experimental Setup.

A: Subjects were seated facing a tangent 21-inch color CRT monitor with their heads restrained by a chin rest. Subjects put their right arms on an armrest with the right palm upturned and gripped a 3D posture sensor. Subjects were not able to observe their own movements. The 3D posture sensor measured Euler angles of subjects’ wrist movements. The pitch angle was referred to as the flexion angle and used to trigger the cursor movement, while the roll angle was referred to as the pronation/supination angle and determined the direction of cursor movement.B: The diagram shows the display on the CRT monitor. The area of the task field was 675×550 pixels. The target appeared on the target line, located 650 pixels from the bottom of the monitor. The initial position of the cursor was 100 pixels to the right of the bottom center of the monitor, and cursor movement was initiated by flexion movement of the wrist. The direction of cursor movement was controlled by the pronation/supination angle, but the vertical velocity was fixed throughout the experimental session. Visual displacement was introduced by rotating the direction of cursor movement and, as a result, the position of the cursor endpoint was displaced in a horizontal direction. Note that in Experiments 1 and 2, the cursor was displayed only at the target line (i.e., impact position), although it was displayed from the initial position to the impact position in the practice session. In Experiment 3, the cursor was not displayed; instead, a timing bar was presented that indicated the vertical position of the cursor.