Adaptation of stuttering frequency during repeated readings: associated changes in acoustic parameters of perceptually fluent speech

Reduced duration of stuttering-like disfluencies and consistent anticipatory slowing during an adaptation task

PURPOSE

The adaptation effect in stuttering, traditionally described as the reduction of stuttering moments over repeated readings, provides a context to investigate fluency facilitation as well as a relatively controlled means of comparing fluent speech in the immediate vicinity of words that were stuttered versus fluently produced. Acoustic studies have documented decreased duration of fluent speech during adaptation but rarely address changes in disfluencies or the speech preceding or following the disfluencies. This study addresses this gap in the research by documenting frequency and duration changes in both fluent and stuttered syllables.

METHOD

Fifteen people who stutter read passages aloud five times in succession. Frequency and duration of fluent syllables, pauses, stuttering-like disfluencies (SLDs) and other disfluencies (ODs) were compared across the five readings. In addition, durations for syllables before and after pauses and SLDs were compared to determine if there were anticipation or carryover effects of SLDs on surrounding syllables.

RESULTS

Durations measured for more than 22 000 fluent syllables, 1531 pauses, 128 ODs and 1752 SLDs. For most of the 15 participants, significant decreases in both frequency and duration of SLDs over the five readings were observed. In addition, lengthening of fluent syllables immediately preceding the disfluent syllables was observed: this pre-SLD lengthening did not change over the five readings.

CONCLUSIONS

Decreased duration of SLDs across readings supports the motor practice hypothesis, which assumes that successive reading of the same text increases the efficiency of the speech motor plans resulting in less stuttering and decreased durations of the stuttering that persists. Pre-SLD lengthening merits further study, because it informs our knowledge of the time course of stuttered events and may be associated with conscious or unconscious anticipation of upcoming SLDs that does not decrease with motor practice.

WHAT THIS PAPER ADDS

What is already known on this subject The frequency of stuttering-like disfluencies (SLDs) can be reduced using a variety of fluency-enhancing strategies. For example, the adaptation effect, in which a reduction of stuttered events occurs over repeated readings of the same material, has been widely studied. Previous studies have shown that durations of fluent syllables decrease during adaptation, supporting the hypothesis that repeated practice of the motor plan leads to increased fluency. However, temporal changes in disfluent syllables and syllables preceding and following SLDs have rarely been studied, so our understanding of the effect of motor practice on stuttering reduction is incomplete. What this study adds This study has two significant findings. First, stuttered disfluencies that persisted after the initial reading of the adaptation task tended to become shorter in duration. Fluently produced syllables and those that were stuttered, both of which are speech events related to motor control of articulators, were affected in a similar manner by the motor practice associated with adaptation. Second, lengthening of fluent syllables immediately preceding stuttered syllables was observed. This pre-stuttering lengthening, however, did not decrease in duration over the five readings: the mechanism that drives this anticipatory behaviour is not affected by repeated practice. What are the clinical implications of this work? People who stutter have neural differences that lead to speech motor planning and/or execution that is less efficient than that of typical speakers. The finding that stuttering is reduced and that persisting SLDs become shorter in duration over repeated readings provides evidence that motor practice can influence the manifestation of stuttering by temporarily making those specific motor plans more efficient. This may inform treatments for stuttering. The observation that fluent syllables immediately before SLDs were lengthened, and that this lengthening was not influenced by repeated practice, extends our understanding of the time course of stuttering events and may be useful in understanding anticipation and listener reactions to stuttering.

Evaluating adaptation effect in real versus virtual reality environments with people who stutter

METHODS

This research aimed at measuring the adaptation effect in real and virtual reality (VR) environments for spontaneous-speech and reading. The objectives were divided into two categories. The first objective aimed at comparing the adaption effect for the real and VR environments on the reading task, while the second objective addressed the same objective, but for the spontaneous-speech task. The study involved 24 participants in the age range of 19-33 years. SSI-4 was administered on the participants.

CONCLUSION

The reduction in dysfluencies was seen for both real and VR testing environments. The reduction in the dysfluency was more marked for reading-task compared to spontaneous-speech task. The results shed light on the relationship between adaptation effect and the test environment.

