Behavioral task design.

<p>A. Delayed reach-to-grasp task with the epochs fixation, cue, planning, and movement. Trials were initiated by placing both hands on hand rest sensors and fixating a red LED. After 500-700ms (fixation epoch), the instruction which grip type to use (precision or power grip, indicated by the color of a second LED) and the target position (by illumination) were revealed (cue epoch). After a planning epoch of 800-1200ms, a blink of the fixation LED instructed the monkey to grasp the target in the dark, while maintaining eye fixation. After successful termination, the animal got rewarded with a fixed amount of liquid. B. The target was grasped with either a precision grip (left) or a power grip (right photo). C. Schematic of the reach-to-grasp experimental setup. After placing both hands on the sensors in front of the body (circles), the monkeys had to grasp for the target positioned in front of them. D. Schematic view of the possible spatial variations. Target (T) and gaze positions (e for eye) were systematically varied, resulting in the subtasks CV (combined variation), with target and gaze presented in five joint positions, TV (target variation), with gaze position in the center, and GV (gaze variation), with target position in the center.