Considerations for Fitting Cochlear Implants Bimodally and to the Single-Sided Deaf.

When listening with a cochlear implant through one ear and acoustically through the other, binaural benefits and spatial hearing abilities are generally poorer than in other bilaterally stimulated configurations. With the working hypothesis that binaural neurons require interaurally matched inputs, we review causes for mismatch, their perceptual consequences, and experimental methods for mismatch measurements. The focus is on the three primary interaural dimensions of latency, frequency, and level. Often, the mismatch is not constant, but rather highly stimulus-dependent. We report on mismatch compensation strategies, taking into consideration the specific needs of the respective patient groups. Practical challenges typically faced by audiologists in the proposed fitting procedure are discussed. While improvement in certain areas (e.g., speaker localization) is definitely achievable, a more comprehensive mismatch compensation is a very ambitious endeavor. Even in the hypothetical ideal fitting case, performance is not expected to exceed that of a good bilateral cochlear implant user.

The Finnish simplified matrix sentence test for the assessment of speech intelligibility in the elderly.

Objective: A simplified version of the Finnish matrix sentence test (FMST) was developed to improve the reliability of hearing diagnostic for children and for patients with limited working memory capacity and/or vocabulary.Design: Study 1 evaluated the word matrix of the Finnish simplified matrix sentence test (FINSIMAT) to rule out systematic differences between the new FINSIMAT test lists, and to provide reference values for normal-hearing (NH) young adults (YA). In Study 2, the FINSIMAT and the FMST were evaluated in elderly listeners with mild-to-moderate hearing impairment (HI).Study sample: Twenty NH YAs participated in Study 1, and 16 elderly HI adults participated in Study 2.Results: For NH YAs, the reference speech reception threshold (SRT50) estimate and the slope for the FINSIMAT were -11.2 ± 1.0 dB signal-to-noise ratio (SNR) and 19.4 ± 1.9%/dB SNR. For the elderly HI listeners, the mean SRT50 estimates for the FINSIMAT and FMST were -4.1 and -3.6 dB SNR, respectively. The correlation between the FMST and FINSIMAT results was strong (r2 = 0.78, p < 0.001).Conclusion: The FINSIMAT showed comparable characteristics to the FMST and proved feasible for measurements in elderly HI listeners.

The development and evaluation of the Finnish digit triplet test.

OBJECTIVES: The aim of the study was to develop a reliable and easily accessible screening test for primary detection of hearing impairment. METHODS: Digits 0-9 were used to form quasirandom digit triplets. First, digit specific intelligibility functions and speech recognition thresholds (SRTs) were determined. To homogenize the test material digits with steep intelligibility function slopes were chosen and level correction up to ±2 dB were applied to the digits as needed. Evaluation measurements were performed to check for systematic differences in intelligibility between the test lists and to obtain normative reference function for normal-hearing listeners. RESULTS: The mean SRT and the final slope of the test lists were -10.8 ± 0.1 dB signal-to-noise ratio (SNR) and 21.7 ± 1.8%/dB, respectively (measurements at constant level; inter-list variability). The mean SRT and slope of the test subjects were -10.8 ± 0.5 dB SNR and 23.4 ± 5.2%/dB (measurements at constant level; inter-subject variability). The mean SRT for normal-hearing young adults for a single adaptive measurement is -9.8 ± 0.9 dB SNR. CONCLUSION: The Finnish digit triplet test is the first self-screening hearing test in the Finnish language. It was developed according to current standards, and it provides reliable and internationally comparable speech intelligibility measurements.

Characteristics and international comparability of the Finnish matrix sentence test in cochlear implant recipients.

OBJECTIVES: The first Finnish sentence-based speech test in noise--the Finnish matrix sentence test--was recently developed. The aim of this study was to determine the characteristics of the new test with respect to test-retest reliability, speech recognition curve, and international comparability in Finnish cochlear implant (CI) recipients. DESIGN: The speech reception thresholds (SRT) were measured by means of an adaptive test procedure and compared with the results of the traditional Finnish word test. Additional measurements for concurrent slope and SRT estimation were conducted to determine the speech recognition curve and to check the test-retest reliability. STUDY SAMPLE: The measurements were performed on 78 Finnish CI recipients. In a subset of 25 patients, additional measurements for test-retest reliability and slope determination were performed. RESULTS: The mean SRT was -3.5 ± 1.7 dB SNR, with only a weak correlation with the Finnish word test. Test-retest reliability was within ± 1 dB and the mean slope of the speech recognition curve was 14.6 ± 3.6 %/dB. The rehabilitation results were similar to the results published for the German matrix test. CONCLUSIONS: The Finnish matrix test was found to be suitable and efficient in CI recipients with similar characteristics as the German matrix test.

The development and evaluation of the Finnish Matrix Sentence Test for speech intelligibility assessment.

