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PubMed1995

The effect of multichannel dynamic compression on speech intelligibility.

In the recent literature on dynamic compression in hearing aids, a controversial discussion about the benefit of multichannel compression with short time constants has been raised. In this paper, some experimental results are contributed to the discussion: For low signal-to-noise ratios, a detrimental effect of fast multichannel compression on speech intelligibility in normal hearing listeners is found. However, a distinct degradation in speech quality and virtually no decrease in speech intelligibility is observed for comparatively high signal-to-noise ratios and compression ratios of up to 3. Since the predictions of the Speech Transmission Index deviate substantially from these results, its applications as an objective measure of intelligibility may not be extended to compressed speech.

Hearing Aids↗
PubMed1986

[A simple speech intelligibility test in the evaluation of voice rehabilitation of laryngectomized patients].

An easy and rapid test system is reported for the quantitative assessment of speech intelligibility following laryngectomy. 20 changing randomised monosyllables and 5 changing sentences are spoken by the patient into a telephone with the investigator listening in without visual contact with the patient. The number of correctly understood words and sentences is determined. Reliability and validity of the linguistic pool as well as reproducibility of the test system can be demonstrated.

Humans↗
PubMed1986

Predictors of speech intelligibility in rooms.

Three different types of acoustical measures were compared as predictors of speech intelligibility in rooms of varied size and acoustical conditions. These included signal-to-noise measures, the speech transmission index derived from modulation transfer functions, and useful/detrimental sound ratios obtained from early/late sound ratios, speech, and background levels. The most successful forms of each type of measure were of similar prediction accuracy, but the useful/detrimental ratios based on a 0.08-s early time interval were most accurate. Several physical measures, although based on very different calculation procedures, were quite strongly related to each other.

Acoustic Stimulation↗
PubMedDate not supplied

Effects of intermodulation distortion on speech intelligibility.

This investigation was designed (1) to investigate further intermodulation distortion in hearing aids, and (2) to determine the effect of this type of distortion on speech intelligibility. After four hearing aids were analyzed for intermodulation distortion, 10 CID sentences were recorded through each instrument and presented to both normally hearing and sensorineurally impaired listeners. Results indicated an inverse relationship between levels of intermodulation distortion and frequency, with the highest distortion levels found below 1 kHz. This low-frequency distortion significantly interfered with speech intelligibility for sensorineurally impaired subjects listening to sentences in quite. For both the normally hearing group and the sensorineural group listening in noise, no significant differences were found. The results were interpreted to suggest that the low-frequency intermodulation distortion resulted in an upward spread of masking which interfered with perception of high-frequency acoustic cues in sensorineural impaired listeners; however, with the addition of a competing signal, the subtle masking effect of intermodulation distortion were obscured. Implications for additional research are discussed.

Adult↗
PubMed1994

Speech intelligibility in tone language (Chinese) laryngectomy speakers.

Tone language speakers use lexical tone or fundamental frequency to signal meaning. Therefore, native tone language alaryngeal speakers encountering difficulty imparting lexical tone variation would suffer loss of speech intelligibility. This study examines the intelligibility of lexical tone produced by four different alaryngeal speech methods, namely: oesophageal speech, electrolarynx, a pneumatic device and tracheo-oesophageal speech. Isolated and embedded monosyllabic Chinese words produced by 53 alaryngeal speakers were presented to three normally hearing, young adult listeners with no prior exposure to laryngectomy speech. The listeners transcribed the speech orthographically. Significant differences were found in the intelligibility level between the different speech methods. Listeners' responses were also pooled together and analysed for tone and segmental errors. Errors of tone alone were found to occur more often than segmental errors.

Aged↗
PubMed2001

Effects of degradation of intensity, time, or frequency content on speech intelligibility for normal-hearing and hearing-impaired listeners.

