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The present study investigates the relationship between sentence intelligibility, band importance, and patterns of spectro-temporal covariation between frequency bands. Sixteen listeners transcribed sentences acoustically degraded to 5, 8, or 15 frequency bands. Half of the sentences retained the frequency bands that captured more signal covariance. The other half retained the bands accounting for less signal covariance. Sentence intelligibility was significantly higher in the high-covariance condition. Critically, this finding was predicted by differences in band importance across reconstructed sentences. These findings provide a mechanistic relationship between the contributions of signal covariance and band importance to sentence intelligibility.

Speaking style variation plays a role in how listeners remember speech. Compared to conversational sentences, clearly spoken sentences were better recalled and identified as previously heard by native and non-native listeners. The present study investigated whether speaking style variation also plays a role in how talkers remember speech that they produce. Although distinctive forms of production (e.g., singing, speaking loudly) can enhance memory, the cognitive and articulatory efforts required to plan and produce listener-oriented hyper-articulated clear speech could detrimentally affect encoding and subsequent retrieval. Native and non-native English talkers' memories for sentences that they read aloud in clear and conversational speaking styles were assessed through a sentence recognition memory task (experiment 1; N = 90) and a recall task (experiment 2; N = 75). The results showed enhanced recognition memory and recall for sentences read aloud conversationally rather than clearly for both talker groups. In line with the "effortfulness" hypothesis, producing clear speech may increase the processing load diverting resources from memory encoding. Implications for the relationship between speech perception and production are discussed.

Though necessary, protective mask wearing in response to the COVID-19 pandemic presents communication challenges. The present study examines how signal degradation and loss of visual information due to masks affects intelligibility and memory for native and non-native speech. We also test whether clear speech can alleviate perceptual difficulty for masked speech. One native and one non-native speaker of English recorded video clips in conversational speech without a mask and conversational and clear speech with a mask. Native English listeners watched video clips presented in quiet or mixed with competing speech. The results showed that word recognition and recall of speech produced with a mask can be as accurate as without a mask in optimal listening conditions. Masks affected non-native speech processing at easier noise levels than native speech. Clear speech with a mask significantly improved accuracy in all listening conditions. Speaking clearly, reducing noise, and using surgical masks as well as good signal amplification can help compensate for the loss of intelligibility due to background noise, lack of visual cues, physical distancing, or non-native speech. The findings have implications for communication in classrooms and hospitals where listeners interact with teachers and healthcare providers, oftentimes non-native speakers, through their protective barriers.

A robust clear speech intelligibility benefit for a variety of talkers, listeners, and communication challenges is well-documented. In this talk, I will review research that focuses on how conversational to clear speech modifications facilitate linguistic processes and cognitive functioning beyond word recognition in noise. In one line of work, using a visual-world paradigm, we showed that clear speech enhanced speech segmentation and reduced lexical competition. In another, we showed that clear speech benefit extended to the improved sentence recognition memory and recall of words and sentences. Finally, in a series of experiments using a dual-task paradigm, we showed that hearing clear speech increased reaction times on a concurrent visual task suggesting that the clear speech processing benefits may arise through the increased engagement of the attentional resources toward the more salient hyperarticulated speech. The results contribute evidence that clear speech facilitates signal-dependent sensory processing as well as deeper linguistic processing abstracted from the input speech. These clear speech findings have implications for our understanding of perceptual mechanisms that underlie improved speech perception, including the use of cognitive resources and listening effort.

Speech signals are acoustically redundant, which could explain why sentence intelligibility is fairly robust even when sentences are acoustically degraded. We investigated the contributions to sentence intelligibility of clear speech redundancy encoded as patterns of spectrotemporal covariation between frequency channels. Participants (N = 16) transcribed 120 clear-speech English sentences acoustically degraded to 5, 8, or 15 frequency bands derived from an ERB-scaled filter bank. Before the acoustic degradation, each sentence was expressed as a linear combination of principal component eigenvectors representing different patterns of covariation between channels. Half of the sentences preserved the channels providing larger score magnitudes for the eigenvector accounting for more spectral covariance (high-covariance condition). These channels represented the spectral covariation patterns that were more dominant in each sentence. The other half of the sentences preserved the bands conveying larger score magnitudes for the eigenvector accounting forless spectral covariance (low-covariance condition). These bands represented the spectral covariation patterns that were less dominant. Participants yielded significantly better transcription accuracy in the high-covariance condition (mixed-effects, ps

