Sarah Hargus Ferguson

Vowel intelligibility in clear and conversational speech for normal-hearing and hearing-impaired listeners

Several studies have demonstrated that when talkers are instructed to speak clearly, the resulting speech is significantly more intelligible than speech produced in ordinary conversation. These speech intelligibility improvements are accompanied by a wide variety of acoustic changes. The current study explored the relationship between acoustic properties of vowels and their identification in clear and conversational speech, for young normal-hearing (YNH) and elderly hearing-impaired (EHI) listeners. Monosyllabic words excised from sentences spoken either clearly or conversationally by a male talker were presented in 12-talker babble for vowel identification. While vowel intelligibility was significantly higher in clear speech than in conversational speech for the YNH listeners, no clear speech advantage was found for the EHI group. Regression analyses were used to assess the relative importance of spectral target, dynamic formant movement, and duration information for perception of individual vowels. For both listener groups, all three types of information emerged as primary cues to vowel identity. However, the relative importance of the three cues for individual vowels differed greatly for the YNH and EHI listeners. This suggests that hearing loss alters the way acoustic cues are used for identifying vowels.

Intelligibility of foreign-accented speech for older adults with and without hearing loss.

BACKGROUND Numerous studies have demonstrated that the negative effect of noise and other distortions on speech understanding is greater for older adults than for younger adults. Anecdotal evidence suggests that older adults may also be disproportionately negatively affected by foreign accent. While two previous studies found no interaction between foreign accent and listener age, these studies reported no audiometric data and assessed speech understanding in quiet only. PURPOSE To examine the effects of foreign accent, listening condition, and listener age and hearing status on word identification. RESEARCH DESIGN A cross-sectional descriptive study. STUDY SAMPLE Experiments 1 and 2 tested young adults with normal hearing (n = 20 and n = 5, respectively), older adults with essentially normal hearing (n = 20 and n = 10, respectively), and older adults with sloping sensorineural hearing loss (n = 20 and n = 10, respectively). DATA COLLECTION AND ANALYSIS The intelligibility of English words produced by a native speaker of English and by a native speaker of Spanish was assessed. In Experiment 1, word intelligibility was measured in quiet, in noise (+3 dB signal-to-babble ratio, or SBR), and in a telephone filter condition. In Experiment 2, intelligibility was measured in three additional noise conditions (+6, +9, and +12 dB SBR). RESULTS English words produced by the native speaker of English were significantly more intelligible than those produced by the native speaker of Spanish. While the negative effect of noise was significantly greater for older listeners than for younger listeners, the effect of foreign accent was independent of listener age, listener hearing status, and listening condition. CONCLUSION The results suggest that, unlike with other forms of distortion, older adults are not disproportionately affected by foreign accent. This suggests, in turn, that talker-related distortions of the speech signal have a qualitatively different impact on speech perception than distortions that are applied to the signal after it has been produced. The nature of these different types of distortion may be a fruitful area for future investigations of speech understanding in older adults.

Acoustic correlates of vowel intelligibility in clear and conversational speech for young normal-hearing and elderly hearing-impaired listeners

The present investigation carried out acoustic analyses of vowels in clear and conversational speech produced by 41 talkers. Mixed-effects models were then deployed to examine relationships among acoustic and perceptual data for these vowels. Acoustic data include vowel duration, steady-state formant frequencies, and two measures of dynamic formant movement. Perceptual data consist of vowel intelligibility in noise for young normal-hearing and elderly hearing-impaired listeners, as reported by Ferguson in 2004 and 2012 [J. Acoust. Soc. Am. 116, 2365-2373 (2004); J. Speech Lang. Hear. Res. 55, 779-790 (2012)], respectively. Significant clear speech effects were observed for all acoustic metrics, although not all measures changed for all vowels and considerable talker variability was observed. Mixed-effects analyses revealed that the contribution of duration and steady-state formant information to vowel intelligibility differed for the two listener groups. This outcome is consistent with earlier research suggesting that hearing loss, and possibly aging, alters the way acoustic cues are used for identifying vowels.

Enhancement of the edges of temporal masking functions by complex patterns of overshoot and undershoot

The purpose of this report is to present new data that provide a novel perspective on temporal masking, different from that found in the classical auditory literature on this topic. Specifically, measurement conditions are presented that minimize rather than maximize temporal spread of masking for a gated (200-ms) narrow-band (405-Hz-wide) noise masker logarithmically centered at 2500 Hz. Masked detection thresholds were measured for brief sinusoids in a two-interval, forced-choice (21FC) task. Detection was measured at each of 43 temporal positions within the signal observation interval for the sinusoidal signal presented either preceding, during, or following the gating of the masker, which was centered temporally within each 500-ms observation interval. Results are presented for three listeners; first, for detection of a 1900-Hz signal across a range of masker component levels (0-70 dB SPL) and, second, for masked detection as a function of signal frequency (fs = 500-5000 Hz) for a fixed masker component level (40 dB SPL). For signals presented off-frequency from the masker, and at low-to-moderate masker levels, the resulting temporal masking functions are characterized by sharp temporal edges. The sharpness of the edges is accentuated by complex patterns of temporal overshoot and undershoot, corresponding with diminished and enhanced detection, respectively, at both masker onset and offset. This information about the onset and offset timing of the gated masker is faithfully represented in the temporal masking functions over the full decade range of signal frequencies (except for fs=2500 Hz presented at the center frequency of the masker). The precise representation of the timing information is remarkable considering that the temporal envelope characteristics of the gated masker are evident in the remote masking response at least two octaves below the frequencies of the masker at a cochlear place where little or no masker activity would be expected. This general enhancement of the temporal edges of the masking response is reminiscent of spectral edge enhancement by lateral suppression/inhibition.

