The effect of rate control on speech rate and intelligibility of dysarthric speech.

PURPOSE This study investigated the effect of rate control methods (RCMs) on speaking rate (SR), articulation rate (AR), and intelligibility in dysarthric speakers. METHOD Nineteen dysarthric patients (7 unilateral upper motor neuron dysarthria, 6 hypokinetic, 3 flaccid, 3 ataxic) participated. SR, AR and intelligibility ratings were determined on the basis of 1-min recorded reading passages. Seven RCMs were applied: voluntary rate control, hand tapping, alphabet board, pacing board and delayed auditory feedback with a delay of 50, 100 and 150 ms. RESULTS Almost all methods resulted in lower mean SRs and ARs (p < 0.05). Rate control did not improve overall intelligibility of the dysarthric population. However, a meaningful increase of intelligibility was found in 5 participants. This study indicates that the effect of rate control on intelligibility is independent of habitual speech rate and type of dysarthria. Degree of intelligibility may be an influencing factor. The most effective methods are: voluntary rate control, alphabet board, hand tapping and pacing board. CONCLUSION RCMs do result in lower speech rates. Some dysarthric individuals do benefit from one or more RCMs, but rate control may also have an inverse effect on intelligibility.