Abstract
Human infant vocalization is viewed as a critical foundation for vocal learning and language. All apes share distress sounds (shrieks and cries) and laughter. Another vocal type, speech-like sounds, common in human infants, is rare but not absent in other apes. These three vocal types form a basis for especially informative cross-species comparisons. To make such comparisons possible we need empirical research documenting the frequency of occurrence of all three. The present work provides a comprehensive portrayal of these three vocal types in the human infant from longitudinal research in various circumstances of recording. Recently, the predominant vocalizations of the human infant have been shown to be speech-like sounds, or ‘protophones’, including both canonical and non-canonical babbling. The research shows that protophones outnumber cries by a factor of at least five based on data from random-sampling of all-day recordings across the first year. The present work expands on the prior reports, showing the protophones vastly outnumber both cry and laughter in both all-day and laboratory recordings in various circumstances. The data provide new evidence of the predominance of protophones in the infant vocal landscape and illuminate their role in human vocal learning and the origin of language.This article is part of the theme issue ‘Vocal learning in animals and humans’.
Highlights
The pursuit of roots for vocal learning in various taxa is hoped to provide perspective on how human vocalization evolved and eventually provided a basis for language
We focus on three broad categories of sounds occurring in vocal communication of both human and other ape infants: (i) cries/screams, the salient distress sounds, (ii) laughs, the salient sounds of playfulness and positively valenced social connection, and (iii) other communicative or potentially communicative vocalizations, used in a variety of social and/or non-social circumstances, often at low intensity
This third category encompasses the speech-like sounds of human infancy, the ‘protophones’, including both non-canonical and canonical babbling
Summary
The pursuit of roots for vocal learning in various taxa is hoped to provide perspective on how human vocalization evolved and eventually provided a basis for language. The predominantly endogenous driving of the protophones suggests that learning of vocal production categories during the first year may be primarily a result of self-organization, a consequence of infant exploration rather than of learning through input from caregivers. There has been considerable emphasis in language development research on acquisition by copying, with caregiver interaction and modelling driving imitation [24,25], a process whereby infants are presumed to absorb the native language’s speech categories. The present paper adds converging empirical data to the body of information reviewed above on the rate of occurrence of the three broad vocal categories (cries, laughs, protophones) of the human infant. For the first time provide longitudinal perspective across the first year for rate of occurrence of all three broad vocal types in human infants; 2. The results will provide a more substantial frame of reference for more extensive planned quantitative comparisons across species in the near future
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