This study assessed the extent to which second-language learners are sensitive to phonetic information contained in visual cues when identifying a non-native phonemic contrast. In experiment 1, Spanish and Japanese learners of English were tested on their perception of a labial/ labiodental consonant contrast in audio (A), visual (V), and audio-visual (AV) modalities. Spanish students showed better performance overall, and much greater sensitivity to visual cues than Japanese students. Both learner groups achieved higher scores in the AV than in the A test condition, thus showing evidence of audio-visual benefit. Experiment 2 examined the perception of the less visually-salient /1/-/r/ contrast in Japanese and Korean learners of English. Korean learners obtained much higher scores in auditory and audio-visual conditions than in the visual condition, while Japanese learners generally performed poorly in both modalities. Neither group showed evidence of audio-visual benefit. These results show the impact of the language background of the learner and visual salience of the contrast on the use of visual cues for a non-native contrast. Significant correlations between scores in the auditory and visual conditions suggest that increasing auditory proficiency in identifying a non-native contrast is linked with an increasing proficiency in using visual cues to the contrast.
The general literature on the phonetic correlates of stress agrees that duration, and in stress accent languages, F0 are consistent correlates of stress. However, the role of amplitude changes in the speech signal is more controversial. In particular, the conflicting results of spectral tilt as a correlate of stress have been attributed to the effects of vowel reduction. We examined the stress correlates of duration, overall intensity and spectral tilt in Catalan and Spanish in both accented and unaccented contexts while controlling for formant frequency differences between morphologically corresponding vowels in stressed and unstressed environments by comparing vowels that maintain the same quality across stress contexts with those that do not. Duration was a consistent stress correlate in all vowels in both languages, regardless of their formant frequency differences across stress contexts and of the absence of pitch accents. In fact, stress-related formant frequency differences between corresponding vowels amplify the duration cues to the stress contrast. On the other hand, the use speakers made of intensity was not as pervasive as that of duration. Specifically, changes in spectral tilt were significant only in Catalan and in those vowels that alternate a more open and peripheral realization in stressed syllables with a mid-central realization in unstressed syllables, indicating that spectral tilt is related to the formant frequency differences linked to the centralization processes rather than to the stress contrast.
In unaccented contexts, formant frequency differences related to vowel reduction constitute a consistent cue to word stress in English, whereas in languages such as Spanish that have no systematic vowel reduction, stress perception is based on duration and intensity cues. This article examines the perception of word stress by speakers of Central Catalan, in which, due to its vowel reduction patterns, words either alternate stressed open vowels with unstressed mid-central vowels as in English or contain no vowel quality cues to stress, as in Spanish. Results show that Catalan listeners perceive stress based mainly on duration cues in both word types. Other cues pattern together with duration to make stress perception more robust. However, no single cue is absolutely necessary and trading effects compensate for a lack of differentiation in one dimension by changes in another dimension. In particular, speakers identify longer mid-central vowels as more stressed than shorter open vowels. These results and those obtained in other stress-accent languages provide cumulative evidence that word stress is perceived independently of pitch accents by relying on a set of cues with trading effects so that no single cue, including formant frequency differences related to vowel reduction, is absolutely necessary for stress perception.
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