Figure 1.

Illustration of task, behavior, and muscle activity

A) Monkeys grasped a hand pedal and cycled through a virtual environment. The schematic illustrates forward cycling, instructed by a green environment. Backward cycling was instructed by an orange, desert-like environment.

B) Trial-averaged hand velocity for seven-cycle, four-cycle, two-cycle and one-cycle movements. Data are for forward cycling, starting at cycle’s bottom (monkey C). Vertical velocity traces are colored from tan to black to indicate time with respect to the end of movement. Black dots indicate target appearance. Gray box with shading indicates the epoch when the pedal was moving (preceding go cue not shown). Shading indicates vertical hand position; light shading indicates cycle apex. Ticks show cycle divisions used for analysis. Small schematics at right illustrate relationship between number of cycles and target distance.

C) Muscle activity, recorded from the medial head of the triceps (monkey D). Intra-muscularly recorded voltages were rectified, filtered, and trial averaged. Data are shown for backward cycling, starting at cycle’s top.