A Study of Disfluency Characteristics According to Auditory Feedback Condition

Ⅰ. Introduction

While research on the causes of stuttering has been conducted with a considerable number of themes, the causes are still unclear and plural (Guitar, 1998). One of many causes of stuttering that are directly associated with intervention is the auditory feedback mechanism. Feedback actions vary in the process of calculating words. Bloodstein (1995) that the normal speech production process is an automatic process that depends on feedback. Feedback in the process of speech is the of interaction between auditory and orosensory clues. Normal speakers create feedback adjusting auditory and orosensory clues properly, whereas stutterers pay a great deal of attention to auditory clues (Barber, 1940).

Thus, choral speech and masking auditory feedback (MAF) have been harnessed as clues to change the auditory feedback conditions for stutterers since the 1930s. Andrews et al. (1982) on a study on three stutterers that presenting a variety of auditory feedback conditions, speech pattern changed stuttering could be reduced. Kiefte & Armson (2008) reported to have reduced the frequency of stuttering when applying and altered auditory feedback (AAF) for 17 adults. Eliminating or changing auditory clues for stutterers and having them rely on oral clues resulted in the removal of stuttering (Ryan, 2001). Afterward, constant research has been conducted on whether stuttering contributes to any damage to the auditory feedback mechanism that supplements speech production among stutterers (Fairbank, 1955; Mysak, 1960; Stromsta, 1972).

In the 1950s, research focused on the contributions of delayed auditory feedback (DAF) to the reduction in stuttering and it was suggested that DAF played a critical role in reducing stuttering among people who stutter (PWS). Howell et al. (1987) used frequency altered feedback (FAF) to reduce stuttering among PWS and suggested a new aspect of auditory feedback conditions.

DAF has long been studied on the part associated with decreased non-fluency behavior. Kalinowski et al. (1999) compared the stuttering frequency in the DAF and natural auditory feedback (NAF) by delaying to 25, 50, and 75ms in a reading monologue conversation task. He subsequently claimed that stuttering behavior is reduced in the DAF rather than the NAF. In addition, leading researchers compared the speech characteristics of the normal group and the PWS group when presenting the DAF (Bloodstein, 1995). Non-fluent behaviors that appear in normal adults include five tones, speech strength increase, and clarity decline (Fukawa & Yoshida, 1985; Howell et al., 1999; Stager & Ludiow, 1993). Researchers have argued that under DAF, the brokenness of the collotry calculate normal adults appears similar to stuttering (Fuwaka, 1985; Kim & Shin, 2019; Kim et al., 2019).

The research on auditory feedback through FAF was again noted by researchers on stuttering in relation to the auditory feedback conditions and then conducted in many areas. In this context, a number of studies, including those using choral speech (Armonson et al., 1998; Freeman & Armson, 1998) and those on masking speech and the characteristics of PWS (Howell et al., 1987; Kalinoski et al., 1993), were conducted. Many different methods have been used by applying DAF (Sparks et al., 2002; Van Borsel et al., 2003) or FAF to characterize PWS (Howell et al., 1999; Kalinowski, 1999; Natke et al., 2001).

Previous studies related to the auditory feedback conditions were accomplished in terms of whether each auditory condition reduced the frequency of stuttering in the stuttering group and, if so, how much it was affected. It was also reported that most of the auditory feedback conditions were effective in reducing the frequency of stuttering. The research described the auditory characteristics of PWS that reduced the frequency of stuttering through distraction (Barber, 1940), injured auditory functions (Stromsta, 1972), and modified voices (Perkins, 1979) but has not presented a definite ground yet.

To clarify the ground, many studies have been to present PWS with auditory feedback mechanism conditions in diverse ways and to use each auditory feedback mechanism condition to reduce stuttering. However, few studies have been performed to indicate the differences among the conditions. In a limited way, recent research made a comparison between DAF and FAF (Kalinowski et al., 2004; Stuart et al., 2004; Zimmerman et al., 1997) and between choral speech and FAF (Freeman & Armson, 1998; Kiefte & Armson, 2007). However, no comprehensive research has been conducted on the contributions of the auditory feedback mechanism conditions to the reduction in stuttering among PWS.

To characterize PWS given auditory feedback conditions, it is possible to specify the characteristic so PWS only by knowing how normal adults react to the auditory feedback conditions. However, research the auditory feedback conditions in the PWNS group is limited to DAF conditions (Fukawa & Yoshida, 1985; Stuart et al., 2004). It is therefore necessary to determine how speech differs by various types of auditory feedback conditions in the PWNS group.