CONCLUSION: The Finnish Matrix Test is the first sentence test in noise for the Finnish language. It was developed according to the HearCom standards and provides reliable speech intelligibility measurements with highly comparable results with the other international matrix tests. OBJECTIVES: The aim of the study was to develop an accurate speech intelligibility test in noise for the Finnish language that is comparable across different languages. METHODS: We chose a matrix sentence test, which comprises a base matrix of 10 names, verbs, numerals, adjectives and nouns. Test lists were formed from this matrix quasi randomly, providing test sentences of the same syntactical structure. The speech material corresponds to everyday spoken language and the phoneme distribution is representative of the Finnish language. The test was optimized by determining the speech recognition thresholds of the individual words and subsequently by applying level corrections of up to ±3 dB. Evaluation measurements were performed to check the equivalence of the different test lists with respect to speech intelligibility and to provide reference values for further clinical applications. RESULTS: After training, the mean speech recognition threshold (SRT) and the slope of the final test lists were -10.1 ± 0.1 dB signal-to-noise-ratio (SNR)and 16.7 ± 1.2%/dB, respectively (measurements at constant level; inter-list variability). The mean SRT and the slope of the test subjects were -10.1 ± 0.7 dB SNR and 17.5 ± 2.2%/dB (measurements at constant level; inter-subject variability). The expected SRT range for normal-hearing young adults for adaptive measurements is -9.7 ± 0.7 dB SNR.

Speech-in-noise tests for multilingual hearing screening and diagnostics1.

PURPOSE: New complementary multilingual speech-in-noise tests in Russian, Turkish, and Spanish for hearing self-screening purposes and follow-up hearing diagnostics are compared to the speech tests of the European project, HearCom (Hearing in the Communication Society). METHOD: The tests consist of spoken numbers (Digit Triplet Test; Smits, Kapteyn, & Houtgast, 2004) or sentences (Matrix Test; e.g., Hagerman, 1982) presented in a background noise and estimate the speech reception threshold, which is the signal-to-noise ratio that yields 50% speech intelligibility. All tests were developed according to the HearCom minimum quality standards for speech intelligibility tests. This report presents a cross-language comparison of reference speech intelligibility functions for monaural headphone measurements with normal-hearing listeners. The same model function was employed to describe the speech intelligibility functions for all of the tests. RESULTS: Reference speech intelligibility functions of the new versions of the Digit Triplet Test and Matrix Test show high comparability to the HearCom tests. In order to achieve the highest possible comparability across languages, language- and speaker-dependent factors in speech intelligibility should be compensated for. CONCLUSION: To date, several complementary tests for screening and diagnostics have been developed in several languages. Adhering to the HearCom standards, the tests are highly comparable across languages. For the Matrix Test, equal syntax and linguistic complexity were maintained across languages due to common methodological standards.

Internationally comparable screening tests for listening in noise in several European languages: the German digit triplet test as an optimization prototype.

OBJECTIVE: A review is given of internationally comparable speech-in-noise tests for hearing screening purposes that were part of the European HearCom project. This report describes the development, optimization, and evaluation of such tests for headphone and telephone presentation, using the example of the German digit triplet test. In order to achieve the highest possible comparability, language- and speaker-dependent factors in speech intelligibility should be compensated for. MATERIALS AND METHODS: The tests comprise spoken numbers in background noise and estimate the speech reception threshold (SRT), i.e. the signal-to-noise ratio (SNR) yielding 50% speech intelligibility. RESULTS: The respective reference speech intelligibility functions for headphone and telephone presentation of the German version for 15 and 10 normal-hearing listeners are described by a SRT of -9.3 ± 0.2 and -6.5 ± 0.4 dB SNR, and slopes of 19.6 and 17.9%/dB, respectively. Reference speech intelligibility functions of all digit triplet tests optimized within the HearCom project allow for investigation of the comparability due to language specificities. CONCLUSIONS: The optimization criteria established here should be used for similar screening tests in other languages.

The Lower Saxony research network design of environments for ageing: towards interdisciplinary research on information and communication technologies in ageing societies.

Worldwide, ageing societies are bringing challenges for independent living and healthcare. Health-enabling technologies for pervasive healthcare and sensor-enhanced health information systems offer new opportunities for care. In order to identify, implement and assess such new information and communication technologies (ICT) the 'Lower Saxony Research Network Design of Environments for Ageing' (GAL) has been launched in 2008 as interdisciplinary research project. In this publication, we inform about the goals and structure of GAL, including first outcomes, as well as to discuss the potentials and possible barriers of such highly interdisciplinary research projects in the field of health-enabling technologies for pervasive healthcare. Although GAL's high interdisciplinarity at the beginning slowed down the speed of research progress, we can now work on problems, which can hardly be solved by one or few disciplines alone. Interdisciplinary research projects on ICT in ageing societies are needed and recommended.

Enhanced signal detectability in comodulated noise introduced by compression.