Many hearing-impaired listeners suffer from distorted auditory processing capabilities. This study examines which aspects of auditory coding (i.e., intensity, time, or frequency) are distorted and how this affects speech perception. The distortion-sensitivity model is used: The effect of distorted auditory coding of a speech signal is simulated by an artificial distortion, and the sensitivity of speech intelligibility to this artificial distortion is compared for normal-hearing and hearing-impaired listeners. Stimuli (speech plus noise) are wavelet coded using a complex sinusoidal carrier with a Gaussian envelope (1/4 octave bandwidth). Intensity information is distorted by multiplying the modulus of each wavelet coefficient by a random factor. Temporal and spectral information are distorted by randomly shifting the wavelet positions along the temporal or spectral axis, respectively. Measured were (1) detection thresholds for each type of distortion, and (2) speech-reception thresholds for various degrees of distortion. For spectral distortion, hearing-impaired listeners showed increased detection thresholds and were also less sensitive to the distortion with respect to speech perception. For intensity and temporal distortion, this was not observed. Results indicate that a distorted coding of spectral information may be an important factor underlying reduced speech intelligibility for the hearing impaired.

Adult↗
PubMedDate not supplied

A diagnostic marker for speech delay associated with otitis media with effusion: the intelligibility-speech gap.

The goal of this study was to determine if notably reduced intelligibility is a potential diagnostic marker for children with speech delay and histories of early recurrent otitis media with effusion (SD-OME). Intelligibility was assessed in one 5-10 minute conversational speech sample from each of 281 speakers. The OME histories of 148 of these children with normal speech acquisition were described in two prior reports. OME histories of 85 additional children with speech delay were obtained from case history reports. For both groups, the children with positive OME (OME+) histories had significantly lower intelligibility scores but significantly higher speech production scores than children with negative OME (OME-) histories. Findings for a diagnostic marker to discriminate speech delayed children with OME+ versus OME- histories were promising, considering that the data were obtained retrospectively and did not include audiological information characterizing children's concurrent fluctuant hearing loss. The formula for the diagnostic marker, termed the Intelligibility-Speech Gap, was identified by a machine learning routine. Diagnostic accuracy findings for the marker were as follows: positive predictive value = 74%, negative predictive value = 86%, sensitivity = 79%, specificity = 83%, positive likelihood ratio = 4.6 and negative likelihood ratio = 0.25. Discussion considers speech processing perspectives on the source of the intelligibility-speech gap in children with suspected SD-OME, and methodological perspectives on its development as a diagnostic marker of one etiological subtype of speech delay.

Child↗
PubMed2002

[A simple audiometry test of speech intelligibility in background noise].

We propose a new audiometric test to assess French speakers' speech discrimination in noise. This soundfield test uses a standard cocktail-party background noise superimposed on Fournier's disyllabic word lists. The background noise is CD-recorded at constant 55 dB SPL. The discrimination score is measured at a signal-to-noise ratio of -5 dB, 0, and dB. In comparison with other audiometric tests in noise, our test requires only 5 minutes and is simple for both patient and audiologist. All patients are tested using the same standard condition, one that approaches daily life and uses a noise of moderate intensity. The result is reproducible and easy to calculate and graph. We propose this test for diagnosing in-noise speech intelligibility disorders and for assisting the process of conventional or implantable hearing-aid fitting.

Audiometry↗
PubMed1981

Pediatric speech intelligibility test. II. Effect of receptive language age and chronological age.

Performance for Pediatric Speech Intelligibility (PSI) Format I and Format II sentences was significantly different in children between the ages of 3 and 6 years. Performance differences were related to chronological age (CA) and receptive language (RL) ability. However, performance for Format I sentences in children with relatively low RL age and performance for Format II sentences in children with relatively high RL age were equivalent. This observation yielded an algorithm that determines the sentence format as a function of the child's RL age in order to yield 'language equivalent' norms for speech audiometry. Performance for PSI word materials was not influenced by differences in RL skill. CA developmental trends were noted for all speech materials.

Age Factors↗
PubMed1985

Improvements in speech intelligibility in quiet and in noise produced by two-channel compression hearing aids.

Eight subjects suffering from bilateral sensorineural hearing losses with recruitment were fitted binaurally with two-channel compression hearing aids, worn behind the ear. After they had worn the aids for some time, measures of speech intelligibility were compared for two conditions: listening unaided, and listening aided. the dynamic range for speech, defined as the difference in level between the speech reception threshold in quiet and the highest comfortable level for speech, was substantially increased in the aided condition for seven of the eight subjects (the exception was a subject with almost normal low-frequency hearing). Speech reception thresholds were also measured in two levels of background noise ('babble'), 60 and 75 dB SPL. Seven of the eight subjects showed a reduced speech reception threshold (i.e. an improvement) in the aided condition for at least one of the two noise levels, although the size of the improvement differed considerably from one subject to another. The subjects were also given a battery of psycho-acoustical tests in an attempt to better characterise their hearing loss, and to gain more insight into individual differences. Results of measurements of frequency selectivity, frequency discrimination, temporal acuity and temporal masking are described and related to the measures of speech intelligibility.

