Goldstein_et_al_2003 - Social interaction shapes babbling:...

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Social interaction shapes babbling: Testing parallels between birdsong and speech Michael H. Goldstein* ² , Andrew P. King , and Meredith J. West *Department of Psychology, Franklin & Marshall College, P.O. Box 3003, Lancaster, PA 17604; and Department of Psychology, Indiana University, 1101 East 10th Street, Bloomington, IN 47405 Communicated by Peter Marler, University of California, Davis, CA, April 24, 2003 (received for review August 22, 2002) Birdsong is considered a model of human speech development at behavioral and neural levels. Few direct tests of the proposed analogs exist, however. Here we test a mechanism of phonological development in human infants that is based on social shaping, a selective learning process first documented in songbirds. By ma- nipulating mothers’ reactions to their 8-month-old infants’ vocal- izations, we demonstrate that phonological features of babbling are sensitive to nonimitative social stimulation. Contingent, but not noncontingent, maternal behavior facilitates more complex and mature vocal behavior. Changes in vocalizations persist after the manipulation. The data show that human infants use social feedback, facilitating immediate transitions in vocal behavior. Social interaction creates rapid shifts to developmentally more advanced sounds. These transitions mirror the normal develop- ment of speech, supporting the predictions of the avian social shaping model. These data provide strong support for a parallel in function between vocal precursors of songbirds and infants. Be- cause imitation is usually considered the mechanism for vocal learning in both taxa, the findings introduce social shaping as a general process underlying the development of speech and song. B irdsong is often considered a model for speech development in humans (1–4). The early vocalizations of both taxa are immature and unstable when compared with adult forms. In addition, the vocalizations of both birds and babies develop by a combination of selective attrition and learning of novel forms. Young songbirds initially produce subsong, characterized by high variability in structure and timing (5). The acoustic and motor patterns of subsong are qualitatively distinct from those of adult forms. It is sung at low amplitude and includes elements that will not be present in adult song. This early phase is followed by a period of plastic song, which contains notes and whistles char- acteristic of adult song, but these elements are poorly articulated and are not sung in a stable order. During plastic song, some elements are repeated and retained whereas others are dropped from the repertoire. Over time, plastic song gradually reduces into crystallized song, comprising a limited set of species-typical song features. The structural and temporal variations of subsong and plastic
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Goldstein_et_al_2003 - Social interaction shapes babbling:...

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