Single Sided Deafness & CROS Aids

People with Single Sided Deafness (SSD) often have a dead ear - which is an unattractive term but unfortunately is what we call it when there is no hearing whatsoever from the ear. This can be a result of disease, surgery, an acoustic neuroma (AN), or typically both AN *and* surgery.


With one dead ear and one hearing ear, there are few options available but CROS or BiCROS hearing aids are an option you should know about.


A CROS system (stands for Contralateral Routing of Sound) is a pair of devices that looks like hearing aids. There is a transmitter and a receiver. On the deaf ear, the transmitter device contains microphone(s) and wireless technology to communicate with its partner. Its job is to detect sound and send it as an electronic signal to the other side. On the hearing ear, the sound signals are picked up by a receiver device which contains a speaker to reproduce the signal as sound. This enables the user to hear sounds that would normally be lost or muffled by the “head shadow” effect. Head shadow is the term for loss/distortion of sound caused by high frequencies bouncing off your skull. Low frequencies travel round the skull to your working ear quite easily, but high frequencies are less adaptable - meaning that what reaches the working ear is duller, less clear/muffled. Head shadow affects everyone, but people with normal hearing do not notice it because their good hearing compensates for one of signals being muffled.


Directionality is affected by SSD too. The brain analyses the time difference of sounds received by the two ears to work out where they came from. If a sound is received by the right ear, and then milliseconds later the same sound comes to the left ear, it means the *source* of the sound is on the right. All this happens incredibly quickly, but the upshot is that you perceive a sound to be on your left or right. SSD sufferers do not have this facility as all sound is perceived as coming from their hearing side, which can be quite disorienting.


The main problem with SSD is simply that they miss a lot of what is going on at the deaf side. In a restaurant setting, it is very difficult to pick up what is being said by the person on the deaf side. This is a practical problem which is very frustrating.


A CROS aid enables the user to detect a good, clear signal on the deaf side, and hear it through their good ear. Conversation is much easier, as the user does not have to turn their head in order to manage the issue, and they pick up, for instance, someone saying their name to get their attention. Simple but invaluable.




A BiCROS system is for a person with one dead ear and one damaged ear. They need amplification on the damaged side. So with BiCROS, the transmitter on the deaf side sends sound over, but you also have a fully working hearing aid on the better side. Sounds from both left and right are amplified and modified by the hearing aid.


So what is it like to hear both left and right in one ear at the same time? How do you know what side it’s coming from if you are only hearing with one ear? That’s really difficult to say, and users of CROS/BiCROS find it difficult to explain too! One patient described it for me when I asked her how she could tell someone was speaking on her deaf (right) side:


“It’s kind of brighter if it’s coming from the right. You can just tell!”.

Some patients say their brain is fooled into thinking their dead ear is actually hearing. Those patients can perceive the sounds coming from the side they never hear on. This is great if it happens to you, but it’s not everyone’s experience!


Some people love it, call CROS/BiCROS a life-saver or a game-changer. Some hate it or just can’t get used to it, especially if it has been many years since they lost the hearing in the dead ear. The other option for someone with a dead ear and a hard of hearing ear is a single hearing aid worn on the better side. This is valuable in itself as it restores clarity and volume. Although head shadow is still an issue, it vastly improves the sound that is available.


In conclusion, results from new CROS/Bi CROS patients are varied and unpredictable! But I highly recommend you try it if you have SSD, because it might just change your life.

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