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.

Music is characterized by acoustical forms that are predictive of its behavioral functions. For example, adult listeners accurately identify unfamiliar lullabies as infant-directed on the basis of their musical features alone. This property could reflect a function of listeners' experiences, the basic design of the human mind, or both. Here, we show that American infants (= 144) relax in response to 8 unfamiliar foreign lullabies, relative to matched non-lullaby songs from other foreign societies, as indexed by heart rate, pupillometry, and electrodermal activity. They do so consistently throughout the first year of life, suggesting the response is not a function of their musical experiences, which are limited relative to those of adults. The infants' parents overwhelmingly chose lullabies as the songs that they themselves would use to calm their fussy infant, despite their unfamiliarity. Together, these findings suggest that infants are predisposed to respond to universal features of lullabies. Music is a human universal 1-3 that appears often in the lives of infants and their families 4-8. Infants demonstrate a remarkable variety of responses to music as they develop: in the first few days of life, newborns remember melodies heard in the womb 9 ; distinguish consonant from dissonant intervals 10 ; and detect musical beats 11. Older infants differentiate synchronous movement from asynchronous movement in response to music 12 ; become attuned to the rhythms of their native culture's music by their first birthday 13 ; garner social information from the songs they hear 14,15 ; and recall music in impressive detail 16,17 after long delays 14. Why are infants so interested in music? One possibility centers on the dynamics of parent-offspring interactions. Relative to other animals, human infants are helpless; to survive, they rely on resources provided by parents and alloparents 18. Such resources, whether material (like food) or not (like attention) constitute parental investment 19. Human parental investment is routinely provided to infants in response to their elicitations, which often take the form of fussiness and crying 20. Infant-directed songs may credibly signal parental attention to infants, conveying information to infants that an adult is nearby, attending to them, and keeping them safe 21,22. Singing indicates the location, proximity, and orientation of the singer (even when the singer is not visible, as at night); and it is also costly, in that the singer could be expending their energy on some other activity. Because parental attention is a key resource for helpless infants, they likely are predisposed to attend to signals of it: infants should be particularly interested in and reassured by vocal music with features suggesting that it is directed toward them. Studies of people with genomic imprinting disorders provide a unique test of this hypothesis because these disorders are characterized by divergent behaviors related to parental investment 23,24. For example, infants with Prader-Willi syndrome eli...

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...

Music is characterized by acoustical forms that are predictive of its behavioral functions. For example, adult listeners accurately identify unfamiliar lullabies as infant-directed on the basis of their musical features alone. This property could reflect a function of listeners’ experiences, the basic design of the human mind, or both. Here, we show that American infants (N = 144) relax in response to 8 unfamiliar foreign lullabies, relative to matched non-lullaby songs from other foreign societies, as indexed by heart rate, pupillometry, and electrodermal activity. They do so consistently throughout the first year of life, suggesting the response is not a function of their musical experiences, which are limited relative to those of adults. The infants’ parents overwhelmingly chose lullabies as the songs that they themselves would use to calm their fussy infant, despite their unfamiliarity. Together, these findings suggest that infants are predisposed to respond to universal features of lullabies.

The temporal organization of sounds used in social contexts can provide information about signal function and evoke varying responses in listeners (receivers). For example, music is a universal and learned human behavior that is characterized by different rhythms and tempos that can evoke disparate responses in listeners. Similarly, birdsong is a social behavior in songbirds that is learned during critical periods in development and used to evoke physiological and behavioral responses in receivers. Recent investigations have begun to reveal the breadth of universal patterns in birdsong and their similarities to common patterns in speech and music, but relatively little is known about the degree to which biological predispositions and developmental experiences interact to shape the temporal patterning of birdsong. Here, we investigated how biological predispositions modulate the acquisition and production of an important temporal feature of birdsong, namely the duration of silent pauses (“gaps”) between vocal elements (“syllables”). Through analyses of semi‐naturally raised and experimentally tutored zebra finches, we observed that juvenile zebra finches imitate the durations of the silent gaps in their tutor's song. Further, when juveniles were experimentally tutored with stimuli containing a wide range of gap durations, we observed biases in the prevalence and stereotypy of gap durations. Together, these studies demonstrate how biological predispositions and developmental experiences differently affect distinct temporal features of birdsong and highlight similarities in developmental plasticity across birdsong, speech, and music.Research Highlights The temporal organization of learned acoustic patterns can be similar across human cultures and across species, suggesting biological predispositions in acquisition. We studied how biological predispositions and developmental experiences affect an important temporal feature of birdsong, namely the duration of silent intervals between vocal elements (“gaps”). Semi‐naturally and experimentally tutored zebra finches imitated the durations of gaps in their tutor's song and displayed some biases in the learning and production of gap durations and in gap variability. These findings in the zebra finch provide parallels with the acquisition of temporal features of speech and music in humans.