Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2013 Apr 16;110(16):6318-23.
doi: 10.1073/pnas.1300337110. Epub 2013 Apr 2.

Functional flexibility of infant vocalization and the emergence of language

D Kimbrough Oller  1 , Eugene H Buder, Heather L Ramsdell, Anne S Warlaumont, Lesya Chorna, Roger Bakeman
Affiliations

Functional flexibility of infant vocalization and the emergence of language

D Kimbrough Oller et al. Proc Natl Acad Sci U S A. .

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 species-specific 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.

PubMed Disclaimer

Conflict of interest statement

Conflict of interest statement: The authors declare no conflict of interest (such as defined by PNAS policy).

Figures

Fig. 1.
Fig. 1.
Frequency and proportion of occurrence of each vocal type. Data on nine infants in the first year of life were collapsed across three observation periods. The emotional signals (cry and laughter) showed (A) proportions and (B) frequencies of occurrence with cries displaying overwhelmingly negative and laughs positive facial affect. In contrast, the protophones (squeals, vocants, and growls), presumed to be precursors to speech, were all used flexibly, showing primarily neutral facial affect and also presenting numerous cases of both positive and negative affect. For description of the vocal types, see SI Appendix, Supporting Background. Briefly, squeals are produced with very high pitch for the individual infant, vocants with midrange pitch, and growls with harsh voice quality or low pitch. Positive, negative, and neutral facial affect correspond roughly to smiling/grinning, frowning/grimacing, and neither (see also SI Appendix, Supporting Methods: Coding training and coding procedures for both vocal type and facial affect).
Fig. 2.
Fig. 2.
Quantitative illustration of the distinction in functional flexibility between protophones and cry/laugh. Key patterns for protophones at all infant ages showed flexibility, as is required in speech, whereas cry and laugh showed consistent affect expression, as occurs in affectively charged vocalizations of other primates. (A) Positivity in facial affect expression: Protophones showed (i) far more positivity than cry but (ii) far less than laugh. (B) Neutrality in facial affect expression: Protophones were (iii) far more neutral than either cry or (iv) laugh. (C) Negativity in facial affect expression: Protophones were (v) far less negative than cry and were (vi) far more negative than laugh. Thus, the results (supported strongly by odds ratios; see SI Appendix, Supporting Results: Odds ratio analyses and SI Appendix, Supporting Tables 2–3) illustrate that in the first year, human infant protophones show the kind of flexibility in affect expression that is required for speech; such flexibility has not been reported as yet in nonhuman primate vocalizations at any age.
Fig. 3.
Fig. 3.
Effects of facial affect on illocutionary force and perlocutionary effect of infant protophones. (A) Distribution of protophones with varying facial affect across three illocutionary groupings by proportion. (i) More than 80% of protophones with positive facial affect were coded as having illocutionary forces supporting protoconversation with the caregiver (e.g., initiating conversation, continuing conversation, expressing joy or exultation, imitating, and so on), whereas (ii) protophones with neutral affect most often were coded as indeterminate (e.g., they were not directed to the caregiver, often being interpreted as vocal play), and (iii) those with negative affect were coded 90% as complaints or pleas for help. (B) Distribution of protophones with varying facial affect across three illocutionary groupings by frequency of occurrence. (C) Distribution of protophones with varying facial affect across three perlocutionary groupings by proportion. (i) The vast majority (88%) of protophones with positive facial affect produced caregiver reactions encouraging protoconversation (e.g., calling to the infant, continuing conversation, praising, expressing joyful surprise, and so on), whereas (ii) those with neutral affect yielded more than twice as many encouragements as attempts to change the situation, along with many responses coded as ambiguous, and (iii) 75% of those with negative affect were responded to by explicit talk about what might be wrong with the baby or by attempts to change the situation or interaction (picking the baby up, attempting to distract him/her, soothing, and so on). (D) Distribution of protophones with varying facial affect across three perlocutionary groupings in frequency of occurrence. For details see SI Appendix, Supporting Methods: Illocutionary force coding and perlocutionary force coding and SI Appendix, Supporting Results: The role of affect expression in the functional interpretation of infant protophones, with SI Appendix Supporting Figs. 9 and 10.
Fig. 4.
Fig. 4.
Observed and expected counts for each facial affect type, separately by protophone. Comparison of observed and expected counts, aggregated across observations of nine infants during the first year of life, illustrates that functional flexibility does not indicate lack of differentiation but instead indicates systematic flexibility in affect expression by infants across the three protophones, the presumed precursors to speech. Darker right-hand bars indicate observed counts of positive, neutral, and negative facial affect for each protophone. Lighter left-hand bars indicate counts expected if facial affect were independent of protophone type. Insets with a light gray background show adjusted residual values (some positive, some negative) corresponding to counts significantly greater than or less than expected (P < 0.05). (A) Compared with the counts generated by the independence model, vocants were significantly more likely to be neutral (9.1 SD more than expected) and were significantly less likely to be either positive or negative. (B) In contrast, squeals were more likely than expected to be both positive and negative and were less likely to be neutral, and (C) growls were more likely to be positive than expected by chance. These outcomes illustrate that although protophones manifest functional flexibility (all were predominantly neutral, and all also showed substantial numbers of cases of positive and negative expression), they were used affectively in systematically different ways with respect to each other. We reason that the ability to produce the same vocalization with differing affective character is a necessary foundation for language, but a random distribution of facial affect with respect to vocalizations would constitute a restriction on the very flexibility that is needed for adaptation of vocal expression to specific contexts and communicative needs. Thus, the systematic patterns in the data are consistent with the idea that infants control affective expression in protophones rather than producing facial affect in random association with the protophones.
Fig. 5.
Fig. 5.
Individual differences in facial affect expression through the protophones. Log-linear analysis of 3 × 3 tables for frequency of occurrence of protophones by facial affect (see text and SI Appendix, Supporting Results: Log-linear analyses) revealed significant differences among the nine infants. At the same time, log-linear analysis of 2 × 3 tables for cry and laugh revealed no such individual differences (because cries were negative and laughs positive for all infants who produced them; see SI Appendix, Supporting Table 4). This figure provides a quantitative illustration of individual differences in patterns of functional flexibility across infants for the protophones based on Contingency Table Analysis. Each square represents one of the nine infants. Cells within squares represent associations of protophones with facial affect types. Darker cells indicate positive adjusted residuals (observed counts greater than expected); a plus indicates an adjusted residual greater than +1.96. Lighter cells indicate negative adjusted residuals (observed counts less than expected); a minus indicates an adjusted residual less than −1.96. The figure indicates that each of the nine infants showed a unique pattern of adjusted residuals. These significant individual differences suggest that the functional flexibility of infants is not the result of an innate tendency specifying use of protophones in terms of affect (as appears to occur with cry and laugh) but rather that infants possess an inclination to explore vocalization in protophones and to be expressive with them, each infant thus developing a personalized path toward a capacity for speech (see also SI Appendix, Supporting Results: Additional contingency table analyses).
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Chomsky N. Language and Thought. Wakefield, RI: Moyer Bell; 1993.
    1. Christiansen MH, Dale R. In: The role of learning and development in language evolution: A connectionist perspective. The Evolution of Communication Systems: A Comparative Approach. Oller DK, Griebel U, editors. Cambridge, MA: MIT Press; 2004.
    1. Pinker S. The Language Instinct. New York: Harper Perennial; 1994. p. 494.
    1. Niyogi P. The Computational Nature of Language Learning and Evolution. Cambridge, MA: MIT Press; 2006.
    1. Bickerton D. Language and Species. Chicago: Univ of Chicago Press; 1990.

Publication types