9th Conference on Laboratory Phonology. June 24-26, 2004. 1. Contrast
enhancement in Croatian clear speech. Rajka Smiljanic & Ann Bradlow.
Northwestern ...
9th Conference on Laboratory Phonology June 24-26, 2004 Contrast enhancement in Croatian clear speech Rajka Smiljanic & Ann Bradlow Northwestern University Under adverse listening conditions, talkers naturally and spontaneously adopt a distinct, intelligibility-enhancing mode of speech production, known as “clear speech.” Previous work on English clear speech production and perception has established that (1) naturally produced clear speech enhances intelligibility for various listener populations under degraded listening conditions and (2) speakers adopt a wide range of acoustic/articulatory adjustments in order to facilitate listeners. These conversational-to-clear speech modifications include a slower speaking rate, a wider dynamic pitch range, greater sound pressure levels, more salient stop consonant releases, expansion of vowel space, etc. An open question is how much these modifications reflect language-general, signal enhancement strategies and how much they reflect languagespecific, structural enhancement strategies. Cross-language comparative data are crucial for addressing this question. More generally, such comparisons provide a window into the interaction of lower-level acoustic-auditory and higher-level phonological factors in spoken language processing. Accordingly, the goal of the present study was to examine clear speech production and perception in a language whose sound structure differs substantially from English, namely Croatian with a phonemic vowel length contrast. Two native speakers of Croatian, one male and one female, read 20 sentences in conversational and clear speech modes. A sentence-in-noise perception test was conducted in order to investigate whether the articulatory adjustments implemented by these two speakers will confer an intelligibility benefit for native Croatian listeners. The results showed a clear speech intelligibility effect for all listeners. Similar to the benefit of clear speech found in English, the Croatian listeners were better at identifying words produced in the clear speech mode than in the conversational speech mode. Additionally, a talker effect was found: The clear speech intelligibility effect was greater for the male talker than for the female talker. Acoustic analyses showed that for both speakers a decreased speaking rate, inclusion of more frequent pauses and a wider pitch range characterized the clear speech mode relative to the conversational speech mode thereby enhancing the overall acoustic salience of the signal. Other adjustments, such as, vowel space expansion and longer stop closure durations, characterize the clear speech productions as well. Crucially, however, the two speakers implemented different strategies in dealing with the lexical vowel length contrast. The male speaker lengthened long and short vowels in an asymmetrical way (short vowels were lengthened by 53% and long vowels by 75% in clear speech). In this way, the length contrast was exaggerated in clear speech. In contrast, the female speaker lengthened both long and short vowels to a similar degree (short vowels were lengthened by 51% and long vowels by 41%). For this speaker, the amount of the phonemic length contrast remained similar in both speaking styles. These results showed that both speakers enhanced the overall acoustic salience of the signal (slower, wider pitch range) but only one speaker enhanced the language specific phonemic vowel length contrast. It is argued that such language specific, structural enhancement contributes to the observed asymmetry in the intelligibility benefit between the male and female talkers. The results of the listening test suggest that enhancing the signal as well as the languagespecific phonemic contrast yields a greater intelligibility benefit than just enhancing the signal.
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9th Conference on Laboratory Phonology June 24-26, 2004 Perception and production of clear speech seems to be guided by principles that reflect both lower-level acoustic-auditory and higher-level phonological factors in spoken language processing.
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