Maximum Speech Intelligibility Research Articles

Speech perception as afunction of cochlear coverage-comparison in bimodally hearing cochlear implant patients. German version

Hearing success in bimodally hearing patients with acochlear implant (CI) and ahearing aid (HA) exhibits different results: while some benefit from bimodal CI and HA, others do not. The aim of this study was to investigate hearing success in terms of speech perception in bimodally fitted patients in relation to the cochlear coverage (CC) of the CI electrodes. Using the OTOPLAN software (CAScination AG, Bern, Switzerland), CC was retrospectively measured from CT scans of the temporal bone of 39patients, who were then categorized into two groups: CC ≤ 65% (CC500) and CC > 65% (CC600). Monaural speech intelligibility for monosyllables at asound pressure level (SPL) of 65 dB in open field was assessed at various timepoints, preoperatively with HA and postoperatively with CI, and compared between the groups. In addition, speech intelligibility was correlated with CC in the entire cohort before surgery and during follow-up (FU). Overall, no significant differences in speech intelligibility were found between CC500 and CC600 patients at any of the FU timepoints. However, both CC500 and CC600 patients showed asteady improvement in speech intelligibility after implantation. While CC600 patients tended to show an earlier improvement in speech intelligibility, CC500 patients tended to show aslower improvement during the first 3months and asteeper learning curve thereafter. The two patient groups converged during FU, with no significant differences in speech intelligibility. There was no significant relationship between unimodal/unilateral free-field speech intelligibility and CC. However, patients with aCC of 70-75% achieved maximum speech intelligibility. Despite anonsignificant correlation between CC and speech discrimination, patients seem to reach their maximum in unimodal/unilateral speech understanding mainly at 70-75% coverage. However, there is room for further investigation, as CC500 was associated with ashorter cochlear duct length (CDL), and long and very long electrodes were used in both groups.

Effects of Task Demands on Neural Correlates of Acoustic and Semantic Processing in Challenging Listening Conditions.

Purpose Listeners shift their listening strategies between lower level acoustic information and higher level semantic information to prioritize maximum speech intelligibility in challenging listening conditions. Although increasing task demands via acoustic degradation modulates lexical-semantic processing, the neural mechanisms underlying different listening strategies are unclear. The current study examined the extent to which encoding of lower level acoustic cues is modulated by task demand and associations with lexical-semantic processes. Method Electroencephalography was acquired while participants listened to sentences in the presence of four-talker babble that contained either higher or lower probability final words. Task difficulty was modulated by time available to process responses. Cortical tracking of speech-neural correlates of acoustic temporal envelope processing-were estimated using temporal response functions. Results Task difficulty did not affect cortical tracking of temporal envelope of speech under challenging listening conditions. Neural indices of lexical-semantic processing (N400 amplitudes) were larger with increased task difficulty. No correlations were observed between the cortical tracking of temporal envelope of speech and lexical-semantic processes, even after controlling for the effect of individualized signal-to-noise ratios. Conclusions Cortical tracking of the temporal envelope of speech and semantic processing are differentially influenced by task difficulty. While increased task demands modulated higher level semantic processing, cortical tracking of the temporal envelope of speech may be influenced by task difficulty primarily when the demand is manipulated in terms of acoustic properties of the stimulus, consistent with an emerging perspective in speech perception.

Efficient Adaptive Speech Reception Threshold Measurements Using Stochastic Approximation Algorithms.

This study examines whether speech-in-noise tests that use adaptive procedures to assess a speech reception threshold in noise (SRT50n) can be optimized using stochastic approximation (SA) methods, especially in cochlear-implant (CI) users. A simulation model was developed that simulates intelligibility scores for words from sentences in noise for both CI users and normal-hearing (NH) listeners. The model was used in Monte Carlo simulations. Four different SA algorithms were optimized for use in both groups and compared with clinically used adaptive procedures. The simulation model proved to be valid, as its results agreed very well with existing experimental data. The four optimized SA algorithms all provided an efficient estimation of the SRT50n. They were equally accurate and produced smaller standard deviations (SDs) than the clinical procedures. In CI users, SRT50n estimates had a small bias and larger SDs than in NH listeners. At least 20 sentences per condition and an initial signal-to-noise ratio below the real SRT50n were required to ensure sufficient reliability. In CI users, bias and SD became unacceptably large for a maximum speech intelligibility score in quiet below 70%. In conclusion, SA algorithms with word scoring in adaptive speech-in-noise tests are applicable to various listeners, from CI users to NH listeners. In CI users, they lead to efficient estimation of the SRT50n as long as speech intelligibility in quiet is greater than 70%. SA procedures can be considered as a valid, more efficient, and alternative to clinical adaptive procedures currently used in CI users.

