Does self-directed speech help or hurt a blind subject's auditory recognition?
It seems apparent that generating and hearing self-directed speech during discriminatory listening would inhibit said discrimination. This is because auditory processing of self-directed speech and audio processing in discriminatory listening would have to compete for resources in decoding auditory information, leading to poorer decoding of the already low-quality muffled audio. 

If on the other hand the self-directed speech is performed only in-between the trials of discriminatory listening, then this competition for auditory-decoding resources no longer occurs.  In this case, I expect that the self-directed speech would effectively prime cognitive resources that are involved in discriminating the source of the muffled speech. This, then, would result in improved discriminatory performance. At least that would be my initial hypothesis.