What is Binaural Hearing Aid fitting?
Hearing loss in both the ears is called binaural hearing loss. Binaural hearing aid is worn in both the ears. The pair is custom coordinated to give you a defined amplification in both the ears. Since, human beings have a binaural type of hearing naturally, binaural hearing aids replicate the natural form.
Wearing two hearing aids have a number of benefits. Binaural hearing aids can amplify sounds at varying degrees and from varying distance. Individual wearing a binaural hearing set will be able to better judge the direction of sound and have more of a realistic experience of hearing.
Benefits of Binaural Hearing and Bilateral Fittings
Let’s start by looking at the benefits of binaural hearing and bilateral hearing aid fits. When you hear the same information from both ears, like two sides of the same coin, you are getting redundant information. As a benefit, binaural hearing gives you two different perspectives in a given auditory environment. You get two sides of the coin. This is not a new knowledge.
If there is a sound source coming from one side of the head, it causes a shadow on the opposite side, thus decreasing the intensity of the sound on the contralateral side of the head. Additionally, it takes sound longer to travel from one side of the head to the other side of the head. The arrival time and intensities of the sound source at each ear are important differences that give rise to the benefits of binaural hearing.
Another binaural benefit is speech recognition. This head-shadow effect can be useful for understanding speech when it is in the presence of an interfering noise (Figure 1). If an interfering noise is on the opposite side of the head from the speech, the interfering noise is reduced at the near ear by the head-shadow effect. The signal-to-noise ratio (SNR) at this near ear is reduced compared to if there was no head shadow effect. You would not have this without two ears.
Another way to understand how location and binaural cues can be useful for understanding speech is to look at how we attend to important sounds. If you can localize where different sounds originate in your environment, you can focus your spatial attention, which is a cognitive capability, on a particular location. This enables you to suppress interfering sounds around you.
Binaural Processing Starts in the Brain
All of this processing starts in the midbrain. The cochlea detects sound and transmits that information to the rest of the brain. Binaural processing, almost by definition, has to happen somewhere centrally in the brain. The information from the two ears has to come together in some way. That happens in the lateral superior olive, which is in the midbrain. The details of it are not critically important; the important thing is to recognize that binaural processing is a benefit we get from the central nervous system.
Bilateral Hearing Aid Fitting
People have investigated the benefit of using two hearing aids for years, and we recognize that bilateral hearing aid fittings are beneficial for speech perception in noise by way of the head-shadow effect and binaural squelch. People do better for sound localization with two hearing aids versus one hearing aid. Sound quality is generally better with two hearing aids than one. There have been arguments over the years that using only one hearing aid may lead to some deprivation effects, where the ear that did not have the hearing aid becomes less effective at using sound. Other research suggests that perhaps bilateral hearing aids minimize this deprivation effect.