Chi-chuen Lau

Enough is enough: A primer on power analysis in study designs

Power analysis APRIL 2011 • VOL. 64 • NO. 4 The dispensing profession has always been driven by a reliance on evidence to support its activities. While various leaders in our field1-3 have outlined the different levels of evidence and specified the criteria to judge the validity of evidence, we continue to come across “evidence” that is quasi-evidence at best. Either the results of the studies are not treated statistically, or the statistical treatment lacks sufficient power to be meaningful. Such evidence can mislead readers to believe in the effectiveness of a particular feature when such efficacy is not present; or to believe in the ineffectiveness of a feature when its true efficacy has not been adequately evaluated. This paper briefly reviews an important factor that affects the interpretation of the results of a study — sample size — in hopes that the information presented will help clinicians and students better understand how to interpret the results of any clinical study.

Development of the ORCA nonsense syllable test.

Objectives: Many new processing features in hearing aids have their primary effects on information located in the high frequencies. Speech perception tests that are optimized for evaluating high-frequency processing are needed to adequately study its effects on speech identification. The goal of the current research was to develop a medium for evaluating the effects of high-frequency processing in hearing aids. Design: A list of 115 consonant-vowel-consonant-vowel-consonant nonsense syllables with American English consonants in all word positions was created in an open-set phoneme identification format. The source material was spoken by a male and a female speaker. A custom computer program was developed for administration of the test and automatic analysis of the test results. Nine normal-hearing listeners were employed in the collection of the normative data. The test was presented to the listeners in quiet (at 68 dB SPL), in noise at five signal-to-noise ratios (SNRs; −10, −5, 0, 5, and 10), and in a low-pass filter condition with cutoff frequencies at 500, 1000, 1500, 2000, and 4000 Hz. The data were examined to evaluate the psychometric properties of the test for different phoneme positions and phoneme classes. In addition, a shortened version of the test was developed based on the data from normal-hearing listeners. The test–retest reliability was verified at 0 dB SNR. The full and shortened versions of the test were repeated in 10 hearing-impaired listeners at their most comfortable listening level in quiet and in noise at various SNRs. Results: The availability of high-frequency output was verified with acoustic analysis. The performance intensity functions for both versions of the test (i.e., male and female speakers) showed expected monotonic growth with SNR and cutoff frequencies. High reliability was seen between test and retest identification scores in normal-hearing and hearing-impaired listeners. Conclusions: The current nonsense syllable test provided a reliable and efficient means for phoneme identification testing.

The Application of Binomial Probability Theory to Paired Comparison Judgments

The paired comparison technique can be potentially useful as a means to enhance the prescriptive fitting of hearing aids. Unfortunately, there are no guidelines to suggest how this technique can be...

Amplification for listeners with a moderately severe high-frequency hearing loss.

BACKGROUND Some evidence exists to support the use of an extended bandwidth (EBW) for those with a relatively mild to moderate degree of hearing loss. The use of frequency lowering is suggested for those with a severe/profound degree of hearing loss. The amplification option for those with a moderately severe hearing loss in the high frequencies is less clear. This study compared three amplification options for listeners with a moderately severe hearing loss in the high frequencies. PURPOSE The efficacy of three amplification options-limited bandwidth to 4000 Hz, EBW, and frequency transposition-were evaluated for listeners with a moderately severe, high-frequency hearing loss. RESEARCH DESIGN The experiment used a factorial repeated-measures design. STUDY SAMPLE A total of 13 adults with bilateral hearing loss of 50-70 dB HL at 4000 Hz served as test participants. DATA COLLECTION AND ANALYSIS The participants rated the sound quality of birdsongs and music when aided with the amplification options. Speech perception in quiet was measured at 50 dB SPL and 68 dB SPL input levels. The participants also completed a questionnaire on the best amplification option to use in different real-life environments during a 2 wk, take-home trial. The data were analyzed with repeated-measures analysis of variance. RESULTS The findings showed that more listeners preferred the EBW for home use but that the frequency transposition was the least preferred. In addition, the performance of the EBW was better than that of the limited bandwidth in speech recognition but similar to that of the frequency transposition. CONCLUSIONS The results supported the fitting of an EBW as the better choice for this group of listeners.

Effect of initial setting on convergence to optimal hearing aid setting using a simplex method

We examined the final preferred frequency gain response (i.e. final setting) selected using different starting points (i.e. initial settings) with a modified simplex procedure. These starting points included a frequency response close to the one recommended by NAL-R (Byrne and Dillon, 1986), a frequency response with the high and low frequency gain set to the maximum (max), a frequency response with the high and low frequency gain set to the minimum (min), and one in-between these values (mid). The time taken to converge to the final setting was also recorded. Subjects judged the clarity of short discourse passages presented at 63 dB(A) in the presence of babble noise (S/N = 0). The results indicated that the majority of subjects selected the same preferred frequency response regardless of initial settings. Variations in initial settings mainly affected the convergence time to the final choice. The frequency response recommended by NAL-R required the least time to converge, while those of the extremes (min and max) required the longest convergence time. Clinical implications are discussed.

Speech intelligibility benefits of hearing AIDS at various input levels.

