right ears can talk to one another. This comparison allows a normal hearing person to do several things. First, it allows us to localize sound... to determine where sound is coming from. Second, it gives us a stereophonic effect that gives depth to the auditory world. Third, it allows us to determine how far away sound is, Fourth, it makes sound louder, increasing our sensitivity for very soft sounds. Finally, two ears allow us to concentrate better on what we want to hear and to ignore the rest.

Why  two hearing aids?

When only one hearing aid is used, the neural impulses that are sent from the right and left ears cannot be compared as described above. Using two hearing aids allows a hearing-impaired person to take advantage of the left/right processing that goes on inside the brain of people with normal hearing. So, what are the advantages of two hearing aids? First, the use of two hearing aids usually helps patients regain sound localization. When only one aid is worn, sound will appear to come from only one direction- the ear with the hearing aid. Thus, a car coming from the right may sound as though it is approaching from the opposite direction! Understanding speech in noisy situations also may be easier using two hearing aids. For example, just knowing that distracting noise is coming from the left and a funny joke is coming from the right allows us to concentrate on the punch line while ignoring the noise!