Factors Affecting the Variation of Maximum Speech Intelligibility in Patients With Sensorineural Hearing Loss Other Than Apparent Retrocochlear Lesions.

ObjectivesTo examine the relationship between speech intelligibilities among the similar level of hearing loss and threshold elevation of the auditory brainstem response (ABR).MethodsThe relationship between maximum speech intelligibilities among similar levels of hearing loss and relative threshold elevation of the click-evoked ABR (ABR threshold - pure tone average at 2,000 and 4,000 Hz) was retrospectively reviewed in patients with sensorineural hearing loss (SNHL) other than apparent retrocochlear lesions as auditory neuropathy, vestibular schwannoma and the other brain lesions.ResultsComparison of the speech intelligibilities in subjects with similar levels of hearing loss found that the variation in maximum speech intelligibility was significantly correlated with the threshold elevation of the ABR.ConclusionThe present results appear to support the idea that variation in maximum speech intelligibility in patients with similar levels of SNHL may be related to the different degree of dysfunctions of the inner hair cells and/or cochlear nerves in addition to those of outer hair cells.

Use of the Speech Transmission Index for the assessment of sound annoyance in open-plan offices

In open-plan offices, employees often have to work despite being distracted by multiple sources of speech close to them. This disturbance is even more severe when the surrounding conversations are intelligible. For this reason the disruptive power of such babble-like noises can be quantified by measuring speech intelligibility. As such, the Speech Transmission Index is usually used to assess the quality of open-plan offices. In this article, the STI is used to evaluate the nuisance potential of sound environments in an open-plan office. 57 subjects were confronted with a serial memory task in four STI conditions (from 0.25 to 0.65). Noise annoyance was assessed objectively by measuring performance, and subjectively using the NASA-TLX questionnaire for measuring cognitive load. A very strong inter-individual variability appeared in performance measurements. Approximately half of the panel was made of high performing subjects, who proved to be insensitive to speech intelligibility. For the other half, performance was reduced when STI increased, as shown in previous studies, with a plateau for STI greater than 0.45. This strong inter-individual variability can explain the discrepancy between results observed in previously published studies. The NASA-TLX questionnaire proved to give useful complementary results. For example, high-performing subjects related a higher workload in the condition of maximum speech intelligibility.

Positive auditory cortical responses in patients with absent brainstem response

ObjectiveTo compare the detectability of the different auditory evoked responses in patients with retrocochlear lesion. MethodsThe 40-Hz auditory steady state response (ASSR) and the N1m auditory cortical response were examined by magnetoencephalography in 4 patients with vestibular schwannoma, in whom the auditory brainstem response (ABR) was absent. ResultsApparent N1m responses were observed despite total absence of the ABR or absence except for small wave I in all patients, although the latency of N1m was delayed in most patients. On the other hand, clear ASSFs could be observed only in one patient. Very small 40-Hz ASSFs could be detected in 2 patients (amplitude less than 1fT), but no apparent ASSFs were observed in one patient, in whom maximum speech intelligibility was extremely low and the latency of N1m was most prolonged. ConclusionThe N1m response and 40-Hz ASSR could be detected in patients with absent ABR, but the N1m response appeared to be more detectable than the 40-Hz ASSR. SignificanceCombined assessment with several different evoked responses may be useful to evaluate the disease conditions of patients with retrocochlear lesions.

A dual space approach to beam tracing for optimal microphone placement.

In many teleconferencing or video-conferencing applications, a high degree of speech intelligibility is difficult to achieve due to sub-optimal microphone placement in the room. In this work, beam tracing in the dual space is used to acoustically model an enclosed space with the goal of discovering optimal positions for microphone placement. In the majority of existing work, beam tracing is used to model empty rooms with simple layouts. This work allows for the addition of freestanding items, such as furniture or support pillars, and more complex room layouts. In addition, currently existing algorithms use beam tracing to predict and simulate the response of a source in a room at a specific location. In this work, both signals of interest as well as interferers will be included in the model. Instead of predicting the response at specific (x,y) locations, this work seeks to guide the placement of microphones for maximum speech intelligibility. The dual space representations for the reflected beams are generated for each source. These representations are overlaid on top of each other to highlight areas with the highest signal to interferer ratio.

