Integer Ratio Priors on Musical Rhythm Revealed Cross-culturally by Iterated Reproduction

Abstract

Probability distributions over external states (priors) are essential to the interpretation of sensory signals. Priors for cultural artifacts such as music and language remain largely uncharacterized, but likely constrain cultural transmission, because only those signals with high probability under the prior can be reliably reproduced and communicated. We developed a method to estimate priors for simple rhythms via iterated reproduction of random temporal sequences. Listeners were asked to reproduce random "seed" rhythms; their reproductions were fed back as the stimulus and over time became dominated by internal biases, such that the prior could be estimated by applying the procedure multiple times. We validated that the measured prior was consistent across the modality of reproduction and that it correctly predicted perceptual discrimination. We then measured listeners' priors over the entire space of two- and three-interval rhythms. Priors in US participants showed peaks at rhythms with simple integer ratios and were similar for musicians and non-musicians. An analogous procedure produced qualitatively different results for spoken phrases, indicating some specificity to music. Priors measured in members of a native Amazonian society were distinct from those in US participants but also featured integer ratio peaks. The results do not preclude biological constraints favoring integer ratios, but they suggest that priors on musical rhythm are substantially modulated by experience and may simply reflect the empirical distribution of rhythm that listeners encounter. The proposed method can efficiently map out a high-resolution view of biases that shape transmission and stability of simple reproducible patterns within a culture.

From random to regular: neural constraints on the emergence of isochronous rhythm during cultural transmission

“…The tendency of subjects to equalise, within a tone sequence, the interval durations, as shown in our results, and by behavioural and neurophysiological works (Povel, 1981; Jacoby and McDermott, 2017), could explain this result. When this process iterates, cultural information is progressively transformed or distorted towards rhythmic sets of fewer (one or two) durational categories, i.e.…”

Editorial: The Evolution of Rhythm Cognition: Timing in Music and Speech

“…Along these lines, recent research has focused on the cultural evolution of musical rhythm and perceptual priors (Savage et al, 2015; Trehub, 2015; Hansen et al, 2016; Le Bomin et al, 2016; Ravignani et al, 2016; Fitch, 2017; Jacoby and McDermott, 2017). Statistical universals found in musical rhythms all over the world (Savage et al, 2015) can emerge via the combined effect of human cognitive biases and cultural transmission (Ravignani et al, 2016).…”

“…Statistical universals found in musical rhythms all over the world (Savage et al, 2015) can emerge via the combined effect of human cognitive biases and cultural transmission (Ravignani et al, 2016). Interestingly, these biases seem at least partly modulated by enculturation (Jacoby and McDermott, 2017). …”

The Evolution of Rhythm Cognition: Timing in Music and Speech

“…Statistical universals found in musical rhythms all over the world (Savage et al, 2015) can emerge via the combined effect of human cognitive biases and cultural transmission . Interestingly, these biases seem at least partly modulated by enculturation (Jacoby and McDermott, 2017).…”

“…Along these lines, recent research has focused on the cultural evolution of musical rhythm and perceptual priors (Savage et al, 2015;Trehub, 2015;Hansen et al, 2016;Le Bomin et al, 2016;Fitch, 2017;Jacoby and McDermott, 2017). Statistical universals found in musical rhythms all over the world (Savage et al, 2015) can emerge via the combined effect of human cognitive biases and cultural transmission .…”