Hearing aid sales, along with advertising and promotion seems to have locked onto the Big Three (cognition, dementia, and Alzheimer’s disease) great fear motivators. (Not all hearing aid advertising, but a significant amount focuses on the Big Three). All three are currently promoted to result in cognition being reduced, slowed, or improved with the use of hearing aids for those having hearing loss.
Is there support for hearing aid use to overcome these developments? The answer remains to be resolved, but even some of the studies in support provide caveats that are essentially totally ignored in hearing aid advertising. These will be explained within the text that follows.
Current Hearing Aids
Current hearing aids make sounds louder to be audible. Additionally, current hearing aids include several technologies that are intended to facilitate language understanding for persons with hearing impairment in challenging listening situations. Some of these include directional microphones, noise reduction, and fast-acting amplitude compression systems,1 and other hearing aid adaptive features.
“However, the processed signal itself may challenge listening to the extent that with specific types of technology, and in certain listening situations, individual differences in cognitive processing resources may determine listening success. It is argued that signal processing designed to improve speech understanding may have both positive and negative consequences, and that these may depend on individual WM (working memory) capacity.” (Bold, underlined, and Italics added)1.
We Hear with Our Ears, But Listen with Our Brain
Since at least 1989, some studies have suggested that hearing loss is directly associated with poorer cognitive (brain) functioning and incident dementia, possibly through the effects of hearing loss on cognitive load and/or mediation through reduced social engagement (Lin, 2013)2. Another study, however, unequivocally stated that hearing aids improve brain function in persons with hearing loss. Lin et. al. go on to say, however, that there are conflicting results that may be explained by variations in the study populations and the methods used for assessments. As a result, they studied the rates of cognitive decline and the risk of incident cognitive impairment and found they were linearly associated with the severity of a person’s hearing loss, stating that hearing loss is independently associated with cognitive decline in older adults.
Caveat – Although there is a strong correlation between hearing loss and cognitive functions, that hearing loss causes cognitive decline has not yet been established. Hearing aid use was associated with slightly attenuated rates of cognitive decline and risk of cognitive impairment amount in individuals with hearing loss, but these results were not significant.2
Improved Hearing Aid Signal Processing the Key to Success?
Some hearing aid reports suggests that advanced signal processing is the key to successfully reduce cognition decline. Other studies report that although hearing aids are designed that use complex processing intended to improve speech recognition, that while many listeners benefit from such processing, “…it can also introduce distortion that offsets or cancels intended benefit for some individuals3.”
Two-Band Compression – One study investigated the use of a commonly-used hearing aid processing feature, that of two-band (Low and high) frequency compression. (Compression is essentially a standard feature in every advanced, and even most very basic hearing aids to reduce loud incoming sounds so they are not over amplified). The purpose was to determine the effects of cognitive ability (working memory) on individual listeners’ responses to distortion caused by this frequency compression (considered an advanced feature) when applied to noisy speech4. Results of the study showed that distortions caused by at least one form of frequency compression can negatively affect laboratory-based measures of intelligibility of noisy speech, and that this effect is greater in older listeners with hearing loss and poor working memory (cognition).
WDRC – When using WDRC (wide dynamic range compression) hearing aids, as the total amount of signal distortion increased, listeners with higher working memory (WM) performed better on an intelligibility task than listeners with lower working memory. Results suggested that older listeners with hearing loss and poor working memory are more susceptible to distortions caused by some types of hearing aid signal processing and noise. Interestingly, and although not a focus of this study, an examination of subject characteristics showed that working memory did not decline with age (subjects ranged from 62 to 92 years of age).5
In other studies, listeners having “poor” cognition performed better with slow-acting compression hearing aids, whereas those listeners having “good” cognition performed better with fast-acting compression hearing aids.6,7,8
Caveat – Current digital signal processing hearing aids employ extensive time-varying adaptive functions (adaptive compression, adaptive directionality, adaptive noise management, etc.). Does this adaptation introduce distortions or complications that might interfere with cognition? Just how these adaptive signal processing functions interact with individual working memory cognitive abilities is not known. Might the complexity of the signal processing be more cognitively demanding depending on individual differences and degrees of loss, as suggested by Lunner and Thorén?
Working memory (WM) is a system for temporarily storing and managing the information required to carry out complex mind tasks such as learning, reasoning, and comprehension. It is involved in the selection, initiation, and termination of information-processing functions such as encoding, storing, and retrieving data. Some believe that working memory includes short-term memory and other processing mechanisms that help to make use of short-term memory.
Caveat – Increased susceptibility to poor working memory resulting from various distortions should be measured and considered in the hearing aid fitting process. Only in this way might a hearing aid’s signal processing characteristics be tailored to an individual’s cognitive ability.
Basic and Advanced Hearing Aid Signal Processing
Hearing aids have multiple types of signal processing, many of them contributing to distortions. Distortion refers not just to total harmonic distortion, but other distortions resulting from the signal processing (amplitude/frequency compression, noise management, and even digital signal processing which has less of the original signal than does analog signal processing).
