71 Neuropsychological Intervention for Developmental Stuttering using Delayed Auditory Feedback Application
Authors: Anzaki Fumiko , Kiryu Shogo 
Published: December 2023

Objective:Brain science demonstrates that people who stutter (PWS) exhibit insufficient activation in the auditory speech area of the left hemisphere (Kikuchi, et al. 2011 ; Garnett, et al. 2018). In this study, we reported the auditory brainstem response of PWS: in PWS with moderate and severe impairment, significantly longer interpeak latencies (IPLs) between waves I and V (IPL [I-V]) of the right ear than those of the left ear were observed. However, in PWS with mild impairment, the IPLs (I-V) of the left ear were significantly longer than those of the right ear (Anzaki et al., 2020). We considered that the differences in the IPLs (I-V) between the right and left ears cause monitoring disturbance in communication, which results in developmental stuttering. It has been reported that stuttering was improved by delayed auditory feedback (DAF) (Stromsta, 1956; Sakai, 2008). Thus, we improved the DAF system and developed an application that can be used by PWS to listen to their own voices with no differences in the IPLs (I-V) between their left and right ears. We verified the effectiveness of this application.Participants and Methods:This study included five male adults with developmental stuttering (ADSs), with a mean age and handedness index of 36 years and 84, respectively. The application was adjusted so that the IPLs (I-V) of the left and right ears were the same. For example, one ADS showed that the IPL (I-V) of their right ear was 0.5 msec longer than that of their left. Subsequently, the application was adjusted so that the IPL (I-V) of his left ear would be delayed by 0.5 msec. We asked the participants to use the application for six months when free talking and reading aloud. Using the Japanese Standardized Test for Stuttering (JSTS) (Ozawa, et al. 2013), we compared their disfluencies with and without the application.Results:As per the JSTS, the stuttering severity in all participants improved. Case 1, who had severe impairment (level 5), showed a moderate improvement (level 4), Cases 2 and 3, who had moderate impairment (level 4), showed a mild improvement (level 3), and Cases 4 and 5, who had mild impairment (level 3), exhibited a normal level of improvement (level 1). We calculated the z-scores of the improvement rates of the JSTS based on the standard deviations according to the severity (Anzaki, 2019). The z-scores of Case 4 and 5 were 4.01 and 2.01, respectively, indicating a significant improvement.Conclusions:In our report last year, although ADSs with moderate and severe impairment showed improvement by stimulation intervention on the left hemisphere through the right ear, those with mild impairment exhibited only a slight or no improvement as per the JSTS (Anzaki, et al. 2021). The application developed in this study was found to significantly improve the disfluencies of all the participants as per the JSTS, especially those with mild impairment. Therefore, we considered that stuttering disorders are layered; ADSs have auditory monitoring disorder in the base.