The motor learning hypothesis and stuttering adaptation

Abstract

Although there have been many acoustic studies of speaking conditions that ameliorate stuttering, to date only two of these have addressed the adaptation effect. Prins and Hubbard (1990) found no consistent changes in acoustic duration measures from the first to the fifth reading in four adapting stuttering subjects, four non-adapting stuttering subjects and four control subjects. Max and Caruso (1998) suggested that motor learning might be expected to be associated with increased speed of motor performance, and hence sought to determine whether evidence of this could be found with eight stuttering subjects from reading one to reading six of a passage. A significant increase in articulation rate was reported, with corresponding decreases in various acoustic duration measures, leading Max and Caruso to conclude that their results were consistent with a motor learning explanation of the adaptation effect. The present study is similar to that of Prins and Hubbard and Max and Caruso in that it looked for changes in the duration of acoustic variables and articulation rate that might shed light on the adaptation effect. Eight stuttering men and eight control men read a passage five times. With conservative statistical analyses, no support was found in articulation rate, voice onset time or vowel duration for the motor learning hypothesis. However, if interpreted liberally, the results are consistent with the presence of a small motor learning effect. We argue that the inconclusive results of this study and Prins and Hubbard and Max and Caruso are a reflection of underpowered research.