Listener-oriented hyperarticulated clear speech facilitates linguistic processing and cognitive functioning associated with speech perception under various listening conditions. Using the visual-world eye-tracking paradigm, we investigated whether clear speech also aids speech segmentation, or the discovery of word boundaries, and examined the dynamic time course of its effect. Native American English speakers (N = 77) heard sentences in which the target word (e.g., ham) was temporarily ambiguous with a longer unintended competitor (e.g., hamster) across a word boundary (e.g., She saw the ham starting…) while viewing images depicting the target, competitor, and unrelated distractors. Clear and conversational sentences were presented in quiet or in speech-shaped noise at +3 dB signal-to-noise ratio. Analysis of eye fixations to the images over time revealed that compared with conversational speech, clear speech facilitated the disambiguation of the target from the competitor even before the disambiguation point was reached. The facilitation was found in both listening conditions but was relatively delayed in noise. These findings suggest that speaking clearly improves word segmentation and reduces lexical competition especially in optimal listening conditions. The speech segmentation facilitation may partly underlie the clear speech benefits observed for other signal-dependent and relatively signal-independent linguistic and cognitive processes.

Talkers dynamically modify their coarticulatory patterns when producing listener-oriented hyperarticulated clear speeches. This study examined how the use of protective face masks interacts with the production of intelligibility-enhancing clear speech to impact coarticulation. A native and a non-native speaker of English read sentences in a clear and conversational speaking style with and without a surgical mask. Coarticulation between word-internal adjacent segments was analyzed with a whole-spectrum analysis including spectral distance and segment overlap duration. Both speakers coarticulated less in clear than in conversational speaking style as indicated by the larger spectral distance and shorter overlap duration between adjacent segments. Coarticulation was further reduced when clear speech was produced with a mask by the native speaker but not by the non-native speaker. The findings showed that producing hyperarticulated intelligibility-enhancing clear speech also involves reducing coarticulatory overlap across adjacent segments. Coarticulatory resistance was adaptively reinforced in the presence of the additional communicative barrier, face mask, particularly for the speaker with extensive experience with the target language. Such cumulative reduction of coarticulation may in part underlie the larger perception-in-noise benefit for clear speech produced with a mask for the native compared to the non-native talker.

Listeners are able to classify talkers by regional dialect of their native language when provided with even short speech samples. However, the way in which American English listeners use segmental and prosodic information to make such decisions is largely unknown. This study used a free classification task to assess native American English listeners' ability to group together talkers from six major dialect regions of American English. Listeners residing in Ohio and Texas were provided with a sentence-long (experiment 1) or paragraph-long (experiment 2) speech sample produced by talkers from each of the six regions presented in one of three conditions: unmodified, monotonized (i.e., flattened F0), and low-pass filtered (i.e., spectral information above 400 Hz removed). In both experiments, listeners in the unmodified and monotonized conditions made more accurate groupings, reflecting their reliance on segmental properties for classifying regional variation. Accuracy was highest for Northern and Western talkers (experiment 1) and Mid-Atlantic talkers (experiment 2). Listeners with experience with multiple dialects as a result of geographic mobility did not show increased accuracy, suggesting a complex relationship between linguistic experience and the perception of available acoustic cues to socioindexical variation.

The present study examined the effect of intelligibility-enhancing clear speech on listeners' recall. Native (n = 57) and non-native (n = 31) English listeners heard meaningful sentences produced in clear and conversational speech, and then completed a cued-recall task. Results showed that listeners recalled more words from clearly produced sentences. Sentence-level analysis revealed that listening to clear speech increased the odds of recalling whole sentences and decreased the odds of erroneous and omitted responses. This study showed that the clear speech benefit extends beyond word- and sentence-level recognition memory to include deeper linguistic encoding at the level of syntactic and semantic information.

We analyzed the degree and time course of coarticulatory vowel nasalization in hyperarticulated clear speech produced in real and imagined communicatively challenging conditions from the LUCID corpus (Baker & Hazan, 2011). Southern British English speakers completed an interactive spot-the-difference task in pairs when there was no overt communication barrier (NB), when the partner was non-native (L2), and when one speaker’s speech was vocoded (VOC) or mixed with talker babble (BABBLE). They also read sentences conversationally (READ-CO) and clearly (READ-CL). The results showed significantly greater overall keyword vowel nasalization in the BABBLE and L2 conditions than in NB, READ-CO, and READ-CL, as well as in VOC than in NB and READ-CO. READ-CL and READ-CO did not differ significantly. Examining vowel nasalization over time revealed that the significant differences emerged, on average, at 7.4% into the vowel. Speakers increased coarticulatory nasalization early in the vowel when producing hyperarticulated speech in response to a real communicative barrier, consistent with the idea that nasal coarticulation facilitates speech processing by cueing upcoming segments. It remains to be determined why nasal coarticulation is increased while coarticulation for other consonant-vowel sequences is decreased during the production of hyperarticulated listener-oriented speaking styles (Guo and Smiljanic, 2021).

