Oh deaf, where is thy sting?

©www.CartoonStock.com

©www.CartoonStock.com

I am half in love with easeful deaf. I am peacefully oblivious while night noises, restaurant clatter and Guy Fawkes fireworks annoy my patient partner. Conversations sometimes take bizarre twists when I answer questions that no one has asked or weirdly mistake topics but I often enjoy this, though those I talk with do not.

Hearing loss in old age has such a characteristic pattern that it has been given the label “elderly presbyacusis”. We become increasingly insensitive to sounds of higher frequencies. While we are very young we can hear high pitched squeaks of bats and the full range of the dawn chorus but from our thirties onward we gradually begin to lose higher frequencies. This makes speech harder to understand because although vowels are still easy to distinguish differences between consonants such as “K” and “P” or “S” and “F” are muffled.

A U.S. survey found that 23% of people aged between 65 and 75 years of age and 40% of those aged 76 and older suffer hearing losses in both ears, especially for the upper frequencies. (1) One cause is mechanical damage from loud sounds to the hair cells on the basilar membrane in the inner ear, particularly those that detect high frequencies. We also lose cells in the nerve pathways from a coding structure called the cochlear nucleus and from the auditory nerve that delivers information from the ear to the brain. This makes it harder to make out the order in which different speech sounds follow each other in rapid sequence, which is crucial for recognizing spoken words (2).

Studies of senior gerbils (3) find that those reared in quiet experience less loss of auditory nerve fibres and have better hearing than litter-mates reared in noise. Age not only muffles the earliest stages of sound registration but also degrades the first computations in the auditory nerve, cochlear nucleus and auditory cortex of the brain that filter and shape information for further interpretation.

Noise damage is not the only cause. A Norwegian survey (4) found that from 30% to 58% of hearing losses “could be explained by age alone” but an additional 1% to 6% was due to lifetime exposure to noise and to other factors such as diabetes and infections. Possibly because older women are less likely than older men to have lived in very noisy environments they experienced smaller hearing losses. Their advantages also seemed related to their better general health, when matched age for age. There are associations between increasing deafness and decline of cognitive abilities but similar data from this and other studies suggests that this is because poor health affects both hearing and the mind. (See also an earlier blog in this series “Age, underpants, balance and he mind”).

This study also checked whether amounts of hearing losses are related to the increase in use of headphones and portable sound systems during people’s lifetimes but found no evidence for this, but few of this elderly sample had used loud sound-systems and headphones in their youth. In contrast, over the last decade, portable sound systems have become very common and incidence of hearing losses among USA adolescents has increased from 14.9% 1988/1994 to 19.5% in 2005-2006 (5). Noise-related hearing losses during adolescence are ominous for old age. A study charmingly titled “Evidence of a misspent youth” (6) found that rats exposed to loud noise when young not only showed immediate neural degeneration and consequent hearing losses and, even without further noise exposure, these losses increased and accelerated as they aged.

For otherwise happily functioning oldies it is a downer to be told that some degree of hearing loss is inevitable, that it does not only affect high pitched sounds but also the ability to make subtle distinctions between the temporal order of sounds, and that it is partly caused and accelerated by, sometimes unavoidable, exposure to loud noises.

For most of us the main issue is how, and how much these changes affect our everyday lives. There are obvious regrets, such the loss of the full spectrum of birdsong, and of other natural noises, but for most of us the poignant problem is degradation of conversation, one of the great joys of life. Mildly deaf people questioned in our Manchester surveys generally agreed that it is usually quite easy and comfortable to talk with one person at a time. During dialogues people rapidly attune to each-other and adjust not only how loud they speak but also the words they use, choosing those that are less likely to be misheard, shortening their sentences and adjusting their speech patterns. Dialogues between people with markedly different accents are a matter of further subtle accommodations and compromises. We get more information from lip reading than we are aware and the more familiar a voice or an accent, the easier things are. We can recognize what family members and close friends say much more easily than we understand strangers. Especially during telephone conversations unfamiliar accents can be difficult. Cold-calling salespersons with unfamiliar accents never make me offers that I can’t refuse but always offers that I can’t understand.

