Brain Activity during Disfluent Speech with Delayed Auditory Feedback: A Functional Near-Infrared Spectroscopy Study

Delayed auditory feedback (DAF) devices allow users to hear their own voice after a delay of several tenths to several hundredths of a second via speakers or earphones. In normal individuals, DAF produces disfluent speech, which is known as the DAF effect. In the present study, we used functional near-infrared spectroscopy (fNIRS) to evaluate the neural correlates of disfluent speech attributable to the DAF effect. Participants performed a reading-aloud task using long sentences during fNIRS under two conditions: Normal auditory feedback (NAF) and DAF. Oxygenated-hemoglobin was significantly increased in the bilateral superior temporal gyrus region during the DAF condition in comparison to the NAF condition. A larger effect was observed in the right superior temporal gyrus region. Furthermore, a positive correlation was found between the frequency of disfluent speech and activity in the right superior temporal gyrus region. Using NIRS may allow one to evaluate the non-fluency utterance of individuals, even in natural environments and conditions. Examining the cerebral blood flow changes may be employed as an indicator to identify speech disorders such as stuttering.