The goal of the study was to examine whether enhancing the clarity of the speech signal through conversational-to-clear speech modifications improves sentence recognition memory for native and non-native listeners, and if so, whether this effect would hold when the stimuli in the test phase are presented in orthographic instead of auditory form (cross-modal presentation). Sixty listeners (30 native and 30 non-native English) participated in a within-modal (i.e., audio-audio) sentence recognition memory task (Experiment I). Sixty different individuals (30 native and 30 non-native English) participated in a cross-modal (i.e., audio-textual) sentence recognition memory task (Experiment II). The results showed that listener-oriented clear speech enhanced sentence recognition memory for both listener groups regardless of whether the acoustic signal was present during the test phase (Experiment I) or absent (Experiment II). Compared to native listeners, non-native listeners had longer reaction times in the within-modal task and were overall less accurate in the cross-modal task. The results showed that more cognitive resources remained available for storing information in memory during processing of easier-to-understand clearly produced sentences. Furthermore, non-native listeners benefited from signal clarity in sentence recognition memory despite processing speech signals in a cognitively more demanding second language.

Two experiments examined the acoustic correlates of the disyllabic tonal accent contrast in the Trøndersk dialect of Norwegian, and how narrow focus and phrasal position shape the contrast. Production results showed that both tonal accents have a high-low (HL) pitch contour, with different timing. In narrow focus, the pitch contrast was enlarged through asymmetrical F0 changes. When at the right edge of an accent phrase (AP), the accents were shown to have a higher L, lower AP H% tone, shorter stressed vowel, and longer final vowel. The alignment changes reflected tonal crowding while segmental modifications were due to the phrase-final lengthening in AP-final position. This work contributes to the literature on prosodic typology as well as on the implementation of prosodic focus and sentence intonation in languages with lexical pitch contrasts.

Purpose This study examined the effect of depressive symptoms on production and perception of conversational and clear speech (CS) sentences. Method Five talkers each with high-depressive (HD) and low-depressive (LD) symptoms read sentences in conversational and clear speaking style. Acoustic measures of speaking rate, mean fundamental frequency (F0; Hz), F0 range (Hz), and energy in the 1–3 kHz range (dB) were obtained. Thirty-two young adult participants (15 HD, 16 LD) heard these conversational and clear sentences mixed with energetic masking (speech-shaped noise) at −5 dB SPL signal-to-noise ratio. Another group of 39 young adult participants (18 HD, 19 LD) heard the same sentences mixed with informational masking (one-talker competing speech) at −12 dB SPL signal-to-noise ratio. The key word correct score was obtained. Results CS was characterized by a decreased speaking rate, increased F0 mean and range, and increased energy in the 1–3 kHz range. Talkers with HD symptoms produced these modifications significantly less compared to talkers with LD symptoms. When listening to speech in energetic masking (speech-shaped noise), listeners with both HD and LD symptoms benefited less from the CS produced by HD talkers. Listeners with HD symptoms performed significantly worse than listeners with LD symptoms when listening to speech in informational masking (one-talker competing speech). Conclusions Results provide evidence that depressive symptoms impact intelligibility and have the potential to aid in clinical decision making for individuals with depression.

Though necessary, protective mask wearing in response to the Covid-19 pandemic presents communication challenges. Speech produced through these masks is quieter, muffled, and lacks important visual cues for listeners. The present study examines how such loss of visual information and signal degradation affects intelligibility and auditory memory of non-native speech. Additionally, we examined whether clear speaking style can alleviate some perceptual difficulty for masked speech. One non-native English speaker recorded short, educationally relevant video clips in three conditions: casual speech without a mask, and casual and clear speech with a mask. In an online study, native English listeners were presented with 15 video clips in each of the three mask / style conditions and transcribed what they heard. Following each condition, listeners answered questions about the content of the clips. Word recognition and memory accuracy will be analyzed. Detailed acoustic analyses will be conducted to assess how face masks and speaking style affect speech production. The results will allow us to quantify speech communication challenges arising from the widespread use of masks. The findings will have implications for communication in classrooms and hospitals where listeners have to understand teachers and healthcare providers, often time non-native speakers, through their protective barriers.

