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Amplification bandwidth and speech intelligibility for two listeners with sensorineural hearing loss.

The intelligibility of speech as a function of its bandwidth was measured for two listeners with similar, moderately severe sensorineural hearing losses. The shape of the speech spectrum was adjusted to approximate the individual listener's contour of most comfortable listening levels (MCLs) and the overall level was set so that the levels in each band were below (-7 dB), near to (+3 dB), or above (+13 or +18 dB) the MCLs. At each level, nine pairings of three low-frequency and three high-frequency cutoffs (266, 375 and 530 Hz; 3,000, 4,242 and 6,000 Hz) were used. These conditions were achieved by passing the speech through a Limiting Master Hearing Aid (LMHA) which allows independent control of gain and maximum output in each of nine, half-octave bands. It was found that the wider the bandwidth, the higher the score, and the greater the amount of speech energy above threshold, the higher the score. Listeners' ability to understand the test material, after adjustment for listener differences, was correlated (0.7 and 0.8) with the articulation index.

Adult↗

The use of single-channel compression for the improvement of speech intelligibility.

In this study, speech perception with commercially available linear and single-channel input- and output-dependent compression aids was investigated. Although compression has been introduced as a method of limiting the maximum output, theoretically expectations have been raised that a gain in speech intelligibility could also be obtained by a better use of the reduced dynamic range of the patient. It turned out that there was no significant difference in speech reception thresholds obtained both in quiet and in noise between the aids used for a group of 12 hearing-impaired hearing-aid users as a whole, or for different subgroups thereof.

Adult↗

Impairment of speech intelligibility in men with amyotrophic lateral sclerosis.

Speech intelligibility was studied in a group of 25 male patients with amyotrophic lateral sclerosis (ALS). The object of the study was to determine the phonetic impairments underlying the speech intelligibility deficits that frequently accompany ALS. Analyses with a word intelligibility test indicated that the most disrupted phonetic features involved phonatory (voicing contrast) function, velopharyngeal valving, place and manner of articulation for lingual consonants, and regulation of tongue height for vowels. The mean error proportion for the five most severely affected features correlated highly (0.97) with the intelligibility score (percent correct). The phonetic feature analyses are one index of bulbar muscle impairment in amyotrophic lateral sclerosis and also may help to direct the speech management in these individuals.

Adult↗

Speech intelligibility and childhood verbal apraxia in children with Down syndrome.

Many children with Down syndrome have difficulty with speech intelligibility. The present study used a parent survey to learn more about a specific factor that affects speech intelligibility, i.e. childhood verbal apraxia. One of the factors that affects speech intelligibility for children with Down syndrome is difficulty with voluntarily programming, combining, organising, and sequencing the movements necessary for speech. Historically, this difficulty, childhood verbal apraxia, has not been identified or treated in children with Down syndrome but recent research has documented that symptoms of childhood verbal apraxia can be found in children with Down syndrome. The survey examined whether and to what extent childhood verbal apraxia is currently being identified and treated in children with Down syndrome. The survey then asked parents to identify certain speech characteristics that occur always, frequently, sometimes or never in their child's everyday speech. There were 1620 surveys received. Survey results indicated that approximately 15% of the parents responding to the survey had been told that their child has childhood verbal apraxia. Examination of the everyday speech characteristics identified by the parents indicated that many more children are showing clinical symptoms of childhood verbal apraxia although they have not been given that diagnosis. The most common characteristics displayed by the subjects included decreased intelligibility with increased length of utterance, inconsistency of speech errors, difficulty sequencing oral movements and sounds, and a pattern of receptive language superior to expressive language. The survey also examined the impact of childhood verbal apraxia on speech intelligibility. Results indicated that children with Down syndrome who have clinical symptoms of childhood verbal apraxia have more difficulty with speech intelligibility, i.e. there was a significant correlation between childhood verbal apraxia and parental intelligibility ratings. Children with apraxia often do not begin to speak until after age 5. There was a significant correlation between speech intelligibility and age at which the child began to speak, i.e. children who began to speak after age 5 had lower parental intelligibility ratings. A diagnosis of difficulty with oral motor skills is more frequently given than a diagnosis of apraxia; 60.2% of parents had been given this diagnosis. According to survey results, it is rare (2%) for a diagnosis of childhood verbal apraxia to be made without a diagnosis of difficulty with oral motor skills.

