Changes in aerodynamic characteristics of stutterers' fluent speech associated with therapy

Stuttering frequency and four aerodynamic measures of articulatory events within perceptually fluent voiced and voiceless intervocalic intervals were obtained from 15 stutterers prior to and at the termination of a concentrated program of stuttering therapy. Three of the four aerodynamic variables showed group changes over the course of therapy concomitant with improvements in fluency. Additional correlational analyses suggested that one of the aerodynamic variables was specifically related to stuttering frequency. It is argued that both fluency enhancing and ancillary components of therapy operate to influence the intervocalic interval.     

Onset of voicing in stuttered and fluent utterances

Electroglottographic (EGG) and acoustic waveforms of the first few glottal pulses of voicing were monitored and voice onset time (VOT) measured during an adaptation task performed by stutterers and controls. The fluent utterances of stutterers resembled those of control subjects. After dysfluencies, however, the EGG signal increased gradually, lending physiological support to the technique of "easy onset" of voicing. EGG waveforms also served to help differentiate mild from severe stutterers. Idiosyncratic ritualized laryngeal behavior, sometimes including physiological tremor, was evident in the EGG record.     

Coordination of oral and laryngeal movements in the perceptually fluent speech of adults who stutter.

This work investigated whether stuttering and nonstuttering adults differ in the coordination of oral and laryngeal movements during the production of perceptually fluent speech. This question was addressed by completing correlation analyses that extended previous acoustic studies by others as well as inferential analyses based on the within-subject central tendency and variability of acoustic and physiological indices of oral-laryngeal control and coordination. Stuttering and nonstuttering adults produced the target /p/ as the medial consonant in C(1)V(1)#C(2)V(2)C(3) sequences (C = consonant; V = vowel or diphthong; # = word boundary) embedded in utterances differing in length and location of the target movements. No between-groups differences were found for across- or within-subject correlations between acoustic measures of stop gap and voice onset time (VOT). However, the acoustic data did show longer durations for devoicing interval and VOT in the stuttering versus nonstuttering individuals, in the absence of a difference for a proportional measure specifically reflecting oral-laryngeal relative timing. Analyses of combined kinematic and electroglottographic data revealed that the stuttering individuals' speech was also characterized by (a) longer durations from bilabial closing movement onset and peak velocity to V(1) vocal fold vibration offset and (b) greater within-subject variability for dependent variables that were physiological indices of devoicing interval and VOT, but again no between-groups differences were found for specific indices of oral-laryngeal relative timing. Overall, findings suggest that, for the production of voiceless bilabial stops in perceptually fluent speech, stuttering and nonstuttering adults differ in the duration of intervals defined by events within as well as across the oral and laryngeal subsystems, but the groups show similar patterns of relative timing for the involved oral and laryngeal movements.     

Comparison of period-by-period fundamental frequency of stutterers and nonstutterers over repeated utterances

The fundamental frequency (f phi) of the first five periods in the acoustic wave form of vowels following stop consonant productions and the f phi of a period approximately 100 ms into the vowel were analyzed in the repeated fluent utterances of 10 nonstutterers and 10 stutterers both pre- and posttherapy. Group data indicate that the nonstutterers and stutterers showed similar f phi diminution patterns in vowels immediately following stop consonants. Additionally, the stutterers were not significantly different from the nonstutterers in their ability to achieve a stable f phi over repeated utterances. These results are discussed with respect to a previous analysis of the present data (Sacco & Metz, 1986) in which it was found that stutterers were significantly more variable than nonstutterers in their ability to achieve a stable f phi over repeated utterances. It is suggested that stutterings in the immediate vicinity of otherwise fluently produced words may influence certain production characteristics of those words.     

