The concept of a temporal integration process in the timing mechanisms in the brain, postulated on the basis of experimental observations from various paradigms (for a review see P$oUppel, 1978), has been explored in a sensorimotor synchronization task. Subjects synchronized their finger taps to sequences of auditory stimuli with interstimulus-onset intervals (ISIs) between 300 and 4800 msec in different trials. Each tonal sequence consisted of 110 stimuli; the tones had a frequency of 500 Hz and a duration of 100 msec. As observed previously, response onsets preceded onsets of the stimuli by some tens of milliseconcls for ISIs in the range from about 600 to 1800 msec. For ISIs longer than or equal to 2400 msec, the ability to time the response sequence in such a way that the response 5 were placed right ahead of the stimuli started to break clown, i.e., the task was fulfilled by reactions to the stimuli rather than by advanced responses. This observation can he understood within the general framework of a temporal integration puce 55 that is supposed to have a maximal capacity (integration interval) of approximately 3 sec. Only if successive stimuli fall within one integration period, can motor programs be initiated properly by a prior stimulus and thus lead to an appropriate synchronization between the stimulus sequence and corresponding motor acts.
Individuals can determine the side of the nose that receives an odorant during unilateral presentation (lateralize) if endings of the trigeminal nerve are stimulated. By using psychophysical methods, olfactory detection and trigeminal lateralization thresholds for l-butanol were obtained from 142 individuals ranging in age from 20 to 89 years. Sensitivity in both chemosensory pathways declined with advancing age, especially in people older than 60 years.
The same isochronous tone sequence was presented simultaneously to two mutually isolated subjects. In half the trials, accentuation in this sequence was accomplished by doubling the duration of the first and then of every fourth tone; in the other half, by doubling the frequency of those tones. The subjects' task was to follow the rhythm of the resulting four-tone patterns by finger tapping to tone onsets. There were four auditory feedback (FB) conditions: (1) no FB; (2) FB from the subject's own motor responses; (3) "alien" FB from the motor responses of the other pair member who, in turn, was listening to FB from his/her own tapping; (4) mutually "crossed" FB, where each pair member listened to FB from the tapping of the other. Tap onsets regularly preceded stimulus onsets. The observed order of the amount of this anticipation (from least to greatest) was: (1) own FB, (2) no FB, (3) alien FB, and (4) crossed FB. No mutual dynamic influence between simultaneously performing subjects was detected. Anticipation was more pronounced for sequences that were accentuated by frequency rather than by duration changes. The type of accent also influenced timing of intertap intervals in the rhythmic patterns. For the frequency accent, regular timing was produced, whereas for the durational accent, shortening of the second and lengthening of the fourth (the last) intertap interval were observed. The presence and source of feedback as well as the character of accentuation are therefore relevant factors in the timing of auditorally controlled rhythmic motor behavior.
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