Candidacy for Bilateral Hearing Aids: A Retrospective Multicenter Study

The goal of this study was to find factors for refining candidacy criteria for bilateral hearing aid fittings. Clinical files of 1,000 consecutive hearing aid fittings were analyzed. Case history, audiometric, and rehabilitation data were collected from clinical files, and an extensive questionnaire on long-term outcome measures was conducted. After at least 2 years of hearing aid use, 505 questionnaires were returned. In order to compare differences in benefits between unilateral and bilateral fittings, two subgroups were composed in which most relevant variables (age, degree of hearing loss, and audiometric asymmetry) were matched for unilateral fittings (n=212) and bilateral fittings (n=477). The bilateral group had significantly higher benefit scores than the unilateral group for detection, speech intelligibility in reverberation, and localization, but poorer scores for comfort of loud sounds. The benefit of bilateral hearing aids was not significantly related to the level of technology of the hearing aids. The analysis of the relation between objective parameters and the subjective outcome measures showed that candidacy for a successful bilateral fitting could not be predicted from age, maximum speech intelligibility, employment, exposure to background noise, or social activities.

Optimal acoustic conditions in classrooms

Computer models of eight classrooms were constructed with varying combinations of absorbent materials on the surfaces of the rooms using the CATT 7.0 computer program. The amount, location and cost of finish materials and the noise levels produced by the air-conditioning system were varied in the models. RASTI values were calculated for six seats in each room. By determining conditions that result in maximum RASTI values, maximum speech intelligibility conditions were obtained. Background noise levels dominated the RASTI values at levels of NC 40 and higher regardless of room finishes. At RASTI values of NC 35 and less, once an amount of absorbent material equal in area to the floor was present, only small changes in RASTI values were observed whether the material was located on the ceiling or the upper parts of the walls or a combination of both. The cost of material and locations of typical furnishings were also considered in the process.

THE SPEECH INTELLIGIBILITY OF THE PUBLIC ADDRESS SYSTEMS AT 14 DUTCH RAILWAY STATIONS

The speech transmission quality of the complete public address system at 14 Dutch railway stations is determined. The listener positions, at which the speech intelligibility is measured, are selected at the platforms, halls and interconnections according to a specially developed measuring procedure. The 14 stations selected are representative of the total of about 400 stations in the Netherlands and are spread over the whole country. The speech intelligibility determined with the objective STI method was found to be “poor” to “fair”. In order to improve the quality, further investigations have begun. Different loudspeaker configurations are optimized by the help of a “ray tracing” computer program. Special attention is given to minimum costs, minimum annoyance in the environment and maximum speech intelligibility at the different platforms of railway stations.

Binaural hearing aid algorithms for noisy and reverberant environments

In noisy and reverberant acoustical environments the human hearing system is capable of concentrating on a desired speaker, while attenuating undesired sounds like noise or reverberation. This so called ‘‘cocktail-party processing’’ is reduced in hearing-impaired persons. New hearing aid strategies try to imitate binaural processing principles to suppress interfering noise or reverberation in order to yield maximum speech intelligibility for the impaired listener. Two algorithms are described that reduce unwanted signal energies by attenuating sound that arises from the sides (lateral suppression) and that remove reverberation and short reflections. They were combined and implemented in real time on a multiprocessor setup to allow for adaptive adjustment of parameters and an optimal fit to the individual hearing loss. The noise reduction performance of the algorithms was tested with normal- and hearing-impaired subjects. Subjective speech quality and speech intelligibility assessments as well as speech intelligibility measurements show that both groups benefit significantly from the preprocessing strategies in anechoic and reverberant acoustical situations with interfering speakers.

Pediatric speech intelligibility test: performance-intensity characteristics.

Performance-intensity (PI) functions for Pediatric Speech Intelligibility (PSI) test materials were obtained in 40 normal-hearing children between 3 and 6 yrs of age. PSI messages were monosyllabic words and sentences presented in quiet and in the presence of a competing speech message. The message-to-competition ratio was constant across intensity levels: +4 dB (words) and O dB (sentences). Maximum speech intelligibility scores were 100% correct in all children for all conditions. The steepness of the PSI-PI functions, defined by the intensity range yielding performance between 20 and 80%, ranged from 8 to 12 dB. Threshold levels (50% correct) ranged from 21 to 26 dB SPL. With one exception, chronological age did not significantly influence the steepness of PSI-PI functions. The exception was the increasing steepness with increasing age noted for sentences in competition. A significant chronological age developmental trend was noted for all speech threshold results.

Review of recent research on the selection of frequency-gain characteristics for hearing aids.

