Reaction time for /s/ and /z/ in stutterers and nonstutterers: a test of discoordination hypothesis

In an attempt to test the hypothesis that stuttering is the result of discoordination between phonation and articulation, 10 adult stutterers and 10 adult nonstutterers were asked to produce prolonged versions of /z/ and /s/ sounds, as quickly as possible, in response to tone stimuli. It was hypothesized that stutterers would exhibit significantly longer reaction time (RT) for the /z/, a voiced sound, than would a similar group of nonstutterers, whereas the two groups would not differ in RT for the /s/ sound, the unvoiced counterpart of /z/. The results showed that stutterers as a group did not differ from nonstutterers in RT for either the /z/ of the /s/ sound. However, it was found that severe stutterers exhibited significantly longer RTs for the /z/ sound than did mild stutterers. There were no differences between severe and mild stutterers in RT for the /s/ sound.