Listening effort increases when perceiving speech masked by noise and when listeners are non-native speakers of the target language (Zekveld and Kramer, 2014; Borghini and Hazan, 2018). Listener-oriented clear speech (CS) improves word recognition in noise and recognition memory (Keerstock and Smiljanic, 2018). It is unclear, however, whether the CS benefit can be explained by reduced listening effort during processing of easier-to-understand speech. The goal of this study was to examine the effect of CS on listening effort associated with degraded listening conditions differing in the source of difficulty and underlying cognitive mechanism: energetic masking, informational masking, and non-native listening. Native and non-native English listeners performed a word recognition in noise task and a visual response task, i.e., pressing keys to indicate the orientation of an arrow on the screen, first separately and then simultaneously. In the word recognition task, listeners repeated back sentences produced in CS and conversational speech and mixed with speech-shaped noise and 2-talker babble. The presentation will discuss analyses aimed at uncovering how hyper-articulated CS and masker type influence listening effort for native and non-native listeners as measured by objective and subjective dual-task cost.

Speaking clearly improves intelligibility particularly in noisy environments—a benefit that may be partly attributed to enhanced ease of speech segmentation. However, speech segmentation is facilitated by coarticulation (Fernandes et al., 2007), which may be reduced in hyper-articulated clear speech (Scarborough and Zellou, 2013). This study investigated the effect of clear speech on speech segmentation in quiet and in noise for native and non-native listeners with an artificial language (AL) learning experiment. Six trisyllabic AL words (e.g., /kutupi/) were produced by a native English speaker both clearly and conversationally. Six speech streams were created, each containing 20 pitch-flattened tokens of each AL word concatenated in random order without intervening pauses. In the learning phase, participants heard either conversational or clear AL speech streams in quiet or masked with speech-shaped noise. Next, in a two-alternative forced-choice test, participants identified the AL words spoken in quiet and in the style they were exposed to. Preliminary results showed that clear speech improved segmentation relative to conversational speech for native English listeners in quiet only. The results suggest that the use of exaggerated information about segment identity aids speech segmentation in optimal listening conditions but is disrupted under perceptual load.

Previous research has shown that native and non-native listeners’ recognition memory is higher for sentences previously heard in clear speech (CS) than in conversational speech (Keerstock and Smiljanic, 2018). The present study investigated whether speaking clearly also enhances talkers’ sentence recognition memory. The production effect (MacLeod et al., 2010) revealed superior retention of material read aloud relative to material read silently during an encoding phase. Vocal production that included an additional distinct element, such as speaking loudly, produced even greater memory benefits than reading aloud (Quinlan and Taylor, 2013). Production of the exaggerated articulatory and acoustic cues in CS could thus lead to enhanced sentence recognition memory relative to conversational style. Native and non-native English speakers produced alternating blocks of 10 conversational and CS sentences for a total of 60 unique sentences. In the test phase, they identified 120 sentences as old (from exposure) or new (distractors). Unexpectedly, preliminary results show lower sentence recognition memory for sentences produced in CS than in conversational speech for both groups of talkers. The results suggest that producing CS, unlike perceiving it, interferes with recognition memory. Allocating cognitive resources to producing hyper-articulated speech may limit their availability for storing information in memory.

This study investigated the extent to which noise impacts normal-hearing young adults' speech processing of sentences that vary in intelligibility. Intelligibility and recognition memory in noise were examined for conversational and clear speech sentences recorded in quiet (quiet speech, QS) and in response to the environmental noise (noise-adapted speech, NAS). Results showed that (1) increased intelligibility through conversational-to-clear speech modifications led to improved recognition memory and (2) NAS presented a more naturalistic speech adaptation to noise compared to QS, leading to more accurate word recognition and enhanced sentence recognition memory. These results demonstrate that acoustic-phonetic modifications implemented in listener-oriented speech enhance speech-in-noise processing beyond word recognition. Effortful speech processing in challenging listening environments can thus be improved by speaking style adaptations on the part of the talker. In addition to enhanced intelligibility, a substantial improvement in recognition memory can be achieved through speaker adaptations to the environment and to the listener when in adverse conditions.

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 OA's speech patterns and intelligibility.