Many examples of natural noise show common amplitude modulations at different frequency regions. This kind of noise has been termed comodulated noise and is widely examined in hearing research, where an enhanced detectability of pure tones and narrow noise bands in comodulated noise compared to unmodulated noise is well known as the CMR or CDD effects, respectively. Here it is shown that only one signal processing step, a compressive nonlinearity motivated by the peripheral auditory system, is sufficient to explain a considerable contribution to these effects. Using an analytical approach, the influence of compression on the detectability of periodic and narrow band signals in the presence of unmodulated and comodulated noise is investigated. This theoretical treatment allows for identifying the mechanism leading to improved signal detection. The compressive nonlinearity constitutes an adaptive gain which selectively boosts a stimulus during time spans of inherently increased signal-to-noise ratio and attenuates it during time spans dominated by noise. On average, these time spans are more pronounced in stimuli with comodulated noise than with unmodulated noise, thus giving rise to the observed CMR and CDD effects.

The role of the auditory periphery in comodulation detection difference and comodulation masking release.

Natural sounds often exhibit correlated amplitude modulations at different frequency regions, so-called comodulation. Therefore, the ear might be especially adapted to these kinds of sounds. Two effects have been related to the sensitivity of the auditory system to common modulations across frequency: comodulation detection difference (CDD) and comodulation masking release (CMR). Research on these effects has been done on the psychophysical and on the neurophysiological level in humans and other animals. Until now, models have focused only on one of the effects. In the present study, a simple model based on data from neuronal recordings obtained during CDD experiments with starlings is discussed. This model demonstrates that simple peripheral processing in the ear can go a substantial way to explaining psychophysical signal detection thresholds in response to CDD and CMR stimuli. Moreover, it is largely analytically tractable. The model is based on peripheral processing and incorporates the basic steps frequency filtering, envelope extraction, and compression. Signal detection is performed based on changes in the mean compressed envelope of the filtered stimulus. Comparing the results of the model with data from the literature, the scope of this unifying approach to CDD and CMR is discussed.

Detecting modulated signals in modulated noise: (II) neural thresholds in the songbird forebrain.

Sounds in the real world fluctuate in amplitude. The vertebrate auditory system exploits patterns of amplitude fluctuations to improve signal detection in noise. One experimental paradigm demonstrating these general effects has been used in psychophysical studies of 'comodulation detection difference' (CDD). The CDD effect refers to the fact that thresholds for detecting a modulated, narrowband noise signal are lower when the envelopes of flanking bands of modulated noise are comodulated with each other, but fluctuate independently of the signal compared with conditions in which the envelopes of the signal and flanking bands are all comodulated. Here, we report results from a study of the neural correlates of CDD in European starlings (Sturnus vulgaris). We manipulated: (i) the envelope correlations between a narrowband noise signal and a masker comprised of six flanking bands of noise; (ii) the signal onset delay relative to masker onset; (iii) signal duration; and (iv) masker spectrum level. Masked detection thresholds were determined from neural responses using signal detection theory. Across conditions, the magnitude of neural CDD ranged between 2 and 8 dB, which is similar to that reported in a companion psychophysical study of starlings [U. Langemann & G.M. Klump (2007) Eur. J. Neurosci., 26, 1969-1978]. We found little evidence to suggest that neural CDD resulted from the across-channel processing of auditory grouping cues related to common envelope fluctuations and synchronous onsets between the signal and flanking bands. We discuss a within-channel model of peripheral processing that explains many of our results.

Processing cotton gin trash to enhance in vitro dry matter digestibility in reduced time.

Cotton gin trash (CGT) in the raw form is poorly digested by ruminants due to lignocellulosic complexes. These structures must be broken down before adequate digestion can occur. This may be performed by physical and/or chemical means. Two methods for improving digestibility are particle size reduction and/or treatment with sodium hydroxide (NaOH). To evaluate the effectiveness of each method, three experiments were performed in which different CGT types were tested. Each type represented trash from a particular cleaning stage in the cotton ginning process. First, each type was ground with a knife-type grinding mill using screen sizes 0.5, 1.0, and 2.0 mm. For the second experiment, particle size was held constant at 2 mm, and all CGT types were treated with 4% and 6% NaOH (w/w) at room temperature. An agitation cycle of 5 min on and 10 min off was used, with the total mixing time being 4 h. Lastly, particle size and NaOH concentration were held constant, and treatments were performed at room temperature, 40 degrees C, and 50 degrees C. The total mixing times were 2 and 3 h for 50 and 40 degrees C, respectively. For all experiments two subsamples of each treatment were tested for in vitro dry matter digestibility (IVDMD). From grinding alone, digestibility increased as particle size decreased. Grinding to 0.5 mm resulted in an average IVDMD of 47.8% while grinding to 2.0 mm resulted in an average IVDMD of only 33.8%. Digestibility also improved with a greater NaOH concentration. An average in vitro digestibility of 70.5% was achieved with 6% NaOH (w/w) treatment, essentially doubling that of the raw CGT. Increasing the reaction temperature did not result in increased digestibility because the mixture dried out, with a consequent reduction in chemical distribution and uniformity in heat transfer. There are still chemical residues in the CGT, and elimination/reduction of these is an issue that needs to be addressed in further research.