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.

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.

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. / Arts, Faculty of / Psychology, Department of / Graduate

Any phonological theory needs to encompass an account of acquisition and any account of acquisition must take its place within a general theory of phonology. This thesis aims to ascribe phonological significance to speech perception in infancy, a move impossible unless phonology is defined, as it is here, from both a psycholinguistic and a formal viewpoint as a dedicated pattern-recognition system. Extant results from infant studies are reviewed and aligned with current phonological theory. In particular, such theory characterises phonology as bi-modular, so the acquisition of individual melodic and prosodic modules and their subsequent orientation with respect to one another must constitute three different developmental tasks. This delivers a relatively simple account of the mapping between psychoacoustics and phonology. Perception and pre-existing theories of segmental complexity are related using an original experiment into the perception of vowel-height contrast in Catalan. If infant perception has phonological import, then disparate phonetic reflexes which are predicted as phonologically identical should show parallels in acquisition. General theory argues that the same abstract melodic objects underlie both laryngeal contrasts in stops and lexical tonal contrasts. Earlier studies show that language-specific attunement to stop contrasts has taken place by the age of six months. New tests are now reported, using children of the same age, which demonstrate that infants acquiring Yorùbá, a language which has a three-way contrast for tone, attend more closely to pitch changes within the minimal domain word than do English controls. Further, they only attend to those pitch changes that possess phonological import within that domain in the steady-state language. In this their perception exactly parallels that displayed by adult speakers. Apparent anomalies in the results of these tests are shown to be closely parallelled by phonological asymmetries in the tonology of Yorùbá.

A recent study by Polka, Rvachew, and Molnar (2008) found that 6- to 8-month-old infants do not discriminate a simple native consonant-vowel contrast when familiarized to it in the presence of distraction noise (i.e., recordings of crickets and birds chirping), even when testing was conducted in quiet. Because the distraction noise did not overlap with the phonemes' frequencies, failure to encode the familiarization phoneme could be due more to a disruption in infant attention than to direct masking effects. Given that infants learn speech under natural conditions involving noise and distraction, it is important to identify factors that may 'protect' their speech perception under non-ideal listening conditions. The current study investigated three possible factors: speech register, face information, and speaker gender. Six-month-old infants watched a video of a female speaker producing a native phoneme in either an adult-directed or infant-directed manner accompanied by the same background noise as in Polka et al. (2008). After habituation, infants were tested with alternating trials of the familiar phoneme and a novel phoneme in quiet. Phoneme discrimination was measured by recording infants' heart rate and looking times during familiar and novel trials. Discrimination was poor in infants who viewed a female speaker using adult-directed speech but was significantly improved (as seen in both dependent measures of attention) when the female speaker used infant-directed speech. Results indicate that common factors in the typical environment of infants can promote speech perception abilities in noise. / Master of Science