Meters that appear in western classical and popular music, called simple meters, generally contain two or more isochronous beat levels with inter-beat intervals (IBIs) related to each other by simple integer ratios such as 2:1 or 3:1. In contrast, non-isochronous beat levels with non-integer ratios are commonplace in the complex meters of traditional music from the Balkans. Although people from this region dance to complex meters and engage in synchronous ensemble performances, North American adults who lack prior exposure to complex meter have great difficulty perceiving and remembering such patterns. Our goal was to understand the extent to which North American adults could synchronize and sustain their tapping to complex meter patterns in the presence and absence of temporal and melodic cues to meter. We asked young adults to tap to drum patterns structured according to two different 7/8 meters common in Balkan music. Each meter contained three drumbeats per measure, with each drumbeat separated by either two or three 250 ms eight-notes in a 2-2-3 or a 3-2-2 pattern. In the synchronization phase of the trial, participants were asked to tap in synchrony with a drum pattern that was accompanied by either a matching or a mismatching Balkan folk melody. In the continuation phase of the trial, the drum patterns were turned off and participants continued tapping the drum pattern accompanied by the same melody or by silence.
Participants produced synchronization inter-tap intervals (ITIs) that were close to the target ratio of 3:2, although they systematically stretched the long ITI toward a simple-meter ratio of 2:1. During continuation participants maintained a similar ITI as long as the melody was present; when the melody was absent the ITI ratios were stretched even more towards 2:1. For the synchronization phase, variability of ITIs was higher when the meter of the melody was mismatching compared to when it was matching, but only for the 3-2-2 drum pattern. For the continuation phase, variability of ITIs was higher when the melody was absent compared to when it was present. These findings demonstrate that people not previously exposed to complex meter patterns find it difficult to synchronize to and continue them, especially in the absence of exogenous tapping cues. This can be explained by intrinsic difficulty in processing complex meter patterns, culture-specific biases for processing simple meters, or a combination of these two factors.