Rajka Smiljanic

Production and perception of clear speech in Croatian and English

Previous research has established that naturally produced English clear speech is more intelligible than English conversational speech. The major goal of this paper was to establish the presence of the clear speech effect in production and perception of a language other than English, namely Croatian. A systematic investigation of the conversational-to-clear speech transformations across languages with different phonological properties (e.g., large versus small vowel inventory) can provide a window into the interaction of general auditory-perceptual and phonological, structural factors that contribute to the high intelligibility of clear speech. The results of this study showed that naturally produced clear speech is a distinct, listener-oriented, intelligibility-enhancing mode of speech production in both languages. Furthermore, the acoustic-phonetic features of the conversational-to-clear speech transformation revealed cross-language similarities in clear speech production strategies. In both languages, talkers exhibited a decrease in speaking rate and an increase in pitch range, as well as an expansion of the vowel space. Notably, the findings of this study showed equivalent vowel space expansion in English and Croatian clear speech, despite the difference in vowel inventory size across the two languages, suggesting that the extent of vowel contrast enhancement in hyperarticulated clear speech is independent of vowel inventory size.

Effects of gender and regional dialect on prosodic patterns in American English

While cross-dialect prosodic variation has been well established for many languages, most variationist research on regional dialects of American English has focused on the vowel system. The current study was designed to explore prosodic variation in read speech in two regional varieties of American English: Southern and Midland. Prosodic dialect variation was analyzed in two domains: speaking rate and the phonetic expression of pitch movements associated with accented and phrase-final syllables. The results revealed significant effects of regional dialect on the distributions of pauses, pitch accents, and phrasal-boundary tone combinations. Significant effects of talker gender were also observed on the distributions of pitch accents and phrasal-boundary tone combinations. The findings from this study demonstrate that regional and gender identity features are encoded in part through prosody, and provide further motivation for the close examination of prosodic patterns across regional and social varieties of American English.

Temporal organization of English clear and conversational speech.

This study investigated the effect of hyperarticulated, intelligibility-enhancing clear speech on temporal characteristics as reflected in number, durations, and variability of consonant and vowel intervals in sentence- and paragraph-length utterances. The results of sentence-in-noise listening tests showed a consistent clear speech intelligibility gain across the utterances of varying complexity indicating that the talkers successfully maintained clear speech articulatory modifications throughout longer stretches of speech. The acoustic analysis revealed that some temporal restructuring accompanied changes in speaking style. This temporal restructuring was observed in the insertion of consonant and vowel segments that were dropped or coarticulated in conversational speech and in an increase in the number of prosodic phrases for clear speech. Importantly, coefficients of variation (variation of consonantal and vocalic intervals normalized for changes in speaking rate) for both consonantal and vowel intervals remained stable in the two speaking styles. Overall, these results suggest that increased intelligibility of clear speech may be attributed to prosodic structure enhancement (increased phrasing and enhanced segmentability) and stable global temporal properties.

A perceptual phonetic similarity space for languages: Evidence from five native language listener groups

The goal of the present study was to devise a means of representing languages in a perceptual similarity space based on their overall phonetic similarity. In Experiment 1, native English listeners performed a free classification task in which they grouped 17 diverse languages based on their perceived phonetic similarity. A similarity matrix of the grouping patterns was then submitted to clustering and multidimensional scaling analyses. In Experiment 2, an independent group of native English listeners sorted the group of 17 languages in terms of their distance from English. Experiment 3 repeated Experiment 2 with four groups of non-native English listeners: Dutch, Mandarin, Turkish and Korean listeners. Taken together, the results of these three experiments represent a step towards establishing an approach to assessing the overall phonetic similarity of languages. This approach could potentially provide the basis for developing predictions regarding foreign-accented speech intelligibility for various listener groups, and regarding speech perception accuracy in the context of background noise in various languages.

Effects of Speech Clarity on Recognition Memory for Spoken Sentences

Extensive research shows that inter-talker variability (i.e., changing the talker) affects recognition memory for speech signals. However, relatively little is known about the consequences of intra-talker variability (i.e. changes in speaking style within a talker) on the encoding of speech signals in memory. It is well established that speakers can modulate the characteristics of their own speech and produce a listener-oriented, intelligibility-enhancing speaking style in response to communication demands (e.g., when speaking to listeners with hearing impairment or non-native speakers of the language). Here we conducted two experiments to examine the role of speaking style variation in spoken language processing. First, we examined the extent to which clear speech provided benefits in challenging listening environments (i.e. speech-in-noise). Second, we compared recognition memory for sentences produced in conversational and clear speaking styles. In both experiments, semantically normal and anomalous sentences were included to investigate the role of higher-level linguistic information in the processing of speaking style variability. The results show that acoustic-phonetic modifications implemented in listener-oriented speech lead to improved speech recognition in challenging listening conditions and, crucially, to a substantial enhancement in recognition memory for sentences.

