Articulatory Rate and Stuttering 1 Effect of Normal and Fast Articulatory Rates on Stuttering Frequency

The effect of speech rate on stuttering frequency was investigated with 20 stutterers. Subjects read two different 300 syllable passages at a normal and fast speech rate. Stuttering counts and articulatory rate was determined for each speech sample. Articulatory rates were derived from portions of the passages which were perceptually fluent. No statistically significant difference in stuttering frequency was found between the two speech rate conditions (p = .16) while a significant difference was observed for articulatory rate (p = .0007). These findings suggest that increased articulatory rate does not determine stuttering frequency with the same consistency as does decreased articulatory rate. It was concluded that a single explanation of the relationship between speech rate and stuttering frequency in terms of speech timing complexity is inadequate. Articulatory Rate and Stuttering 3 Effect of Normal and Fast Articulatory Rates on Stuttering Frequency It is well documented that stuttering is dramatically reduced at speech rates which are below an individual's normal rate (Adams, Lewis, and Besozzi, 1973; Perkins, Bell, Johnson, & Stocks, 1979; Wingate, 1976). The fact that stutterers speak more fluently at slow speech rates has suggested to some theorists (e.g., Perkins, Bell, Johnson, & Stocks, 1979; Starkweather, 1982; Kent; 1984) that stutterers have difficulty coordinating the multiple physiological events of the speech mechanism during speech production. It is reasoned that the task of coordination is simplified at a slow speech rate due to production of fewer gestures per unit time (Starkweather, 1982); slowed transitional movements from sound to sound (Perkins et al., 1979); and/or longer time for planning or programming movement coordination (Perkins et al., 1979; Kent, 1984). It has been speculated that if stuttering is reduced under conditions in which coordination is simplified, then stutterers must have reduced capacity for speech movement coordination. While there has been a great deal of interest in investigating the relationship between slowed speech rate and stuttering, there has been little interest in determining the effect of increased speech rate on stuttering frequency. A tacit assumption of clinicians and theorists, however, is that stuttering increases when stutterers are under time pressure (Sheehan, 1958; Perkins, Kent, & Curlee, 1991). This notion is consistent with the theory that stutterers have reduced capacity for speech Articulatory Rate and Stuttering 4 movement coordination. More specifically, if stuttering is reduced at slow rates because of reduced speech timing complexity, then at a fast rate, where temporal complexity and/or demands are presumably greater, stuttering should increase. Unfortunately, there is a paucity of data exploring this prediction. Moreover, much of these data is difficult to interpret. Johnson and Rosen (1937) included a fast rate condition in an early investigation of the relationship between changes in stutterers' speech patterns and stuttering frequency. They reported essentially identical mean values for 18 subjects of 7.6% and 7.7% for the first normal rate condition and the fast rate condition, respectively. However, because order of condition was held constant for all subjects and there is evidence that stuttering decreased over the course of the experiment, it is possible that the results were confounded by order effects. Thus, Johnson and Rosen's findings should be interpreted with caution. In a more recent investigation, Ingham, Martin, and Kuhl (1974) used a single subject, ABA design to assess the relationship between speech rate and stuttering frequency for three adult stutterers. In the fast rate condition, their two subjects decreased, rather than increased, stuttering frequency relative to the initial normal speech rate condition. Only one subject exhibited more stuttering in the fast rate condition than in the initial control condition. However, these findings were complicated by the fact that stuttering frequency for two subjects failed to return to baseline in the final control condition. Therefore, it is Articulatory Rate and Stuttering 5 not clear whether changes can be attributed to manipulation of speech rate, or to changes in some other unspecified variable. A fundamental problem common to both these experiments is their measurement of speech rate. Johnson and Rosen (1937) used total reading time to indicate speech rate while Ingham et al. (1974) measured word output (that is, words per minute). In both cases, stuttered as well as fluent words were included in the measures. As such, speech rate was not assessed independent of stuttering frequency. The impact of any increases in stuttering frequency, therefore, would have been to reduce the absolute value of the speech rate measure. For example, the one subject in the Ingham et al. study who increased stuttering frequency in the fast speech rate condition relative to the initial control condition showed little change in word output. It would not be possible, therefore, to conclude that this speaker increased stuttering in conjunction with increased speech rate. One could say only that under instructions to speak quickly, the speaker exhibited more stuttering than under normal speaking conditions. In order to assess speech rate independent of stuttering frequency, it is necessary to obtain a measure of articulatory rate. An important aspect of calculating articulatory rate is the removal of lengthy pauses as well as stuttering. Removal of both stuttering moments and lengthy pauses are necessary to obtain an accurate representation of the gestures produced per unit time. The removal of lengthy pauses also increases the likelihood that inaudible stuttering moments will be excluded from the sample. Articulatory Rate and Stuttering 6 To the best of our knowledge, there is only one study which has obtained measures of stuttering frequency in conjunction with measures of normal and fast articulatory rates. Kalinowski, Armson, RolandMiezskowski, Stuart, and Gracco (1993) investigated the effect of speaking at normal and fast rates under conditions of altered auditory feedback on stuttering frequency. Under conditions of nonaltered feedback, mean stuttering frequency (that is, the number of stutterings per 300 syllable sample) for nine subjects speaking at a fast rate was higher than their stuttering frequency at a normal rate: 45.4 and 22.6 respectively. Although this difference was substantial, it did not reach statistical significance (p = .072). While the group trend was to increase stuttering frequency with an increase in articulatory rate, relative to the normal rate condition, one of the nine subjects stuttered less and one stuttered the same amount. In conclusion, the relationship between increased articulatory rate and stuttering frequency remains unclear. The purpose of this study was, therefore, to further investigate the effect of increased articulatory rate on stuttering frequency in a relatively large sample of adult stutterers. It was hypothesized that if decreased stuttering at a slowed articulatory rate is a consequence of reduced timing complexity, stuttering should increase at a fast articulatory rate when timing complexity presumably increases. That is, stutterers should stutter more when asked to speak at an increased articulatory rate compared to their normal articulatory rate. If increases in stuttering frequency occur with increases in articulatory rate, an Articulatory Rate and Stuttering 7 explanation of rate effects in terms of alterations in the temporal complexity of speech would be supported. On the other hand, if stutterers approximate the same stuttering frequency at an increased articulatory rate compared to their normal rate or stutter less, an alternative explanation of the relationship between articulatory rate and stuttering frequency is indicated. Methods