Aged↗
PubMed2002

Direct magnitude estimates of speech intelligibility in dysarthria: effects of a chosen standard.

Direct magnitude estimation (DME) has been used frequently as a perceptual scaling technique in studies of the speech intelligibility of persons with speech disorders. The technique is typically used with a standard, or reference stimulus, chosen as a good exemplar of "midrange" intelligibility. In several published studies, the standard has been chosen subjectively, usually on the basis of the expertise of the investigators. The current experiment demonstrates that a fixed set of sentence-level utterances, obtained from 4 individuals with dysarthria (2 with Parkinson disease, 2 with traumatic brain injury) as well as 3 neurologically normal speakers, is scaled differently depending on the identity of the standard. Four different standards were used in the main experiment, three of which were judged qualitatively in two independent evaluations to be good exemplars of midrange intelligibility. Acoustic analyses did not reveal obvious differences between these four standards but suggested that the standard with the worst-scaled intelligibility had much poorer voice source characteristics compared to the other three standards. Results are discussed in terms of possible standardization of midrange intelligibility exemplars for DME experiments.

Aged↗
PubMed1991

Comparison of objective and subjective measures of speech intelligibility in elderly hearing-impaired listeners.

Three experiments were performed to evaluate the use of subjective intelligibility estimations as a method for measuring hearing aid benefit. Subjective and objective speech intelligibility scores were compared for young normal-hearing and elderly hearing-impaired listeners. Objective intelligibility scores were obtained using the Connected Speech Test (CST). This test consists of conversationally produced passages of speech that the listener repeats sentence by sentence. To provide subjective intelligibility scores, listeners estimated the percentage that they understood of each CST passage. Comparison of the two types of scores revealed that they were closely related in both groups of subjects (r = .82-.92). Although the two types of scores were essentially equal for normal-hearing subjects, the hearing-impaired listeners tended to produce subjective estimations of intelligibility that were significantly lower than their objective scores. Manipulation of visual cues and amplification, in an attempt to influence the hearing-impaired listeners' expectation of understanding speech, had no effect on the subjective-objective score differential. The difference between subjective and objective scores in the hearing-impaired group was not related to audiometric variables such as speech reception threshold, audiogram, or duration of hearing loss. It was concluded that comparative hearing aid evaluations using subjective intelligibility estimates would usually produce the same relative outcome as evaluations using the objective intelligibility measurement procedure. However, scores obtained with the objective procedure had smaller critical differences. Thus, when both types of scores are based on the same number of passages, the objective measurement procedure would be the more sensitive to differences among hearing aids.

Adolescent↗
PubMed2000

Identification of a pathway for intelligible speech in the left temporal lobe.

It has been proposed that the identification of sounds, including species-specific vocalizations, by primates depends on anterior projections from the primary auditory cortex, an auditory pathway analogous to the ventral route proposed for the visual identification of objects. We have identified a similar route in the human for understanding intelligible speech. Using PET imaging to identify separable neural subsystems within the human auditory cortex, we used a variety of speech and speech-like stimuli with equivalent acoustic complexity but varying intelligibility. We have demonstrated that the left superior temporal sulcus responds to the presence of phonetic information, but its anterior part only responds if the stimulus is also intelligible. This novel observation demonstrates a left anterior temporal pathway for speech comprehension.

Acoustic Stimulation↗
PubMed2001

Comparing loudness normalization (IHAFF) with speech intelligibility maximization (NAL-NL1) when implemented in a two-channel device.

