Kurzfassung:
Making fast decision such as football scoring or musical rhythm modulation requires timing accuracy. Wing & Kristofferson (1973b) reported in the negative correlation between successive intertap intervals of repetitive discrete motor responses based on the assumed two independent processes (timekeeper and motor delay). Helmut & Ivry (1996) reported the better performance of the repetitive tapping task when individuals tapped with two hands in comparison to single-handed tapping. A pilot experiment replicated this topic but with repetitive mental task and different peripheral motor implementations. Numerous daily activities require timing and performing more than one task simultaneously. Multi-tasking necessitates motor coordination. A challenging behavioral requirement especially in multitasking is to maintain both spatial and temporal accuracy of all motor actions given in response to an emergency, where possible resource bottlenecks may become apparent. Laboratory investigations on this topic often use dual-task experiments, e.g. bimanual tapping (BM, i.e. hitting a key or a surface by a finger tip) with different instructions for the right and left hand, respectively. A conventional experimental setup for tapping data measurement consists only of the ground contact sensors like micro switches for the motor action observation; the evaluation of the discrete events provided by these switches is quite simple, but also the amount of obtained information is limited. A novel experimental design for tapping experiments with high-resolution recording of the complete time course of the continuous finger movements was approached and the required evaluation procedures for the biomechanical and EMG data is described. The latter are based on sophisticated maximum-likelihood-techniques, which again is an example of progress in research through advanced bio-signal processing. The finger tapping task as designed by Stevens (1886) was used. The experimental paradigm consists of synchronization and continuation phase. Tapping included normal tapping, contact-free tapping, and isometric tapping for both single-task (ST) and dual-task (DT) conditions. Furthermore voice tapping and mental tapping in combination with normal tapping in ST condition were approached. ST covers the control experiment as reference and experiments studying timing of periodic movement. Finger positions and ground contact forces was recorded. The DT was performed on different limbs. The coordination of periodic right hand tapping with single stimulus evoked discrete left hand taps was investigated to check for task interactions and a possible relationship between “phase resetting” (tapping literature, e.g. J. Yamanishi, Kawato, & Suzuki, 1979) and “phase entrainment” (tremor literature, e.g. R.J. Elble, Higgins, & Hughes 1994). In ST only the results of voice tapping consistently confirmed the proposed model of Wing & Kristofferson (1973). The correlation biased to zero or even positive in isometric tapping and sometime in contact-free and normal tapping. The bimanual advantage in repetitive tapping performance was observed in isometric and in combined mental-normal tapping whereas disadvantage was observed in normal tapping and sometimes in contact-free tapping. The results proved that the different motor implementations leading to different motor delay and different feedback in closed-loop control contributed differentially to the correlation function in successive intertap intervals. The integration of central commands already occurs at high level in brain in case of combined mental/normal tapping. Additional to correction process in timing based on feedback a second correction process based on asynchrony between both fingers exists and caused the absence of bimanual advantage sometime in contact-free tapping and more effective in normal tapping. \r\nFour different types of coordination schemes were observed in DT tapping behavior: Marginal Tapping Interaction (MTI), Periodic Tap Retardation (PTR), Periodic Tap Hastening (PTH) and Discrete Tap Entrainment (DTE); MTI and PTR correspond to the phase resetting effect as described earlier in tapping for the coordination of periodic tapping with single discrete taps. (DTE) reflected the impact of the periodic tapping on the discrete tap and PTH of the discrete tap on the periodic tapping both leading to a synchronized execution of the two concurrent tapping tasks are the observed novel aspects. All subjects showed a dominant tapping behavior but also other non-dominant forms of the four reported coordination schemes in some trials. Even MTI presents marginal interaction, continuous trajectory revealed hidden mutual interaction such as mutual modification of tap duration and slope duration, tap embedding, varied force or amplitude, tap delay and tap cancelling although rhythm is stable. The results reflect possible constraints of the sensorimotor system in handling two competing tasks.