Detecting perturbations in polyrhythms: effects 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 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.