My very limited understanding is that a BAHA is only valuable if one is SSD. Somehow the use of it does give directionality.
BAHAs were actually developed for people who, for various reasons, are unable to wear a traditional hearing aid (due to malformation or a variety of ear "conditions"). In these cases, the BAHA is worn instead of a traditional hearing aid, but it provides a similar function. The BAHA sends sounds to the ear on that
side of the head. If they have a BAHA on the left
side of their head, it's actually assisting the hearing in their left
ear. If they wear two BAHAs, which is actually fairly common, the left-sided BAHA is assisting the left-sided ear, and the right-sided BAHA is assisting the right-sided ear.
It wasn't until some time after the development of the BAHA that it was determined that the BAHA could help single-sided deaf individuals. In those instances, there's just one functioning ear, so the BAHA is placed on the non-functioning ear's side of the head and the sound is transmitted, via bone conduction, to the functioning ear on the other side of the head.
With regard to the issue of directionality, I attended an ANA/NJ seminar a couple of years ago at which a doctor who implants BAHAs spoke. He said that he always makes sure that his SSD patients understand two things before he implants a BAHA: (1) the BAHA will not not affect their degree of tinnitus -- it will neither make it better nor make it worse; and (2) the BAHA will not restore their ability to determine directionality. His theory is that shortly after becoming SSD (I believe he said it was a matter of a few weeks) the brain permanently loses its ability to distinguish directionality. I know that there are some BAHA-wearing folks on this forum who feel that they have regained directionality, so this theory may not hold true in every case. I suppose the assumption could be made that BAHA users who are not SSD do have a sense of directionality because their brain never lost that capability.
I think the important thing for us to remember is that not every BAHA user is SSD and the functionality of the BAHA differs depending on the user's condition.
Catherine (JerseyGirl 2)