Neural response time of stutterers and nonstutterers in selected oral motor tasks.

Neural response time (NRT) was compared for 12 adult stutterers and 12 matched normal speakers on two verbal tasks (production of /pae/ and /bae/) and one oral, nonverbal task (lip closure) in response to visual and auditory stimulation. The auditory response stimulus was presented separately to the left and right ears, and the visual stimulus to both eyes. NRT was defined as the time interval between stimulus offset and the onset of electromyographic (EMG) activity from orbicularis oris superior muscle. Results show, in general, that stutterers are slower in NRT for all response tasks in both stimulus modes. Significant differences were found, however, for only the auditory mode. Analyses of the differences between and within groups for response tasks and stimulus modes are discussed in terms of recent research in and theory of timing disturbances in stuttering.