Methods of interval selection, presence of noise and their effects on detectability of repetitions and prolongations.

Accurate methods for locating specific types of stuttering events are necessary for diagnosis, treatment, and prognosis. A factor that could add variability to assessment of stuttering is noise on recordings. The effects of noise were assessed by adding noise to intervals of speech containing all fluent material, fluent material with a repetition, or fluent material with a prolongation. These intervals allow a unique dysfluency response to be made. A statistical analysis of the occurrence of such intervals in spontaneous speech showed that only a limited number of intervals met these criteria. This demonstrated that selecting intervals at random from spontaneous speech (as in time interval analysis procedure) will infrequently lead to a unique and unambiguous dysfluency specification for the interval. Intervals were selected for testing from the intervals that met the stipulated criteria. These were presented for dysfluency judgment when the position of the stuttering within an interval was varied and with different amounts of added noise (no added noise, 3 dB, and 6 dB of noise relative to mean speech amplitude). Accuracy in detecting stuttering type depended on noise level and the stuttering's position in the interval, both of which also depended on the type of stuttering: Noise level affected detection of repetitions more than prolongations: Repetitions were more difficult to detect when they occurred at the end of an interval whereas prolongations were more difficult to detect when they were at the beginning of an interval. The findings underline the importance of adopting rigorous recording standards when speech is to be employed to make stuttering assessments.