A common recommendation for communication partners of people with hearing loss is to speak clearly, but how effective is this simple instruction? Does everyone produce clear speech using the same strategies? Is clear speech produced when given minimal instruction the same as that produced when competing background noise is present? The present study examined the acoustic characteristics of passage level speech produced in four different conditions. Twelve talkers (8 female, 4 male) with a mean age of 21 years were audio recorded reading three paragraph length passages. In the first condition talkers read each passage conversationally as though speaking to a friend. In the three experimental conditions, talkers were instructed to speak as clearly as they could, speak as clearly as they could in the presence of multitalker babble, and speak as clearly as they could in the presence of speech-shaped noise. The babble and noise were presented over headphones at a level of 75 dB SPL. Acoustic measures examined changes in rate, frequency, and intensity across condition. Results of this study help clarify what changes talkers make in response to instructions to speak clearly compared to conditions with competing background noise.

This study investigated the extent to which noise impacts speech processing of sentences that vary in intelligibility for normal-hearing young adults. Intelligibility and recognition memory in noise were examined for conversational and clear speech sentences recorded in quiet (QS) and in response to the environmental noise, i.e. noise adapted speech (NAS). Results showed that 1) increased intelligibility through conversational-to-clear speech modifications lead 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 better sentence recall. These results demonstrate that acoustic-phonetic modifications implemented in listener-oriented speech enhance speech processing beyond word recognition. The results are in line with the effortfulness hypothesis (McCoy et al., 2005), which states that speech perception in challenging listening environments requires additional processing resources that might otherwise be available for encoding speech in memory. This resource reallocation may be offset 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. / text

Older adults often experience hearing loss in one or both ears, and as a result, many participate in aural rehabilitation programs. Often these programs incorporate communication partners and train them to use compensatory strategies. One common compensatory strategy cited is encouraging communication partners to speak more clearly to their loved one with hearing loss. Clear speech often encompass several different strategies such as speaking slower, louder, or over articulating. However, it is unclear what acoustic changes talkers employ when cued to speak in these different ways. The present study evaluated the effect of different cues (i.e., control (habitual), clear, slow, loud, and over articulate) and speaking tasks (oral reading versus monologue) on the acoustic characteristics of speech produced by eight older adults with hearing in the normal range. All speech was recorded in a sound treated booth and analyzed acoustically along six dimensions: articulation rate, percent change in fundamental frequency from control, change in sound pressure level from control, voice range density area, vowel space density area, and cepstral peak prominence. Results revealed statistically significant acoustic changes between conditions for all six acoustic measures. There was also significant effect of task for three acoustic measures. Findings show both group trends as well as individual talker variability. Further research is needed to determine how the acoustic changes associated with different instructional cues negatively or positively impact listeners with hearing loss.

Modifications to speech production made by adult talkers in response to instructions to speak clearly have been well documented in the literature. Targeting adult populations has been motivated by efforts to improve speech production for the benefit of the communication partners, however, many adults also have communication partners who are children. Surprisingly, there is limited literature on whether children can change their speech production when cued to speak clearly. Pettinato, Tuomainen, Granlund, and Hazan (2016) showed that by age 12, children exhibited enlarged vowel space areas and reduced articulation rate when prompted to speak clearly, but did not produce any other adult-like clear speech modifications in connected speech. Moreover, Syrett and Kawahara (2013) suggested that preschoolers produced longer and more intense vowels when prompted to speak clearly at the word level. These findings contrasted with adult talkers who show significant temporal and spectral differences between speech produced in control and clear speech conditions. Therefore, it was the purpose of this study to analyze changes in temporal and spectral characteristics of speech production that children aged 6-10 made in these experimental conditions. It is important to elucidate the clear speech profile of this population to better understand which adult-like clear speech modifications they make spontaneously and which modifications are still developing. Understanding these baselines will advance future studies that measure the impact of more explicit instructions and children's abilities to better accommodate their interlocutors, which is a critical component of children’s pragmatic and speech-motor development.

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This dissertation examines how age affects the ability to produce intelligibility- enhancing speaking style adaptations in response to environment-related difficulties (noise-adapted speech) and in response to listeners’ perceptual difficulties (clear speech). Materials consisted of conversational and clear speech sentences produced in quiet and in response to noise by children (11-13 years), young adults (18-29 years), and older adults (60-84 years). Acoustic measures of global, segmental, and voice characteristics were obtained. Young adult listeners participated in word-recognition-in-noise and perceived age tasks. The study also examined relative talker intelligibility as well as the relationship between the acoustic measurements and intelligibility results. Several age-related differences in speaking style adaptation strategies were found. Children increased mean F0 and F1 more than adults in response to noise, and exhibited greater changes to voice quality when producing clear speech (increased HNR, decreased shimmer). Older adults lengthened pause duration more in clear speech compared to younger talkers. Word recognition in noise results revealed no age-related differences in the intelligibility of conversational speech. Noise-adapted and clear speech modifications increased intelligibility for all talker groups. However, the acoustic changes implemented by children when producing noise-adapted and clear speech were less efficient in enhancing intelligibility compared to the young adult talkers. Children were also less intelligible than older adults for speech produced in quiet. Results confirmed that the talkers formed 3 perceptually-distinct age groups. Correlation analyses revealed that relative talker intelligibility was consistent for conversational and clear speech in quiet. However, relative talker intelligibility was found to be more variable with the inclusion of additional speaking style adaptations. 1-3 kHz energy, speaking rate, vowel and pause durations all emerged as significant acoustic-phonetic predictors of intelligibility. This is the first study to investigate how clear speech and noise-adapted speech benefits interact with each other across multiple talker groups. The findings enhance our understanding of intelligibility variation across the lifespan and have implications for a number of applied realms, from audiologic rehabilitation to speech synthesis. / text

