Auditory deprivation, Dr Rodney Taylor, Advanced Hearing Aid Clinic
The human body functions best when it’s used. It functions optimally when all the parts are given a workout each day, whether it’s a brisk walk around the block, a workout at the gym, a swim at the cottage, etc. The human body operates on a “use it or lose it” scenario and the auditory system is no different.
Auditory deprivation describes a significant decrease in an unaided ear’s ability to recognize speech and a decrease in general hearing ability due to a lack of auditory stimulation. In other words, the ability of the auditory system to process speech declines due to lack of stimulation (hearing loss). With auditory deprivation, the brain gradually loses some of its auditory processing ability, which would affect one’s general hearing ability.
When you get a hip or knee replacement, the day after surgery, the physical therapists encourage you to walk. It has been proven that the sooner you get to work on that stainless steel body part, the faster your recovery period.
The body’s various systems – skeletal, sensory, muscular and other systems will atrophy – become weakened – with prolonged non-use. For example, if you take up jogging, the first morning jog may have you aching all over the next day. The most effective way to do it is to start off slowly, and gradually increase the exercise time.
Hearing loss is most often gradual in nature, and therefore, a hearing problem may not be evident for some time. As we age, our bodies become less efficient and organs run less efficiently.
There is a growing collection of research and detailed studies that indicate that individuals
with hearing loss are better helped when they act quickly to resolve their hearing difficulties. When the hearing nerves and areas within the brain are deprived of sound, they tend to atrophy or weaken over time. Kral et al. (2000) found neuronal structural differences in the auditory cortex of auditory deprived brains compared to brains that were not deprived. Kral et al. (2005) found that the functional development of the auditory cortex critically depends on the auditory experience. Turgeon et al. (1995) found that the neurons in the inferior colliculus, a key relay station in the primary and secondary auditory cortex, are considerably altered by auditory deprivation. Prolonged lack of stimulation makes the process of wearing a hearing aid more difficult. We refer to this as auditory deprivation, first reported in 1984 (Silman et al., 1992).
More recently, studies have noted the development of Associate Auditory Cortical areas to
take over the function of damaged Primary Cortical areas with sound stimulation. These areas, with time, resemble the Primary Auditory Cortex, in that they are well organized with respect to frequency organization.
The key to avoid auditory deprivation and an adverse affect on your hearing is to keep the
auditory system active and not to let the parts of the auditory system stay dormant. The sooner you activate these centers of the auditory system and the brain when you first notice hearing loss, the greater the success you will have to hear.
Adult-Onset Hearing Loss & Auditory Deprivation
Children are often diagnosed with hearing problems quicker, as there are programs within newborn units to assess high risk children. Ensuring that a child can hear results in better
speech development. Our ability to speak stems from listening to others. The sooner a child is fit with appropriate hearing aids, the better.
For adults, however; a hearing loss is typically left unattended for several years. This deprivation results in a situation where the auditory pathways and areas in the brain are ‘starved’ of sound, and atrophy occurs.
In normal-hearing individuals, the sound that is processed through the auditory system is not actually interpreted as sound until the auditory centers in the brain are activated. The centers of the brain not only interpret the sound itself, but also the location and proximity.
Under-stimulated and under-utilized centers of the brain also tend to weaken or atrophy as a result of auditory deprivation. A dysfunctional auditory system that does not provide the proper information for the auditory centers of the brain to interpret will atrophy over time
due to a lack of stimulation. Siegenthaler & Craig (1981) and Hurley (1999) described the affect of late-onset auditory deprivation on speech discrimination ability when an individual presents with hearing loss in both ears and only one ear was amplified. The unaided ear showed a significant decrease in speech recognition ability and this deterioration was shown over the subsequent few years.
Several researchers have found that accompanying the decrease in speech recognition ability with the unaided ear, there may be a small increase in the aided ear that is referred to as acclimatization (Gatehouse, 1989). Given the fact that both deprivation and acclimatization exist is suggestive that plasticity or neural reorganization occurs in the auditory system. In layman’s terms, this simple means that neural reorganization occurs when the structures of the auditory system change or deteriorate. Current research suggests that neural plasticity can occur, even in older patients. New brain structures can develop to take over the function of damaged areas. These areas, with the proper sound stimulation, tonotopically arrange themselves from low to high frequencies, much like the primary auditory cortex.
