Francis Kuk

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.

Effects of attention on the auditory evoked potentials recorded from the vertex (ABR) and the promontory (CAP) of human listeners

Auditory brainstem response (ABR) and the compound whole nerve action potential (CAP) of four human listeners were recorded while they were performing either visual duration or auditory frequency discrimination tasks with both types of stimuli presented simultaneously. The evoking tone bursts had the same center frequency as the standard discrimination tones and were presented between the discrimination tones. Waveforms between the two discrimination tasks did not differ in shape or latency, suggesting that the attention demand of the present task is not a central factor in the control of the auditory efferents.

Evaluation of a localization training program for hearing impaired listeners.

Objective: To evaluate the effectiveness of a home-based and a laboratory-based localization training program. Design: This study examined the effectiveness of a localization training program on improving the localization ability of 15 participants with a mild-to-moderately severe hearing loss. These participants had worn the study hearing aids in a previous study. The training consisted of laboratory-based training and home-based training. The participants were divided into three groups: a control group, a group that performed the laboratory training first followed by the home training, and a group that completed the home training first followed by the laboratory training. The participants were evaluated before any training (baseline), at 2 weeks, 1 month, 2 months, and 3 months after baseline testing. All training was completed by the second month. The participants only wore the study hearing aids between the second month and the third month. Localization testing and laboratory training were conducted in a sound-treated room with a 360 degree, 12 loudspeaker array. There were three stimuli each randomly presented three times from each loudspeaker (nine test items from each loudspeaker) for a total of 108 items on each test or training trial. The stimuli, including a continuous noise, a telephone ring, and a speech passage “Search for the sound from this speaker” were high-pass filtered above 2000 Hz. The test stimuli had a duration of 300 ms, whereas the training stimuli had five durations (3 s, 2 s, 1 s, 500 ms, and 300 ms) and four back attenuation (−8, −4, −2, and 0 dB re: front presentation) values. All stimuli were presented at 30 dB SL or the most comfortable listening level of the participants. Each participant completed 6 to 8, 2 hr laboratory-based training within a month. The home training required a two-loudspeaker computer system using 30 different sounds of various durations (5) by attenuation (4) combinations. The participants were required to use the home training program for 30 min per day, 5 days per week for 4 weeks. Results: Localization data were evaluated using a 30 degree error criterion. There was a significant difference in localization scores for sounds that originated from the back between baseline and 3 months for the two groups that received training. The performance of the control group remained the same across the 3 month period. Generalization to other stimuli and in the unaided condition was also seen. There were no significant differences in localization performance from other directions between baseline and 3 months. These results indicated that the training program was effective in improving the localization skills of these listeners under the current test set-up. Conclusions: The current study demonstrated that hearing aid wearers can be trained on their front/back localization skills using either laboratory-based or home-based training program. The effectiveness of the training was generalized to other acoustic stimuli and the unaided conditions when the stimulus levels were fixed.

A screening procedure for modified simplex in frequency-gain response selection.

The preference for hearing aid frequency-gain responses selected using the modified simplex procedure over that prescribed by NAL-R is not universal. A screening protocol used before individualized fitting may help streamline its use and ensure effective use of clinical time. In this protocol, listeners compare the prescribed frequency-gain response with selected alternate frequency-gain responses. Evaluation with the modified simplex procedure is indicated only when listeners consistently prefer the alternate frequency-gain responses in the screening procedure. Ten hearing aid wearers completed the screening protocol and the full modified simplex procedure. In addition, subjects compared their satisfaction for the prescribed and individually selected frequency-gain responses. The results were examined for efficiency, reliability, sensitivity, and efficacy of the selected frequency-gain response. Findings revealed that the screening protocol allowed reliable identification of listeners who needed fine-tuning of the prescribed frequency-gain response. Furthermore, satisfaction for selected frequency-gain response over prescribed frequency-gain response increased as more differences between the two responses were noted.

Effects of coordinated compression and pinna compensation features on horizontal localization performance in hearing aid users.

BACKGROUND Hearing-impaired listeners localize sounds better unaided than aided. Wide dynamic range compression circuits operating independently at each ear in bilateral fittings, and microphone positions of different hearing aid styles, have been cited as a reason. Two hearing aid features, inter-ear coordinated compression (IE) and pinna compensation (PC), were developed to mitigate the compromised aided localization performance. PURPOSE This study examined the effect of IE and PC on aided localization performance in the horizontal plane with hearing-impaired listeners. RESEARCH DESIGN A single-blind, repeated-measures design was used. STUDY SAMPLE A total of 10 experienced hearing aid users with bilaterally symmetrical sensorineural hearing loss who had previously participated in localization training were evaluated. DATA COLLECTION AND ANALYSIS Localization performance was measured using 12 loudspeakers spaced 30° apart on the horizontal plane. Aided performance was evaluated using a behind-the-ear hearing aid at four settings: omnidirectional microphone (Omni), Omni microphone with the PC feature, Omni microphone with IE, and Omni microphone with the PC feature and IE together. In addition, unaided localization performance was measured. RESULTS Significant improvement in the localization accuracy was measured for sounds arriving from the back when comparing the PC with the Omni conditions. The use of IE reduced the magnitude of errors for some listeners for sounds originating from ±90°. The average reduction in the errors was 7.3°. CONCLUSIONS This study confirmed that the use of the PC feature improved localization for sounds arriving from behind the listener. The use of IE may improve localization for some listeners for sounds arriving from the sides.

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.

Intensity Operating Range Measures as Predictors of Word-Recognition Ability in Cochlear Implant Subjects

The purposes of the experiment were to examine the appropriateness of pre- and post-implant intensity measures (thresholds, most comfortable listening level, and loudness discomfort level) as predictors of post-implant phoneme-recognition ability and to study the relationship between pre- and post-implant intensity measures. Pre-implant intensity measures were obtained on 16 subjects who were eventually implanted with either a Nucleus device (n = 8) or a Symbion device (n = 8). Phoneme scores on a NU-6 word list were obtained on these 16 subjects at 1 month post-implant. Post-implant intensity measures were also made on the 8 Symbion subjects at 1 month post-implant. The results showed that none of the pre-implant intensity measures correlated significantly with post-implant phoneme scores. In addition, pre-implant intensity measures did not correlate with the same post-implant intensity measures. However, post-implant MCLs and LDLs correlated significantly with phoneme scores as reflected by correlation coefficients that were larger than 0.8. These preliminary results suggest that although intensity measures may relate to phoneme-recognition ability, their use as predictive measures (as in pre-implant measures) for post-implant ability is questionable.

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.

Effects of attention on auditorily evoked potentials

Auditorily evoked responses to tone bursts (4‐ms duration with 1‐ms rise/fall) were recorded from the promontory as well as the ipsilateral mastoid of five human listeners while they were performing a visual duration (standard light flash of 50 ms) and an auditory frequency (center frequency at 2, 4, and 8 kHz; 250‐ms duration) discrimination task. Response evoking tone bursts were presented prior to and between the discrimination tone bursts. Visual and auditory stimuli were presented simultaneously. ABR and AP measurements were made during separate sessions. The method of constant stimuli was used for the discrimination tasks and the separation between stimuli was set for the value of the difference limen determined during a training session. Recordings obtained with acceptable discrimination performance were analyzed. No difference in amplitude, latency, or shape of the recordings was observed between the two discrimination tasks. The results suggest that the attention demand of the present task is not...