Okay, might be worthwhile trying to get this thread moving again: I was just reminded a moment ago of something that's occurred to me from time to time, but I had never had the thought so clearly defined before.
When listening to a sound you may do so at several levels of concentration: the analogy is with the eye, you may notice something which is a bit blurred, perhaps because of the time of day, movement of yourself or the object, or your eyes aren't what they used to be ... hah!! Now, if you apply yourself to the situation -- and I believe this would apply to most people -- you can "force" your eyes to work momentarily better, so that you can satisfactorily resolve what you're trying to see. The classic example is of someone squinting, or otherwise "working" on reading something in the paper. Now if you were to do this continually you would end up feeling very unpleasant, out of sorts ...
My thought is that the same approach is used with your ears: when the sound is not quite right, say in normal circumstances, for real sound a situation of the sound being soft, but in hifi if the far more common situation of the distortion levels being too high, then you effectively squint with your ears. That is, you actually apply concentration to the process of listening so that you hear "better", clearer. I just now noted myself doing that while listening to Adele, I was "squinting" with my ears to hear the sound more clearly, to make it resolve as being correct: when I deliberately relaxed, immediately the sound became harsher, more unpleasant.
So if this is the case, then there are some obvious consequences. It makes it very obvious why listener fatigue occurs, your body is "working" constantly to decipher the sound, to separate the good stuff from the bad, and eventually exhaustion wins the battle. But there is one other very serious consequence, which is to throw DBT and such like into grave danger: if the person doing the test is hyped up to do his best, then that's exactly what he'll do -- he'll extract the extra information out of the poorer sound to match the better sound, because his whole physiology is revved up to accomplish the goal. If he were to relax, or was so from the beginning, his performance, and results, would, could be very, very different.
Of course, I could be completely off the track with this thought. Hopefully someone like Gary might know if research has been done in this area; if it has a name for what I'm talking about, I am not aware of such ...
Frank