Why Do We Have Two Ears?

You may have been told as a child that we have two ears and one mouth because we’re supposed to listen twice as much as we talk – there may be a ring of truth to this but there is a lot more to binaural hearing (that is, hearing with two ears), chatterboxes will be relieved to know. The concept of binaural hearing is also relevant to those with double-sided hearing impairment when considering hearing aids (or cochlear implants) for one or both sides.

 
Amplification of Sound
Two heads are better than one for big ideas and problem solving, and two ears are definitely better than one when it comes to picking up sounds. In a concept known as binaural loudness summation, two working ears mean that the brain essentially receives double the amount of sensory input (at least for sounds coming from the front of the listener, thereby reaching both ears equally). Simply put, sounds are louder and easier to detect when you can hear them with two ears instead of one.

 
Better Discrimination of Sound
Binaural hearing allows us to be more sensitive to small differences in the quality of sound, such as frequency (the pitch) and intensity (the volume). This means better discrimination and recognition of an important sound event over unimportant background noise – is that your wife calling your name over the sound of the vacuum cleaner, and is her tone pleased or displeased right now? Does she want to show you the hundred-dollar bill she found while Hoovering under the couch or did you not put out the trash last night like you said you would? Binaural hearing is imperative for the best chances of survival.

 
Increased Tolerance of Loud Noises
With the use of two ears, sounds can be louder before causing discomfort or pain when compared to receiving a sound monaurally (that is, with one ear only). This is relevant also for those with hearing impairment – the volume controls of hearing aids can be placed at a lower setting when binaural, allowing better tolerance of loud noises. For those with cochlear implants, the sound volume threshold can be doubled before reaching discomfort if both ears have implants rather than just one.

 
Sound Localization and Direction
Get this – sound waves from a source reach the closest ear first. Mind-bogglingly logical, right? And, wait for it – sound reaches the farthest ear second! This slight inter-ear delay helps the brain to pinpoint the direction in which the sound is emanating, and can help also to direct your attention such as when in a noisy environment. The use of two ears helps to create what can be termed as a 3D sound landscape, rather than a flat 2D sound environment. The position of the head (which, in case you were wondering, is right between your two ears), also serves to attenuate the signal-to-noise ratio when the source of a signal is coming from the opposite direction from the source of the noise, which further helps with sound/signal localization; this is known as the head shadow. The signal-to-noise ratio is greater in the farthest ear from the noise as the head absorbs some of this noise and shelters the ear closer to the signal, where a higher ratio means a louder signal (important sound) than noise (unwanted background noises).

 
Wider Range of Hearing
With two ears on opposite sides of the head, we can receive sounds from 360 degrees instead of 180, leading to a more balanced stimulation. Our brains can also interpret a wider range of sound information when binaural.

 
Less Effort and Strain
Just as two people carrying a piano reduces the effort and strain, so does listening with two ears. Straining to listen to conversation or even to the sounds of the environment with just one ear can be fatiguing. Those with hearing aids report participating in conversation is more pleasant and enjoyable with two aids instead of one and also means the listener doesn’t need to keep turning the good ear towards the speaker.

Though humanity no longer relies on binaural hearing for real survival (unless you really didn’t put out the trash last night like you said you would), having two ears comes with obvious advantages and these advantages also apply to situations of hearing loss. For those with bilateral hearing impairment, one hearing aid or cochlear implant is definitely better than none but two is even better than one. Studies have also shown that children with bilateral cochlear implants before the age of three and half have the best opportunity to develop language skills, while adults with bilateral aids have a better experience in social situations and are less subject to isolation and withdrawal as a result of hearing impairment. As our understanding of binaural processing advances so will technology in the hearing aid technology space.

 

 
References
Why do we have two ears? https://www.healthyhearing.com/report/51383-Why-do-we-have-two-ears
The advantages of two ears. https://www.cbrown.org/the-advantages-of-two-ears/
Importance of binaural hearing. https://www.karger.com/Article/PDF/3807411
Listening with two ears instead of one. https://pdfs.semanticscholar.org/efda/11409dd8f753c899ddbf1937ea2e989d7d18.pdf
Binaural advantage. https://www.audina.net/en/content/14
Two ears are better than one. https://www.medel.com/us/bilateral/