Effects of speech motor practice and linguistic complexity on articulation rate in adults who stutter*

This study aimed to investigate speech motor control in adults who stutter (AWS) by testing whether articulation rate changes with practice and linguistic complexity. Eleven AWS and 11 adults who do not stutter (AWNS) repeated four sentences of different lengths and syntactic complexity [simple-short (SS), simple-long (SL), complex-long (CL), and faulty-long (FL) sentences]. Overall articulation rates of each sentence were measured and compared between groups. Practice effects were evaluated by comparing the articulation rates of the first three, middle four, and last three productions. Overall, the AWS had significantly slower articulation rates than AWNS across the four sentences. The longer sentences showed significantly slower articulation rates than the baseline sentence (SS). The articulation rates of the middle four and the last three productions were significantly faster than those of the first three productions of each sentence in both groups. The articulation rates of the SS, SL, and CL sentences indicated a consistent practice effect. The slower articulation rates of the AWS are consistent with a speech motor limitation. There was no interaction with linguistic complexity or practice, so a slower articulation rate may be a general feature of the speech of AWS. Both AWS and AWNS showed practice effects with faster articulation rates which may reflect a degree of adaptation to the stimuli.