Similar within-utterance loci of dysfluency in acquired neurogenic and persistent developmental stuttering

Although the underlying neural mechanisms remain unknown for both persistent developmental stuttering (PSD) and acquired neurogenic stuttering (ANS), few studies have examined similarities/differences between these two disorders. We evaluated in both PDS (n = 35) and ANS (n = 5) phonetic, word class, word length, and word position variables that are widely believed to influence at which loci within utterances PDS speakers' stuttering is most likely to occur. For both groups, (a) word weights based on the combination of variables were greater for stuttered vs. fluent words, and (b) stuttered words were loaded more by individual variables. However, contrary to long-standing views regarding PDS, greater loading for stuttered words was not found for the position variable. Findings suggest similar loci of stuttering in adults with PDS and ANS, and, for both groups, the probability of stuttering on a given word was more influenced by motor production variables than language variables.

Fluency adaptation in speakers with Parkinson disease: a motor learning perspective

PURPOSE

Fluency adaptation is characterised by a reduction in stuttering-like behaviours over successive readings of the same speech material and is an effect that is typically observed in developmental stuttering. Prominent theories suggest that short-term motor learning associated with practice explain, in part, fluency adaptation. The current investigation examined the fluency adaptation effect in a group of speakers with Parkinson disease (PD) who exhibited stuttering-like disfluencies.

METHOD

Individuals with PD (n = 21) and neurologically healthy controls (n = 19) read a passage five times. Per cent syllables stuttered was measured and calculated for each reading passage.

RESULT

Participants in the PD group exhibited significantly more stuttering-like disfluencies than control speakers. Twelve individuals in the PD group exhibited at least three per cent syllable stuttered on at least one reading. Statistical trends revealed that the subgroup of individuals with PD who stuttered exhibited a significant reduction in stuttering moments over the five successive readings.

CONCLUSION

A significant fluency adaptation effect was observed for the group of speakers with PD who exhibited stuttering-like disfluencies. Results of the current study are discussed within the framework of the motor learning hypothesis of fluency adaptation.

Lexical tone and stuttering in Cantonese

Cantonese is a tone language, in which the variation of the fundamental frequency contour of a syllable can change meaning. There are six different lexical tones in Cantonese. While research with Western languages has shown an association between stuttering and syllabic stress, nothing is known about whether stuttering in Cantonese speakers is associated with one or more of the six lexical tones. Such an association has been reported in conversational speech in Mandarin, which is also a tone language, but which varies markedly from Cantonese. Twenty-four native Cantonese-speaking adults who stutter participated in this study, ranging in age from 18-33 years. There were 18 men and 6 women. Participants read aloud 13 Cantonese syllables, each of which was produced with six contrastive lexical tones. All 78 syllables were embedded in the same carrier sentence, to reduce the influence of suprasegmental or linguistic stress, and were presented in random order. No significant differences were found for stuttering moments across the six lexical tones. It is suggested that this is because lexical tones, at least in Cantonese, do not place the task demands on the speech motor system that typify varying syllabic stress in Western languages: variations not only in fundamental frequency, but also in duration and intensity. The findings of this study suggest that treatments for adults who stutter in Western languages, such as speech restructuring, can be used with Cantonese speakers without undue attention to lexical tone.

Lexical priming in fluent and with developmental stuttering children

PURPOSE

To examine the possible relationship between lexical variables (categorization and naming) and developmental stuttering.

METHODS

Thirty Brazilian Portuguese speaking children with ages ranging from 7 to 9 years and 11 months participated in the study. We applied a lexical priming paradigm to experimentally investigate whether children with developmental stuttering (Research Group) differed from their fluent peers (Control Group), with respect to reaction time in three conditions - control (without prime); semantically related prime, and semantically independent prime - of two experimental tasks: categorization and naming of the target stimulus.

RESULTS

No difference between groups was observed in reaction time on the categorization task. However, there was a condition effect showing that, for both groups, reaction time was shorter in the semantically related prime condition when compared to the no prime condition. In the naming task, a between-group difference was observed in reaction time, indicating a longer reaction time in the Research Group than the Control Group. There was no condition effect on naming, i.e. the Research Group showed slower reaction time regardless of prime type.

