You started using hearing aids a few weeks ago. You can hear people talking, but you cannot fully comprehend what people are saying, the speech clarity is not as you expected. In this article, I will discuss what the problems might be and how they can be fixed.
Why does hearing loss start with a lack of speech clarity?
Let's take a look at the following audiogram which is from one of my patients I helped with a hearing test this week (Figure 1). This audiogram is a typical case of hearing loss due to ageing, a mild to moderate sloping sensory neural hearing loss (SNHL).
As a reminder, when the hearing thresholds (plotted in red circles for the right ear and blue crosses for the left ear) fall between zero and 20 decibels we classify them as no hearing loss (learn more on How do I read my audiogram?), so you can see the patient's thresholds of hearing are all right at low frequencies (250 and 500 Hz), go down at 1 and 2 KHz to 25 dB, and then sharply drop to 50 to 70 decibels at 2 to 8 KHz.
Figure 1 - Audiogram of hearing loss due to ageing
In addition to the patient's hearing thresholds in each frequency, I have plotted speech sounds called Phonemes. The phonemes form the grey curved shape we call the "speech banana". The vowels, as well as v, z, d, b, r l, j, m, n, g and c, are in the first group or cloud which is low frequency. This group has a range of energy spread between about 30 to 60 dB.
As you can see in Figure 1, the patient's hearing threshold (blue and red lines) is well above the first group of phonemes, hence this patient can hear these phonemes naturally. The second group of phonemes are mid-frequency with a span of energy from 25 to 45 dB. This group consists of p, h, ch, sh and g. Again the hearing thresholds of the patient are more sensitive than the energy level of these phonems hence the patient should be able to hear them in a quiet room. However, if the patient is in a noisy environment the noise will bring his hearing thresholds lover to the the extent that s/he may not be able to notice or hear these phonemes any more. In such a case noise will have a masking effect in mid-frequency phonemes.
The 3rd group are consonants k, t, f, s and th. This group is high frequency by nature and its energy level is quite lower than the other two groups, only about 25 dB. As you can notice in Figure-1 the hearing threshold of the patient is at 60 dB, meaning that the patient cannot hear the sound components of the speech at this frequency range unless they are at least 60 dB and louder.
So you can guess that a patient with the above audiogram misses a lot of details in the speech sound, let's say the crispiness of the sound. The speech is perceived as someone is mumbling or the speech is not clear.
Hearing aids come to the rescue!
Absolutely, the hearing aids when programmed properly will amplify sound at each frequency to compensate for the hearing loss at that frequency. From a technical point of view, your audiologist will consider:
Output power - Your hearing aid and the speaker unit that goes in the ear canal can provide enough power for your level of hearing loss
Your hearing aids are fitted properly i.e. closed/open fitting, wire length, dome type/size
Your hearing aids have the optimum prescription for the profile of your hearing loss
Your hearing aids have enough channels and are sophisticated enough (e.g. noise reduction, AI, DNN, directionality, etc.) to adjust to different soundscapes depending on your lifestyle
Your hearing aids are programmed and the REM (real ear measurement) is done so they provide an amplification profile as close as possible to what your ears need at the eardrum
Each of the above factors is critical in hearing speech and understanding it in the auditory cortex of the brain. I do not intend to discuss the details of each line in this article (please reach out if interested). Just as an example, the new generation of hearing aids with artificial intelligence (AI) and deep neural network (DNN) processing can do a better job of understanding speech in noisy environments (please see references). So setting up such a feature and tuning it up to the lifestyle of the patient links to items 2, 3, 4 and 5 of the above list. I'll reflect on AI and DNN in hearing aids soon.
One of my observations is that the public believes that when you drop the hearing aids in the ear, the hearing is fully restored. The buzz around artificial intelligence (AI) admittedly has raised this expectation. Often multiple sessions are needed to fine and tune the hearing aids especially for the first-time users of hearing aids when their brain is getting used to the processed sound in the first 2-3 months.
Figure 2 - Phonak default fitting to a sloping mild to moderate SNHL
Can assistive listening devices help?