The ultimate goal of treating PWS is to develop fluency in every situation (Ryan, 2001). If auditory feedback conditions contribute to the reduction in stuttering among PWS, it is necessary to determine what utterance task has the greatest impact. However, Zimmerman et al. (1997) me rely investigated the effects for PWS in the situation of telephone and most related researches were limited to utility in reading situations (Howell et al., 1999; Kalinowski et al., 2004). It is therefore necessary to determine by utterance tasks with the objective of clarifying the differences in the auditory feedback conditions for PWS and applying them to treatment more usefully. Based on the significances of the research, the purpose was to characterize disfluency speech under diverse types of auditory feedback conditions in stuttering adults according to auditory feedback conditions.

Ⅱ. Methods

1. Subject

This study was conducted among 10 PWS and PWNS. PWS had stuttered without cerebral injury since their childhood and were diagnosed with severe stuttering by a speech therapist by means of a stuttering severity instrument (SSI). The mean age was 29.6 years (range=19~42; SD=7.22). Each of them possessed normal hearing and carried no problem with speech or language but with fluency. PWNS were selected as subjects who had never been diagnosed with stuttering. PWNS exhibited normal hearing no problems with spoken language besides fluency.

Table 1.

Information of participants

Ⅲ. Results

1. Frequency of Stuttering

1) Reading Task

Reading tasks were implemented to determine the differences in the frequency of stuttering by the feedback conditions between the PWS and PWNS groups. The mean and standard deviation of the frequency of stuttering under each auditory feedback condition is as presented in Table 2.

Table 2.

Average and standard deviation stuttering frequency in reading

Two-way ANOVA was performed to determine the differences in the frequency of stuttering between the two groups by the feedback conditions and the results are as presented in Table 3. Significant differences were found in the interaction effects between the auditory feedback conditions and grouping, as presented in Table 3 (F_{(4, 90)}=4.247, p<.01). There were significant inter-group differences (F_{(1, 90)}=16.481, p<.01). Significant differences were found among the feedback conditions (F_{(4, 90)}=5.570, p<.01).

Table 3.

Two-way ANOVA analysis results in reading

Scheffe test was carried out to determine the significant differences among the feedback conditions and the results are as presented in Table 4. As presented in Table 4, NAF differed significantly from masking and choral speech, DAF, and FAF (p<.05), whereas no significant difference was found among the other conditions.

Table 4.

Post hoc analysis in reading task

Figure 1 was presented to determine the differences in the frequency of stuttering between PWS and PWNS groups among the auditory feedback conditions for the reading tasks. As shown in Figure 1, the PWS group more frequently stuttered than PWNS group under all the conditions but DAF. The PWS group had stuttering decreased under the other auditory feedback conditions than NAF. In contrast, the PWNS group rather had stuttering increased under DAF, as compared with NAF. As for the comparison between PWS and PWNS groups by the auditory feedback conditions for the reading tasks, the PWNS group showed no stuttering under masking and choral speech and FAF. It more frequently showed stuttering under DAF than the PWS group.

Figure 1.

Differences in the frequency of stuttering between groups in reading taskNote. PWNS=people who not stutter; PWS=people who stutter; NAF=natural auditory feedback; MAF=masking auditory feedback; CS=choral speech; DAF=delayed auditory feedback; FAF=frequency altered feedback.

2) Monologue Task

Monologue tasks were implemented to determine the differences in the frequency of stuttering by the feedback conditions between the PWS and PWNS groups. The mean and standard deviation of the frequency of stuttering under each auditory feedback condition is as presented in Table 5.

Table 5.

Average and standard deviation stuttering frequency in monologue

Two-way ANOVA was performed to determine the differences in the frequency of stuttering between the two groups by the feedback conditions and the results are as presented in Table6. Significant differences were found in the interaction effects between the auditory feedback conditions and grouping, as presented in Table 6 (F_{(3, 72)}=6.714, p<.01). There were significant inter-group differences (F_{(2, 72)}=82.370, p<.01). Significant differences were found among the feedback conditions (F_{(3, 72)}=5.894, p<.01).

Table 6.

Two-way ANOVA analysis results in monologue

Scheffe test was carried out to determine the significant differences among the feedback conditions and the results are as presented in Table 7. As presented in Table 7, NAF differed significantly from DAF and FAF (p<.01) but didn’t differ significantly from masking. No significant difference was found among the remaining conditions.

Table 7.

Post hoc analysis in monologue

Figure 2 was presented to determine the differences in the frequency of stuttering between the PWS and PWNS groups among the auditory feedback conditions for the monologue tasks. As shown in the Figure 2, the PWS group more frequently stuttered than the PWNS group under every condition. The PWS group had stuttering decreased under the other auditory feedback conditions than NAF. The PWNS group rather had stuttering increased in DAF and FAF than NAF. As for the comparison between the PWS and PWNS groups by the auditory feedback conditions for the monologue tasks, the PWNS group showed no stuttering under masking.

