A new study has investigated whether cognitive and auditory factors affect the ability of a listener to hear in background noise[i].
Although many patients with elevated pure tone thresholds report difficulty with distinguishing speech in background noise, it is not unusual for someone with standard pure tone thresholds to report the same difficulty.
It can therefore be implied that there must be factors which contribute towards a person’s ability to hear speech in noise other than hearing loss caused by a loss of cochlear hair cells. In other words, there must be factors outside of audiometry detection, which contribute towards a person’s ability to hear speech in noise.
One potential factor is ‘hidden hearing loss’. This occurs when synapses in the ear are damaged. This does not impair a listener’s ability to hear pure tones, but does cause a listener to have difficulty when distinguishing speech in noise. We have previously discussed hidden hearing loss in editions 113 (here) and 184 (here) of BC Disease News.
The New Study
122 adults with normal, or near-normal hearing, participated in the new study. After undertaking tasks which assessed their ability to hear speech in noise, the participants were each given a composite speech-in-noise score (CSS). The researchers identified the 30 best performing participants and compared their hearing thresholds, temporal perception, noise exposure, attention and working memory against the 30 worst performing participants.
Analysis showed that working memory scores and extended high-frequency (EHF) (above 8 kHz) thresholds were significantly different between the two groups. The EHF hearing levels and working memory scores were responsible for 41% of the variations in CSS scores. Moreover, working memory scores and EHF thresholds were able to correctly predict low CSS with ‘reasonable’ (76%) accuracy.
For listeners with normal audiometry, this study insinuates that their ability to hear speech in noise is influenced by EHF hearing loss and working memory.
If working memory is related to the ability to hear speech in noise, this may explain why some patients with normal hearing report difficulties.
Similarly, a claimant may produce normal audiogram but also have elevated EHF thresholds, which are not routinely included in audiometric testing.
As a result, the study authors recommend that audiologists examine the working memory and EHF thresholds of patients who report difficulty with hearing speech in noise. Further, they advise that:
‘For those who have a history of noise exposure, clinicians could point out that poor EHF thresholds are often associated with noise exposure and focus on the importance of avoiding excessive noise exposure, or using hearing protection when avoidance is not possible’.
It must be noted that this study is not without its limitations. For example, participants in the worst CSS group did not necessarily find it difficult to hear speech in noise. They were simply the least able. Age may also have adversely impacted the low performing group, which was, on average, 6.1 years older than the high performing group.
EHF Thresholds and Speech in Noise
The authors in the latest study base their assertion that “poor EHF thresholds are often associated with noise exposure” on two studies.
The 1st study was authored by Charles Liberman, who was also co-author of the ‘hidden hearing loss’ hypothesis.[ii] Here, college students, with normal hearing thresholds up to 8 kHz, were split into two groups. One group was regularly exposed to loud noise and the other group was not. Subsequently, the participants’ hearing was tested between 8 kHz and 16 kHz. Those at risk of noise damage exhibited greater hearing loss in this region. Findings were consistent with animal studies, which demonstrate that the first frequencies to be affected by noise are the highest that the species can hear.
The 2nd study, authored by Garreth Prendergast, found that noise exposure was associated with elevated thresholds at 16 kHz in females[iii]. As was also the case with the Liberman study, participants who had been exposed to noise were more likely to have elevated thresholds at 16 kHz, despite all participants having similar hearing at 8 kHz and below.
Working Memory and Speech in Noise
The mechanism of working memory creates temporary storage and allows the brain to manipulate the necessary information for completing complex tasks, e.g. language comprehension, learning and reasoning[iv]. A 2014 study found that both older and younger listeners with poor working memory were less able to distinguish speech in background noise, regardless of their age.[v] Working memory does not appear to be affected by noise exposure.
Hidden Hearing Loss and Speech in Noise
The same research group that produced the new paper also published two published papers on ‘hidden hearing loss’ in humans. In both papers, they reported no link, or no significant relationship, between lifetime exposure to noise and ability to hear speech in noise.[vi] [vii]
In the 2nd paper, the researchers concluded that that synapse damage is, at most, one of several factors that play a role in humans’ speech in noise performance.
The latest paper concludes that both auditory (function of the ear) and cognitive (function of the brain) factors may contribute towards speech in noise issues in listeners with normal audiograms.
If future studies find that working memory is involved with the detection of speech in noise, then this could provide an additional defence against a claimant who has minimal hearing loss at noise sensitive frequencies, yet alleges an inability to distinguish speech.
Conversely, if a common view develops that there is a link between noise exposure, EHF hearing loss and speech in noise detection, claimants may begin producing audiograms that show hearing loss at higher frequencies as proof of causative noise-induced losses.
[i] Yeend, I., Beach, E. F. & Sharma, M. Working Memory and Extended High-Frequency Hearing in Adults: Diagnostic Predictors of Speech-in-Noise Perception. Ear Hear (2018). doi:10.1097/AUD.0000000000000640 https://europepmc.org/abstract/med/30052557 (Accessed 17 September 2018)
[ii] Liberman, M. C., Epstein, M. J., Cleveland, S. S., Wang, H. & Maison, S. F. Toward a Differential Diagnosis of Hidden Hearing Loss in Humans. PLOS ONE 11, e0162726 (2016). https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0162726 (Accessed 19 September 2018)
[iii] Prendergast, G. et al. Effects of noise exposure on young adults with normal audiograms I: Electrophysiology. Hearing Research 344, 68–81 (2017). https://www.sciencedirect.com/science/article/pii/S0378595516303203 (Accessed 19 September 2018)
[iv] Baddeley, A. Working memory. Science 255, 556–559 (1992). http://science.sciencemag.org/content/255/5044/556 (Accessed 19 September 2018)
[v] Gordon-Salant, S. & Cole, S. S. Effects of Age and Working Memory Capacity on Speech Recognition Performance in Noise Among Listeners With Normal Hearing. Ear Hear 37, 593–602 (2016). https://www.ncbi.nlm.nih.gov/pubmed/27232071 (Accessed 20 September 2018)
[vi] Yeend, I., Beach, E. F., Sharma, M. & Dillon, H. The effects of noise exposure and musical training on suprathreshold auditory processing and speech perception in noise. Hearing Research 353, 224–236 (2017). https://www.sciencedirect.com/science/article/pii/S0378595517300710 (Accessed 20 September 2018)
[vii] Valderrama, J. T. et al. Effects of lifetime noise exposure on the middle-age human auditory brainstem response, tinnitus and speech-in-noise intelligibility. Hearing Research 365, 36–48 (2018). https://www.sciencedirect.com/science/article/pii/S0378595517306287 (Accessed 20 September 2018)