Figure 1. Task paradigm.

A) Prior to the start of each trial, participants fixated on a crosshair for 3.75 s. After this baseline period, a series of three numbers (each corresponding to a digit on the finger) appeared on the screen for 0.5 s. There were two conditions corresponding to differing levels of motor plan complexity. In the “simple” condition, the series of numbers in the plan were sequential (i.e., “1-2-3”, “2-3-4”, “4-3-2” or “3-2-1”), and thus corresponded to tapping three adjacent fingers. In the “complex” condition, each number in the sequence was at least one number away from the previous number (i.e., “1-4-2”, “2-4-1”, “3-1-4”, or “4-1-3”), and thus mapped to a sequence in which the finger being tapped was not adjacent to the previous finger tapped. After the numbers were displayed in black for 0.5 s, the numbers changed color which cued the participant to move. The participant then had 2.25 s to complete the motor plan and return to rest. After 2.25 s, the numbers disappeared and only the fixation crosshair remained. This combination of slides constituted one trial. Trials were pseudo-randomized and a total of 80 trials for each condition were completed (160 total trials), totaling about 16 minutes for the task. B) The button pad used during this task. Each button on the pad corresponded to a specific finger; the thumb was not used for task performance.