Assistive listening devices can certainly help hearing speech better in the presence of background noise. This is even more true if your hearing loss is at a severe to profound level. The technique is very simple and effective. You will have an additional set of microphones closer to the speaker so you can hear the speaker's voice louder compared to the surrounding noise. More advanced devices such as Phonak Roger can have an even bigger impact as they have an array of microphones installed on the table microphone that detect and tune to the direction where the speaker is and also have dynamic sound processors to filter the noise at the source and send the cleaned up speech signal to your hearing aids.
What else could cause poor speech understanding?
If your hearing aids are programmed and fitted considering the above 5 points and your audiologist has exhausted all the options to tunning them but you still find speech understanding a challenge then there is a chance that your auditory cortex needs a check-up.
As you know we hear sound with our ears but we understand speech with our brain (our auditory cortex to be precise). At a higher age, our cognitive processing resources may not be as sharp as a young person's. The result is that speech understanding especially in the presence of background noise can be challenging in ages 60 and higher even with the best setting of a hearing aid. Such a patient may notice that he or she needs to hear speech a bit slower and also to be pronounced clearer to be able to understand the conversation.
Besides ageing, vascular injury, such as an ischemic or hemorrhagic stroke, is the most common form of insult to the primary auditory cortex.
Some research defines two components for the overall speech understanding impairment, class A (A for attenuation) is mainly because the peripheral auditory (your ears) cannot send the signal loud enough to the brain, and class D (D for distortion) that is caused due to deterioration of the cognitive power in our auditory cortex (in the brain) which is usually responsible about a third of our speech intelligibility. The same research indicates that a hearing aid can compensate for class‐A hearing losses, giving difficulties primarily in quiet, but not for class‐D hearing losses, giving difficulties primarily in noise. The latter class represents the first stage of auditory handicap, beginning at an average hearing loss of about 24 dB.
How often should I visit my audiologist?
To make sure that your hearing aids are optimally setup for your level of hearing loss you need to visit your hearing care professional every 12 to 18 months. Some underlying health issues could have a sudden impact on human hearing, those health problems include (but are not limited to) gout, diabetes, any vascular problem, the use of strong antibiotics, the use of strong painkillers, and some types of anti-depression medication.
Can Yoga and meditation improve my cognitive power and speech understanding?
The academic community has been quite interested in assessing and measuring the improvement (if any) that Yoga and meditation may have on our sensorineural system. The reduced level of stress following meditation practice may make patients more responsive to specific stimuli. Sahaja Yoga meditation for example appears to bring about changes in some of the electrophysiological responses studied in epileptic patients (see references for more details). Research shows that meditation can alter the functioning of the encoding of speech sounds in individuals who practice meditation.
Nevertheless, the research still has a long way to measure the improvements in our speech intelligibility in the presence of background noise for those who practice meditation, yoga and mindfulness.
Conclusion
Hearing aids can certainly help patients with hearing loss to hear speech better, but they need to be set up and tuned properly to get the best of their technology. Also if you have severe to profound hearing loss and based on your work or lifestyle you struggle to manage a conversation in noisy environments you might benefit from assistive listening devices.
References
Mangold SA, Das JM. Neuroanatomy, Cortical Primary Auditory Area. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK554521/
R. Rajan, K.E. Cainer, Ageing without hearing loss or cognitive impairment causes a decrease in speech intelligibility only in informational maskers, Neuroscience,
Volume 154, Issue 2, 2008, Pages 784-795, ISSN 0306-4522.
Reinier Plomp; Auditory handicap of hearing impairment and the limited benefit of hearing aids. J. Acoust. Soc. Am. 1 February 1978; 63 (2): 533–549. https://doi.org/10.1121/1.381753
Panjwani, U., Selvamurthy, W., Singh, S.H. et al. Effect of Sahaja Yoga Meditation on Auditory Evoked Potentials (AEP) and Visual Contrast Sensitivity (VCS) in Epileptics. Appl Psychophysiol Biofeedback 25, 1–12 (2000). https://doi.org/10.1023/A:1009523904786
Sinha, S. K., & Sahu, M. (2021). Individuals practising meditation have enhanced subcortical auditory processing of speech. Hearing, Balance and Communication, 20(1), 15–20. https://doi.org/10.1080/21695717.2021.1943777
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