Two ears are not always better than one

My team of researchers has discovered that as many as one in two individuals with hearing loss experience abnormal fusion, or a blending of dissimilar sounds, when wearing either bilateral hearing aids or a cochlear implant with a hearing aid.

This “averaging” of sounds worsens their ability to hear others’ speech.

Typically, two hearing devices, when possible, are better than one. But some individuals with bilateral hearing loss hear speech better when using a hearing aid or cochlear implant in only one ear.Doctor Fitting Female Patient With Hearing Aid

For more than a half-century, hearing scientists and audiologists have been puzzled as to why.

This study, published in the Journal of the Association for Research in Otolaryngology illuminates the cause of the abnormal processing that results in this phenomenon.

This understanding will enable scientists to develop ways to improve patients’ ability to hear.

Typical-hearing listeners only fuse similar sounds between the ears.  We found that many hearing-impaired listeners fuse sounds less discriminately, fusing those that are both similar and different between ears, such as a low-frequency sound, a man’s voice or low tone on the piano, for example, in one ear with a high frequency sound, like a woman’s voice or high tone, in the other ear.

This would be like fusing the image of your thumb in your left eye with the image of your pinky in the right eye into a single finger.

The fusion also leads to averaging and distortion of the different sounds between the ears, similar to averaging of color between the eyes with the old-style red and blue 3-D glasses used at the movies.  For many hearing-impaired individuals, this fusion only distorts a few speech sounds.  However, for other individuals, fusion distorts the majority of speech sounds, and listening with two ears is so difficult that they choose not to use a second hearing device.

Our study also sheds light on why hearing-impaired listeners have difficulty understanding speech in background noise, and how abnormal fusion may contribute to this. If different voices are fused together, it is more difficult to attend to a particular person in a crowded room.

In the future, scientists hope to be able to offer patients with hearing loss brain retraining programs to help correct this abnormal brain processing.


This research was supported by grants R01 DC013307, P30 DC010755, and P30 DC005983 from the National Institutes of Deafness and Communication Disorders, National Institutes of Health. [The laboratory cochlear implant Freedom processor was provided by Cochlear and the laboratory hearing aid was provided by Oticon.]

10 responses to “Two ears are not always better than one

  1. Interesting stuff Lina… might explain my Mom’s situation too as she didn’t quite like having two hearing aids either despite bilateral loss. =)

  2. I use a hearing aid in my ‘offside ear’ with a CI in the right ear. I use it to listen to music. Helps with those Bass notes!
    When I’m not listening to music, I take the HA off.

  3. I’ve had Cochlear implant since 1986 in one ear. I’ve understood speech fine in one ear. And also, when I take it out at bedtime I get tinnitus. In the morning it’s a relief for me to wear my CI piece all day. I think it’s a hassle to wear bilateral implant when one will do just fine.

  4. I am a firm believer that two ears are better than one. I have an AB implant, but do not use a hearing aid in the other ear. Although I am doing great with my implant, I would be happy to have an implant on the other side to see how this would work for me.

  5. I wore hearing aids bilaterally for over 40 years. I have had bilateral cochlear implants for 10. Your study does nothing to HELP us. The word here is HINDER. That is what you are doing. Further your study was exclusively for Cochlear Americas and Oticon. That is only one of several Cochlear Implant technologies and one hearing aid manufacturer. This study should not be looked upon to represent the entire hearing impaired population who utilize hearing aids and cochlear implants.

  6. What about sound location? With only one ear Hearing, we lose the ability to tell where sound is coming from. Believe me, it makes a BIG difference ……. traffic, working out who’s talking, people walking, ……

  7. Thanks everyone for your comments and interest in the study. To clarify, most people do overall better on speech perception with two ears, but there are some who have trouble with two devices, and this study helps to explain why. If we can understand why, then we can help those people.

    Sound localization can help normal-hearing listeners with separating (“hearing out”) different voices in background noise. It is also likely to help the half of hearing-impaired people with normal processing. But this may be different also for the other half of hearing-impaired people with abnormal fusion of sounds between ears. Because many sounds are blended together, those individuals may not be able to localize the multiple sounds if they are all fused into one sound. We are currently doing a follow-up study to see if that is the case.

    To the other post, I would say that for now, our study was limited to one implant company and several hearing aid companies (the loaner hearing aid was provided by Oticon, but we tested people with their own hearing aids too). We have found something similar in people with MED-EL and are currently working to also add AB devices to our studies.

  8. And yes, speech understanding isn’t the only thing that is important. There are trade-offs to balance as noted above. Sound localization and a feeling of “balance” are important, and you mostly get those with two devices. Music perception is often better with a cochlear implant combined with a hearing aid, than a cochlear implant alone. It might be that if you’re one of those people who do worse on speech understanding with two ears, you might wear the second device for specific situations.

    But really, in the long term we don’t want to discourage people from wearing two devices. Instead, we plan to develop new brain training strategies or improve the devices to reduce this interference so that everyone does better with two ears.

  9. This is great news! I wear a cochlear implant only on left side. I was not a candidate for right due to Mondini Malformation which II was diagnose during MRI as requirement for CO.

Comments are closed.