Bidirectional clear speech perception benefit for native and high-proficiency non-native talkers and listeners: intelligibility and accentedness.

This study investigated how native language background interacts with speaking style adaptations in determining levels of speech intelligibility. The aim was to explore whether native and high proficiency non-native listeners benefit similarly from native and non-native clear speech adjustments. The sentence-in-noise perception results revealed that fluent non-native listeners gained a large clear speech benefit from native clear speech modifications. Furthermore, proficient non-native talkers in this study implemented conversational-to-clear speaking style modifications in their second language (L2) that resulted in significant intelligibility gain for both native and non-native listeners. The results of the accentedness ratings obtained for native and non-native conversational and clear speech sentences showed that while intelligibility was improved, the presence of foreign accent remained constant in both speaking styles. This suggests that objective intelligibility and subjective accentedness are two independent dimensions of non-native speech. Overall, these results provide strong evidence that greater experience in L2 processing leads to improved intelligibility in both production and perception domains. These results also demonstrated that speaking style adaptations along with less signal distortion can contribute significantly towards successful native and non-native interactions.

Regional variation in temporal organization in American English

Abstract The goal of the current study was to explore the temporal organization of six regional dialects of American English to gain a better understanding of the perceptual impressions of speaking rate variation. The study further examines whether regional dialects form different groupings based on their segmental vs. global temporal characteristics. Acoustic measures included articulation rate, pause frequency and duration, and vowel and consonant duration variability. The results revealed that Southern American English is characterized by a slow overall articulation rate, long pauses, and highly variable syllable-to-syllable vowel durations, whereas the New England dialect is characterized by a fast overall articulation rate, short pauses, and highly variable syllable-to-syllable consonant durations. The patterns for the other dialects are more mixed: the Northern and Western dialects are characterized by low variability vowel durations, the Midland dialect shares a slow articulation rate with the Southern dialect, and the Mid-Atlantic dialect exhibits no unique temporal properties among those examined. Thus, temporal variation in regional dialects of American English is orthogonal to vowel variation, in which New England, Midland, and Western dialects are often characterized together as “General American”. Taken together, the results are consistent with the stereotype that Southerners talk slowly and Northerners talk quickly and suggest that pausing and segmental duration variability may contribute to the perceived speaking rate differences.

Can older adults enhance the intelligibility of their speech?a)

Speech understanding difficulties for older adults (OAs) are well documented. Very little is known about whether age-related changes affect their speech production as well. Intelligibility of conversational and clear speech sentences produced by five OA talkers was examined. The results of the sentence-in-noise listening tests revealed that OAs enhanced their intelligibility for young adult (YA) listeners through clear speech modifications. Importantly, though, OAs were less effective at improving their speech to benefit listeners compared to YA talkers [reported in Smiljanic and Bradlow, J. Acoust. Soc. Am. 118(3), 1677-1688 (2005)]. The results suggest that auditory and cognitive changes across lifespan can affect OAs speech patterns and intelligibility.

Compensation for vocal tract characteristics across native and non-native languages

Perceptual compensation for speaker vocal tract properties was investigated in four groups of listeners: native speakers of English and native speakers of Dutch, native speakers of Spanish with low proficiency in English, and Spanish–English bilinguals. Listeners categorized targets on a [sofo] to [sufu] continuum. Targets were preceded by sentences that were manipulated to have either a high or a low F1 contour. All listeners performed the categorization task for targets that were preceded by Spanish, English and Dutch precursors. Results show that listeners from each of the four language backgrounds compensate for speaker vocal tract properties regardless of language-specific vowel inventory properties. Listeners also compensate when they listen to stimuli in another language. The results suggest that patterns of compensation are mainly determined by auditory properties of precursor sentences.

Acoustics of Clear and Noise-Adapted Speech in Children, Young, and Older Adults

Purpose This study investigated acoustic-phonetic modifications produced in noise-adapted speech (NAS) and clear speech (CS) by children, young adults, and older adults. Method Ten children (11-13 years of age), 10 young adults (18-29 years of age), and 10 older adults (60-84 years of age) read sentences in conversational and clear speaking style in quiet and in noise. A number of acoustic measurements were obtained. Results NAS and CS were characterized by a decrease in speaking rate and an increase in 1-3 kHz energy, sound pressure level (SPL), vowel space area (VSA), and harmonics-to-noise ratio. NAS increased fundamental frequency (F0) mean and decreased jitter and shimmer. CS increased frequency and duration of pauses. Older adults produced the slowest speaking rate, longest pauses, and smallest increase in F0 mean, 1-3 kHz energy, and SPL when speaking clearly. They produced the smallest increases in VSA in NAS and CS. Children slowed down less, increased the VSA least, increased harmonics-to-noise ratio, and decreased jitter and shimmer most in CS. Children increased mean F0 and F1 most in noise. Conclusions Findings have implications for a model of speech production in healthy speakers as well as the potential to aid in clinical decision making for individuals with speech disorders, particularly dysarthria.