What this means, is if the WM has a heightened chance of accessing incorrect or irrelevant information due to hearing aid distortions (low WM), for some individuals, a hearing aid can actually hinder, rather than facilitate speech processing. On the other hand, those having a high WM may be able to benefit from more advanced signal processing.
Therefore, it appears that the solution to cognition improvement is more than just advanced signal processing. A person’s working Memory Capacity (WMC) appears to be a significant issue. Lunner and Sundewall-Thorén, in working with individuals wearing hearing aids, measured WMC and found that “Participants with low WMC showed better comprehension with basic signal processing, whereas those with high WMC heard better with the more advanced signal processing.” 5 (Emphasis added).
Caveat – This increased susceptibility to poor working memory resulting from various distortions should be considered in the fitting process.
Hearing Aids and The Big Three Hearing Loss Fears
Are certain cautions being heeded, or is it “damn the torpedoes and full speed ahead” when it comes to hearing aids and treatment of the promoted “Big Three Hearing Loss Fears?”
Hearing Aid Fitting and Selling Responsibilities for Manufacturers and Dispensers
- According to research, it is important for both hearing aid manufacturers and dispensers to be aware that only people with a high WMC (working memory capacity) are likely to benefit from more advanced signal processing. As such, hearing aid fittings should be based on more than the person’s auditory perception of speech.
- For some individuals having a low WMC, signal processing that is too advanced impedes, rather than helps, cognitive processing of the signal.
- Is WMC being measured to determine the best amplification options? This appears not to be the case in hearing aid sales. If basic signal processing is being used, are we helping or hurting a person’s rehabilitative process? And, if advanced signal processing costs more, and the user is unlikely to benefit from it, is this being fair to the patient? Is it ethical?
- High WMC shields the auditory system from distraction, thus supporting the attention process. This may assist to separate speech from background noise, and provide an important cognitive shield against fatigue9.
- Reliable brain indices of cognitive disturbance and effort designed to coordinate with age-related hearing impairment, which may then improve hearing aid fitting, need to be developed.
- Not all hearing impaired seem to benefit from advanced signal processing. Individuals with low WM showed better comprehension with basic signal processing, whereas those with high WM performed better with more advanced signal processing. However, is this distinction made in the hearing aid fitting process? It seems not, because the “story” implies that all individuals need the most advanced signal processing available, regardless of their WM. The implication being that the most advanced signal processing is also the least distorted amplified signal. It may be, but is this significant? And, what about the level of the WM?
- It seems that when the signal becomes difficult to follow, regardless of the reason, a person’s WM becomes fully occupied by attempting to resolve the misinterpretations and misunderstandings2,10. And, the more adverse the listening conditions, the less spare capacity is available to encode the information into long-term memory.
- Cognitive hearing science relates also to lip reading and visual language. Little, if anything, is represented in hearing aid advertising relative to the importance of these in managing cognition, dementia, or Alzheimer’s disease.
What Seems to be Needed
- Reliable brain indices of cognitive disturbance and effort as related to the hearing mechanism
- Studies evaluating the effects of WM training, and whether any improvements transfer to other skills, such as understanding in noise
- Understanding of the roles of speech reading and visual language (sign language), not just the auditory aspects of speech
- How current WM tests are being used for hearing aid use recommendations
- Tests to measure cognitive performance under complex listening circumstances.
Improved hearing aid signal processing to reduce cognitive function have generated mixed results.
- Lunner T, Rudner M, Rönnberg J. (2009). Cognition and hearing aids. Scand J Psychol. Oct:50(5):395-403.
- Lin FR, Yaffe K, Xia J, Li Xue Q, Harris TB, Purchase-Helzner E, Satterfield S, Ayonayon HN, Ferrucci L, and Simonsick EM. (2013). Hearing loss and cognitive decline among older adults. JAMA Intern Med. Feb 25; 173(4):293-299.
- Rönnberg, J. (2016). Hearing with your ears, listening with your brain. APS Association for Psychological Science. February.
- Arehart KH, Souza P, Baca R, and Kates JM. (2013). Working memory, age, and hearing loss: susceptibility to hearing aid distortion. Ear and Hearing, Vol 34, No. 3, 251-260.
- Lunner, T., & Sundewall Thorén, E. (2007). Interactions between cognition, compression, and listening conditions: effects on speech-in- noise performance in a two-channel hearing aid. Journal of the American Academy of Audiology, 18, 604–617.
- Gatehouse S, Naylor G, Elberling C. (2003) Benefits from hearing aids in relation to the interaction between the user and the environment. Int J Audiol 42(Suppl. 1):S77–S85.
- Gatehouse S, Naylor G, Elberling C. (2006) Linear and non-linear hearing aid fittings—2. Patterns of candidature. Int J Audiol 45:153–171.
- Lunner T. (2003) Cognitive function in relation to hearing aid use. Int J Audiol 42(Suppl. 1):S49–S58.
- Rönnberg, J. (2016). Hearing with your ears, listening with your brain. APS Association for Psychological Science. February.
- Alessandro P, Simon JZ, and Anderson S. (2016). Effect of informational content of noise on speech representation in the aging midbrain and cortex. Journal of Neurophysiology, September, 2016.
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