Comparison of upper and lower lip muscle activity between stutterers and fluent speakers

OBJECTIVE: There is a widespread clinical view that stuttering is associated with high levels of muscles activity. The proposal of this research was to compare stutterers and fluent speakers with respect to the electromyographic activity of the upper and lower lip muscles. METHODS: Ten individuals who stutter and 10 fluent speakers (control group) paired by gender and age were studied (mean age: 13.4 years). Groups were defined by the speech sample analysis of the ABFW-Language Test. A K6-I EMG (Myo-tronics Co., Seattle, WA, USA) with double disposable silver electrodes (Duotrodes, Myo-tronics Co., Seattle, WA) being used in order to analyze lip muscle activity. The clinical conditions investigated were movements during speech, orofacial non-speech tasks, and rest. Electromyographic data were normalized by lip pursing activity. The non-parametric Mann-Whitney test was used for the comparison of speech fluency profile, and the Student t-test for independent samples for group comparison regarding electromyographic data. RESULTS: There was a statistically significant difference between groups regarding speech fluency profile and upper lip activity in the following conditions: lip lateralization to the right and to the left and rest before exercises (P<0.05). There was no significant difference between groups regarding lower lip activity (P>0.05). CONCLUSION: The EMG activity of the upper lip muscle in the group with stuttering was significantly lower than in the control group in some of the clinical conditions analyzed. There was no significant difference between groups regarding the lower lip muscle. The subjects who stutter did not present higher levels of muscle activity in lip muscles than fluent speakers.     

Modification of listener-judged naturalness in the speech of stutterers

This study investigated the effect of regular feedback of listener-judged speech naturalness ratings on the speech of stutterers. Six adult stutterers each participated in a time-series ABA experiment. During the treatment phase the stutterer was instructed to improve a clinician's rating, on a 9-point scale, of the naturalness of each 30-s interval of the stutterer's spontaneous speech. The results indicate that the naturalness ratings and stuttering for 5 of the subjects made favorable changes during the treatment phase. Analyses of the findings show that only some of the naturalness judgments were influenced by stuttering frequency and speech rate. A perceptual analysis of the speech of 2 subjects suggested that the speech naturalness ratings were also probably influenced by other less obvious variables.     

Kinematic analysis of lip closure in stutterers' fluent speech

An analysis of lip and jaw motion was carried out in order to evaluate previous observations on the fluent speech of stutterers and to describe possible effects of speech therapy. A strain gauge system was used to transduce lip and jaw movements during fluent repetitions of "sapapple" in adult stutterers and nonstutterers. Fifteen movement parameters were measured on lip closure for the initial /p/ sound in a group of 10 normal speakers, 10 stutterers who had no recent speech therapy, and 8 stutterers who had been through an intensive speech therapy program involving modification of speech timing. The no-therapy group and nonstutterers did not differ significantly in terms of any movement parameter. Stutterers who had been through speech therapy showed significant increases in jaw movement duration and time to peak velocity of the upper lip, lower lip, and jaw. The expected timing pattern for lip and jaw velocity peaks on lip closure (UL-LL-J) was the most frequently occurring pattern, but deviations from this pattern were observed in both stutterers and nonstutterers. The occurrence of reversals was most prevalent in the therapy group, and it was associated with increases in jaw movement duration across subjects. It is suggested that for the type of movement studied here, anomalies in stutterers' fluent speech are likely to be the result of acquired adjustments rather than properties of the speech neuromotor system that underly dysfluency.     

Duration of the speech disfluencies of beginning stutterers

This study compared the duration of within-word disfluencies and the number of repeated units per instance of sound/syllable and whole-word repetitions of beginning stutterers to those produced by age- and sex-matched nonstuttering children. Subjects were 10 stuttering children [9 males and 1 female; mean age 4:1 (years:months); age range 3:2-5:1), and 10 nonstuttering children (9 males and 1 female; mean age 4:0; age range: 2:10-5:1). Mothers of the stuttering children reported that their children had been stuttering for 1 year or less. One 300-word conversational speech sample from each of the stuttering and nonstuttering children was analyzed for (a) mean duration of sound/syllable repetition and sound prolongation, (b) mean number of repeated units per instance of sound/syllable and whole-word repetition, and (c) various related measures of the frequency of all between- and within-word speech disfluencies. There were no significant between-group differences for either the duration of acoustically measured sound/syllable repetitions and sound prolongations or the number of repeated units per instance of sound/syllable and whole-word repetition. Unlike frequency and type of speech disfluency produced, average duration of within-word disfluencies and number of repeated units per repetition do not differentiate the disfluent speech of beginning stutterers and their nonstuttering peers. Additional analyses support findings from previous perceptual work that type and frequency of speech disfluency, not duration, are the principal characteristics listeners use in distinguishing these two talker groups.     