Adolescent↗

Interaction between children with cerebral palsy and their mothers: the effects of speech intelligibility.

Children with cerebral palsy and severe speech disorders have been described as passive communicators, whose conversation partners control and dominate interaction. This paper studies the effects of speech intelligibility on interaction between mothers and their children with cerebral palsy to examine if similar patterns of child passivity and adult domination are also observed in dyads in which children are physically dependent but naturally intelligible to their parents. Two groups, each of 20 children who had four-limb cerebral palsy and who differed in their speech intelligibility, participated in the study. Children in Group 1 (whose interaction has been previously reported) were unintelligible to their parents out of context. Children in Group 2 had speech that was understood without situational cues. Children and their mothers were videotaped playing with a set of toys that had been shown to elicit from non-disabled children a full range of the conversational moves and speech acts targeted in the study. Videotaped interaction was transcribed and coded at three levels to show conversation structure, the pragmatic functions expressed and the method of communication used. Percentage distribution of coding categories was compared across groups using coda. Results showed that verbally intelligible children initiated more conversations and used their communication for a wider range of functions than did non-speaking children, for whom more restricted patterns of conversation were noted. Unexpectedly, few differences were observed between the two groups of mothers, who initiated and closed most exchanges. Implications for intervention are discussed.

Cerebral Palsy↗

Age at fitting of hearing aids and speech intelligibility.

This paper reports on the effect of age at fitting of hearing aids on subsequent achievements in speech intelligibility among hearing-impaired children. Four groups of hearing-impaired children were included in this investigation. Group A (n = 32) started using hearing aids in their first 6 months of life; Group B (n = 32) in their second 6 months of life; Group C (n = 38) in their second year of life and Group D (n = 51) in their third year of life. The children in each group were matched with regard to age, sex, age at onset of deafness, degree of hearing loss and educational establishment attended. The speech intelligibility of each child was rated by his/her class teacher on a 7-point scale. It was found that the speech intelligibility of the children in Group A was significantly superior to the speech intelligibility of the children in the other three groups. All other differences in speech intelligibility obtained between groups (Group B v. Group C v. Group D) were small and none proved to be statistically significant.

Age Factors↗

Speech intelligibility of children with multichannel cochlear implants.

The purpose of this longitudinal study is to document improvements in speech intelligibility in children who have received multichannel cochlear implants, to compare their performance to that of a matched group of children with different levels of hearing loss who use conventional hearing aids. Speech intelligibility was measured by panels of listeners who analyzed recorded speech samples preimplant and at 6-month intervals following implantation. The results of this study demonstrate that prelingually deafened children with the Nucleus multichannel cochlear implant achieved significant improvements in speech intelligibility. By the 4.5- to 7.5-year intervals, the speech intelligibility exceeded 40%.

Child↗

Connected speech intelligibility of children with cochlear implants and children with normal hearing.

The objective of this study was to compare the connected speech intelligibility of children who use cochlear implants with that of children who have normal hearing. Previous research has shown that speech intelligibility improves from before cochlear implantation to after implantation and that the speech intelligibility of children who use cochlear implants compares favorably with that of children who use conventional hearing aids. However, no research has yet addressed the question of how the speech intelligibility of children who use cochlear implants compares to that of children with normal hearing. In the current study, archival data on connected speech intelligibility from 51 children with cochlear implants were compared with newly collected data from 47 children with normal hearing. Results showed that for children with cochlear implants, greater intelligibility was associated with both increased chronological age and increased duration of cochlear implant use. Consistent with previous studies, children with normal hearing achieved adult-like or near-adult-like intelligibility around the age of 4 years, but a similar peak in intelligibility was not observed for the children who used cochlear implants. On the whole, children with cochlear implants were significantly less intelligible than children with normal hearing, when controlling both for chronological age and for length of auditory experience. These results have implications for the socialization and education of children with cochlear implants, particularly with respect to on-time placement in mainstream educational environments with age peers.

