Detecting perturbations in polyrhythms: eVects of complexity and attentional strategies

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 beneWt 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 diVerent 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 eVect 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. Introduction Perception and production of polyrhythms have been of considerable interest to researchers in music cognition and motor control because of the challenges they pose, and because of the important role they play in the music of various cultures. The polyrhythms studied usually consist of two isochronous sequences (pulse streams) whose periods are related by a non-integer ratio, such as 2:3 or 3:4. The pulse streams are usually distinguished by an auditory feature such as pitch and/or by the limb that is used to produce them (e.g., left or right hand). They typically start in phase, and successive points of coincidence deWne the cycles of the polyrhythm. Polyrhythmic ratios generally stay reasonably simple in this research, otherwise the duration of the cycle would become overly long or the tempo would become overly fast. Moreover, even polyrhythms with relatively simple ratios such as 3:4 or 3:5 can be diYcult to produce and may pose problems for perception as well. Studies of polyrhythm production generally focus on the relative diYculty of execution as a function of ratio complexity, cognitive strategies, and practice. DiYculty increases with ratio complexity (Deutsch, 1983), and more complex polyrhythms tend to be simpliWed in production, especially when the tempo is increased (Peper, Beek, & van Wieringen, 1995). A number of studies have also shown that the isochronous pulse streams of a polyrhythm are easier to execute simultaneously when they are conceptualized as a sequentially integrated rhythmic pattern (Pressing, Summers, & Magill, 1996; Summers, 2002; Summers, Ford, & Todd, 1993a; Summers & Kennedy, 1992; Summers, Rosenbaum, Burns, & Ford, 1993b; Summers, Todd, & Kim, 1993c). Indeed, much of the evidence suggests that integration is the only way to produce polyrhythms accurately. B. C. Fidali · È. Poudrier Yale University, New Haven, CT, USA B. H. Repp (&) Haskins Laboratories, 300 George Street, New Haven, CT 06511-6624, USA e-mail: [email protected]