Brent Edwards

Hearing impairment and cognitive energy: the Framework for Understanding Effortful Listening (FUEL)

The Fifth Eriksholm Workshop on “Hearing Impairment and Cognitive Energy” was convened to develop a consensus among interdisciplinary experts about what is known on the topic, gaps in knowledge, the use of terminology, priorities for future research, and implications for practice. The general term cognitive energy was chosen to facilitate the broadest possible discussion of the topic. It goes back to Titchener (1908) who described the effects of attention on perception; he used the term psychic energy for the notion that limited mental resources can be flexibly allocated among perceptual and mental activities. The workshop focused on three main areas: (1) theories, models, concepts, definitions, and frameworks; (2) methods and measures; and (3) knowledge translation. We defined effort as the deliberate allocation of mental resources to overcome obstacles in goal pursuit when carrying out a task, with listening effort applying more specifically when tasks involve listening. We adapted Kahneman’s seminal (1973) Capacity Model of Attention to listening and proposed a heuristically useful Framework for Understanding Effortful Listening (FUEL). Our FUEL incorporates the well-known relationship between cognitive demand and the supply of cognitive capacity that is the foundation of cognitive theories of attention. Our FUEL also incorporates a motivation dimension based on complementary theories of motivational intensity, adaptive gain control, and optimal performance, fatigue, and pleasure. Using a three-dimensional illustration, we highlight how listening effort depends not only on hearing difficulties and task demands but also on the listener’s motivation to expend mental effort in the challenging situations of everyday life.

Phonemic restoration by hearing-impaired listeners with mild to moderate sensorineural hearing loss

The auditory system is capable of perceptually restoring inaudible portions of speech. This restoration may be compromised as a result of hearing impairment, particularly if it is combined with advanced age, because of degradations in the bottom-up and top-down processes. To test this hypothesis, phonemic restoration was quantitatively measured with hearing-impaired listeners of varying ages and degrees of hearing impairment, as well as with a normal hearing control group. The results showed that the restoration benefit was negatively correlated with both hearing impairment and age, supporting the original hypothesis. Group data showed that listeners with mild hearing loss were able to perceptually restore the missing speech segments as well as listeners with normal hearing. By contrast, the moderately-impaired listeners showed no evidence of perceptual restoration. Further analysis using the articulation index showed that listeners with mild hearing loss were able to increase phonemic restoration with audibility. Moderately-impaired listeners, on the other hand, were unable to do so, even when the articulation index was high. The overall findings suggest that, in addition to insufficient audibility, degradations in the bottom-up and/or top-down mechanisms as a result of hearing loss may limit or entirely prevent phonemic restoration.

A comparison of CIC and BTE hearing aids for three-dimensional localization of speech.

Abstract Three-dimensional sound localization of speech in anechoic space was examined for eleven listeners with sensorineural hearing loss. The listeners were fitted bilaterally with CIC and BTE hearing aids having similar bandwidth capabilities. The goal was to determine whether differences in microphone placement for these two styles (CICs at the ear canal entrance; BTEs above the pinna) would influence the availability of pinna-related spectral cues and hence localization performance. While lateral and polar angle localization was unaffected by the hearing aid style, the rate of front-back reversals was lower with CICs. This pattern persisted after listeners accommodated to each set of aids for a six week period, although the overall rate of reversals declined. Performance on all measures in all conditions was considerably poorer than in a control group of listeners with normal hearing. Sumario Se evaluó la localización tridimensional de sonidos del habla en un espacio anecoide en once personas con pérdida auditiva sensorineural. A los once se les adaptaron CIC y BTE bilateralmente con capacidad de ancho de banda similar. El objetivo fue determinar si las diferencias en la colocación del micrófono con ambos tipos (CIC en el ingreso del conducto auditivo; BTE sobre el pabellón auricular) podría influenciar la disponibilidad de claves espectrales relacionadas con el pabellón y por ello, el rendimiento para la localización. Mientras que la localización del ángulo lateral y polar no fue afectada por el tipo de auxiliar, la tasa de inversiones frente-atrás fue menor con los CIC. Este patrón persistió después de que estas personas se acostumbraron a cada set de auxiliares por un período de seis semanas, a pesar de que declinó la tasa global de reversiones. El rendimiento en todas las mediciones y condiciones fue considerablemente más pobre que en el grupo control de personas con audición normal.

Acclimatization to hearing aids.

