Volume 115, Issue 1, January 2004
Index of content:
- SPEECH PERCEPTION 
Vowel normalization for accent: An investigation of best exemplar locations in northern and southern British English sentences115(2004); http://dx.doi.org/10.1121/1.1635413View Description Hide Description
Two experiments investigated whether listeners change their vowel categorization decisions to adjust to different accents of British English. Listeners from different regions of England gave goodness ratings on synthesized vowels embedded in natural carrier sentences that were spoken with either a northern or southern English accent. A computer minimization algorithm adjusted F1, F2, F3, and duration on successive trials according to listeners’ goodness ratings, until the best exemplar of each vowel was found. The results demonstrated that most listeners adjusted their vowel categorization decisions based on the accent of the carrier sentence. The patterns of perceptual normalization were affected by individual differences in language background (e.g., whether the individuals grew up in the north or south of England), and were linked to the changes in production that speakers typically make due to sociolinguistic factors when living in multidialectal environments.
115(2004); http://dx.doi.org/10.1121/1.1635842View Description Hide Description
Sentences spoken “clearly” are significantly more intelligible than those spoken “conversationally” for hearing-impaired listeners in a variety of backgrounds [Picheny et al., J. Speech Hear. Res. 28, 96–103 (1985); Uchanski et al., ibid. 39, 494–509 (1996); Payton et al., J. Acoust. Soc. Am. 95, 1581–1592 (1994)]. While producing clear speech, however, talkers often reduce their speaking rate significantly [Picheny et al., J. Speech Hear. Res. 29, 434–446 (1986); Uchanski et al., ibid. 39, 494–509 (1996)]. Yet speaking slowly is not solely responsible for the intelligibility benefit of clear speech (over conversational speech), since a recent study [Krause and Braida, J. Acoust. Soc. Am. 112, 2165–2172 (2002)] showed that talkers can produce clear speech at normal rates with training. This finding suggests that clear speech has inherent acoustic properties, independent of rate, that contribute to improved intelligibility. Identifying these acoustic properties could lead to improved signal processing schemes for hearing aids. To gain insight into these acoustical properties, conversational and clear speech produced at normal speaking rates were analyzed at three levels of detail (global, phonological, and phonetic). Although results suggest that talkers may have employed different strategies to achieve clear speech at normal rates, two global-level properties were identified that appear likely to be linked to the improvements in intelligibility provided by clear/normal speech: increased energy in the 1000–3000-Hz range of long-term spectra and increased modulation depth of low frequency modulations of the intensity envelope. Other phonological and phonetic differences associated with clear/normal speech include changes in (1) frequency of stop burst releases, (2) VOT of word-initial voiceless stop consonants, and (3) short-term vowel spectra.