Child↗

Orofacial myofunctional therapy in dysarthria: a study on speech intelligibility.

Various types of orofacial myofunctional disorders co-exist with speech problems in individuals with dysarthria. Controlled studies stating the efficacy of orofacial myofunctional therapy (OMT) in dysarthric individuals are very scant. The present study was undertaken to examine the efficacy of OMT in twelve patients diagnosed with mild to moderate dysarthria following right hemisphere brain damage. Pre-therapy assessment focused on existing orofacial myofunctional problems and speech intelligibility in the clients. The goals of OMT were to increase strength and mobility of buccal, facial, labial, and lingual musculature. No speech intervention was provided while OMT was in progress. Post-therapy measures indicated significant improvements in the stated goals as well as in speech intelligibility for single words. Patients observed functional improvements in swallowing functions too. A high positive correlation was found between speech intelligibility and diadochokinetic rate. Clinical implications regarding use of OMT in dysarthria are discussed.

Aged↗

The influence of speaking rate on vowel space and speech intelligibility for individuals with amyotrophic lateral sclerosis.

The relationship between speaking rate, vowel space area, and speech intelligibility was studied in a group of 9 subjects with amyotrophic lateral sclerosis (ALS) and 9 age- and gender-matched controls. Subjects read a standard passage (the Farm Passage) at three speaking rates, including HABITUAL, FAST, and SLOW. Vowel segment durations and target formant frequencies were measured at each speaking rate from select words containing the vowels /i/, /ae/, /a/, and /u/. To quantify changes in vowel space area across speaking rate, the area of the vowel quadrilateral was calculated for each speaker at each speaking rate. In addition, intelligibility estimates at each speaking rate were obtained for the dysarthric speakers. Results revealed that dysarthric speakers exhibited smaller vowel space areas and less systematic changes in vowel space as a function of speaking rate, when compared to the neurologically intact speakers. In an examination of the relationship between vowel space area and speech intelligibility, vowel space was found to account for 45% of the variance in speech intelligibility. This result suggests that vowel space area is an important component of global estimates of speech intelligibility.

Adult↗

Effects of whitening and peak-clipping on speech intelligibility in the presence of a competing message.

The purpose of this experiment was to determine the effects of peak clipping on speech intelligibility when both a target speech and a competing message were simultaneously peak-clipped. A competing message composed of 5 talkers was electrically mixed with CNC discrimination words. This composite signal was presented to normally hearing subjects in three ways: unmodified, whitened, and whitened and peak-clipped. Discrimination functions were obtained for the CNC material by varying the signal-to-competition ratio. Under these conditions, essentially identical discrimination functions were yielded by the unmodified and whitened speech, whereas substantially reduced discrimination scores were obtained with the whitened/clipped speech. These results would suggest that speech intelligibility is reduced by whitening and peak clipping when more than one talker is present. This is true even though earlier studies have shown that whitening and peak clipping do not reduce speech intelligibility when only a single talker is present. Such a finding has implications for wearable amplification.

Acoustic Stimulation↗

Horizontal localization and speech intelligibility with bilateral and unilateral hearing aid amplification.

