[Using delayed auditory feedback in the treatment of stuttering: evidence to consider]

There is some indication that the use of delayed auditory feedback (DAF) is a potentially helpful technique in the treatment of stuttering. Several devices for DAF are also commercially. However, not all individuals who stutter experience a positive effect on speech fluency when speaking under DAF. And those who do show a positive effect, may differ considerably as to the degree and the conditions in which the effect is seen. Therefore, the decision whether or not to attempt the use of DAF in an given client is usually not straightforward.

Starting from a literature review, the present paper discusses and illustrates factors to take into account when considering the use of RAA in an individual client. Four types of factors are distinguished: factors inherent to the client such as gender, age, stuttering severity, dysfluency pattern, origin of stuttering, and biological subtype; factors outside the client including delay time, intensity, manner of delivery, speech mode, and speech situation; possible side-effects like a reduction in speech rate, an increase of speaking fundamental frequency and vocal intensity, lengthening of vowels, and a possible effect on speech naturalness; others namely cosmetics, finances, and the long-term effect.

The review shows that most likely multiple factors play a role, but with the currently available data it is very hard to predict whether a given individual will or will not benefit from the use of DAF. Overall, the evidence for the influence of the different factors is still meager. Moreover, some studies present data of a quality that can hardly be considered "evidence".