Early bilinguals often show as much sensitivity to L2-specific contrasts as monolingual speakers of the L2, but most work on cross-language speech perception has focused on isolated segments, and typically only on neighboring vowels or stop contrasts. In tasks that include sounds in context, listeners' success is more variable, so segment discrimination in isolation may not adequately represent the phonetic detail in stored representations. The current study explores the relationship between language experience and sensitivity to segmental cues in context by comparing the categorization patterns of monolingual English listeners and early and late Spanish-English bilinguals. Participants categorized nonce words containing different classes of English- and Spanish-specific sounds as being more English-like or more Spanish-like; target segments included phonemic cues, cues for which there is no analogous sound in the other language, or phonetic cues, cues for which English and Spanish share the category but for which each language varies in its phonetic implementation. Listeners' language categorization accuracy and reaction times were analyzed. Our results reveal a largely uniform categorization pattern across listener groups: Spanish cues were categorized more accurately than English cues, and phonemic cues were easier for listeners to categorize than phonetic cues. There were no differences in the sensitivity of monolinguals and early bilinguals to language-specific cues, suggesting that the early bilinguals' exposure to Spanish did not fundamentally change their representations of English phonology. However, neither did the early bilinguals show more sensitivity than the monolinguals to Spanish sounds. The late bilinguals however, were significantly more accurate than either of the other groups. These findings indicate that listeners with varying exposure to English and Spanish are able to use language-specific cues in a nonce-word language categorization task. Differences in how, and not only when, a language was acquired may influence listener sensitivity to more difficult cues, and the advantage for phonemic cues may reflect the greater salience of categories unique to each language. Implications for foreign-accent categorization and cross-language speech perception are discussed, and future directions are outlined to better understand how salience varies across language-specific phonemic and phonetic cues.

Listener-oriented speaking style adaptations improve sentence recognition memory in quiet and in noise (Van Engen et al. 2012, Gilbert et al. 2014). It is not clear if this advantage arises from the available cognitive resources, or enhanced memory traces. The present study investigated what may underlie the improved recognition memory for clear speech. In the within-modal condition, monolingual English listeners heard a total of 40 unique meaningful sentences in conversational and clear speaking styles, followed by a test phase in which they identified 80 audio sentences as old or new. In the cross-modal condition, the acoustic input in the test phase was replaced by written text. Results showed that while accuracy was high in both conditions, conversational-to-clear speech modifications significantly improved sentence recognition memory only in the within-modal condition. In the cross-modal condition, speaking style had no effect on sentence recognition memory. The results suggest that the benefit of cl...

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.

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 assess 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.

Recognition memory (i.e., identifying items as old or new) is higher for sentences spoken clearly than for sentences spoken casually. The clear speech benefit on recognition memory was observed for both native and non-native English listeners. The current study investigated the effect of clear speech on sentence recall, a more complex and effortful type of declarative memory that requires processing at phonological, lexical-semantic, morphosyntactic, and syntactic levels. Thirty native and 30 non-native English listeners heard 72 meaningful sentences (e.g., “The grandfather drank the dark coffee”) produced in conversational and clear speaking styles by a female native English speaker. Participants were presented with 12 sentences blocked by speaking style, and instructed to memorize them. After each block of 12 sentences, participants wrote down what they remembered. Blocks were counterbalanced for speaking style. Responses were scored by number of keywords correctly recalled (verbatim memory) and sentence-level comprehension (gist memory). Preliminary results show enhanced verbatim memory for clear speech (i.e., higher rate of key words correctly recalled for sentences produced in clear speech) for both listener groups suggesting that hyper-articulated clear speech provides cognitive release and aids retention of surface form.Recognition memory (i.e., identifying items as old or new) is higher for sentences spoken clearly than for sentences spoken casually. The clear speech benefit on recognition memory was observed for both native and non-native English listeners. The current study investigated the effect of clear speech on sentence recall, a more complex and effortful type of declarative memory that requires processing at phonological, lexical-semantic, morphosyntactic, and syntactic levels. Thirty native and 30 non-native English listeners heard 72 meaningful sentences (e.g., “The grandfather drank the dark coffee”) produced in conversational and clear speaking styles by a female native English speaker. Participants were presented with 12 sentences blocked by speaking style, and instructed to memorize them. After each block of 12 sentences, participants wrote down what they remembered. Blocks were counterbalanced for speaking style. Responses were scored by number of keywords correctly recalled (verbatim memory) and sentenc...

