University of Iowa, Iowa City, Iowa
Changes in pupil size were studied in 24 stuttering and 30 nonstuttering adults during a 4-sec period following the presentation of single-word auditory stimuli and before a signal to respond. Subjects were required first to respond with a single word which was the opposite of the word presented and later to give a one-word free-association response to words of both emotional and neutral connotations. Pupil size was measured also while subjects merely listened to the word stimuli. The process of attending to an auditory stimulus was associated with pupil dilation. Pupil response was significantly greater (in absolute diameter and in dilation) when subjects were required to give an oral response to the stimulus than when they simply listened to the stimulus. Furthermore, the extent of the pupil reaction was related to the nature of the stimulus presented. Such differences in arousal did not occur to any greater degree in stutterers than in nonstutterers. Moreover, among stutterers, measures of pupil size were not predictive of stuttering. Thus, the cues which the stutterer associates with the anticipation of stuttering do not appear to be reflected in the physiological changes associated with pupillary movement.