Figure 2.

Differences in the frequency of stuttering between groups in monologue taskNote. PWNS=people who not stutter; PWS=people who stutter; NAF=natural auditory feedback; MAF=masking auditory feedback; DAF=delayed auditory feedback; FAF=frequency altered feedback.

2. Speech Rate

1) Reading Task

Reading tasks were implemented to determine the differences in the frequency of stuttering by the feedback conditions between the PWS and PWNS groups. The mean and standard deviation of the speech rate under each auditory feedback condition is as presented in Table 8.

Table 8.

Average and standard deviation speech rate in reading task

Two-way ANOVA was performed to determine the differences in the speech rate between the two groups by the feedback conditions and the results are as presented in Table 9. Significant differences were found in the interaction effects between the auditory feedback conditions and grouping, as presented in Table 9 (F_{(4, 90)}=2.706, p<.05). There were significant inter-group differences (F_{(1, 90)}=51.465, p<.01). Significant differences were found among the feedback conditions (F_{(4, 90)}=2.462, p<.05).

Table 9.

Two-way ANOVA analysis results in reading

Scheffé test was carried out to determine the significant differences among the feedback conditions and the results are as presented in Table 10. As presented in Table 10 NAF, masking and choral speech, DAF, and FAF all made no significant difference.

Table 10.

Post hoc analysis in reading task

Figure 3 was presented to determine the differences in the speech rate between the PWS and PWNS groups among the auditory feedback conditions for the reading tasks. As shown in the Figure 3, the PWS group was slower in speech than the PWNS group under every condition. The PWS group had the speech rate raised under the other auditory feedback conditions than FAF, as compared with NAF, in terms of stuttering. The PWS group rather had the speech rate lowered under all the conditions, as compared with NAF.

Figure 3.

Differences in the speech rate between groups in reading taskNote. PWNS=people who not stutter; PWS=people who stutter; NAF=natural auditory feedback; MAF=masking auditory feedback; CS=choral speech; DAF=delayed auditory feedback; FAF=frequency altered feedback.

2) Monologue Task

Reading tasks were implemented to determine the differences in the frequency of stuttering by the feedback conditions between the PWS and PWNS groups. The mean and standard deviation of the speech rate under each auditory feedback condition is as presented in Table 11.

Table 11.

Average and standard deviation speech rate in monologue task

Two-way ANOVA was performed to determine the differences in the speech rate between the two groups by the feedback conditions and the results are as presented in Table 12. No interaction effect was found between the auditory feedback conditions and grouping, as presented in Table 12. There were significant inter-group differences (F_{((1, 72)}=31.251, p<.01). No significant difference was found among the feedback conditions.

Table 12.

Two-way ANOVA analysis results in monologue task

Ⅳ. Discussion and Conclusion

This study aimed to determine the behavioral characteristics of stuttering according to the auditory feedback mechanism conditions. Significant differences were found between the stuttering and normal adult groups in the frequency of stuttering for the reading and monologue tasks. The results of this study were consistent with those of the previous research (Fukawa & Yoshida, 1985).

Attention is paid to the fact that the normal group stuttered under DAF and FAF for the reading and monologue tasks. For the reading task, the normal group made no stuttering under any other condition than NAF but committed more stuttering under DAF 200 than even the stuttering group.

This result is consistent with the finding that altered auditory feedback led to speech breakdown for normal speakers (Fukawa & Yoshida, 1985; Howell, 1990; Stager & Ludlow, 1993). In particular, it has been suggested that normal speakers show an increase in speech rate fluctuation, syllable repetition, omission, and misarticulation, generating artificial speech, like stuttering (Johne & Striemer, 2007). In addition, it has been indicated that in the normal group, children are more likely to show breakdown than adults and that the older , the less likely they are to be affected by auditory feedback conditions (Fabbro & Darro, 1995).

Fukawa & Yoshida (1985) investigated sensitivity during a reading task under DAF in 40 PWS and 40 PWNS. Under DAF, the stuttering group was significantly more sensitive while the normal adult group was responsive. This study also found that the stuttering group was less likely to stutter under DAF than under NAF. Therefore, the PWNS, as well as the PWS, may produce speech under the influence of the auditory feedback conditions. This result confirms that altered auditory feedback has an auditory impact in speakers while they speak (Bauer et al., 2006; Butnett et al., 1997; Jone & Munhall, 2000).

In addition, the frequency of stuttering was lower under other auditory feedback conditions than NAF. This result conforms to the suggestion that altered auditory feedback can reduce the frequency of stuttering for PWS (Howell et al., 1987; Kalinowski et al., 1993; Stuart et al., 2004). Researchers assumed that PWS would be affected by auditory feedback due to auditory and perceptive deficiency (Cherry & Sayers, 1956; Mysak, 1960). They also assumed that altered auditory feedback mechanism could make PWS more fluent speakers (Wingate, 1970).