Objective: Evidence for a clinically significant effect of acclimatization to hearing aids is mixed. The aim of this study was to test for auditory acclimatization effects in new unilateral and bilateral adult hearing aid users. Hypotheses were i) there would be improvements in aided speech recognition in new hearing aid users, compared with unaided listening and with a control group of experienced hearing aid users, and ii) improvements would correlate with severity of hearing loss, hearing aid use, and cognitive capacity. Design: Speech recognition in noise was measured for a 65 and a 75 dB SPL target with the Four Alternative Auditory Feature test. Speech recognition in noise was measured within 1 week of fitting and retested at 12 weeks postfitting in new hearing aid users (16 unilateral and 16 bilateral fit). A control group of experienced hearing aid users (n = 17) was tested over a similar time scale. Cognitive capacity (reaction time and working memory) was measured, and self-reported change in performance was assessed using the Speech, Spatial and Qualities of Hearing Scale. Hearing aid use was assessed via data logging at the completion of the study. Results: Mean improvements in speech recognition of up to 4% were observed across conditions and across groups consistent with a general practice effect. On average there was no evidence of auditory acclimatization in the new hearing aid user groups in terms of improvement in aided listening conditions above that observed in unaided recognition or in the control group. There was no correlation between change in aided speech recognition and severity of hearing loss, hearing aid use, or cognitive capacity. New users reported significant improvement over time in aided performance on a self-report questionnaire compared with the control group. Conclusions: On average, there was no improvement over time in new users’ aided speech recognition relative to unaided recognition or to the control group. This does not support a robust acclimatization effect with nonlinear hearing aids. Test–retest variability may obscure small average acclimatization effects; variability was not accounted for by individual differences in severity of hearing loss, hearing aid use, or cognitive capacity. New users’ subjective report of increased benefit over time may be reflective of other aspects of adjustment to hearing aid use not examined in this study.

Using genetic algorithms with subjective input from human subjects : Implications for fitting hearing aids and cochlear implants

Objective: To present a comprehensive analysis of the feasibility of genetic algorithms (GA) for finding the best fit of hearing aids or cochlear implants for individual users in clinical or research settings, where the algorithm is solely driven by subjective human input. Design: Due to varying pathology, the best settings of an auditory device differ for each user. It is also likely that listening preferences vary at the same time. The settings of a device customized for a particular user can only be evaluated by the user. When optimization algorithms are used for fitting purposes, this situation poses a difficulty for a systematic and quantitative evaluation of the suitability of the fitting parameters produced by the algorithm. In the present study, an artificial listening environment was generated by distorting speech using a noiseband vocoder. The settings produced by the GA for this listening problem could objectively be evaluated by measuring speech recognition and comparing the performance to the best vocoder condition where speech was least distorted. Nine normal-hearing subjects participated in the study. The parameters to be optimized were the number of vocoder channels, the shift between the input frequency range and the synthesis frequency range, and the compression-expansion of the input frequency range over the synthesis frequency range. The subjects listened to pairs of sentences processed with the vocoder, and entered a preference for the sentence with better intelligibility. The GA modified the solutions iteratively according to the subject preferences. The program converged when the user ranked the same set of parameters as the best in three consecutive steps. The results produced by the GA were analyzed for quality by measuring speech intelligibility, for test-retest reliability by running the GA three times with each subject, and for convergence properties. Results: Speech recognition scores averaged across subjects were similar for the best vocoder solution and for the solutions produced by the GA. The average number of iterations was 8 and the average convergence time was 25.5 minutes. The settings produced by different GA runs for the same subject were slightly different; however, speech recognition scores measured with these settings were similar. Individual data from subjects showed that in each run, a small number of GA solutions produced poorer speech intelligibility than for the best setting. This was probably a result of the combination of the inherent randomness of the GA, the convergence criterion used in the present study, and possible errors that the users might have made during the paired comparisons. On the other hand, the effect of these errors was probably small compared to the other two factors, as a comparison between subjective preferences and objective measures showed that for many subjects the two were in good agreement. Conclusions: The results showed that the GA was able to produce good solutions by using listener preferences in a relatively short time. For practical applications, the program can be made more robust by running the GA twice or by not using an automatic stopping criterion, and it can be made faster by optimizing the number of the paired comparisons completed in each iteration.