Following the Harvard master hearing aid study in 1947 there was little research on linear amplification. Recently, however, there have been a number of studies designed to determine the relationship between the frequency-gain characteristic of a hearing aid and speech intelligibility for persons with sensorineural hearing loss. These studies have demonstrated that a frequency-gain characteristic that rises at a rate of 6 dB/octave, as suggested by the Harvard study, is not optimal. They have also demonstrated that high-frequency emphasis of 10-40 dB above 500-1000 Hz is beneficial. Most importantly, they have demonstrated that hearing aids as they are presently being fit do not provide maximum speech intelligibility. Percent word correct scores obtained with the best frequency-gain characteristics tested in various studies have been found to be 9 to 19 percentage points higher than scores obtained with commercial aids owned by subjects. This increase in scores is equivalent to an increase in signal-to-noise ratio of 10 to 20 dB. This is a significant increase which could allow impaired listeners to communicate in many situations where they presently cannot. These results demonstrate the need for further research on linear amplification aimed at developing practical suggestions for fitting hearing aids.

Rehabilitation Strategies for Sensorineural Hearing Loss,

This book comprises clinical and research articles presented at the Second Symposium on the Application of Signal Processing Concepts to Hearing Aids, Pennsylvania State University, March 23-24, 1979. The initial article presents the role of the otolaryngologist, as viewed by an otolaryngologist, in the hearing rehabilitation process. There are four articleson hearing aid selection procedures. One stresses the need for working closely with the patient during a period of weeks in matching electroacoustical factors with needs in everyday situations. Another compares different real-ear procedures in which amplification is evaluated by behavioral responses. In a third article, the question of binaural vs monaural hearing aids is discussed, and it is emphasized that the decision must rest on thorough testing of hearing aid use in both modes. The fourth article points out the advantages of frequency-selective amplification and output limiting in providing maximum speech intelligibility and comfort. Topics treated in other articles

Auditory findings in brain stem disorders.

Audiometric tests were administered to 16 patients with intra-axial brain stem lesions. Eight patients showed some audiometric loss in one or both ears. Maximum speech intelligibility (PB) scores were at least 80% in 10 patients. In the remaining, depressed PB maximum performance was found either on both ears or on the ear contralateral to the site of lesion. Performance-intensity (PI) functions for PB words yielded a consistent difference between ears across all intensity levels in nine patients. Performance on synthetic sentence identification (SSI) materials was disporportionately poor for sentences in the presence of ipsilateral competing speech messages (ICM). In the presence of contralateral competing speech messages (CCM), SSI performance generally remained within the normal range. A relatively greater performance deficit for the ICM task than for the CCM task was an important characteristic of brain stem disorder.

Optimal and Preferred Listening Levels for Speech in Aircraft Acoustical Environments

There is some question as to whether pilots and aircrew personnel routinely adjust the audio level of their radio receivers for maximum speech intelligibility and minimal damage risk to hearing. In an effort to answer this question, data have been obtained on the preferred listening levels (PPLs) of student naval flight officers in aircraft acoustical environments. Thirty subjects were given the task of tracking continuous speech in quiet and in the presence of three levels of background noise (70, 85, and 100 dB SPL). They were asked to adjust the level of the speech for maximum intelligiblilty. Two different tracking procedures were employed: one utilizing a Békésy-type switch and the other an adjustable hold-type switch, similar to a normal radio gain control. PLLs obtained for the three noise conditions revealed that as the noise level decreased, the subjects preferred a more favorable signal-to-noise ratio. Normative PLL data and intelligibility test data for selected signal-to-noise ratios will be presented and discussed.

Some Examinations to Determine the Best Frequency Characteristic of Hearing Aids for Patients with Hearing Loss in the High-Tone Range

The purpose of the present investigation was to study the possibility of improving the hearing aid treatment of patients suffering from high tone loss with recruitment. Unlike previous projects of similar character where the aim was to obtain maximum speech intelligibility, our aim was to determine the frequency response curve giving the most comfortable sound impression for the patient. With this in mind our hypothesis is that the optimal frequency response will depend upon the input sound pressure. It is postulated that the frequency response should be flat up to a given frequency, the audiogram's cut off frequency, and thereafter should rise with a variable slope to a certain level (treble amplification), slope and treble amplification being functions of input sound pressure level. Ten patients were examined with response curves synthesized on laboratory equipment using earphone presentation. Current speech was used as test signal. In the first part of the examination the test promotor chose at random ...

New Types of Ear Protectors

In the construction of ear plugs the chief problem is to combine the necessary sound insulation with comfort and sufficient speech intelligibility. Ear plugs are described which fulfill these requirements to a reasonable degree. They can be used for the attenuation of all audible frequencies or, with minor adaptation, as low-pass filters attenuating the more dangerous high frequencies only. For maximum speech intelligibility, both kinds of sound insulation are adequate for steady noises, whereas the low-pass filter is better for intermittent noises, detonations, and noise that can be interrupted to permit communication. Extensive experiments in industry and the armed forces have shown that low-pass filters with a cut-off frequency of 1000 cps provide sufficient hearing protection in most situations.