On-line programming in simple movement sequences : An application of the probe reaction in time paradigm

The main goal of this experiment was to detect on-line programming as it occurred during the execution of forearm extension movements by including a probe reaction time paradigm within an extension-flexion movement task. The experiment included a primary and a secondary task condition and subjects performed these tasks in both single and dual-task situations. For the primary task in the single task condition, subjects performed forearm extension (E), and two types of extension-flexion movements for which the time between successive extension and flexion movements was varied (i.e., this time period was 50-100 msec (EFS) or 250-300 msec (EFL)). For the secondary task in the single task condition, subjects wore headphones through which an auditory stimulus (i.e., probe) was delivered at seven positions, either before or after the primary task stimulus. The onset of this probe was determined by either an absolute time interval, or by on-line analysis of EMG and acceleration profile data. Subjects closed their jaw as quickly as possible following the probe. In the dual task condition, the forearm movement and the jaw clench response were performed simultaneously. The reaction times were comparable for E, EFS and EFL movements in the dual task condition, suggesting that subjects programmed the flexion movement during the execution of the extension movement. By combining probe reaction time measures with those from the initial latency period, a more accurate description could be given of where in time these on-line control processes took place. Specifically, the probe reaction times were lengthened when the probe occurred at the end of the extension movement for EFL movements. It appeared that subjects delayed the execution of the jaw clench response until the programming of the flexion movement had been completed and hence the jaw clench and flexion response were initiated concurrently at this probe position (evidenced by EMG activity of the Masseter and Biceps muscles). Subjects appeared to use this same strategy for probes occurring during the pause time for EFL movements and at the point at which peak velocity was obtained for EFS movements.Education, Faculty ofKinesiology, School ofGraduat