Differences of articulation rate and utterance length in fluent and disfluent utterances of preschool children who stutter

Purpose

The purpose of this study was to investigate characteristics of four types of utterances in preschool children who stutter: perceptually fluent, containing normal disfluencies (OD utterance), containing stuttering-like disfluencies (SLD utterance), and containing both normal and stuttering-like disfluencies (SLD + OD utterance). Articulation rate and length of utterance were measured to seek the differences. Because articulation rate may reflect temporal aspects of speech motor control, it was predicted that the articulation rate would be different between perceptually fluent utterances and utterances containing disfluencies. The length of utterance was also expected to show different patterns.

Method

Participants were 14 preschool children who stutter. Disfluencies were identified from their spontaneous speech samples, and articulation rate in syllables per second and utterance length in syllables were measured for the four types of utterances.

Results and discussion

There was no significant difference in articulation rate between each type of utterance. Significantly longer utterances were found only in SLD + OD utterances compared to fluent utterances, suggesting that utterance length may be related to efforts in executing motor as well as linguistic planning. The SLD utterance revealed a significant negative correlation in that longer utterances tended to be slower in articulation rates. Longer utterances may place more demand on speech motor control due to more linguistic and/or grammatical features, resulting in stuttering-like disfluencies and a decreased rate.

Learning outcomes

The reader will learn about and be able to: (a) distinguish the difference between measures of overall speaking rate and articulation rate; (b) explain the theoretical and clinical trends of articulation rate in stuttering; (c) discuss how utterances containing stuttering-like disfluencies, utterances containing other disfluencies, and utterances containing both stuttering-like disfluencies and other disfluencies influence articulation rate; and (d) discuss how the length of utterances is related to disfluencies.     

A comparison of young stutterers' fluent versus stuttered utterances on measures of length and complexity

This investigation attempted to clarify the relationship between stuttering in young children and the language factors of length and grammatical complexity. Sentences containing stutterings within the first few words, as produced by 12 stutterers (4-6 years old) in spontaneous conversational dyads, were analyzed for length and grammatical complexity. Results indicated that sentences in which an episode of stuttering occurred within the first three words were significantly longer and more complex than sentences that were free of perceptible stuttering and all other forms of fluency failure. Implications of these findings for the clinician are presented and discussed.     

Acoustic analysis of stutterers' fluent speech before and after therapy

The speech of 14 stutterers was analyzed prior to and at the termination of a 5-week stuttering therapy program to examine the relationship between nine selected acoustic variables and stuttering frequency. Group analyses indicated that pre- to post-therapy changes in stuttering frequency were accompanied by mean changes in five of the nine acoustic variables, a finding which is consistent with previous literature. Correlational analyses indicated that only silence in the voiced stop consonant intervocalic interval (IVI) was significantly correlated with stuttering frequency prior to therapy (i.e., lower stuttering frequency values were associated with shorter durations of silence during the IVI). Furthermore, the degree of reduction in silence was positively correlated with the magnitude of reduction in stuttering frequency due to therapy. These findings suggest that silence in the IVI may reflect the operational status of some mechanism which may underlie disfluent speech.     

The structure of disfluency behaviors in the speech of adult stutterers

Throughout the stuttering literature numerous references to a twofold classification of disfluency types are found. However, no rigorous empirical test of that dichotomous classification has been reported in the literature. This investigation was designed to conduct such a test in order to provide an empirical foundation for that distinction. The hypotheses stated that the relationships among disfluency behaviors were consistent with an underlying two-dimensional structure and specified the group of variables (disfluency behaviors) having primary association with each dimension. Instrumentation and procedures permitting reliable identification and coding of nine disfluency behaviors were developed. This observational system was applied to baseline monologues obtained from 180 adult stutterers. Results of factor analyses supported the hypotheses on the two-factor structure and on the disposition of the disfluency variables.