Humans often produce vocalizations for infants that differ from vocalizations for adults. Is this property common across societies? The forms of infant-directed vocalizations may be shaped by their function in parent-infant communication. If so, infant-directed song and speech should be differentiable from adult-directed song and speech on the basis of their acoustic features, and this property should be relatively invariant across cultures. To test this hypothesis, we built a corpus of 1,614 recordings of infant-and adult-directed singing and speech produced by 411 people living in 21 urban, rural, and small-scale societies. We studied the corpus in a massive online experiment and in a series of acoustic analyses. Naïve listeners (N = 13,218) reliably identified infant-directed vocalizations as infant-directed, and adult-directed speech (but not songs) as adult-directed, at rates far higher than chance. Ratings of infant-directed song were the most accurate and the most consistent across all societies; infant-directed speech was accurately identified on average, but inconsistently across societies. To determine the mechanisms underlying these results, we extracted many acoustic features from each recording and identified those that most reliably characterize infant-directed song and speech across cultures, via preregistered exploratory-confirmatory analyses and machine classification. The features distinguishing infant-and adult-directed song and speech concerned pitch, rhythmic, phonetic, and timbral attributes; a hypothesis-free classifier with cross-validation across societies reliably identified all vocalization types, with highest accuracy for infant-directed song. Last, we isolated 12 acoustic features that were predictive of perceived infant-directedness; of these, two pitch attributes (median F0 and its variability) were by far the most explanatory. These findings demonstrate cross-cultural regularities in infant-directed vocalizations that are suggestive of universality; moreover, infant-directed song appears to be more cross-culturally stereotyped than infant-directed speech, informing hypotheses of the functions and evolution of both.

Humans often produce vocalizations for infants that differ from vocalizations for adults. Is this property common across societies? The forms of infant-directed vocalizations may be shaped by their function in parent-infant communication. If so, infant-directed song and speech should be differentiable from adult-directed song and speech on the basis of their acoustic features, and this property should be relatively invariant across cultures. To test this hypothesis, we built a corpus of 1,614 recordings of infant-and adult-directed singing and speech produced by 411 people living in 21 urban, rural, and small-scale societies. We studied the corpus in a massive online experiment and in a series of acoustic analyses. Naïve listeners (N = 13,218) reliably identified infant-directed vocalizations as infant-directed, and adult-directed speech (but not songs) as adult-directed, at rates far higher than chance. Ratings of infant-directed song were the most accurate and the most consistent across all societies; infant-directed speech was accurately identified on average, but inconsistently across societies. To determine the mechanisms underlying these results, we extracted many acoustic features from each recording and identified those that most reliably characterize infant-directed song and speech across cultures, via preregistered exploratory-confirmatory analyses and machine classification. The features distinguishing infant-and adult-directed song and speech concerned pitch, rhythmic, phonetic, and timbral attributes; a hypothesis-free classifier with cross-validation across societies reliably identified all vocalization types, with highest accuracy for infant-directed song. Last, we isolated 12 acoustic features that were predictive of perceived infant-directedness; of these, two pitch attributes (median F0 and its variability) were by far the most explanatory. These findings demonstrate cross-cultural regularities in infant-directed vocalizations that are suggestive of universality; moreover, infant-directed song appears to be more cross-culturally stereotyped than infant-directed speech, informing hypotheses of the functions and evolution of both.The forms of many animal signals are shaped by their functions, a link arising from production-and reception-2 related rules that help to maintain reliable signal detection within and across species 1-6 . This is especially 3 true of vocal signals, where form-function links have been demonstrated across many species, including 4 nonhuman primates 3 , meerkats 7 , grackles 8 , frogs 9 , and fish 10 . 5The link between form and function in vocalizations is also evident from listeners' behavior. For example, 6 humans 11 , red deer 12 , and canines 13 reliably detect the intentions of heterospecific signalers on the basis of 7 the sounds of their signals. A classic demonstration of this fact is the ability of some species to eavesdrop 8 on the alarm signals of other species, whether or not their own species has an extended vocal repertoire 14,15 . 9 In humans, an area of...

The hierarchical organization of speech rhythm into meter putatively confers cognitive affordances for perception, memory, and motor coordination. Meter also aligns with phrasal structure in systematic ways. In this paper, we show that this alignment affects the robustness of syntactic comprehension and discuss possible underlying mechanisms. In two experiments, we manipulated meter-syntax alignment while sentences with relative clause structures were either read as text (experiment 1, n = 40) or listened to as speech (experiment 2, n = 40). In experiment 2, we also measured the stability with which participants could tap in time with the metrical accents in the sentences they were comprehending. In addition to making more mistakes, sensorimotor synchronization was disrupted when syntactic cues clashed with the metrical context. We suggest that this reflects a tight coordination of top-down linguistic knowledge with the sensorimotor system to optimize comprehension.