OBJECTIVE: At least two rationales are available for fitting wide dynamic range compression hearing aids. The goal of one rationale is to normalize loudness, and the goal of the second rationale is to maximize speech intelligibility. Neither rationale has been validated against other fitting rationales for the range of input levels common to the hearing aid user in the real world. The goal of the study was to compare the two rationales when implemented in a 2-channel compression hearing aid. DESIGN: Loudness normalization and speech intelligibility maximization were implemented using the Independent Hearing Aid Fitting Forum (IHAFF) and the National Acoustic Laboratories' Nonlinear (NAL-NL1) prescriptive formulas. Twenty-four subjects (eight for each of three groups of mild flat, moderate/severe flat, and steeply sloping hearing loss) participated in the study. Each subject completed an initial laboratory test, field test, and final laboratory test. The laboratory test consisted of a paired-comparison judgment for each prescriptive formula using four stimuli under both quiet and noisy listening conditions and a sentence recognition test using Bamford-Kowal-Bench sentences. In the field test, subjects evaluated the two rationales in individually selected everyday listening conditions for 4 wk. A digital simulation of the fitting rationales implemented in two channels was used for laboratory testing and a digital 2-memory, 2-channel device was used for field testing. Subjects adjusted the overall gain of each response to their preferred listening level in both the laboratory and in the field. RESULTS: Data collected in the laboratory before and after the field test showed no indication of significant learning or acclimatization effects. For each stimulus presented in the paired-comparison test more subjects preferred NAL-NL1 than preferred IHAFF. For the sentence recognition test, subjects performed significantly better with NAL-NL1 than IHAFF in a low-frequency weighted background noise. Sixteen out of 22 subjects who completed the field test reported a preference for the NAL-NL1 response. The remaining six subjects preferred IHAFF. The paired-comparison test and field test revealed that while the achieved root-mean-square (rms) difference between fittings for an input level of 65 dB SPL was small, the preference for either rationale was small. As the rms difference between fittings increased, the score in favor of NAL-NL1 increased. The correlation between the differences in satisfaction score obtained in the field test and the rms differences between the responses fitted was statistically significant. CONCLUSIONS: When the two fitting rationales prescribed substantially different responses for a 65 dB SPL input and these differences were achieved in the fitting, then the subjects preferred NAL-NL1. Even when the difference between fittings was small, the subjects preferred and performed better with NAL-NL1 when listening in a low-frequency weighted background noise.

Acoustic Stimulation↗
PubMed1993

Disturbed speech intelligibility in noise despite a normal audiogram: a defect in temporal resolution?

Patients with complaints of disturbed speech intelligibility in noise, despite normal standard audiograms, constitute a unique yet not uncommon population of listeners. The literature on this patient group is reviewed, and the term Idiopathic Discriminatory Dysfunction (IDD) is introduced in an attempt to standardize and qualify the distinct characteristics of this entity. Preliminary studies of these patients have hypothesized both frequency and temporal resolution deficits underlying this impairment. A representative group of 15 patients suffering from IDD were tested using a new speech-in-noise paradigm designed to test temporal resolution. These patients were found to have near-normal temporal resolving capacity as determined by this task.

Adult↗
PubMed1988

Noradrenergic cerebral stimulation of sensorineural impaired subjects: yohimbine effects on speech intelligibility and the auditory brain response.

Norepinephrine has been shown to improve signal-to-noise ratios of sensory systems, including that of the auditory system. Yohimbine has been observed to cause a selective increase of cerebral norepinephrine. It was administered in one dose to sensorineurally impaired subjects with the object of improving their speech hearing in noise. Speech intelligibility was measured by the adaptive procedure. Mild, significant improvement was noted in one of the hearing components, "attenuation," and an adverse effect was shown on "distortion," owing to noise. Auditory brainstem response was improved significantly. The objective of temporarily improving intelligibility in noise was not attained.

Aged↗
PubMed1994

Effects of temporal alterations on speech intelligibility in parkinsonian dysarthria.

The effect of two types of temporal alterations, paced and synthetic, on the intelligibility of parkinsonian dysarthric speech was investigated. Six speakers with idiopathic Parkinson's disease served as subjects. Paced temporal alterations were created by slowing each speaker to 60% of his/her habitual speaking rate. The synthetic alterations were created by modifying the habitual rate speech samples using digital signal processing. Three types of synthetic alterations were examined: Pause Altered, Speech Duration Altered, and Pause and Speech Duration Altered. The 60% of habitual speaking rate condition was more intelligible than the synthetic conditions. In addition, none of the synthetic alterations were found to be more intelligible than samples produced at habitual speaking rates. The results suggest that simple alterations of speech signals do not explain the differences in intelligibility that have been observed when parkinsonian dysarthric speakers reduce speaking rates. Reasons for the failure of synthetic alterations to increase speech intelligibility scores are discussed.

Aged↗