Starkey Research & Clinical Blog

Listening is more effortful for new hearing aid wearers

Ng, E.H.N., Classon, E., Larsby, B., Arlinger, S., Lunner, T., Rudner, M., Ronnberg, J. (2014). Dynamic relation between working memory capacity and speech recognition in noise during the first six months of hearing aid use. Trends in Hearing 18, 1-10.

This editorial discusses the clinical implications of an independent research study and does not represent the opinions of the original authors.

Numerous studies have illustrated the relationship between working memory, cognitive resources and speech perception and suggest that listeners with limited working memory or cognitive resources are more likely to struggle with speech recognition in noise (Gatehouse, et al., 2003; Lunner, 2003). Conversely, larger working memory capacity may allow more rapid and successful matching between speech inputs and stored lexical templates.  This concept is described by the Ease of Language Understanding (ELU) model, which proposes that cognitive processing demands vary according to the degradation of the speech signal in different environments (Ronnberg, 2003; Ronnberg et al., 2008). In quiet, favorable listening conditions, speech inputs are easily matched to stored representations and the processing is automatic. In difficult listening environments, more explicit processing is required to match inputs to stored representations. How efficiently this goal is achieved is dependent upon working memory capacity.

Using these concepts as underpinning, Ng and her colleagues proposed that working memory and cognitive processing may have more of an impact on speech recognition for new hearing aid users than for experienced hearing aid users. Hearing aids improve speech audibility and directional microphones and noise reduction can help preserve speech in adverse listening conditions, which should reduce the need for explicit working memory processing. However, if phonological representations stored in memory have been degraded by hearing loss over time, amplified speech perceived by new hearing aid users will not match their stored templates. Therefore, more explicit processing in working memory may be required to identify words. Over time, as the individual becomes acclimated to the amplified sound, stored templates may adapt and become more similar to their acoustic counterparts, reducing the working memory and cognitive load requirements for correct identification. Following this reasoning, Ng and her colleagues proposed that there would be a significant relationship between cognitive functioning and speech recognition in new, first-time hearing aid users but that the relationship would become weaker over time as stored speech representations based on amplified sound become more established.

To examine this hypothesis, 27 first-time hearing aid users were recruited from a pool of subjects at a Swedish university Audiology clinic. All had mild to moderately-severe sensorineural hearing loss and no previous experience with hearing aids. Nine of the subjects were fitted monaurally and 18 were fitted binaurally. Four participants had in-the-ear or canal instruments and 23 had behind-the-ear instruments. Most of the subjects became full-time hearing aid users and the rest were consistent, part-time users.

Approximately four months prior to being fitted with their hearing aids, subjects attended an experimental session at which they completed speech recognition in noise and cognitive testing. Four cognitive tests were administered: the Reading Span test, a physical matching task, a lexical decision making task and a rhyme judgment test. The Swedish version of the Reading Span test was used to assess working memory or listeners’ ability to process and store verbal information in a parallel task design (Ronnberg et al., 1989). After hearing a list of sentences, subjects were asked to recall either the first or final word of each sentence in the list.  The test was scored according to the total number of words correctly recalled. The physical matching test (Posner & Mitchell, 1967), which measured general processing speed, required participants to judge whether two examples of the same letter were visibly identical or different in physical shape (e.g., A-A vs. A-a). Scores were based on reaction time for correct trials. The lexical decision making task required subjects to judge whether a string of 3 letters presented on a screen was a real Swedish word. Scores were based on reaction time for correct trials. The rhyme judgment test required subjects to determine whether two words, presented on a screen, rhymed or not (Baddeley & Wilson, 1985). This test was intended to measure the quality of stored phonological representations and was scored based on percentage of correct judgments.

The speech recognition in noise test was conducted again at the hearing aid fitting appointment (0 months) and again at approximately 3 month intervals (3 months and 6 months). The investigators chose to evaluate speech recognition and its relationship to cognitive tests at these intervals based on previous reports suggesting that a familiarization period of 4-9 weeks was required to reduce cognitive load (Rudner et al., 2011).

