Abstract
Prosody facilitates perceptual segmentation of the speech stream into a sequence of words and phrases. With regard to speech timing, vowel lengthening is well established as a cue to an upcoming boundary, but listeners' exploitation of consonant lengthening for segmentation has not been systematically tested in the absence of other boundary cues. In a series of artificial language learning experiments, the impact of durational variation in consonants and vowels on listeners' extraction of novel trisyllables was examined. Language streams with systematic lengthening of word-initial consonants were better recalled than both control streams without localized lengthening and streams where word-initial syllable lengthening was confined to the vocalic rhyme. Furthermore, where vowel-consonant sequences were lengthened word-medially, listeners failed to learn the languages effectively. Thus the structural interpretation of lengthening effects depends upon their localization, in this case, a distinction between lengthening of the onset consonant and the vocalic syllable rhyme. This functional division is considered in terms of speech-rate-sensitive predictive mechanisms and listeners' expectations regarding the occurrence of syllable perceptual centres.
Highlights
Variations in suprasegmental dimensions—pitch, duration, loudness—are consistently associated with speech structure at prosodic heads and edges (e.g., Beckman, 1992)
Even in the absence of other segmental and prosodic cues, listeners interpret lengthened onset consonants to indicate the start of a new word, providing a segmentation boost when the timing cues were congruent with statistically defined boundaries
The sequence of lengthened vocalic rhyme and lengthened onset consonant was, in contrast, effective at inhibiting segmentation when it occurred within a statistically defined word and was more effective than either word-medial vowel or consonant lengthening alone. The latter results show the power of combined vocalic rhyme plus onset consonant lengthening cues for defining an intervening boundary, reinforcing previous findings regarding the perceptual significance of preboundary vowel lengthening (e.g., Price et al, 1991; Saffran et al, 1996b)
Summary
Variations in suprasegmental dimensions—pitch, duration, loudness—are consistently associated with speech structure at prosodic heads and edges (e.g., Beckman, 1992). Word-initial consonant lengthening, together with word-final vowel lengthening and other naturally occurring cues to prosodic boundaries, affects the interpretation of ambiguous sequences such as pay per vs paper in English-learning infants as young as ten months (Gout et al, 2004) as well as French adults given parallel stimuli in their native language (Christophe et al, 2004). Listeners have consistently been shown to be able to learn and subsequently recall novel words from a nonsense speech stream when the syllable-to-syllable transitional probabilities within words are higher than those between words (e.g., Saffran et al, 1996a; Saffran et al, 1996b) Exploiting such a paradigm, we obviate the need to use near-homophonous sequences from natural languages and eliminate the presence of other potential cues to word boundaries. This allows us to focus precisely on the key question: does longer duration make consonants more likely to be interpreted as word-initial? After directly examining this question in Experiment 1, we compare the effects of vowel vs consonant lengthening in the word-initial syllable in Experiment 2, and test the effectiveness for segmentation of lengthened vowel þ consonant sequences in Experiment 3
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