Why Do We Hear Better with Two Ears?

Got two ears? Use them!. Ned Frisk/Getty Images

Audiologists are often asked “Do I really need two hearing aids?” Often, this question is rooted in cost and cosmetic concerns. The answer is rooted in science.

Auditory Processing

Auditory processing actually starts at ear level. We know that when sound is introduced to the right ear, the auditory pathway will bring that sound to the left hemisphere and, when sound is introduced to the left ear the auditory pathway will bring that sound to the right hemisphere.

In a study using OAE measurements, it was shown that the left ear essentially amplifies music-like tones while the right ear increases rapid sounds like one would hear in speech sounds. This corresponds to the right hemisphere processing tones and music and the left hemisphere processing speech understanding and rapid acoustic signals. Aiding both ears ensures better access to all types of information.

Timing and Loudness Cues

When both ears hear equally, the minute differences in timing and loudness of a sound between the ears will tell the brain where the sound is coming from. Localization of sounds is important for safety; for example, with poor localization one will be unable to tell which direction a car or emergency siren is coming from. Some hearing aids take this a step further and have wireless communication between the hearing aids; based on the loudness and timing that the hearing aid microphones pick up, the hearing aids will process sounds and keep these cues intact to help the brain localize.

Picking up these differences also impact the ability of a person to hear better in background noise and be able to focus their attention on what they want to hear. It is interesting to note that localization is a skill that can be learned as part of auditory processing rehabilitation.

Loudness Summation

Loudness summation is exactly what it sounds like.

The sum of the loudness when hearing with both ears is more than what is heard from one ear. This advantage ranges from 3dB to 10dB depending on the sound level of the stimuli.

Auditory Deprivation

If both ears have hearing loss and only one ear is aided, the unaided ear may progressively lose its ability to understand speech over time. This effect can be seen as little as one year post fitting. Use it or lose it!


Trying to listen in less than optimal conditions is tiring. People with hearing loss must focus and attend more than a person with normal hearing sensitivity to get the same information. When both ears are aided, fatigue of listening is decreased.

Exceptions to the Rule

In approximately 10% of elderly patients, hearing with both ears causes difficulty. This phenomenon is called “binaural interference”. It is unknown whether this is due to age-related changes in the brain or auditory processing difficulties, but these individuals will hear better when only one ear (usually the right ear) is aided.

Most audiologists offer a trial period when one is purchasing hearing aids; the trial period is a great time to experiment and wear both aids, try the left aid alone, and try the right aid alone. 90% of the time, binaural (hearing in both ears) offers more improvement. For the 10%, it is an opportunity to determine what will best meet their needs.  



Sininger YS, Cone-Wesson B. Asymmetric Cochlear Processing Mimics Hemispheric Specialization. Science 305 (2004) p. 1581.

Schmidt, E (9 September 2004). Left and Right Ears Not Created Equal as Newborns Process Sound, UCLA/University of Arizona Scientists Discover. UCLA Newsroom. Accessed 06/25/2015 from http://newsroom.ucla.edu/releases/Left-and-Right-Ears-Not-Created-5480?RelNum=5480

Kuk, F, Korhonen, P. (21 August 2014). Localization 101: Hearing Aid Factors in Localization. The Hearing Review. Accessed 06/25/2015 from http://www.hearingreview.com/2014/08/localization-101-hearing-aid-factors-localization/#sthash.GH1xY0S6.dpuf

Dillon, H (2012). Hearing Aids (2nd Ed). New York, NY: Thieme.

Jerger J, Silman S, Lew HL, Chmiel R. Case studies in binaural interference: converging evidence from behavioral and electrophysiologic measures. J Am Acad Audiol. 1993 Mar;4(2):122-31.

Continue Reading