Speech intelligibility and horizontal localization of 19 subjects with mild-to-moderate hearing loss were studied in order to evaluate the advantages and disadvantages of bilateral and unilateral hearing aid (HA) fittings. Eight loudspeakers were arranged in a circular array covering the horizontal plane around the subjects. Speech signals of a sentence test were delivered by one, randomly chosen, loudspeaker. At the same time, the other seven loudspeakers emitted noise with the same long-term average spectrum as the speech signals. The subjects were asked to repeat the speech signal and to point out the corresponding loudspeaker. Speech intelligibility was significantly improved by HAs, bilateral amplification being superior to unilateral. Horizontal localization could not be improved by HA amplification. However, bilateral HAs preserved the subjects' horizontal localization, whereas unilateral amplification decreased their horizontal localization abilities. Front-back confusions were common in the horizontal localization test. The results indicate that bilateral HA amplification has advantages compared with unilateral amplification.

Aged↗

Compression and expansion of the temporal envelope: evaluation of speech intelligibility and sound quality.

Sensorineural hearing loss is accompanied by loudness recruitment, a steeper-than-normal rise of perceived loudness with presentation level. To compensate for this abnormality, amplitude compression is often applied (e.g., in a hearing aid). Alternatively, since speech intelligibility has been modeled as the perception of fast energy fluctuations, enlarging these (by means of expansion) may improve speech intelligibility. Still, even if these signal-processing techniques prove useful in terms of speech intelligibility, practical application might be hindered by unacceptably low sound quality. Therefore, both speech intelligibility and sound quality were evaluated for syllabic compression and expansion of the temporal envelope. Speech intelligibility was evaluated with an adaptive procedure, based on short everyday sentences either in noise or with a competing speaker. Sound quality was measured by means of a rating-scale procedure, for both speech and music. In a systematic setup, both the ratio of compression or expansion and the number of independent processing bands were varied. Individual hearing thresholds were compensated for by a listener-specific filter and amplification. Both listeners with normal hearing and listeners with sensorineural hearing impairment participated as paid volunteers. The results show that, on average, both compression and expansion fail to show better speech intelligibility or sound quality than linear amplification.

Adult↗

Speech intelligibility enhancement using hearing-aid array processing.

Microphone arrays can improve speech recognition in the noise for hearing-impaired listeners by suppressing interference coming from other than desired signal direction. In a previous paper [J. M. Kates and M. R. Weiss, J. Acoust. Soc. Am. 99, 3138-3148 (1996)], several array-processing techniques were evaluated in two rooms using the AI-weighted array gain as the performance metric. The array consisted of five omnidirectional microphones having uniform 2.5-cm spacing, oriented in the endfire direction. In this paper, the speech intelligibility for two of the array processing techniques, delay-and-sum beamforming and superdirective processing, is evaluated for a group of hearing-impaired subjects. Speech intelligibility was measured using the speech reception threshold (SRT) for spondees and speech intelligibility rating (SIR) for sentence materials. The array performance is compared with that for a single omnidirectional microphone and a single directional microphone having a cardioid response pattern. The SRT and SIR results show that the superdirective array processing was the most effective, followed by the cardioid microphone, the array using delay-and-sum beamforming, and the single omnidirectional microphone. The relative processing ratings do not appear to be strongly affected by the size of the room, and the SRT values determined using isolated spondees are similar to the SIR values produced from continuous discourse.

Aged↗

Methodological aspects of assessing speech intelligibility among children with impaired hearing.