Sentences produced in a clear speech speaking style are typically more intelligible than sentences produced in a conversational style. However, factors that lead to the intelligibility difference are not fully understood. This study investigated the role of semantic context in intelligibility of temporally compressed clear and conversational speech. Grammatically correct English sentences, which were either semantically meaningful or semantically anomalous, were presented to 70 normal-hearing listeners in clear or conversational speaking style. The sentences were temporally compressed to produce seven different syllabic rates (6-12), matched across clear and conversational sentences to control for the original durational differences between clear and conversational speech. Results for semantically anomalous sentences indicate no differences in the rate of intelligibility decline across compression rates for clear and conversational speech. In contrast, for semantically meaningful sentences, the rate of intelligibility decline was smaller for the semantically meaningful clear-speech sentences over semantically anomalous conversational-speech sentences. At the highest compression rate of 12 syllables per second, intelligibility of semantically meaningful clear-speech sentences (~68% correct) was similar to that of semantically anomalous sentences at 9 syllables per second. These findings suggest that semantic context can modulate the effect of speaking style on the intelligibility of temporally compressed sentences.

This article provides an overview of the research concerning the nature of the distinct, listener-oriented speaking style called ‘clear speech’ and its effect on intelligibility for various listener populations. We review major findings that identify talker, listener and signal characteristics that contribute to the characteristically high intelligibility of clear speech. Understanding the interplay of these factors sheds light on the interaction between higher level cognitive and lower-level sensory and perceptual factors that affect language processing. Clear speech research is, thus, relevant for both its theoretical insights and practical applications. Throughout the review, we highlight open questions and promising future directions.

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.

Much of daily communication occurs under a range of suboptimal conditions related to talker, listener, and signal characteristics. These “adverse” conditions (Mattys et al., 2012) increase intelligibility variation and impact perceptual processes, representations, attention, and memory functions. In this talk, I focus on two factors that condition intelligibility variation, namely, when interlocutors are non-native speakers of a target language and when communication occurs in noise. First, I will discuss a set of experiments examining how native and non-native talkers modify their speech with the goal of enhancing their intelligibility and the extent to which these modifications enhance word recognition in noise for native and non-native listeners. I also present results from studies examining how listeners adapt to more and less familiar foreign accents of varying intelligibility when presented in noise. These studies provide insights into the interplay between physical and mental factors in the production and perception of intelligible speech. They further reveal constraints on talker-listener adaptation processes during communication. A detailed understanding of speech intelligibility variation for native and non-native talkers and listeners will enhance our understanding of the compensatory and cognitive mechanisms that allow speech comprehension in naturalistic conditions.

Historically, most research on regional variation in American English (AE) examined lexical and segmental sources of variability. Focusing on prosodic variation, we have demonstrated significant effects of regional dialect on overall articulation rate, distributions of pauses, pitch accents, phrasal-boundary tone combinations, and syllable-to-syllable vowel and consonant duration variability (Clopper & Smiljanic, 2015, 2011). In this talk, we examine whether native AE listeners utilize prosodic and segmental cues to classify AE talkers by region and whether listener familiarity with different dialects affects classification. Using free classification with unmodified, monotone (flattened F0), and low-pass filtered (removed segmental information) stimuli, listeners from Ohio and Texas grouped 60 talkers based on perceived regional similarities. Listeners were more accurate in classifying talkers with the unmodified and monotone stimuli than with the low-pass filtered stimuli. There were no differences betwe...

It is well established that native listeners outperform non-native listeners on word recognition tasks involving both speech-shaped noise (SSN) and competing speech (speech babble). The present study examined whether this non-native disadvantage can be compensated for by speaking style enhancements. We also explored how these acoustic-articulatory modifications interact with energetic and informational masking at different signal-to-noise ratios to determine intelligibility for the two listener groups. Native and non-native participants heard noise-adapted (NAS) and clear speech (CL) sentences mixed with either SSN, two-talker (2T), or six-talker (6T) babble. CL and NAS significantly improved word recognition in noise, but native listeners were better able to use the intelligibility-enhancing modifications. Results revealed an interaction between noise type and SNR such that the intelligibility gain was larger for SSN at an easier SNR, but for 6T babble at a harder SNR. The speaking style modifications en...