CONCLUSIONS

The results confirm the hypothesis that, in children with developmental stuttering, readiness in motor programming of speech is slowed when compared to fluent children. There is no difference between groups when the lexical function does not require speech readiness.

Motor Learning Cannot Explain Stuttering Adaptation

When persons who stutter (PWS) read a text repeatedly, there is a progressive reduction in stutter frequency over the course of three to five readings. Recently, this phenomenon has been attributed by some researchers to motor learning—the acquisition of relatively permanent motor skills that facilitate fluency through practice in producing words. The current study tested this explanation. 23 PWS read prose passages five times in succession. The number of ‘new’ and ‘old’ stutters during repeated readings (words stuttered in the current reading but spoken fluently in the previous reading and words stuttered also in the previous reading) were analyzed. If motor learning facilitated fluency during repeated readings in PWS, words read fluently in a reading should not be stuttered in a later reading in significant numbers. Contrary to this prediction, there was no statistical difference in the number of new words stuttered across five readings. A plausible alternative explanation, which requires further study to verify, is offered.

Speech sequence skill learning in adults who stutter

The present study compared the ability of 12 people who stutter (PWS) and 12 people who do not stutter (PNS) to consolidate a novel sequential speech task. Participants practiced 100 repetitions of a single, monosyllabic, nonsense word sequence during an initial practice session and returned 24-h later to perform an additional 50 repetitions. Results showed significantly slower sequence durations in the PWS compared to PNS following extensive practice and consolidation. However, the hypothesis that poor performance gains in PWS compared to PNS during practice would be maintained following a 24-h consolidation period was not supported. Further descriptive analysis revealed large within group differences in PWS which to some extent were attributed to a subgroup of PWS who failed to show any improvements in performance following practice or consolidation. The results and the possible presence of subgroups of PWS are discussed with regard to their limitations in motor learning abilities.

EDUCATIONAL OBJECTIVES

The reader will be able to (1) explain the difference between practice and learning, (2) define consolidation and explain the importance of measuring performance following a consolidation period, (3) understand past research on PWS' performance during both speech and nonspeech motor tasks, and (4) explain why individual differences in practice effects and learning may have important implications for client variability in treatment outcome.

Detecting anticipatory effects in speech articulation by means of spectral coefficient analyses

Few acoustic studies have attempted to examine anticipatory effects in the earliest part of the release of stop consonants. We investigated the ability of spectral coefficients to reveal anticipatory coarticulation in the burst and early aspiration of stops in monosyllables. Twenty American English speakers produced stop (/k,t,p/) - vowel (/æ,i,o/) - stop (/k,t,p/) sequences in two phrase positions. The first four spectral coefficients (mean, standard deviation, skewness, kurtosis) were calculated for one window centered on the burst of the onset consonant and two subsequent, non-overlapping windows. All coefficients showed an influence of vowel-to-consonant anticipatory coarticulation. Which onset consonant showed the strongest vowel effect depended on the specific coefficient under consideration. A context-dependent consonant-to-consonant anticipatory effect was observed for onset /p/. Findings demonstrate that spectral coefficients can reveal subtle anticipatory adjustments as early as the burst of stop consonants. Different results for the four coefficients suggest that comprehensive spectral analyses offer advantages over other approaches. Studies using these techniques may expose previously unobserved articulatory adjustments among phonetic contexts or speaker populations.

Speech skill learning of persons who stutter and fluent speakers under single and dual task conditions

Two studies compared the accuracy and efficiency of initiating oral reading of nonsense syllables by persons who stutter (PWS) and fluent speakers (PNS) over practise. Findings of Study One, comparing 12 PWS and 12 PNS, replicated previous findings of slow speech sequence initiation over practise by PWS relative to PNS. In Study Two, nine PWS and eight PNS practised reading syllable sequences under single, and then dual task conditions in which a colour recognition distracter task was introduced. The speech sequences of PWS were initiated significantly slower than those of PNS. Significant GroupxCondition interactions for reaction time and accuracy were interpreted to suggest that PNS, but not PWS, demonstrated the ability to switch between an attention-demanding movement strategy under dual task conditions and a relatively automatic (little attention required) movement strategy after practise under single task conditions.

