This doctoral dissertation investigated basic acoustic features of persons who stutter (PWS) and persons who do not stutter (PNS) who read a short passage out loud under the anxiety condition controlled by the presence / absence of audience.

Chapter 1 reviewed stuttering, anxiety, and articulatory working, and provides the aim of this dissertation.

The purpose of Chapter 2 was to investigate the changes in subjective anxiety. The analytical study suggested that the presence of audience can make the PWS feel much more anxiety than person who do not stutter (PNS).

The following four chapters, the third to the sixth chapters, investigated utterances which were recognized as fluent.

F1/ F2 values of vowels and changes in vowel space were examined in Chapter 3. Under the condition of the presence of audience, the centralization of the tongue only in the PWS were suggested.

Voice Onset Time (VOT) was investigated in Chapter 4. It was indicated that the presence of audience might influence timing of articulatory working.

In Chapter 5, changes in the total speech time and average length of moras were investigated. Although the average lengths of moras were not different between the PWS and the PNS, the PWS showed a longer mean speech time. This dfference thus must be attributable to other factors except the articulatory speed associated with the total speech time.

Chapter 6 provides the study of average pause length and pause rate. The finding showed that the PWS increased their average pauses the length in sentences and phrases and average pause rates in clauses, with the presence of audience. It suggests that one of the causes for prolonging the total speech time is the pause discussed in Chapter 5.

Chapter 7 investigated utterances which contained stuttering. It was confirmed that the condition with the presence of the audience increases the stuttering rate. Furthermore, stuttering symptoms got worse under the same condition. The presence itself might influence not only the stuttering rate but also the stuttering symptoms.

In Chapter 8, overall research of the PWS' speech conditions under the anxiety condition was discussed, based on the research results of the previous chapters. Significant suggestions were made dealing with anxiety and stuttering rate and other topics which remain to be solved in the future.