The extent to which late-onset auditory deprivation occurs varies and is quite likely dependant upon the degree of hearing loss that an individual presents with. Gelfand et al. (1987) investigated speech discrimination scores of varying degrees of hearing loss of hearing impaired individuals and found that with mild, moderate, and severe sensorineural hearing losses, there was a mean decrease in speech discrimination scores of 7% in the unaided ear compared to 4% in the aided ear. In an individual with a profound loss, a 40% decrease was noted (Dillon, 2001). One study of individuals with symmetric conductive losses found a 30% difference in speech understanding between an aided and unaided ear.
Initially, researchers investigated this difference between aided vs. non-aided ears in individuals with moderate to severe hearing losses and found similar deterioration on the non-aided side. More recently, these changes have been seen with hearing losses of milder levels (Gelfand et al., 1987, Hurley, 1993). Hurley (1999) suggests that after a comparative analysis of studies done indicate that the greater the degree of loss, the more the effect of auditory deprivation.
Are Sounds Other than Speech Affected?
Differences other than speech between unaided vs. aided ears have also been seen. Robinson and Gatehouse (1995) found that intensity discrimination is better in the aided ear vs. the unaided ear for intense sounds, however; for weaker sounds, the unaided ear outperforms the aided ear. In other words, the ears perform best for the sensation levels that they typically receive.
Is it Really Auditory Deprivation?
Dillon (2001) suggests that the phenomenon of decreased speech discrimination ability may be more complex than just merely a lack of stimulation. Gelfand et al. (1987) found that individuals with similar hearing levels between ears that do not aid their ears see little effect of deprivation. Hood (1984) found that individuals with a slight difference in hearing levels between ears often showed a marked difference in speech discrimination ability when looking at individuals with Meniere’s disease. This is also routinely seen in our clinics in individuals with Meniere’s Disease. Hood suggests that the speech recognition for an impaired ear in a unilateral loss is more likely to be worse than the speech understanding at the same degree of loss in an individual with a symmetric bilateral loss. Dillon suggests that these results are indicative of an ear becoming strongly dominant for speech intelligibility since the other ear is initially somewhat a bit inferior. He further suggests that the initial inferiority seen may be due to aiding only one ear in a slightly asymmetrical hearing loss. Gatehouse (1989) indicates that an unaided ear can actually have better speech discrimination ability when both ears are presented with with speech below a comfortable loudness level and suggests that the brain is more used to receiving low level signals from the unaided ear than from the aided ear. When presented with low level signals, the unaided ear may be just simply better at dealing with it.
Dillon (2001) suggest that a better term than auditory deprivation would be Auditory Inferiority, Auditory Inactivity, or Lazy Ear. He further states that the term deprivation is
useful since the underlying cause is an inadequate output from the cochlea or organ of hearing. Dieroff (1993) showed that speech scores under headphones in unaided ears in individuals with symmetric conductive losses were 33% lower than scores from normally aided ears, suggestive that the attenuation of signals prior to the level of the cochlea is evidence that auditory deprivation can and does occur.
Common Causes of Auditory Deprivation in Adults
A person that chooses to ignore their hearing problems and does not treat their hearing loss with hearing aids results in the nerves and areas of the brain to be deprived of stimulation and gradually become weakened. Research has shown consistently that when there is a hearing loss in both ears and only one ear is fit with a hearing aid, the auditory nerve in the unaided ear can atrophy, resulting in auditory deprivation. This asymmetrical setup causes one ear to take on more of the listening activity than the other. This results in the weakening of the unaided ear over time. Silman et al. (1992) demonstrated deprivation on an individual with symmetric sensorineural hearing levels, fit only with one hearing aid initially and a second hearing aid at much later date. Following the fitting of the second hearing aid, the word recognition ability of the second ear improved significantly.
