The parsing of undifferentiated tone sequences into groups of qualitatively distinct elements is one of the earliest rhythmic phenomena to have been investigated experimentally (Bolton, 1894). The present study aimed to replicate and extend these findings through online experimentation using a spontaneous grouping paradigm with forced-choice response (from 1 to 12 tones per group). Two types of isochronous sequences were used: equitone sequences, which varied only with respect to signal rate (200, 550, or 950 ms interonset intervals), and accented sequences, in which accents were added every two or three tones to test the effect of induced grouping (duple vs. triple) and accent type (intensity, duration, or pitch). In equitone sequences, participants’ grouping percepts (N = 4,194) were asymmetrical and tempo-dependent, with “no grouping” and groups of four being most frequently reported. In accented sequences, slower rate, induced triple grouping, and intensity accents correlated with increases in group length. Furthermore, the probability of observing a mixed metric type—that is, grouping percepts divisible by both two and three (6 and 12)—was found to be highest in faster sequences with induced triple grouping. These findings suggest that lower-level triple grouping gives rise to binary grouping percepts at higher metrical levels.

THE SIMULTANEOUS PRESENCE OF DIEEERENTmeters is not uncommon in Western art music and the music of various non-Western cultures. However, it is unclear how listeners and performers deal with this situation, and whether it is possible to cognitively establish and maintain different beats simultaneously without integrating them into a single metric framework. The present study is an attempt to address this issue empirically. Two rhythms, distinguished by pitch register and representing different meters (2/4 and 6/8), were presented simultaneously in various phase relation-ships, and participants (who were classically trained musicians) had to judge whether a probe fell on the heat in one or both rhythms. In a selective attention condition, they had to attend to one rhythm and to ignore the other, whereas in a divided attention condition, they had to attend to both. In Experiment 1, participants performed significantly better in the divided attention condition than predicted if they had been able to attend to only one rhythm at a time. In Experiments 2 and 3, however, which used more complex combinations of rhythms, performance did not differ significantly from chance. These results suggest that in Experiment 1 participants relied on the composite beat pattern (i.e., a nonisochronous sequence corresponding to the serial ordering of the two underlying beats) rather than tracking the two beats independently, while in Experiments 2 and 3, the level of complexity of the composite beat pattern may have prevented participants from tracking both beats simultaneously.. Diagrams of the test periods for each of the three phase conditions of Experiment 1, including aii event onsets (verticai lines) and probe positions (numbered from 0 to 12), with beat designations ("b"). Diagram (a) shows the in-phase condition, (b) shows the A-first condition, and (c) shows the B-first condition. The corresponding composite beat pattern is shown in musical notation beiow each diagram.

Jones et al. in Journal of Experimental Psychology Human Perception and Performance 21:293-307, 1995, showed that a temporal perturbation is easier to detect in a 3:2 polyrhythm than in a single-stream isochronous baseline condition if the two isochronous pulse streams forming the polyrhythm are perceptually integrated: integration creates shorter inter-onset interval (IOI) durations that facilitate perturbation detection. The present study examined whether this benefit of integration outweighs the potential costs imposed by the greater IOI heterogeneity and memory demands of more complex polyrhythms. In "Experiment 1", musically trained participants tried to detect perturbations in 3:5, 4:5, 6:5, and 7:5 polyrhythms having one of two different pitch separations between pulse streams, as well as in an isochronous baseline condition. "Experiment 2" included an additional 2:5 polyrhythm, additional pitch separations, and instructions to integrate or segregate the two pulse streams. In both experiments, perturbation detection scores for polyrhythms were below baseline, decreased as polyrhythm complexity increased, and tended to be lower at a smaller pitch separation, with little effect of instructions. Clearly, polyrhythm complexity was the main determinant of detection performance, which is attributed to the interval heterogeneity and/or memory demands of the pattern formed by the integrated pulse streams. In this task, perceptual integration was disadvantageous, but apparently could not be avoided.

The tapping paradigm has played an important role in formulating beat induction models. However, experimental studies that make use of actual music as source materials to investigate pulse finding mechanisms in complex rhythmic sequences are lacking. The present study proposes to use the concept of mensural determinacy, that is, the emergence of temporal expectations that may or may not be realized (Hasty, 1997), to explore the relative salience of an implied beat in two contrasting rhythmic sequences extracted from Elliott Carter's 90+ for piano (1994), and test the influence of style-specific expertise on listeners' spontaneous tapping performance. The results of the experiment were consistent with the hypothesis that familiarity with the style represented by the source materials contributes to a more stable tapping period. In addition, although accent was found to have a main effect on tapping behavior, it also interacted with global temporal structure and a number of musical parameters and participant characteristics, including gender. Exploratory analyses of several additional musical parameters and participants' characteristics are also suggestive of how experimental methods could be complemented by post-hoc score analysis to investigate the contributions of specific factors to the relative influence of first-and second-order periodicity on musicians' beat percepts.

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