Phonetic perception becomes native-like by 10 months of age. A potential mechanism of change, distributional learning, affects the perception of 6-8-month-old infants (Maye et al., 2002). However, it was anticipated that perception may be more difficult to change by 10 months of age, after native categories have developed. In fact, some evidence suggests that by this age, the presence of social interaction may be an important element in infants’ phonetic change (Kuhl et al., 2003). The current work advances the hypothesis that infants’ level of attention, which tends to be higher with social interaction, may be a salient factor facilitating phonetic change. Three experiments were designed to test infants’ phonetic plasticity at 10 months, after phonetic categories have formed. A non-social distributional learning paradigm was chosen, and infants’ attention was monitored to probe whether a facilitating role would be revealed. In Experiment 1, 10-month-old English-learning infants heard tokens from along a continuum that is no longer discriminated at this age that formed a distribution suggestive of a category boundary (useful distinction). The results failed to reveal evidence of discrimination, suggesting that the distributional information did not have any effect. A second experiment used slightly different sound tokens, ones that are farther from the typical English pronunciation and are heard less frequently in the language environment. Infants still failed to discriminate the sounds following the learning period. However, a median split revealed that the high attending infants evinced learning. Experiment 3 increased the length of the learning phase to allow all infants to become sufficiently high attending, and revealed phonetic change. Thus, after phonetic categories have formed, attention appears to be important in learning.

Thesis (Ph.D.) -- University of Texas at Arlington, 2008.

Thesis (Ph.D.)--University of Melbourne, Dept. of Electrical and Electronic Engineering and Dept. of Otolaryngology, and the Bionic Ear Institute, 2009. / Typescript. Includes bibliographical references.

Thesis (MScIng)--University of Stellenbosch, 2003. / Includes bibliographical references. Also available via the Internet.

Thesis--M. Phil., University of Hong Kong, 1985.

Thesis (Ph. D.)--University of Washington, 2002. / Vita. Includes bibliographical references (leaves 451-504).

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Phonetic perception becomes native-like by 10 months of age. A potential mechanism of change, distributional learning, affects the perception of 6-8-month-old infants (Maye et al., 2002). However, it was anticipated that perception may be more difficult to change by 10 months of age, after native categories have developed. In fact, some evidence suggests that by this age, the presence of social interaction may be an important element in infants’ phonetic change (Kuhl et al., 2003). The current work advances the hypothesis that infants’ level of attention, which tends to be higher with social interaction, may be a salient factor facilitating phonetic change. Three experiments were designed to test infants’ phonetic plasticity at 10 months, after phonetic categories have formed. A non-social distributional learning paradigm was chosen, and infants’ attention was monitored to probe whether a facilitating role would be revealed. In Experiment 1, 10-month-old English-learning infants heard tokens from along a continuum that is no longer discriminated at this age that formed a distribution suggestive of a category boundary (useful distinction). The results failed to reveal evidence of discrimination, suggesting that the distributional information did not have any effect. A second experiment used slightly different sound tokens, ones that are farther from the typical English pronunciation and are heard less frequently in the language environment. Infants still failed to discriminate the sounds following the learning period. However, a median split revealed that the high attending infants evinced learning. Experiment 3 increased the length of the learning phase to allow all infants to become sufficiently high attending, and revealed phonetic change. Thus, after phonetic categories have formed, attention appears to be important in learning.

Previous research has revealed that very young infants discriminate most speech contrasts with which they are presented whether the contrasts are native or non-native while adults have difficulty discriminating non-native speech contrasts but easily discriminate those contrasts holding meaningful (phonemic) status in their native language. Several studies have shown that this reorganization in phonetic perception from language-general perception to language-specific perception occurs at about 10 to 12 months: infants this age attend only to native phonemic contrasts. It is of interest to determine if exposure to a phonetic variant plays an important role in influencing perception. We know from previous research that absence of exposure does not always lead to a lack of discrimination. This thesis was designed to determine if exposure per se maintains discriminability. To this end English-speaking adults and infants were tested using a phonetic distinction that does not hold phonemic status in English but does occur in English. This distinction involves the phonetic variants [da] and the stop produced following /s/ transcribed as [ta]. When tested in an identification procedure, English-speaking adults identify both [da] and (s)[ta] as members of one English phonemic category (i.e. [da]). When tested in a discrimination procedure and a category change procedure, adults discriminate (s) [ta] from [da] (albeit not as well as would be expected for a native phonemic contrast). With respect to infants, 6- to 8-month-olds discriminate this distinction revealing further support for broad-based phonetic perception at this age. However, 10- to 12-month-old infants do not discriminate, suggesting that the native phonemic status of the contrast (but not exposure) is the important factor in the reorganization. Discussion centers around how these results add to the existing literature and why infants of 10- to 12-months would fail to discriminate a native phonetic distinction.