Inter-tap interval dependence of the subdivision effect in auditory-synchronised tapping.

Precise temporal synchronisation between action and perception is crucial in daily life. Interestingly, synchronised tapping for every other tone or more (1: n tapping) is more precise than that for each tone (1:1 tapping), and this phenomenon is called 'subdivision benefit.' One hypothesis to explain this phenomenon is that there is a tendency to underestimate an empty interval, but the subdivision is used as an additional temporal reference and causes an illusionary longer inter-tap interval (ITI). The other hypothesis is based on strong/weak beats in a tone sequence made by subdivision. Since the strong beat improves the sensitivity of duration perception, synchronisation with strong beats should be better compared to other beats. Instead, the first hypothesis suggests that the subdivision benefit occurs irrespective of beat strength. The present study aimed to clarify this discrepancy using a 1:3 tapping task for a sequence of three-tone patterns and a 1:1 tapping task for a sequence of a single tone repetition. A further aim was to clarify the effect of musical experience. When the ITI was 900 ms or more, the variability of tapping showed the subdivision benefit, irrespective of beat strength. This result supports the first hypothesis, and musicians obtained more benefits than non-musicians. Instead, the timing of tap did not shorten by subdivision, except for the ITI of 900 ms. The findings implicate that the subdivision benefit is due to the additional temporal reference by the subdivided tones, and the benefit is dependent on the ITI length.