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The study of bilingualism has often focused on two contradictory possibilities: that the learning of two languages may produce deficits of performance in each language by comparison with performance of monolingual individuals, or on the contrary, that the learning of two languages may produce linguistic or cognitive advantages with regard to the monolingual learning experience. The work reported here addressed the possibility that the very early bilingual experience of infancy may affect the unfolding of vocal precursors to speech. The results of longitudinal research with 73 infants aged 0;4 to 1;6 in monolingual and bilingual environments provided no support for either a bilingual deficit hypothesis nor for its opposite, a bilingual advantage hypothesis. Infants reared in bilingual and monolingual environments manifested similar ages of onset for canonical babbling (production of well-formed syllables), an event known to be fundamentally related to speech development. Further, quantitative measures of vocal performance (proportion of usage of well-formed syllables and vowel-like sounds) showed additional similarities between monolingual and bilingual infants. The similarities applied to infants of middle and low socio-economic status and to infants that were born at term or prematurely. The results suggest that vocal development in the first year of life is robust with respect to conditions of rearing. The biological foundations of speech appear to be such as to resist modifications in the natural schedule of vocal development.

Final Syllable Lengthening (FSL) has been extensively examined in infant vocalizations in order to determine whether its basis is biological or learned. Findings suggest there may be a U-shaped developmental trajectory for FSL. The present study sought to verify this pattern and to determine whether vocal maturity and deafness influence FSL. Eight normally hearing infants, aged 0;3 to 1;0, and eight deaf infants, aged 0;8 to 4;0, were examined at three levels of prelinguistic vocal development: precanonical, canonical, and postcanonical. FSL was found at all three levels suggesting a biological basis for this phenomenon. Individual variability was, however, considerable. Reduction in the magnitude of FSL across the three sessions provided some support for a downward trend for FSL in infancy. Findings further indicated that auditory deprivation can significantly affect temporal aspects of infant speech production.

The production of voice-onset time (VOT) was studied in a group of Spanish- and English-learning subjects at 1 and 2 years of age. Voice-onset time of initial stop consonants from canonical utterances was measured oscillographically. At one year no significant difference in VOT production was found between Spanish and English learners at any place of articulation. Mean VOT values for infants fell in the short lag range. By two years, four of the seven children in the English group and four of the children in the Spanish group showed significant evidence of having acquired the VOT distinction in stop consonants appropriate for their native language.

Two experiments tested the semantic feature hypothesis with children younger than those previously studied. Two predictions were considered: (1) that order of acquisition of dimensional adjective pairs corresponds with their order of semantic generality; (2) that at an early stage of development, the marked members of dimensional pairs are interpreted as having the meaning of the unmarked members. In general, both experiments supported prediction one but failed to support prediction two. In Experiment II, a possible confounding variable (non-semantic size preference) was examined. Two general conclusions were reached: (1) that it is difficult to rule out semantically irrelevant factors (size preference) from experiments investigating the learning of dimensional adjectives; and (2) that refinements of the semantic feature theory may be necessary to accommodate individual differences (which may be age dependent) in strategies for learning dimensional adjectives.

The possibility that early linguistic experience affects infant speech perception was investigated in a cross-linguistic study with naturally produced speech stimuli. Using the Visually Reinforced Infant Speech Discrimination paradigm, three contrasts were presented to Spanish-and English-learning infants 6–8 months of age. Both groups of infants showed statistically significant discrimination of two contrasts, English and Czech. Only the Spanish-learning infants provided evidence of discrimination of the Spanish contrast. The groups discriminated the English contrast at similarly high levels, but the Spanish-learning infants showed significantly higher performance than the English on both the Spanish and the Czech contrast. The results indicate that early experience does affect early discrimination, and further (since the stimuli were natural) that the effect may be of practical consequence in language learning.