Unilateral and bilateral hearing aids, spatial release from masking and auditory acclimatization

Spatial release from masking (SRM) was tested within the first week of fitting and after 12 weeks hearing aid use for unilateral and bilateral adult hearing aid users. A control group of experienced hearing aid users completed testing over a similar time frame. The main research aims were (1) to examine auditory acclimatization effects on SRM performance for unilateral and bilateral hearing aid users, (2) to examine whether hearing aid use, level of hearing loss, age or cognitive ability mediate acclimatization, and (3) to compare and contrast the outcome of unilateral versus bilateral aiding on SRM. Hearing aid users were tested with and without hearing aids, with SRM calculated as the 50% speech recognition threshold advantage when maskers and target are spatially separated at ±90° azimuth to the listener compared to a co-located condition. The conclusions were (1) on average there was no improvement over time in familiar aided listening conditions, (2) there was large test-retest variability which may overshadow small average acclimatization effects; greater improvement was associated with better cognitive ability and younger age, but not associated with hearing aid use, and (3) overall, bilateral aids facilitated better SRM performance than unilateral aids.

Brainstem processing following unilateral and bilateral hearing-aid amplification

Following previous research suggesting hearing-aid experience may induce functional plasticity at the peripheral level of the auditory system, click-evoked auditory brainstem response was recorded at first fitting and 12 weeks after hearing-aid use by unilateral and bilateral hearing-aid users. A control group of experienced hearing-aid users was tested over a similar time scale. No significant alterations in auditory brainstem response latency or amplitude were identified in any group. This does not support the hypothesis of plastic changes in the peripheral auditory system induced by hearing-aid use for 12 weeks.

A Model of Auditory-cognitive Processing and Relevance to Clinical Applicability.

Hearing loss and cognitive function interact in both a bottom-up and top-down relationship. Listening effort is tied to these interactions, and models have been developed to explain their relationship. The Ease of Language Understanding model in particular has gained considerable attention in its explanation of the effect of signal distortion on speech understanding. Signal distortion can also affect auditory scene analysis ability, however, resulting in a distorted auditory scene that can affect cognitive function, listening effort, and the allocation of cognitive resources. These effects are explained through an addition to the Ease of Language Understanding model. This model can be generalized to apply to all sounds, not only speech, representing the increased effort required for auditory environmental awareness and other nonspeech auditory tasks. While the authors have measures of speech understanding and cognitive load to quantify these interactions, they are lacking measures of the effect of hearing aid technology on auditory scene analysis ability and how effort and attention varies with the quality of an auditory scene. Additionally, the clinical relevance of hearing aid technology on cognitive function and the application of cognitive measures in hearing aid fittings will be limited until effectiveness is demonstrated in real-world situations.

Restoration of loudness summation and differential loudness growth in hearing-impaired listeners

When normal-hearing (NH) listeners compare the loudness of narrowband and wideband sounds presented at identical sound pressure levels, the wideband sound will most often be perceived as louder than the narrowband sound, a phenomenon referred to as loudness summation. Hearing-impaired (HI) listeners typically show less-than-normal loudness summation, due to reduced cochlear compressive gain and degraded frequency selectivity. In the present study, loudness summation at 1 and 3 kHz was estimated monaurally for five NH and eight HI listeners by matching the loudness of narrowband and wideband noise stimuli. The loudness summation was measured as a function both of noise bandwidth and level. The HI listeners were tested unaided and aided using three different compression systems to investigate the possibility of restoring loudness summation in these listeners. A compression system employing level-dependent compression channels yielded the most promising outcome. The present results inform the development of future loudness models and advanced compensation strategies for the hearing impaired.

PSYCHOACOUSTIC EQUIVALENCE OF FREQUENCY MODULATION AND QUASI-FREQUENCY MODULATION

Frequency modulation (FM) is known to be reasonably approximated by quasi-frequency modulation (QFM) for small modulation indices, beta, but the range of beta for which this approximation is appropriate is unclear. Thresholds for discrimination between FM and QFM with equal betas are obtained in order to estimate an upper bound on beta for determining when this approximation is valid psychoacoustically, i.e., when FM and QFM are indiscriminable. At low modulation frequencies (fm < or = 4 Hz), QFM is never a valid approximation to FM at any detectable modulation level since discrimination thresholds are below FM detection thresholds. For modulation frequencies between 8 and 32 Hz, discrimination thresholds are approximately -2.5 dB (20 log beta) and can be accounted for by detection of envelope fluctuations in the QFM signal. For modulation frequencies at 64 Hz and above, discrimination thresholds improve with increasing modulation frequency in the same manner as FM and QFM detection thresholds. Discrimination in this frequency region seems to be mediated by detection of the component 2fm Hz below the carrier, i.e., by the most detectable component in the FM signal which does not occur in the QFM signal.