The lower photoelectric sensor was placed at a height just above the finger when placed on the pressure sensing board. The upper photoelectric sensor was placed at the height of the extended index finger in a position parallel to the table. During the tapping tasks, the peripheral movement onset of index finger extension was defined as the time when the light beam of the lower photoelectric sensor was interrupted by the extended index finger. The upper photoelectric sensor was used to signal the elevation level of the extended index finger during tapping. During tapping movements, omissions were registered when the index finger did not reach the upper photoelectric sensor level. Figure 1D illustrates how information concerning movement events was determined during the pressing and tapping tasks. The peripheral movement onsets recorded online were visually verified afterward for mechanical or performance errors.
