Birdsong fails to support object categorization in human infants

Recent evidence reveals a precocious link between language and cognition in human infants: listening to their native language supports infants’ core cognitive processes, including object categorization, and does so in a way that other acoustic signals (e.g., time-reversed speech; sine-wave tone sequences) do not. Moreover, language is not the only signal that confers this cognitive advantage: listening to vocalizations of non-human primates also supports object categorization in 3- and 4-month-olds. Here, we move beyond primate vocalizations to clarify the breadth of acoustic signals that promote infant cognition. We ask whether listening to birdsong, another naturally produced animal vocalization, also supports object categorization in 3- and 4-month-old infants. We report that listening to zebra finch song failed to confer a cognitive advantage. This outcome brings us closer to identifying a boundary condition on the range of non-linguistic acoustic signals that initially support infant cognition.

A definition of song from human music universals observed in primate calls

Musical behavior is likely as old as our species with song originating as early as 60 million years ago in the primate order. Early singing likely evolved into the music of modern humans via multiple selective events, but efforts to disentangle these influences have been stifled by challenges to precisely define this behavior in a broadly applicable way. Detailed here is a method to quantify the elaborateness of acoustic displays using published spectrograms (n=832 calls) culled from the literature on primate vocalizations. Each spectrogram was scored by five trained analysts via visual assessments along six musically relevant acoustic parameters:tone, interval, transposition, repetition, rhythm, andsyllabic variation. Principal Components Analysis (PCA) was used to reduce this multivariate assessment into a simplified measure of musical elaborateness. The resulting “acoustic reappearance diversity” index simultaneously captures syllabic variation and spectral/temporal redundancy in a single continuous variable. The potential utility of this index is demonstrated by applying it to several social and habitat-based theories of acoustic display origins. Our results confirm that primate species living in small, monogamous groups have song-like calls, while forest habitat had a less pronounced association.

Flexible usage and social function in primate vocalizations

Vocalizations are a pervasive feature of nonhuman primate social life, yet we know surprisingly little about their function. We review studies supporting the hypothesis that many primate vocalizations function to facilitate social interactions by reducing uncertainty about the signaler’s intentions and likely behavior. Such interactions help to establish and maintain the social bonds that increase reproductive success. Compared with humans, songbirds, and a few other mammals, primates have small vocal repertoires that show little acoustic modification during development. However, their ability to modify call usage is extensive and tuned to variation in the social context, including the historical relationship between caller and listener and the caller’s assessment of how a listener is likely to respond. We suggest parallels between the decision to vocalize and neurophysiological studies of other, nonvocal social decisions between interacting monkeys. The selective factors driving the early stages of language evolution may have come from the need to make decisions about when and how to call within the context of social challenges.

Very young infants' responses to human and nonhuman primate vocalizations

Recent evidence from very young human infants' responses to human and nonhuman primate vocalizations offers new insights – and brings new questions – to the forefront for those who seek to integrate primate-general and human-specific mechanisms of acoustic communication with theories of language acquisition.