Previous work indicates that listeners are able to adapt quickly to changes in accent [Clarke & Garrett, 2004; Bradlow & Bent, 2008] and that adaptation is faster for familiar accents [Witteman et al., 2013; Blanco et al., 2014]. The present study examines how listeners adapt to more and less familiar accents presented in noise as compared to quiet, since noisy listening environments are more perceptually challenging [Vaden et al., 2013; Gilbert et al., 2014] but also more closely represent typical listening conditions. Native English listeners heard blocks of sentences produced by native- or foreign-accented talkers (Korean, Spanish) and responded to a visual probe. Listener accuracy and reaction times were compared across accent and speaker blocks. Results showed that, unlike in quiet, listeners were unable to adapt to the less-familiar Korean accent. Processing of the familiar Spanish accent was successful in noise and quiet. Adaptation in noise was furthermore correlated with talker intelligibility: less intelligible talkers elicited lower accuracy and slower response; in quiet, there was no talker effect. The results revealed that the ability to adapt to a novel foreign accent is disrupted, as the extra perceptual effort in noise prevents listeners from generalizing about systematic variability of foreign-accented features.

The role of visual cues in native listeners' perception of speech produced by nonnative speakers has not been extensively studied. Native perception of English sentences produced by native English and Korean speakers in audio-only and audiovisual conditions was examined. Korean speakers were rated as more accented in audiovisual than in the audio-only condition. Visual cues enhanced word intelligibility for native English speech but less so for Korean-accented speech. Reduced intelligibility of Korean-accented audiovisual speech was associated with implicit visual biases, suggesting that listener-related factors partially influence the efficiency of audiovisual integration for nonnative speech perception.

While the relationship of clear speaking style to intelligibility under challenging conditions has been established, it is a common observation that some speakers seem to be more intelligible than others for most listeners. In previous work, we have reported that automatic measures based on the technique of Landmark Detection appear to track differences between Clear and Conversational speaking style. One question that remains is whether Landmark measures can be used to predict which speakers are most likely to produce highly intelligible speech. In this study, we took advantage of a set of previously acquired databases to examine correlations between our Landmark-based measures and the Clear Speech productions of highly intelligible speech. Across these databases, we had data on intelligibility for a range of speakers. Results showed that speakers with high overall intelligibility in Clear Speech showed significantly different patterns on Landmark-based automatic measures, compared to speakers with more moderate performance on intelligibility measures. Applications of these results to problems in speech technology, linguistic education and clinical practice will be discussed.

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.

Signal distortions are more detrimental to speech perception by native than non-native listeners. We investigated how speech clarity and semantic context influence the perception of interrupted speech. Native and non-native American English listeners heard semantically meaningful or anomalous sentences produced as conversational or “clear” speech, gated at different rates (0.5–16 Hz). Results showed that both semantic context and speech clarity had a significant rate-dependent impact on the intelligibility of interrupted speech. In general, intelligibility was higher for native than non-native listeners. However, the magnitude of the clear-speech benefit varied across the two listener groups. The clear-speech benefit was obtained for gating rates of 2 Hz and above, except for meaningful sentences with native listeners where the benefit begin at 1 Hz. Both listener groups were able to use contextual information but native listeners derived more benefit at lower gating rates, indicating greater ability to a...

It is well established that non-native listeners perform worse on speech perception in noise tasks compared to native listeners. However, few studies have directly compared the effect of speaking style adaptations on speech perception in energetic and informational maskers for these two listener groups. The present study examined intelligibility of conversational (CO), clear (CS) and noise-adapted (NAS) meaningful sentences mixed with speech shaped noise (SSN) and 2-talker (2T) babble. Sentences were presented at −5 dB signal to noise ratio (SNR) to native and −3 dB SNR to non-native listeners. The results revealed that CS and NAS significantly improved word recognition in noise for both listener groups. However, the gains in intelligibility were substantially greater for native compared to non-native listeners. Word recognition was overall better in 2T babble than in SSN. Our findings confirm that both native and non-native listeners benefited from speaking style adjustments, but native listeners were be...

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.

Even though speech communication is a fundamental part of our daily behavior, its mechanisms are not yet well understood. Speech communication research examines how spoken language is produced, transmitted, and perceived. Speech communication research involves a number of different disciplines, from linguistics and experimental psychology to speech and hearing sciences, and electrical engineering. The field covers a wide range of physiological, psychological, acoustic, and linguistic phenomena. In this talk, I will focus on research examining variation in speech intelligibility, the degree to which spoken language can be comprehended. Even in ideal communicative settings, in quiet environments between normal-hearing, native speakers of a language, speech intelligibility is variable. The variation increases in adverse communication situations that can arise from degradation related to talker (e.g., when second language learners produce non-canonical signal), signal (e.g., when target speech is masked by competing speech), or listener (e.g., when listeners use cochlear implants) characteristics (Mattys et al., 2012). Examining speech intelligibility variation from all these perspectives provides insights into the perceptual, physiological, linguistic, cognitive, and neurophysiological mechanisms underlying speech processing. This line of inquiry also has implications for improving speech processing when communicative conditions are compromised.

