This site reports study that was done with participants wearing an audio feedback device for 3 months. At one time, I read somewhere that AFD are not effective because eventually, the adherent becomes immune to the effects of it. Sort of like how one gets accustomed to "white noise"...though the analogy isn't perfect.

This website seems to believe, based upon the findings of the study, that the use of the AFD does not gradually become ineffective and that long-term fluency can result from their use. Read for yourself: http://www.intertapeww.com/eng/research.html

The report is authored by Prof. J. Van Borsel, Gent University...but I don't know if he was the person conducting the study. The website does, however, sell an Audio Feedback Device, though I couldn't determine how to get one or how much it costs.

Is it just me...or does it seem there is a huge marketing/entrepreneurial opportunity here for someone who can produce a relatively inexpensive AFD that is easily accessible by people who aren't wealthy?