Conscious control of movements: increase of temporal precision in voluntarily delayed actions

The variability of simple actions with response to auditory stimuli was stu died under different delay conditions. Subjects reacted as fast as possible or with a defined time delay (from 250 to 750 ms) to a tone switching off by pressing a response-key with the left index finger (controlled by the ri ght hemisphere) or with the right one (left hemisphere). For short delays ( requested response times below 350 ms) variability of responses was much la rger then for longer delays (above 350 ms), especially for the right hand. Thus, precise temporal control on consciously mediated actions sets only in after a rather long delay (in some cases after half a second). Neuronal me chanisms underlying conscious temporal control of actions appear to be diff erent for the two hemispheres.