A less obvious problem is that even when we can correctly make out what is said mild deafness increases the effort and time that time that we need to do this. The task of resolving sounds into words shares information-processing bandwidth with memory and interpretation. Even young people with good hearing using noisy telephones forget words that they have heard despite having correctly repeated them as they were spoken (7). As we age this problem of combining the separate tasks of interpreting noises as words, remembering the words and making sense of sentences becomes much harder because, in addition to increasing deafness, we become slower at processing information of any kind. An uncomfortable result is that the wit and pertinence of our responses declines and when we eventually find apt and clever rejoinders these fall lame because their moments have passed. Choking back undelivered aphorisms is an acknowledged curse of deafness (at least among the intensely eloquent Manchester and Newcastle volunteers whom we polled).

For the same reasons it is a trial for even slightly deaf elderly to interact with speakers who talk very fast. Even more so if they ostentatiously pause at random moments to check that you are keeping up before they gabble on again. Of course it is an enormous benefit to have partners, children, grandchildren and friends who know you well and are so vigilant for lapses that they can be relied on to silence an entire room full of people while they patiently and clearly explain your condition and your errors to them and to you. Bless you every one.

Attempts at compensatory strategies cause other social problems. Seriously deaf elderly often must choose between extreme passive social smiling or taking bullying initiatives to seize and keep control. You never miss changes of topic if you initiate all of them yourself and you never mishear questions or comments for which you leave no space. Whether to seem silent and stupid or, worse, silent and resentful or to become a tyrannical bore is an interesting choice.

The inevitable time-coupling of increasing peripheral hearing losses with slowing of mental computation can make our conversation seem much duller than it might be. Aphorisms emerge too late, sluggish interpretations and miss-hearings can be mistaken for slow-wittedness. Spending increasing mental bandwidth to hear what is being said borrows from the limited capacity that we have (8,9). This reduces the accuracy with which we can remember what has gone on and make correct inferences from what has been said. Our studies also found that, unsurprisingly, even slight deafness makes it far harder to attend to long lectures, especially if the topics are both stodgy and intellectually demanding.

Problems with deafness can be counteracted to some extent by higher intelligence but even for the most able, in this very restricted practical sense, deafness does indeed reduce their apparent “conversational IQ”. I do not like this way of putting it but cling to the thought that I shall soon be issued with new batteries for my fine National Health hearing aid. Then Deaf shall have no Dominion.

(With acknowledgements and warm respect to the best and funniest novel written on deafness, David Lodge’s “Deaf Sentence”).

References

  1. Seidman, M.D., Ahmad, N. & Bai, U. (2002). Molecular mechanisms of age-related hearing loss. Ageing Research Reviews, 1, 331-343.
  2. Tremblay, K.L., Piskosz, M., Souza, P. (2003). Effects of age and of age-related hearing loss on the neural representation of speech cues. Clinical Neurophysiology, 114, 1332-1343.
  3. Schmiedt, R.A., Mills, J.H. & Boettcher, F.A. (1996) Age-related loss of activity of auditory nerve-fibres, Journal of Neurophysiology, 76, 2799-2803.
  4. Tambs, K., Hoffman, H.J., Borchgevink, H.M., Holmen, J. & Samuelson, S.O. (2003). Hearing loss induced by noise, ear infections and head injuries: results from the Norf-Trondewlag Hearing Loss Study. Informa, healthcare, 42, 89-105.
  5. Shargorodsky, J., Curhan, S.G., Curhan, G.C., Eavey, R. (2010). Change in Prevalence of Hearing loss in US Adolescents. Journal of the American Medical Association, 2010, 772-778.
  6. S.G. Kujawa & M. C. Liberman, (2006). Acceleration of Age-Related Hearing Loss by Early Noise Exposure: Evidence of a Misspent Youth. Journal of Neuroscience, 26, 2115 – 2123.
  7. Rabbitt, P. M. A. (1966). “Recognition: Memory for words correctly heard in noise. “Psychonomic Science 6, 383-384.
  8. Rabbitt, P. (1991). Mild Hearing Loss can cause apparent memory failures which increase with age and reduce with IQ. Acta Oto-laryngologica, 111, 167-176.
  9. Wingfield, A. Tun, P. & McCoy, S. (2005). Hearing Loss in Older Adulthood. What it is and how it interacts with Cognitive Performance. Current Directions in Psychological Science   14, 144-148

About Gray Rabbitt

Grumpy gerontologist
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