Multifractal analysis reveals music-like dynamic structure in songbird rhythms

Abstract

Music is thought to engage its listeners by driving feelings of surprise, tension, and relief through a dynamic mixture of predictable and unpredictable patterns, a property summarized here as “expressiveness”. Birdsong shares with music the goal to attract its listeners’ attention and might use similar strategies to achieve this. We here tested a thrush nightingale’s (Luscinia luscinia) rhythm, as represented by song amplitude envelope (containing information on note timing, duration, and intensity), for evidence of expressiveness. We used multifractal analysis, which is designed to detect in a signal dynamic fluctuations between predictable and unpredictable states on multiple timescales (e.g. notes, subphrases, songs). Results show that rhythm is strongly multifractal, indicating fluctuations between predictable and unpredictable patterns. Moreover, comparing original songs with re-synthesized songs that lack all subtle deviations from the “standard” note envelopes, we find that deviations in note intensity and duration significantly contributed to multifractality. This suggests that birdsong is more dynamic due to subtle note timing patterns, often similar to musical operations like accelerando or crescendo. While different sources of these dynamics are conceivable, this study shows that multi-timescale rhythm fluctuations can be detected in birdsong, paving the path to studying mechanisms and function behind such patterns.

Bringing the Nonlinearity of the Movement System to Gestural Theories of Language Use: Multifractal Structure of Spoken English Supports the Compensation for Coarticulation in Human Speech Perception

“…This point here thus leads us to the strange but tantalizing possibility that the perception of speech enlists the movement system in ways that undermine the seemingly passive reception of speech sounds. Taken together with recent evidence that prosodic sing-song structure of spoken communication supports comprehension (Kelty-Stephen et al, 2018 ) and that song-like vocalizations exhibit multifractality due to nonlinear sources (Roeske et al, 2018 ), present results may extend to long-range speech comprehension.…”

Parallels in the sequential organization of birdsong and human speech

“…For speech, our observations of non-Markovian processes are not unexpected. For birdsong, they explain a variety of complex sequential dynamics observed in prior studies, including long-range organization 20 , music-like structure 19 , renewal processes 17,18 , and multiple timescales of organization 23,29 . In addition, the dominance of Markovian dynamics at shorter timescales may explain why such models have seemed appealing in past descriptions of birdsong 28,30 and language 43 which have relied on relatively small data sets parsed into short bouts (or smaller segments) where the non-Markovian structure is hard to detect (Supplementary Fig.…”

Complexity in Economic and Social Systems: Cryptocurrency Market at around COVID-19

“…Multifractal analysis is one of the most promising methods of studying empirical data representing natural and social systems as it is able to quantify complexity of such systems and express it in a relatively simple way with a small set of associated quantities. It has already been applied in many works to univariate and multivariate data sets from a number of different systems: Physics [ 54 ], biology [ 55 ], chemistry [ 56 ], geophysics [ 57 ], hydrology [ 58 ], atmospheric physics [ 59 ], quantitative linguistics [ 60 ], behavioral sciences [ 61 ], cognitive structures [ 62 ], music [ 63 ], songbird rhythms [ 64 ], physiology [ 65 ], human behaviour [ 66 ], social psychology [ 67 ] and even ecological sciences [ 68 ], but especially financial markets [ 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 ].…”