The results of the speech recognition in noise test showed, not surprisingly, that aided SRT was significantly better than unaided SRT.  The change in SRT over time was also significant, in that the SRT measured at 6 months was significantly better than at 0 months. The 3 month SRT was not significantly different from the 0 month or 6 month tests.  Age and pure-tone-average (PTA) were significantly correlated with SRT at 0, 3 and 6 month tests. At 0 and 3 months, the cognitive measures of reading span, physical matching and lexical decision were all correlated with SRT. At 6 months, only the correlations between lexical decision and reading span were significant. These results indicate that the relationship between cognitive measures and speech recognition declined over the first 6 months of hearing aid use.  Regression analysis showed a similar pattern in that reading span and PTA were significant predictors of speech recognition at 0 months, but by 6 months, only PTA was a significant predictor.

The pattern of results in this study supports the authors’ proposal that for first-time hearing aid users, working memory and cognitive processing play a more important role in speech perception in noise immediately after fitting than they do after acclimatization. Their hypothesis that stored perceptual representations are altered by long-term hearing loss and are therefore mismatched with newly amplified speech inputs is supported by their clinical observations. First-time hearing aid users typically experience amplified speech as “tinny”, “metallic”, or in some way “artificial”.  For most new hearing aid users, this perception resolves within a few weeks or so, though others may require longer periods of use to become acclimated. As time goes on, new hearing aid users usually report that speech sounds more natural and the data presented here support the assertion that stored lexical representations, after becoming distorted from long-term hearing impairment, may be adapting based on consistently restored audibility of speech sounds.

The results of this study support the importance of cognitive functioning for speech perception in noise and suggest that new hearing aid users experience increased cognitive demands for understanding speech as compared to experienced hearing aid users. It follows that individuals who have limited working memory or impaired cognition may also experience longer acclimatization periods with their new hearing aids.

Clinicians are accustomed to counseling patients to wear their hearing aids consistently; for most of the day, every day.  The authors of this study did not examine the usage patterns of their subjects with reference to their hypothesis, but future studies should investigate the potential effects of limited hearing aid use on the relationship between cognition and speech recognition in noise. If full-time use results in a more rapidly waning relationship between these variables (indicating a more rapid decrease in cognitive load required for speech recognition) it would underscore the importance of consistent hearing aid use for new users, especially those with cognitive or working memory limitations.

 

References

Baddeley, A. & Wilson, B. (1985). Phonological coding and short term memory in patients without speech. Journal of Memory and Language 24(1), 490-502.

Gatehouse, S., Naylor, G., & Elberling, C. (2003). Benefits from hearing aids in relation to the interaction between the user and the environment. International Journal of Audiology 42 (Suppl. 1), S77-S85.

Hagerman, B. & Kinnefors, C. (1995). Efficient adaptive methods for measuring speech reception threshold in quiet and in noise. Scandinavian Audiology 24 (1), 71-77.

Lunner, T. (2003). Cognitive function in relation to hearing aid use. International Journal of Audiology 42, (Suppl. 1), S49-S58.

Lunner, T., Rudner, M. & Ronnberg, J. (2009). Cognition and hearing aids. Scandinavian Journal of Psychology 50, 395-403.

McCoy, S.L., Tun, P.A. & Cox, L.C. (2005). Hearing loss and perceptual effort: downstream effects on older adults’ memory for speech. Quarterly Journal of Experimental Psychology A, 58, 22-33.

Ng, E.H.N., Classon, E., Larsby, B., Arlinger, S., Lunner, T., Rudner, M., Ronnberg, J. (2014). Dynamic relation between working memory capacity and speech recognition in noise during the first six months of hearing aid use. Trends in Hearing 18, 1-10.

Posner, M. & Mitchell, R. (1967). Chronometric analysis of classification. Psychological Review 74(5), 392-409.

Ronnberg, J., Arlinger, S., Lyxell, B. & Kinnefors, C. (1989). Visual evoked potentials: Relation to adult speechreading and cognitive function. Journal of Speech and Hearing Research 32(4), 725-735.

Ronnberg, J. (2003). Cognition in the hearing impaired and deaf as a bridge between signal and dialogue: a framework and a model. International Journal of Audiology 42 (Suppl. 1), S68-S76.

Ronnberg, J., Rudner, M. & Foo, C. (2008). Cognition counts: A working memory system for ease of language understanding (ELU). International Journal of Audiology 47 (Suppl. 2), S99-S105.

Rudner, M., Ronnberg, J. & Lunner, T. (2011). Working memory supports listening in noise for persons with hearing impairment. Journal of the American Academy of Audiology 22, 156-167.