I’m assuming your question here refers to how to learn to filter out the noise embedded in the speech, which is the same as the noise around you, but different in that it still clings on to the speech even after you have isolated the speech and focus on it. To help with this clarification and maybe eventually answer your question, let me try an analogy first. Let’s say the restaurant is the forest, noise is all the green leaves, and speeches are the trees. And your hearing is your vision. If you can’t tune out anything, then all you see is the green forest and you don’t see the trees. If you’re interested only in seeing ONE particular tree, then your vision has to first learn to ignore all the surrounding trees (voices and noise that you’re not interested in hearing) and find the tree of interest and zoom in and stay focused on it. But this tree is still covered with green leaves, and you’re only interested in the outline of the tree and its branches. If that tree has too much leaves on it (very noisy restaurant), it’s going to be much harder to make out the outline of the tree. If there are much less leaves on that tree (less noisy restaurant), it’s easier to see past the leaves on this tree and shape out in your mind the outline of the tree and its branches.
I hope this analogy makes sense so far. Now let me take the analogy a step further. Let’s say people with normal hearing is analogous to having 20/20 vision, and can see not only clearly but has a better depth perception on their vision, maybe better color recognition, shade perception, etc. Let’s say hearing challenged people are analogous to people with bad eye sight and have to wear glasses (the hearing aid are obviously analogous to the glasses in this case). The traditional hearing aids is analogous to maybe a very small pair of eyeglasses. It blocks out vision of the big forest so you can focus on the tree of interest only. The OPN is analogous to a very big pair of eye glasses that let you see the whole forest. But you have to play “I spy” to zoom in on the tree of interest and ignore the rest of the forest (analogous to your brain hearing tuning out the noise and focus on the speech).
OK, so now let’s say you have 3 different people looking at this tree. One guy has 20/20 vision (normal hearing), one guy wears the small glasses (the traditional hearing aids), and one guy wears the big glasses (the OPN HA). They all now focus on this one tree of interest, but unfortunately, this tree is very hairy/full of leaves which makes it very hard to make out its outline and branches further. The 20/20 vision guy uses his other vision acuities that the 2 guys with glasses don’t have to help him try to make out the outline of the tree. Acuity like depth perception, better shadow and light sensitivity, better color perception, etc. Meanwhile the 2 guys with glasses see the same tree but don’t have the other acuities like the 20/20 guy to make out the tree any better than what their glasses allow them to see, which is more or less just a 2 dimensional vision (I’m dumbing down the glasses to have only 2 dimensional vision here to emphasize the analogy to limitations of the hearing aids which can only more or less amplify the sound but can’t recover other lost hearing acuities like maybe level sensitivity, soft sound detection, noise tolerance, etc).
So now back to your question in the quote -> “is there any technique or method that we could train the brain to re-establish the capability to filter out noise from the speech?”. The analogous question here is can the 2 guys wearing glasses train their brain to see that tree any better than what their 2 dimensional glasses allow them to see? Personally I think the answer is no. That is because you’ve reached the limitation of what the glasses can do to correct their vision. The brain, as powerful as it is, if it is given limited information, then it can’t do any more further processing of the information that it doesn’t have in the first place. It’s not the brain’s fault. It’s the limitation of the aid.
But what if the big glasses (the OPN HA in this case) can apply a green filter to remove the green color surrounding that tree? Then that will help the guy wearing those glasses see the outline of the tree better for sure. In this case it’s not the brain that does this processing. It’s the HA that does this processing. That is the extra step and the differentiation of what the OPN can do on noise removal that traditional HAs don’t do. So that’s why I think for folks who have trouble in noisy restaurant and the traditional HA with directional beam forming noise reduction doesn’t seem to help them, maybe try out this different approach with this different HA to see if it’s any better. Maybe it won’t be any better for them, because it does require commitment in terms of the willingness and the ability and the time to retrain your brain hearing, which is a critical factor to its success. But if you’re frustrated and you’re looking for something different to try, I think this is something else worth trying.