Research has been conducted continuously to test these hypotheses. Such auditory feedback conditions as choral speech (Bloodstein, 1950; Freeman & Armson, 1998), MAF (Conture & Brayton. 1975; Kalinowski et al., 1993), DAF (Kalinowski et al., 1993; Spark et al., 2002), and FAF (Armson, & Stuart, 1998; Hargrave et al., 1994; SStuart et al., 1993) were found to be effective in reducing stuttering. The auditory feedback conditions have been used to test PWS (Goldiamond, 1970; Ryan, 1964; Van Borsel, 2003). The auditory feedback conditions were also useful in treating stuttering.

The PWS group registered significantly lower in speech rate for both reading and monologue tasks than the normal group. With the exception of the DAF, which involves an artificial decrease in the rate, NAF produced the slowest speech in the stuttering group. Wingate (1970) is consistent with the view that the fluency enhancement effect of all DAF is slowing down speech rate. In addition, Kailnowski et al. (1999) suggested that it is not essential to improve stuttering by inducing fluency to vary the speed of speaking. Under NAF, they received feedback related to their speech production and naturally produced stuttering. This leads to the same prediction as previous research made that stutterers are slow in speech due to closed time during stuttering (Ryan, 2001). This study looked at the relevance of the FAF and the stutterer's speech rate change. Researchers do not notice a significant difference in the speech rate of stutterers depending on FAF pitch ingest edits (Hargrave et al., 1994; Kalinowski et al., 1993; Stuart et al., 2004). For these results, the researchers argue that the FAF does not affect speed because the sound is adjusted.

We looked for significant differences in stuttering frequency and speech rate between normal and stuttering groups by auditory feedback. First of all, there were differences in stuttering behavior in reading and monologue tasks under shielding conditions. When the normal person heard or did not hear his voice, he was able to reassert himself that everyone had the ability to adjust naturally. On the other hand, the level of anxiety that a PWS group creates when it hears itself stuttering when it is not able to hear it (Bloodstein, 1995). However, it can be seen that even in the PWS group, the PWS and PWNS groups show significant differences.

While the frequency of stuttering was different between groups under the conditions of the CS, there was no statistically significant difference between the stuttering and PWNS group under the conditions of the CS conducted in the reading task. The conditions of the CS were that the speech rate was calculated at the same speech rate as the PWS and PWNS groups because they presented pre-recorded materials. Therefore, it can be considered once again that auditory feedback conditions are factors that can affect the stutter. It is clear that a CS is an auditory feedback condition suitable for a stuttering person so that it does not differ from the normal group not only in terms of stuttering frequency but also in terms of speech rate. However, the CS is not being used to treat stuttering. This is because the ultimate goal of stuttering treatment is to produce autonomous spoken language, because talking together is limited to formalized spoken or read tasks. It is also limited to include a joint spoken word in treatment because it requires the participation of others.

The PWS may think that the use of the DAF condition will reduce the stutter behavior (Kalinowski, 1996; Spark et al, 2002) and the PWNS group will yield the stutter (Bauer et al., 2006; John, 2007), thereby eliminating the difference in stutter behavior. The PWNS group showed stuttering behavior in both reading and monologue tasks under the DAF conditions, the same result of studies by Zannini et al. (1999) that normal subjects had speech errors when they delayed the DAF by 200 ms rather than by using the DAF.

Under FAF conditions, speech rate differed in both reading and monologue tasks. It could be found that the PWS and PWNS groups had similar characteristics. This could confirm that auditory feedback conditions were affecting not only stuttering but also normal groups.

On the basis of these results, a few suggestions can be made for further research

First, this study was limited to the adult stuttering group. Further research needs to forma comparison between children and adults to determine how the auditory feedback conditions affect by age among PWS and if the characteristics vary.

Second, the auditory feedback conditions exerted an impact on the PWNS group, as well as on the PWS group, as shown in the results. However, the research was limited to the frequency of stuttering and the speech rate so as to make a comparison the stuttering groups but it failed to characterize them clearly. Further research needs to analyze frequency fluctuation, speech clarity, and mal articulation patterns and determine the effects of auditory feedback mechanism more specifically in the PWNS.

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참 고 문 헌

• 교육과학기술부 (2010). 고등학교 국어(하). 서울: 두산동아.
• 김효정, 신명선 (2019). 국내외 아동 말더듬 중재에 대한 문헌 고찰. 언어치료연구, 28(2), 129-144.
• 김효정, 장현진, 신명선 (2019). 말더듬 청소년 및 성인의 국내외 치료 연구 동향. 언어치료연구, 28(4), 21-37.