In this paper we investigate the effect of clear speech, a distinct, listener-oriented, intelligibility-enhancing mode of speech production, on vowel and stop consonant contrasts along the temporal dimension in English and Croatian. Our previous work has shown that, in addition to enhancing the overall acoustic salience of the speech signal through a decrease in speaking rate and expansion of pitch range, clear speech modifications increased the spectral distances between vowel categories in both languages despite the different sizes of their vowel inventories (+10 in English, 5 in Croatian). Here, we examine how clear speech affects the duration of English tense ('long') vs. lax ('short') vowels, English vowels preceding voiced ('long') vs. voiceless ('short') coda stops, Croatian long vs. short vowels and Croatian and English VOT duration for voiced and voiceless stops. Overall, the results showed that the proportional distance between the 'short' and 'long' vowel categories and between the voiced and voiceless stop categories was remarkably stable across the two speaking styles in both languages. These results suggest that, in combination with the spectral enhancement of vowel contrasts, language-specific pronunciation norms along the temporal dimension are maintained in clear and conversational speech.

Children must learn to process variations in the pronunciation of their language(s), but they must also learn the social meaning of particular kinds of variation. By preschool, children’s initially overly specific lexical representations have generalized to reflect commonalities in pronunciations, thus allowing children to recognize accented productions as instances of familiar lexical items (Best et al., 2009; Schmale, et al., 2010, 2011, 2012; Stager and Werker, 1997). However, elementary-school-aged children struggle to use the phonetic variation present in accented speech to understand social differences among talkers (Floccia et al., 2009; Girard et al., 2008). In the present study, we investigated children’s ability to associate acoustic cues with a particular language as a function of their language background (monolingual, significant L2 exposure, or bilingual). Children decided whether nonce words containing language-specific sounds were produced by a Spanish speaker or an English speaker. Language-specific cues included phonemes unique to Spanish (/r/) or English (/ɹ, θ/), or sound categories common to both languages but produced differently in each (/l, u/). The categorization patterns and reaction times of the three groups were compared, and results indicate that children with exposure to or proficiency in Spanish categorized the nonce words more accurately than monolinguals.

This study investigated the time-course of word recognition in adverse listening conditions. Specifically, we examined the effect of different listener-oriented speaking styles and semantic context on lexical access in quiet and in noise. Young adult listeners participated in an online visual word recognition experiment. They heard sentences with a high- versus low-predictability semantic context, produced in Conversational (CO), Infant-Directed (IDS), and Clear (CS) speech while fixating two pictures on a screen: a target that matched the last word of the auditory stimulus and a distractor. All sentences were presented either in quiet, or mixed with speech-shaped noise at a −5 dB SNR. Results showed that IDS provided similar perceptual benefits to adult listeners as CS. Relative to low-predictability CO baseline, IDS and CS increased speed of word recognition for high-predictability sentences, in quiet and in noise equally. However, in the quiet condition, lexical access was eventually facilitated by contextual cues even in CO, but listeners in noise reliably focused the target only when a combination of contextual cues and exaggerated acoustic-phonetic cues was available. These findings suggest that both semantic cues and listener-oriented acoustic enhancements are needed for reliable and rapid lexical access, especially in adverse conditions.

Speech understanding in noisy environments can be compromised through energetic (EM) and informational (IM) masking. EM reduces intelligibility of target speech through spectro-temporal overlap with the masker at the auditory periphery level. IM refers to the higher-level interference, such as competing attention, linguistic interference, and increased cognitive load. The present study examined the effects of EM and IM on foreign-accent adaptation. Native English listeners heard blocks of sentences produced by native-accented (NA) or foreign-accented (FA) talkers (Korean, Spanish) mixed with speech-shaped noise (SSN) or two-talker, native-accented babble and responded to a visual probe. Preliminary results show that listeners were more accurate and faster in babble compared to SSN. The more successful FA adaptation in the babble condition may be related to the presence of dips in the masker energy or the ability of listeners to successfully separate FA target from the NA background speech. Additionally, the acoustic properties of the target sentences, such as speaking rate and pausing, are examined to understand their effect on FA adaptation in each of the two noise conditions. These findings suggest that IM was less disruptive than EM for FA adaptation even though listeners were processing FA speech with an increased cognitive load.