Exploring the perception of phonemic vowel length contrasts: evidence from infants and adults

Infants tune into native sound categories as early as in their first year, but in order to understand the language, they must become aware of the phonemic function of the sounds as well. A number of studies have investigated infants’ phonemic awareness of consonant and vowel quality contrasts at the early word learning stage, however, there has been no research directly examining infants’ early understanding of phonemic vowel length contrasts in a language where vowel duration can signal word meaning alone, such as Japanese, Finnish, Arabic, and even Australian English. Since vowels can also vary in duration as a function of prosodic context, an investigation of how phonemic vowel length is acquired is essential for understanding early phonological development more generally. This thesis therefore focuses on the perception of phonemic vowel length contrasts. It is comprised of three studies, targeting three populations respectively: Japanese infants, Australian English infants, and bi-dialectal Australian English adults. The first study revealed that Japanese infants have developed awareness of phonemic vowel length contrasts by 18 months, which is probably related to the systematicity and robustness of the contrasts manifesting in the language. The second study showed that Australian English-learning infants have become sensitive to mispronunciations of phonemic vowel length by at least 24 months, possibly earlier than often thought. The third study indicated that native Australian English adults, who have had early exposure to another English dialect that does not have contrastive vowel length, might have established more flexible phonological categories of phonemic vowel length, compared to those without this early exposure. Taken together, the findings of this thesis suggest that the development of phonemic vowel length contrasts is tied to the systematicity and stability of these contrasts in the language being learned.