Function word repetitions emerge when speakers are operantly conditioned to reduce frequency of silent pauses.

Beattie and Bradbury (1979) reported a study in which, in one condition, they punished speakers when they produced silent pauses (by lighting a light they were supposed to keep switched off). They found speakers were able to reduce silent pauses and that this was not achieved at the expense of reduced overall speech rate. They reported an unexpected increase in word repetition rate. A recent theory proposed by Howell, Au-Yeung, and Sackin (1999) predicts that the change in word repetition rate will occur on function, not content words. This hypothesis is tested and confirmed. The results are used to assess the theory and to consider practical applications of this conditioning procedure.

Exchange of stuttering from function words to content words with age.

Dysfluencies on function words in the speech of people who stutter mainly occur when function words precede, rather than follow, content words (Au-Yeung, Howell, & Pilgrim, 1998). It is hypothesized that such function word dysfluencies occur when the plan for the subsequent content word is not ready for execution. Repetition and hesitation on the function words buys time to complete the plan for the content word. Stuttering arises when speakers abandon the use of this delaying strategy and carry on, attempting production of the subsequent, partly prepared content word. To test these hypotheses, the relationship between dysfluency on function and content words was investigated in the spontaneous speech of 51 people who stutter and 68 people who do not stutter. These participants were subdivided into the following age groups: 2-6-year-olds, 7-9-year-olds, 10-12-year-olds, teenagers (13-18 years), and adults (20-40 years). Very few dysfluencies occurred for either fluency group on function words that occupied a position after a content word. For both fluency groups, dysfluency within each phonological word occurred predominantly on either the function word preceding the content word or on the content word itself, but not both. Fluent speakers had a higher percentage of dysfluency on initial function words than content words. Whether dysfluency occurred on initial function words or content words changed over age groups for speakers who stutter. For the 2-6-year-old speakers that stutter, there was a higher percentage of dysfluencies on initial function words than content words. In subsequent age groups, dysfluency decreased on function words and increased on content words. These data are interpreted as suggesting that fluent speakers use repetition of function words to delay production of the subsequent content words, whereas people who stutter carry on and attempt a content word on the basis of an incomplete plan.

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.

Development of a two-stage procedure for the automatic recognition of dysfluencies in the speech of children who stutter: I. Psychometric procedures appropriate for selection of training material for lexical dysfluency classifiers.

This program of work is intended to develop automatic recognition procedures to locate and assess stuttered dysfluencies. This and the following article together, develop and test recognizers for repetitions and prolongations. The automatic recognizers classify the speech in two stages: In the first, the speech is segmented, and, in the second, the segments are categorized. The units that are segmented are words. Here assessments by human judges on the speech of 12 children who stutter are described using a corresponding procedure. The accuracy of word boundary placement across judges, categorization of the words as fluent, repetition or prolongation, and duration of the different fluency categories are reported. These measures allow reliable instances of repetitions and prolongations to be selected for training and assessing the recognizers in the subsequent paper.

Development of a two-stage procedure for the automatic recognition of dysfluencies in the speech of children who stutter: II. ANN recognition of repetitions and prolongations with supplied word segment markers.

This program of work is intended to develop automatic recognition procedures to locate and assess stuttered dysfluencies. This and the preceding article focus on developing and testing recognizers for repetitions and prolongations in stuttered speech. The automatic recognizers classify the speech in two stages: In the first the speech is segmented and in the second the segments are categorized. The units segmented are words. The current article describes results for an automatic recognizer intended to classify words as fluent or containing a repetition or prolongation in a text read by children who stutter that contained the three types of words alone. Word segmentations are supplied and the classifier is an artificial neural network (ANN). Classification performance was assessed on material that was not used for training. Correct performance occurred when the ANN placed a word into the same category as the human judge whose material was used to train the ANNs. The best ANN correctly classified 95% of fluent, and 78% of dysfluent words in the test material.