There are four main reasons why binaural (two eared) listening is superior to monaural (one eared) listening. Better Hearing in Noise: An individual's hearing in noise can be improved if the signal reaching each ear arrives at a slightly different moment in time. This is technically referred to as phase. When the brain receives slightly different, yet still audible signals at the two ears, it has the ability to cross-correlate and process the primary signal (usually speech) better than if the signal is received monaurally.
Improved Signal versus Noise Level from Optimizing Position: Sound loses intensity (loudness) when it travels across the head. This occurs mostly for the high frequencies which are the most important for understanding of consonants, such as /s/, /t/, /f/, and /sh/. If you have a hearing aid on only one ear, say the left one; and the person you wish to hear is speaking to you from the right side, the consonants may be decreased by nearly 20 decibels by the time it gets to your aided ear. Unfortunately, noise in the room may occur from any or all directions, so while the noise level is not decreased, the speech level is. Wearing two hearing aids ensures that the speech sounds will not be diminished any more than necessary because of your position in the room.
Improved Localization Ability: We determine where a sound is coming from on the basis of 1) the relative time in which the sound arrives at each ear, 2) the relative difference in loudness at the two ears, and 3) the relative difference in the pitch of the sound at the two ears. When there is a large difference in hearing between two ears (as might occur when a person with similar hearing in both ears only wears one hearing aid) the brain cannot make use of these subtle relative differences and their ability to locate sounds may suffer.
Possible Deterioration of the Unaided Ear: We hear in our brain, not in our ears. The ultimate goal of hearing aids is not just to send sound into the ear. It is also essential to retrain the central auditory system in the brain. While it is uncertain whether hearing sensitivity (ability to hear soft sounds) will decrease if your ear is not stimulated adequately, research now suggests that there can be changes in the way in which your brain processes sound when it is "starved." Thus, providing stimulation may be important in preserving your auditory potential.
When choosing your next step in purchasing a hearing aid, please keep these points in mind.