OBJECTIVE: In the assessment of speech intelligibility, procedures that are easy to use, but also valid and reliable, are needed. The aim of this study was to explore the reliability and concurrent validity of two scaling methods for assessing the speech intelligibility of children with impaired hearing. MATERIAL AND METHODS: A total of 51 children aged 4-17 years with a mild to profound hearing impairment performed a naming task comprising 62 single words. Altogether, 85 inexperienced listeners, divided into 17 panels, assessed the speech production of the children. A percent correct score (for identification of the words) was obtained from every listener. The listeners were also asked to judge the overall intelligibility of each child using a visual analogue scale (VAS) and a four-point ordinal level rating scale with verbal descriptors. RESULTS: The percent correct score correlated significantly both with the VAS and the rating scale with verbal descriptors (Pearsons' coefficient 0.90 and Spearman's coefficient 0.78, respectively). Also, the VAS and the scale with verbal descriptors were significantly intercorrelated (Spearman's rho 0.85). Moderate to high correlations were usually obtained for all grades of hearing impairment, both sexes, different age groups and main communication modes. CONCLUSIONS: Especially for assessing the need for remediation of speech and in monitoring its effectiveness, a quick overall estimate of speech intelligibility can be obtained quite reliably using the above rating scales. Item identification is more time-consuming but is often needed in research and therapy planning, where acoustic and linguistic phenomena that reduce intelligibility need to be traced.

Adolescent↗

A Speech Intelligibility Index-based approach to predict the speech reception threshold for sentences in fluctuating noise for normal-hearing listeners.

The SII model in its present form (ANSI S3.5-1997, American National Standards Institute, New York) can accurately describe intelligibility for speech in stationary noise but fails to do so for nonstationary noise maskers. Here, an extension to the SII model is proposed with the aim to predict the speech intelligibility in both stationary and fluctuating noise. The basic principle of the present approach is that both speech and noise signal are partitioned into small time frames. Within each time frame the conventional SII is determined, yielding the speech information available to the listener at that time frame. Next, the SII values of these time frames are averaged, resulting in the SII for that particular condition. Using speech reception threshold (SRT) data from the literature, the extension to the present SII model can give a good account for SRTs in stationary noise, fluctuating speech noise, interrupted noise, and multiple-talker noise. The predictions for sinusoidally intensity modulated (SIM) noise and real speech or speech-like maskers are better than with the original SII model, but are still not accurate. For the latter type of maskers, informational masking may play a role.

Attention↗

A procedure for testing speech intelligibility in a virtual listening environment.

OBJECTIVE: The development of a test of virtual speech intelligibility in noise that enables assessment in typical, everyday listening situations. To eliminate extraneous confounding factors, digital signal processing was incorporated to simulate listening environments and source locations and allow presentation of stimuli via earphones. DESIGN: Source-to-eardrum transfer functions measured on KEMAR for various source locations in anechoic and reverberant environments were used to process monosyllabic words and speech-spectrum noise. Speech intelligibility was measured for three speech and noise configurations in two environments using an adaptive procedure to determine the signal-to-noise (S/N) ratio for 50% intelligibility. RESULTS: Normal-hearing listeners achieved 50% intelligibility of monosyllabic words at significantly lower S/N ratios in a virtual anechoic environment than in a virtual reverberant environment. Speech intelligibility improved significantly in both environments when the speech and noise sources were separated, but the intelligibility gain in the anechoic environment was four times larger than in the reverberant environment. CONCLUSIONS: This test is easy to administer and score, and it provides a means for measuring: 1) the effects of separating speech and noise sources and 2) the effects of reverberation on speech intelligibility in noise while eliminating confounding factors such as calibration.

Hearing↗

Effects of human middle ear muscle contractions on speech intelligibility.

The present study assessed the relationship between the acoustic reflex and speech intelligibility. Monosyllabic words mixed with noise were presented at -6, -3.0 and +3 dB signal-to-noise ratios. The word lists were presented with a 2000-Hz tone in the contralateral ear at a level 15 dB above or 20 dB below the acoustic reflex threshold to evaluate intelligibility differences with the acoustic reflex contracted and relaxed. The results indicated that a significant decrement in speech intelligibility differences with the acoustic reflex contracted and relaxed. The results indicated that a significant decrement in speech intelligibility occurred with the reflex contracted at signal-to-noise ratios of -3, and 0 dB. Slight but not significant decrements were seen at -6 and +3 dB signal-to-noise ratios. These results are discussed along with possible reasons for the lack of agreement with previous research.

Adult↗