Acoustic and physiological reaction times of stutterers and nonstutterers.

This study investigates reaction times in the fluent speech utterances of stutterers and nonstutterers under several experimental conditions. Twenty adult stutterers and twenty matched controls produced utterances of three lengths--one syllable words, polysyllabic words, and sentences--in two conditions of time pressure (high and low) and two conditions of preparation (delayed and immediate responding) in a reaction-time paradigm. Recordings were made of EMG signals from the orbicularis oris inferior and from the extrinsic laryngeal area, as well as electroglottographic and acoustic signals. Measures were made of the duration of intervals between the stimulus, the acoustical onset of voicing, the onset of laryngeal EMG activity, and the onset of lip EMG activity. The durations of subintervals between the stimulus, the three physiological signals, and the acoustic signal were also measured. The results suggest that the reaction times of stutterers and nonstutterers are both increased by longer utterances, and that the effect is proportionally greater for the stutterers. The requirement to respond with minimal preparation produced longer reaction times in both groups, particularly for longer utterances, but this finding was stronger for stutterers than for nonstutterers, particularly in the prelaryngeal subintervals. The high time-pressure condition produced an unusual pattern of responding in many subjects. The analysis of subintervals indicated that the additional time taken by stutterers in responding was located in the earlier parts of the response, particularly when the utterances were longer. The results are interpreted as suggesting that stutterers may have difficulty in the motor programming of speech behavior.