Subjective ratings of sentences in clear versus conversational speech.

Investigations of the relationship between speech acoustics and intelligibility face a significant methodological challenge, especially when using materials produced by multiple talkers and/or in multiple speaking styles. Ideally, acoustic analyses comparing talkers or styles will use identical materials for each. In contrast, intelligibility studies using meaningful stimuli must use either different materials or different listener groups to avoid learning effects. The latter solution becomes prohibitive when the number of talkers is large, such as in the Ferguson clear speech database (2004). While talkers recorded different materials in each speaking style, materials were the same for all talkers. For word intelligibility, familiarization prior to testing can prevent learning effects. For sentences, however, different listeners would be needed for each talker, resulting in 41 listener groups. An alternative solution is to use subjective rather than objective measures. This project explored the feasibili...

Listener estimations of talker age: A meta-analysis of the literature

Numerous studies, most of them cross-sectional studies using one sample per talker, have demonstrated that listeners make relatively accurate age judgments from hearing talkers’ voices. The current study analyzed the results of several such direct age estimation studies to characterize better the perception of talker age over a larger number of individuals. A review of the direct age estimation literature was performed. Data sets from seven papers were reconstituted, and an analysis of the combined data (meta-analysis) including 530 data points was conducted. The reconstituted and combined data included talkers aged 10–90. Listeners appeared to overestimate age when talkers were younger and to underestimate it when talkers were older.

Effects of dialect on vowel acoustics and intelligibility

A great deal of recent research has focused on phonetic variation among American English vowels from different dialects. This body of research continues to grow as vowels continuously undergo diachronic formant changes that become characteristic of certain dialects. Two experiments using the Nationwide Speech Project corpus (Clopper & Pisoni 2006a) explored whether the Midland dialect is more closely related acoustically and perceptually to the Mid-Atlantic or to the Southern dialect. The goal of this study was to further our understanding of acoustic and perceptual differences between two of the most marked dialects (Mid-Atlantic and Southern) and one of the least marked dialects (Midland) of American English. Ten vowels in /hVd/ context produced by one male talker from each of these three dialects were acoustically analyzed and presented to Midland listeners for identification. The listeners showed the greatest vowel identification accuracy for the Mid-Atlantic talker (95.2%), followed by the Midland talker (92.5%), and finally the Southern talker (79.7%). Vowel error patterns were consistent with vowel acoustic differences between the talkers. The results suggest that, acoustically and perceptually, the Midland and Mid-Atlantic dialects are more similar than are the Midland and Southern dialects.

Perceived sexual orientation and speech style: A perceptual and acoustic analysis of intentionally clear and conversational speech.

Munson et al. [Journal of Phonetics (2006)], found a correlation between perceived speech clarity and perceived sexual orientation (PSO) of male talkers: those who had been rated to sound gay were rated by an independent group to produce speech clearly. A smaller, opposite influence was found for women talkers. Munson et al. hypothesized that gay male speech styles might be based, in part, on clear speech styles. One weakness of Munson et al.’s study was that none of the speech examined was intentionally clear. This study follows up on this finding. A new group of 29 listeners rated the PSO of four men and four women producing conversational and intentionally clear speech, recorded as part of a larger study on interspeaker differences in talker intelligibility. PSO was rated using a five‐point scale. Speech style had a moderate, statistically significant influence on PSO. In contrast with previous research, both men and women were rated as gayer‐sounding when producing clear styles than when producing con...

Vowel intelligibility in clear and conversational speech

Several studies have demonstrated that instructions to speak clearly yield significant improvements in speech intelligibility along with a wide variety of acoustic changes relative to conversational speech. The current study explored the relationship between acoustic properties of vowels and their identification in clear and conversational speech, as well as the effects of hearing loss on this relationship. The goals were, for both normal and impaired listeners: (1) to determine what acoustic factors underlie the intelligibility differences observed between speaking styles and (2) to explore the relative contribution of various acoustic cues to vowel identification, using stimuli that vary naturally in intelligibility. Monosyllabic words were excised from sentences spoken either clearly or conversationally and presented in a background of 12‐talker babble for vowel identification by young normal‐hearing and elderly hearing‐impaired listeners. Vowel identification performance was correlated with the result...

Auditory temporal microstructure: Evidence of under‐ and over‐shoot at onset and offset of a narrow‐band noise masker measured in an off‐frequency masked detection task

Detection thresholds were measured as a function of the temporal position of a 5‐ms sinusoidal signal presented within one of two 500‐ms observation intervals. Both intervals contained a 400‐Hz‐wide noise masker, logarithmically centered at 2500 Hz, that was gated on at 150 ms and off at 350 ms within each interval. The signal and masker were both gated with 2‐ms linear ramps. The level of the signal was tracked adaptively in blocks of forty 2I 2AFC trials to estimate a 70.7% correct detection threshold. Thresholds were measured at 43 temporal signal positions within the observation interval, with detailed sampling around the onset and offset of the masker to assess temporal edge effects. Experiments to date with four listeners have focused on signals presented at 1900 or 2100 Hz. The temporal microstructure of the detection functions has characteristically revealed a complex pattern of under‐ and over‐shoot (i.e., enhanced and diminished detection, respectively). These effects, which have been observed a...