Temporal control and motor control: two functional modules which may be influenced differently under microgravity

Three subjects performed sequences of periodic movements by synchronizing their movements (button pressing with the thumb) to a series of visual stimuli (induction phase), and by continuing to produce the movements with the same rhythm after the metronome had been switched off (continuation phase). The required inter-response intervals (IRIs) were 450, 550 or 650 ms. Two subjects were members of the EUROMIR 94 spaceflight mission. The inter-response intervals of the continuation phase were analyzed in terms of mean and variability. The mean inter-response intervals did not differ systematically during spaceflight from the pre- and post-flight values. The variability of the inter-response intervals significantly increased during the flight with both experimental subjects. The total variance of the inter-response intervals was partitioned into variance due to the internal timekeeper and variance due to the motor implementation processes, following the method proposed by Wing, A.M., Kristofferson, A.B., 1973. Response delays in the timing of discrete motor responses. Perception and Psychophysics 14, 5-12. The variance attributed to the timekeeper showed a significant increase with both subjects, whereas the variance attributed to the motor processes showed inconsistent trends during the spaceflight. It is concluded that during spaceflight, the functioning of the internal timing module may undergo some changes, as the result of which the regularity of the motor timing is slightly impaired.