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Differential thresholds for tempi (with interonset intervals ranging from 100 to 1,500 msec) were measured using an adaptive 2IFC paradigm for several types of auditory sequences. In Experiment 1, the number of intervals in an isochronous sequence was varied to compare the sensitivity for single intervals with that for sequences oftwo to six intervals. Mean relative just noticeable differences (JNDs) decreased as the number of intervals increased (single intervals = 6%, two intervals = 4%, four intervals = 3.2%, six intervals = 3%) and were optimal at intermediate tempi for both sequences and single intervals (as low as 1.5% in the range between 300 and 800 msec), In Experiment 2, the sensitivity for different types of irregular sequences was studied. Globally, JNDs for irregular sequences were of an intermediate level between that observed for single intervals and that observed for regular sequences. However, the closer a sequence was to regularity, the lower its relative JND. Experiment 3 demonstrated that musicians were more sensitive than nonmusicians to changes in tempo, and this was true for single intervals and for regular and irregular sequences, demonstrating the role of training on these abilities. The results are discussed in terms of possible underlying mechanisms, in particular those providing a mental representation of the mean and dispersion of successive interval durations.How small a change in duration are we able to detect? The psychoacousticalliterature on time perception suggests that when subjects are asked to compare two intervals (empty or filled by a sound) they are able to say which is longer or shorter when there is a difference of at least 6% to 10% of the standard duration (Abel, 1972;Allen, 1979;Creelman, 1962;Getty, 1975Getty, , 1976Small & Campbell, 1962;Woodrow, 1951). This is true within a range of 200-2,000 msec, and the actual precision depends on many different factors, in particular the method used and the physical characteristics of the events marking the intervals. A similar level of sensitivity is also found when subjects are asked to detect a change in duration of one or two of the intervals contained in regular and rhythmic sequences (Drake, 1990(Drake, , 1992(Drake, , 1993 Drake, Botte, & Gerard, 1989; Drake, Gerard, & Botte, in press;Halpern & Darwin, 1982;Hirsh, Monahan, Grant, & Singh, 1990; van Noorden, 1975). However, when subjects are asked to compare the rate or tempo of two isochronous sequences, the little data available suggests that subjects are much more sensitive to changes, since they are able to detect a change of about 2% (Michon, 1964).How can we explain this greater sensitivity to changes in tempo of sequences than to changes in duration of single intervals? An obvious answer is that in the case of We wish to thank Professors Douglas Creelman, Ken Grant. and Peter Killeen for their helpful reviews and Mari Jones, Jean Lorenceau, and Steve McAdams for their comments on previous versions of this manuscript. Correspondence should be addressed to C. Drak...

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We investigate how the presence of performance microstructure (small variations in timing, intensity, and articulation) influences listeners' perception of musical excerpts, by measuring the way in which listeners synchronize with the excerpts. Musicians and nonmusicians tapped on a drum in synchrony with six musical excerpts, each presented in three versions: mechanical (synthesized from the score, without microstructure), accented (mechanical, with intensity accents), and expressive (performed by a concert pianist, with all types of microstructure). Participants' synchronizations with these excerpts were characterized in terms of three processes described in Mari Riess Jones's Dynamic Attending Theory: attunement (ease of synchronization), use of a referent level (spontaneous synchronization rate), and focal attending (range of synchronization levels). As predicted by beat induction models, synchronization was better with the temporally regular mechanical and accented versions than with the expressive versions. However, synchronization with expressive versions occurred at higher (slower) levels, within a narrower range of synchronization levels, and corresponded more frequently to the theoretically correct metrical hierarchy. We conclude that performance microstructure transmits a particular metrical interpretation to the listener and enables the perceptual organization of events over longer time spans. Compared with nonmusicians, musicians synchronized more accurately (heightened attunement), tapped more slowly (slower referent level), and used a wider range of hierarchical levels when instructed (enhanced focal attending), more often corresponding to the theoretically correct metrical hierarchy. We conclude that musicians perceptually organize events over longer time spans and have a more complete hierarchical representation of the music than do nonmusicians.

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The phenomenon commonly known as subjective accenting refers to the fact that identical sound events within purely isochronous sequences are perceived as unequal. Although subjective accenting has been extensively explored using behavioral methods, no physiological evidence has ever been provided for it. In the present study, we tested the notion that these perceived irregularities are related to the dynamic deployment of attention. We disrupted listeners' expectancies in different positions of auditory equitone sequences and measured their responses through brain event-related potentials (ERPs). Significant differences in a late parietal (P3-like) ERP component were found between the responses elicited on odd-numbered versus even-numbered positions, suggesting that a default binary metric structure was perceived. Our findings indicate that this phenomenon has a rather cognitive, attention-dependent origin, partly affected by musical expertise.

Perceptual studies suggest that the segmentation of a musical sequence is influenced by three accent structures: rhythmic grouping, melodic, and metric accent structures. We investigate whether performers emphasize these types of accents with systematic performance variations (intensity, interonset timing, and articulation). In three experiments, skilled pianists performed sequences of various musical complexities: simple sequences containing only one accent structure (Experiment 1), more complex sequences containing coinciding or conflicting accent structures (Experiment 2), and a concert pianist's performance of a sonata containing coinciding and conflicting accent structures (Experiment 3). In all three musical contexts, similar systematic performance variations were observed in relation to each type of accent. Variations corresponding to rhythmic grouping accents were most consistent across musical contexts and dominated when the accent structures conflicted. These findings suggest perceptual correlates for the accent structures in music performance that may facilitate listeners' segmentation of musical sequences.

Many sequential events, musical rhythms in particular, can be described by a hierarchical structure, with lower order events recursively combining to form higher levels. This study investigated factors influencing the ease of reproduction of short musical rhythms that reflect various organizational principles. For adults and children, reproduction was better for rhythms with the following characteristics: (1) binary rather than ternary subdivision, (2) two rather than three different durations, (3) the ability to be segmented into two shorter rhythms of identical duration, and (4) intensity accents on important hierarchical positions. These findings suggest that a prototypical temporal structure--that is, a regular beat with binary subdivisions--is functional in childhood. The ability to process complex hierarchical structure appeared to be influenced more by musical training than by passive acculturation.