Recently, it was found that self-directed speech was helpful to sighted subjects engaging in a visual search task:
Participants searched for common objects, while being sometimes [sic] asked to speak the target’s name aloud. Speaking facilitated search, particularly when there was a strong association between the name and the visual target. As the discrepancy between the name and the target increased, speaking began to impair performance. Together, these results speak to the power of words to modulate ongoing visual processing.
So, if the subject were to be looking for a chair in a picture, saying the word "chair" aloud would lead to a more effective search. Since the two modalities (vision and hearing) are separate, one set of information can compliment the other set and constructively interferes, if you will, in the scenario above.
I'm wondering how repeating a word to oneself would affect a blind (since birth) subject's ability to discriminate muffled or otherwise disguised words that they were asked to hear and identify as part of a task. Would the degree to which it was helpful still depend on the similarity between the word spoken out loud and the word to be discriminated? Or would there be a "destructive interference" under any circumstances due to the identical modality of hearing being used for the both discrimination of the information and the self-directed speech?
Lupyan, G., Swingley, D. (2011). Self-directed speech affects visual search performance. The Quarterly Journal of Experimental Psychology, iFirst, 1-18. http://dx.doi.org/10.1080/17470218.2011.647039