He attributed this phenomenon of recovery from the adult-onset deprivation to the use of hearing aids and the stimulation of the auditory system.
An honest attempt at the consumer level to save money by only purchasing one hearing aid may, in fact, be causing more harm. Not all individuals are suited for two hearing aids. At our clinics, we have a protocol for assessing the effectiveness of binaural hearing aid fittings. If two hearing aids are more appropriate and you opt to only amplify one ear, the unaided ear is going to gradually lose more and more functionality. When you do get around to purchasing a second hearing aid, the unaided ear will likely have a much more difficult time to adapt to sound. Further, with the use of one hearing aid when two are indicated, the necessary neuronal changes for optimal hearing does not occur.
Other causes of deprivation include a unilateral conductive impairment, a conductive hearing loss, a mixed hearing loss or an improper hearing aid fitting or lack of follow up care.
There are many causes of auditory deprivation and no shortage of individuals who experience it. This situation results in the general weakening of the entire hearing system.
What Can be Done to Avoid Auditory Deprivation?
Numerous studies indicate that the auditory system can recover from the effects of auditory deprivation. Some authors have described the effects of auditory deprivation by indicating that it can occur as soon as seven months from wearing a hearing aid in one ear only, on a bilateral hearing loss (the ear with the hearing aid tends to do all the work, leaving the unaided ear with nothing to do).
While the exact time course of auditory deprivation is still unknown, there seems to be a general consensus that individual speech scores can significantly decrease anywhere from 7 months to five years. A study in 1995 showed that even after auditory deprivation has occurred, many patients can regain their ability to understand speech when they are fit with a hearing instrument in the affected ear. Other studies indicate that “the resolution of auditory deprivation is generally significant but incomplete following binaural amplification”. In other words, the auditory system can improve with two hearing aids, but there may be some residual effects due to neglecting to tackle the problem immediately.
Therefore, the sooner the hearing loss is recognized and the sooner an individual gets
treatment for hearing loss, the more success they will have in the long term.
How Much Improvement in Speech Understanding Can I Expect?
The vast majority of studies that investigated improvement in speech recognition scores
following corrective action show an significant increase.
Silman et al. (1992) and Silverman & Silman (1990) found that increases in speech discrimination ability did not always occur. Other researchers have found upwards to 40%
improvement in unaided ears. Gelfand (1995) and Hurley (1993) found that recovery to any degree is not guaranteed. Some studies have only seen partial recovery in speech discrimination ability (Gelfand, 1995 and Hurley, 1993). Gelfand (1995) suggests that individuals that have a rapid onset of auditory deprivation will have a more rapid improvement with proper action taken.
What Can I do?
Research clearly indicates that the longer you ignore hearing loss, the more difficult it is
to treat. The sooner you address hearing loss with hearing aids, the better the outcome you will have with hearing aids and the process of adapting to hearing aids. Regardless, the best treatment for auditory deprivation is to take the necessary steps to avoid it in the first place.
Many individuals may give up using a second hearing aid as they may find the sound quality poorer than when only using one hearing aid (Hurley, 1993). Given time, research indicates that recovery of speech recognition does occur to some degree, so it is important to persevere with two hearing aids.
Over 50% of individuals with hearing loss suffer from a hearing loss in both ears. In general for these individuals, two ears are needed to hear optimally (please see our information under Consumer Information under “Are Two Ears Better than One” as there are exceptions to this rule). It is important to ensure that your hearing/auditory system is stimulated and not deprived of sound. See one of our professionals if you suspect a hearing loss. Hearing aids will improve your overall quality of life and hearing ability, however; they must be fine tuned appropriately for your hearing loss. It is important to have annual audiologic evaluations to take into account any changes in your hearing
levels and to ensure that your hearing aids are adjusted optimally for your hearing loss.
Today’s latest hearing aids are better than ever (lightweight, sleek, discrete) and packed with benefits that make hearing fun again. Hearing is a vital sense that keeps us connected to the world. The sooner you act when a hearing loss is suspected, the better prognosis for your personal hearing success and quality of life.