BACKGROUND Although the benefits of hearing aids are generally recognized for soft- and conversational-level sounds, most studies have reported negative benefits (i.e., poorer aided than unaided performance) at high noise inputs. Advances in digital signal processing such as compression, noise reduction, and directional microphone could improve speech perception at high input levels. This could alter our view on the efficacy of hearing aids in loud, noisy situations. PURPOSE The current study compared the aided versus the unaided speech intelligibility performance of hearing-impaired (HI) listeners at various input levels (from 50-100 dB SPL) and signal-to-noise ratios (SNRs; quiet, +6, +3, and -3 dB) in order to document the benefits of modern hearing aids. In addition, subjective preference between aided and unaided sounds (speech and music) at various input levels was also compared. RESEARCH DESIGN The experiment used a factorial repeated-measures design. STUDY SAMPLE A total of 10 HI adults with symmetrical moderate to severe hearing losses served as test participants. In addition, speech intelligibility scores of five normal-hearing (NH) listeners were also measured for comparison. INTERVENTION Speech perception was studied at 50 and 65 dB SPL input levels in quiet and also in noise at levels of 65, 85, and 100 dB SPL with SNRs of +6, +3, and -3 dB. This was done for all participants (HI and NH). In addition, the HI participants compared subjective preference between the aided and unaided presentations of speech and music stimuli at 50, 65, 85, and 100 dB SPL in quiet. DATA COLLECTION AND ANALYSIS The data were analyzed with repeated-measures analysis of variance. RESULTS The results showed a decrease in aided benefits as input levels increased. However, even at the two highest input levels (i.e., 85 and 100 dB SPL), aided speech scores were still higher than the unaided speech scores. Furthermore, NH listeners and HI listeners in the aided condition showed stable speech-in-noise performance between 65 and 100 dB SPL input levels, except that the absolute performance of the NH listeners was higher than that of the HI listeners. Subjective preference for the unaided sounds versus the aided sounds increased as input level increased, with a crossover intensity at approximately 75 dB SPL for speech and 80 dB SPL for music. CONCLUSIONS The results supported the hypothesis that the study hearing aid can provide aided speech-in-noise benefit at very high noise inputs in a controlled environment.

Tracking of Noise Tolerance to Measure Hearing Aid Benefit

Background: The benefits offered by noise reduction (NR) features on a hearing aid had been studied traditionally using test conditions that set the hearing aids into a stable state of performance. While adequate, this approach does not allow the differentiation of two NR algorithms that differ in their timing characteristics (i.e., activation and stabilization time). Purpose: The current study investigated a new method of measuring noise tolerance (Tracking of Noise Tolerance [TNT]) as a means to differentiate hearing aid technologies. The study determined the within‐session and between‐session reliability of the procedure. The benefits provided by various hearing aid conditions (aided, two NR algorithms, and a directional microphone algorithm) were measured using this procedure. Performance on normal‐hearing listeners was also measured for referencing. Research Design: A single‐blinded, repeated‐measures design was used. Study Sample: Thirteen experienced hearing aid wearers with a bilaterally symmetrical (≤10 dB) mild‐to‐moderate sensorineural hearing loss participated in the study. In addition, seven normal‐hearing listeners were tested in the unaided condition. Data Collection and Analysis: Participants tracked the noise level that met the criterion of tolerable noise level (TNL) in the presence of an 85 dB SPL continuous discourse passage. The test conditions included an unaided condition and an aided condition with combinations of NR and microphone modes within the UNIQUE hearing aid (omnidirectional microphone, no NR; omnidirectional microphone, NR; directional microphone, no NR; and directional microphone, NR) and the DREAM hearing aid (omnidirectional microphone, no NR; omnidirectional microphone, NR). Each tracking trial lasted 2 min for each hearing aid condition. Normal‐hearing listeners tracked in the unaided condition only. Nine of the 13 hearing‐impaired listeners returned after 3 mo for retesting in the unaided and aided conditions with the UNIQUE hearing aid. The individual TNL was estimated for each participant for all test conditions. The TNT index was calculated as the difference between 85 dB SPL and the TNL. Results: The TNT index varied from 2.2 dB in the omnidirectional microphone, no NR condition to −4.4 dB in the directional microphone, NR on condition. Normal‐hearing listeners reported a TNT index of −5.7 dB using this procedure. The averaged improvement in TNT offered by the NR algorithm on the UNIQUE varied from 2.1 dB when used with a directional microphone to 3.0 dB when used with the omnidirectional microphone. The time course of the NR algorithm was different between the UNIQUE and the DREAM hearing aids, with the UNIQUE reaching a stable TNL sooner than the DREAM. The averaged improvement in TNT index from the UNIQUE directional microphone was 3.6 dB when NR was activated and 4.4 dB when NR was deactivated. Together, directional microphone and NR resulted in a total TNT improvement of 6.5 dB. The test–retest reliability of the procedure was high, with an intrasession 95% confidence interval (CI) of 2.2 dB and an intersession 95% CI of 4.2 dB. Conclusions: The effect of the NR and directional microphone algorithms was measured to be 2–3 and 3.6–4.4 dB, respectively, using the TNT procedure. Because of its tracking property and reliability, this procedure may hold promise in differentiating among some hearing aid features that also differ in their time course of action.