The transition to increased automaticity during finger sequence learning in adult males who stutter

The present study compared the automaticity levels of persons who stutter (PWS) and persons who do not stutter (PNS) on a practiced finger sequencing task under dual task conditions. Automaticity was defined as the amount of attention required for task performance. Twelve PWS and 12 control subjects practiced finger tapping sequences under single and then dual task conditions. Control subjects performed the sequencing task significantly faster and less variably under single versus dual task conditions while PWS' performance was consistently slow and variable (comparable to the dual task performance of control subjects) under both conditions. Control subjects were significantly more accurate on a colour recognition distracter task than PWS under dual task conditions. These results suggested that control subjects transitioned to quick, accurate and increasingly automatic performance on the sequencing task after practice, while PWS did not. Because most stuttering treatment programs for adults include practice and automatization of new motor speech skills, findings of this finger sequencing study and future studies of speech sequence learning may have important implications for how to maximize stuttering treatment effectiveness.

EDUCATIONAL OBJECTIVES

As a result of this activity, the participant will be able to: (1) Define automaticity and explain the importance of dual task paradigms to investigate automaticity; (2) Relate the proposed relationship between motor learning and automaticity as stated by the authors; (3) Summarize the reviewed literature concerning the performance of PWS on dual tasks; and (4) Explain why the ability to transition to automaticity during motor learning may have important clinical implications for stuttering treatment effectiveness.

Effect of reading with reversed speech on frequency of stuttering in adults

This study explored the effect of reading with reversed speech on the frequency of stuttering. Eight adults who stutter served as participants and read four 300-syllable passages while listening to three types of speech stimuli: normal speech (choral reading), reversed speech at normal speed, reversed speech at half speed, and a control condition of no auditory feedback. A repeated-measures analysis of variance showed a significant decrease in stuttering frequency in the choral reading condition but not in reversed speech at normal and half speed. However, the reversed speech at half-speed condition showed a large effect size (omega2 = 0.32). Data suggest that a forward moving speech feedback is not essential to decrease the frequency of stuttering in adults who stutter.

Lexical priming in picture naming of young children who do and do not stutter

The purpose of this investigation was to assess the influence of lexical/semantic priming on the speech reaction time of young children who do and do not stutter during a picture-naming task. Participants were 23 children who stutter, age-matched (+/-4 months) to 23 children who do not stutter, ranging in age from 3;0 (years;months) to 5;11. Procedures involved a computer-assisted picture-naming task, during which each participant was presented with the same set of 28 pictures in each of 3 different conditions: (a) no-prime condition, in which no auditory stimulus was presented before picture display; (b) related-prime condition, in which a word, semantically related to the target picture, was presented auditorily 700 ms before picture display; and (c) unrelated-prime condition, in which a semantically unrelated word was presented auditorily 700 ms before picture display. Results indicated that when compared with a no-prime condition, presentation of semantically related words before the picture-naming response led to shorter or faster speech reaction times for children who do not stutter, but for children who stutter, it led to longer or slower speech reaction times. Moreover, children who do not stutter and who had higher receptive vocabulary scores exhibited faster speech reaction times and a greater semantic priming effect, whereas no such relationships were found for children who stutter. Findings were taken to suggest that children who stutter may exhibit subtle difficulties with lexical encoding and that this difficulty with speech-language planning may be one variable that contributes to childhood stuttering.

Durational characteristics of the first productions of novel trochees and iambs in children with and without speech delay

The durational characteristics of novel words produced in repeated trials were evaluated in separate groups of children with, and without speech delay (SD). Children produced disyllabic novel words containing either a trochaic or iambic stress pattern. Results of acoustic analysis indicated a significant interaction between trial number and speaker group. The duration of words produced by children without SD decreased more abruptly across successive trials as compared to children with SD. In addition, duration decreased at a faster rate for trochaic words as compared to iambic words in both groups. Variability of word duration was greater in iambs than trochees. The results are discussed in terms of speech motor learning patterns that may underlie difficulties associated with SD.