The purpose of this study was to compare the effects on speech acoustics of a wide variety of speaking instructions that have been used across different studies on clear speech, and to investigate the acoustic and articulatory changes that occur in response to these instructions and in different talking environments. Five young adult females were recorded speaking under different instructions meant to elicit more intelligible speech, and measures of speaking rate, speaking F0 and intensity were found to distinguish instructions to speak "as if to someone with hearing loss" from instructions to speak "clearly" or "slowly", which produced different results from instructions to speak "loudly" or as if in noise. Preliminary acoustic and articulatory data are described for a sixth talker who spoke under a subset of these instructions, and in both a quiet and a noisy talking environment.

The purpose of this study was to compare the effects on speech acoustics of a wide variety of speaking instructions that have been used across different studies on clear speech, and to investigate the acoustic and articulatory changes that occur in response to these instructions and in different talking environments. Five young adult females were recorded speaking under different instructions meant to elicit more intelligible speech, and measures of speaking rate, speaking F0 and intensity were found to distinguish instructions to speak "as if to someone with hearing loss" from instructions to speak "clearly" or "slowly", which produced different results from instructions to speak "loudly" or as if in noise. Preliminary acoustic and articulatory data are described for a sixth talker who spoke under a subset of these instructions, and in both a quiet and a noisy talking environment.

Clear speech is a speaking style that has been shown to improve intelligibility in adverse listening conditions, for various listener and talker populations. Clear-speech phonetic enhancements include a slowed speech rate, expanded vowel space, and expanded pitch range. Although clear-speech phonetic enhancements have been demonstrated across a variety of talkers, only a subset of these changes may be required for listeners to benefit perceptually from clear speech. Furthermore, while current literature has provided some understanding of the phonetic enhancements that are typical of clear speech and the improvements in intelligibility resulting from its use, less is understood regarding how listeners benefit from clear speech. Understanding the mechanisms underlying the effectiveness of clear speech will provide insight into speech processing more generally. To that end, two studies were conducted to investigate the possible mechanisms underlying clear-speech benefits. The first study tests the hypothesis that clear speech reduces the amount of information needed for syllable identification. The amount of information presented to listeners was controlled using a silent-center syllable paradigm, in which various amounts of the center or edge of the syllables were removed. The second study tests the hypothesis that phonetic processing of clear speech requires fewer neuro-cognitive resources than typical, or conversational, speech. An Event Related Potential (ERP) paradigm, focused on the Phonological Mismatch Negativity (PMN) component, was used to compare participants’ neurophysiological responses to conversational- and clear-speech stimuli. Results from the first experiment supported the hypothesis of a clear-speech benefit in partial syllables, although the effect was stronger for some vowels than for others. The second experiment demonstrated differences in the way the brain responds to clear versus conversational speech, for syllables in which only the nucleus varied across stimuli. Match-mismatch differences were found in the MMN and PMN components, while the N600 component was found to respond to style differences.

Research on clear speech has shown that the type of clear speech produced can vary depending on the speaker, the listener and the medium. Although prior research has suggested that clear speech is more intelligible than conversational speech for normal-hearing listeners in noisy environments, it is not known which acoustic features of clear speech are the most responsible for enhanced intelligibility and comprehension. This thesis focused on investigating the acoustic characteristics that are produced in clear speech to foreigners and infants. Its aim was to assess the utility of these features in enhancing speech intelligibility and comprehension. The results of Experiment 1 showed that native speakers produced exaggerated vowel space in natural interactions with foreign-accented listeners compared to native-accented listeners. Results of Experiment 2 indicated that native speakers exaggerated vowel space and pitch to infants compared to clear read speech. Experiments 3 and 4 focused on speech perception and used transcription and clarity rating tasks. Experiment 3 contained speech directed at foreigners and showed that speech to foreign-accented speakers was rated clearer than speech to native-accented speakers. Experiment 4 contained speech directed at infants and showed that native speakers rated infant-directed speech as clearer than clear read speech. In the fifth and final experiment, naturally elicited clear speech towards foreign-accented interlocutors was used in speech comprehension tasks for native and non-native listeners with varying proficiency of English. It was revealed that speech with expanded vowel space improved listeners’ comprehension of speech in quiet and noise conditions. Results are discussed in terms of the Lindblom’s (1990) theory of Hyper and Hypoarticulation, an influential framework of speech production and perception.