Functional flexibility of infant vocalization and the emergence of language

Abstract

We report on the emergence of functional flexibility in vocalizations of human infants. This vastly underappreciated capability becomes apparent when prelinguistic vocalizations express a full range of emotional content-positive, neutral, and negative. The data show that at least three types of infant vocalizations (squeals, vowel-like sounds, and growls) occur with this full range of expression by 3-4 mo of age. In contrast, infant cry and laughter, which are speciesspecific signals apparently homologous to vocal calls in other primates, show functional stability, with cry overwhelmingly expressing negative and laughter positive emotional states. Functional flexibility is a sine qua non in spoken language, because all words or sentences can be produced as expressions of varying emotional states and because learning conventional "meanings" requires the ability to produce sounds that are free of any predetermined function. Functional flexibility is a defining characteristic of language, and empirically it appears before syntax, word learning, and even earlier-developing features presumed to be critical to language (e.g., joint attention, syllable imitation, and canonical babbling). The appearance of functional flexibility early in the first year of human life is a critical step in the development of vocal language and may have been a critical step in the evolution of human language, preceding protosyntax and even primitive single words. Such flexible affect expression of vocalizations has not yet been reported for any nonhuman primate but if found to occur would suggest deep roots for functional flexibility of vocalization in our primate heritage.esearch on evolution and development of language has been devoted primarily to syntax, the uniquely human capacity to produce well-formed complex sentences (1-4). Additional work has targeted the emergence of simpler communicative structures and thus has shifted attention back in evolutionary time to an earlier possible split of hominins from the primate background. For example, research has considered the presumably earlier evolution of simple sentences or "protosyntax" (5). Other work influenced by recent trends in evolutionary developmental biology (evo-devo) (6, 7) has focused on infrastructure for language, invoking capabilities logically more foundational even than protosyntax and presumably moving the communicative differentiation of hominins from other primates much farther back. For example, symbolic expression in single words beginning in modern human development at about 12 mo is a precursor to even the simplest syntax (8). Moving the evolutionary focus even farther back in time, joint attention-infant pointing with gaze alternation between an object and an adult interactor, occurring before the end of the first year-is deemed a critical precursor to words (9). Similarly, canonical babbling (onset at about 7 mo) is a crucial step toward verbal vocabulary because development and imitation of canonical syllables (e.g., "baba") is required for extensive word lear...

Biology, culture, evolution and the cognitive nature of sound systems

“…This aspect of learning language is abstracted away from in much of the research reviewed here, and learning has been considered as a monolithic, abstract behavior. Oller et al (2013) provide evidence that this may not be the whole story and language learning may be based on a series of evolutionarily older developmental processes. This perspective may help better elucidate the precise mechanisms that have undergone selective pressure related to speech and language.…”

Developmental changes of cognitive vocal control in monkeys

“…It suggests that one important aspect of flexible communication is grounded in the primate lineage and could be exploited during the emergence of functional flexibility of prelinguistic vocalizations of human infants (Oller et al, 2013). As a phylogenetic pre-adaptation, volitional control of vocal utterances would be a crucial subcomponent in the complex multi-component system 'human language' and instrumental for all higher level linguistic characteristics emerging in human development, such as semantic compositionality or the grasp and mastering of a symbol system (Deacon, 1997;Nieder, 2009).…”

How social learning adds up to a culture: from birdsong to human public opinion

“…We suspect that the developmental transition to categorical signal tends to be weaker in vocal-learning mammals. Even in human, where there is a clear developmental transition from vocal babbling to categorical speech, acoustically the signal remains surprisingly variable (Oller et al, 2013), which is why automatic speech recognition is so difficult. Songbirds are therefore unique in their strong developmental transition from highly variable to highly stereotyped vocalization ( Fig.…”