Formant transitions in the fluent speech of Farsi-speaking people who stutter

PurposeSecond formant (F2) transitions can be used to infer attributes of articulatory transitions. This study compared formant transitions during fluent speech segments of Farsi (Persian) speaking people who stutter and normally fluent Farsi speakers.MethodsTen Iranian males who stutter and 10 normally fluent Iranian males participated. Sixteen different “CVt” tokens were embedded within the phrase “Begu CVt an”. Measures included overall F2 transition frequency extents, durations, and derived overall slopes, initial F2 transition slopes at 30 ms and 60 ms, and speaking rate.Results(1) Mean overall formant frequency extent was significantly greater in 14 of the 16 CVt tokens for the group of stuttering speakers. (2) Stuttering speakers exhibited significantly longer overall F2 transitions for all 16 tokens compared to the nonstuttering speakers. (3) The overall F2 slopes were similar between the two groups. (4) The stuttering speakers exhibited significantly greater initial F2 transition slopes (positive or negative) for five of the 16 tokens at 30 ms and six of the 16 tokens at 60 ms. (5) The stuttering group produced a slower syllable rate than the non-stuttering group.ConclusionsDuring perceptually fluent utterances, the stuttering speakers had greater F2 frequency extents during transitions, took longer to reach vowel steady state, exhibited some evidence of steeper slopes at the beginning of transitions, had overall similar F2 formant slopes, and had slower speaking rates compared to nonstuttering speakers. Findings support the notion of different speech motor timing strategies in stuttering speakers. Findings are likely to be independent of the language spoken.Educational objectives This study compares aspects of F2 formant transitions between 10 stuttering and 10 nonstuttering speakers. Readers will be able to describe: (a) characteristics of formant frequency as a specific acoustic feature used to infer speech movements in stuttering and nonstuttering speakers, (b) two methods of measuring second formant (F2) transitions: the visual criteria method and fixed time criteria method, (c) characteristics of F2 transitions in the fluent speech of stuttering speakers and how those characteristics appear to differ from normally fluent speakers, and (d) possible cross-linguistic effects on acoustic analyses of stuttering.     

Atypical non-verbal sensorimotor synchronization in adults who stutter may be modulated by auditory feedback

PurposeTo investigate if non-verbal sensorimotor synchronization abilities in adult individuals who stutter (IWS) differ from non-stuttering controls (NS) under various performance conditions (tempo, auditory feedback, use of hands [single/both] and rhythm).MethodsParticipants were 11 IWS (5 males, 6 females, Mean age = 25.8, SD = 8.7) and 11 age- and gender-matched controls (Mean age = 24.4, SD = 8.4). During the experiment, participants were asked to prepare three melodies and subsequently perform them with a metronome at different rates and auditory feedback modalities (non-altered and suppressed). For each task/condition we tracked timing asynchrony related to the steady metronome beat.Results and conclusionsOverall, IWS displayed significantly higher timing asynchrony. Of all conditions, auditory-feedback distinguished IWS from NS most strongly, a subgroup of IWS significantly benefitting from the absence of auditory feedback. In addition, IWS showed a non-significant trend of higher negative mean asynchrony (NMA) and were more affected by the slower rate and increased rhythmic complexity and occasionally suggested poorer beat perception. These results suggest aberrant timing of sensorimotor network interaction associated with the origin of developmental stuttering.     

Evidence for a time constant in rate of speech under delayed auditory feedback

This experiment investigates an apparent discrepancy in experimental measurements of the effect of texture predictability upon reading disruption under delayed auditory feedback (DAF). By measuring relative DAF decrement in three different ways, it is shown that the previous findings can be related; Fillenbaum's hypothesis of increased disruption by DAF with an increase in predictability of the material is rejected, less disruption being obtained after practice on a particular passage. Almost identical ratios of DAF rate divided by normal rate are found irrespective of the type of reading material and stage in practice. This has not been reported previously and suggests that behaviour under DAF may be related to behaviour under normal conditions by a multiplicative constant. These results are also consistent with the notion of limited channel capacity and the partitioning of attention between two sources of information.     

A technique for controlling speech disfluencies induced by delayed auditory feedback

On the basis of cybernetic models of speech it was hypothesized that “stuttering” induced by delayed auditory feedback could be significantly reduced if the Ss were provided with an alternate input to which they could attend. The results of the experiment supported the hypothesis. The possible implications for the treatment stuttering are discussed.     

Effect of phonological and morphological factors on speech disfluencies of Kannada speaking preschool children who stutter

PurposeEmpirical investigations have revealed a strong association between linguistic factors and stuttering, specifically phonological and morphological factors. However, the effect of these factors is suggested to vary across languages owing to the differences in their linguistic structure. Further, the trend is found to vary between AWS and CWS. Literature in this regard is scarce in the Kannada language, particularly in children. Hence, the study was driven by the need to understand the effect of phonological and morphological factors on stuttering in Kannada speaking CWS.MethodSpontaneous speech samples were obtained from twenty Kannada speaking preschool CWS with a confirmed diagnosis of stuttering by an experienced speech-language pathologist. The recorded samples were transcribed, and disfluencies were marked. Further, the stuttered words were analysed for phonological and morphological features. The phonological factors included were phoneme position in a word, phoneme type and word length. Morphological factors consisted of word class and word end inflectional morphology. The percentage of stuttering was calculated with respect to each of the factors mentioned above.ResultsPhoneme in the initial position of a word and words beginning with consonants had a higher rate of stuttering. Word length, word class and word end inflections were found to have no significant effect on the rate of stuttering in CWS.ConclusionOverall, current findings revealed that stuttering might manifest differently across languages varying in their linguistic structures.     

The impact of threat and cognitive stress on speech motor control in people who stutter

PurposeIn the present study, an Emotional Stroop and Classical Stroop task were used to separate the effect of threat content and cognitive stress from the phonetic features of words on motor preparation and execution processes.MethodA group of 10 people who stutter (PWS) and 10 matched people who do not stutter (PNS) repeated colour names for threat content words and neutral words, as well as for traditional Stroop stimuli. Data collection included speech acoustics and movement data from upper lip and lower lip using 3D EMA.ResultsPWS in both tasks were slower to respond and showed smaller upper lip movement ranges than PNS. For the Emotional Stroop task only, PWS were found to show larger inter-lip phase differences compared to PNS. General threat words were executed with faster lower lip movements (larger range and shorter duration) in both groups, but only PWS showed a change in upper lip movements. For stutter specific threat words, both groups showed a more variable lip coordination pattern, but only PWS showed a delay in reaction time compared to neutral words. Individual stuttered words showed no effects. Both groups showed a classical Stroop interference effect in reaction time but no changes in motor variables.ConclusionThis study shows differential motor responses in PWS compared to controls for specific threat words. Cognitive stress was not found to affect stuttering individuals differently than controls or that its impact spreads to motor execution processes.Educational objectives: After reading this article, the reader will be able to: (1) discuss the importance of understanding how threat content influences speech motor control in people who stutter and non-stuttering speakers; (2) discuss the need to use tasks like the Emotional Stroop and Regular Stroop to separate phonetic (word-bound) based impact on fluency from other factors in people who stutter; and (3) describe the role of anxiety and cognitive stress on speech motor processes.     

The effect of fast speech rate on stuttering frequency during delayed auditory feedback

Delayed auditory feedback (DAF) has been documented to improve fluency in those who stutter. The increased fluency has been attributed to the slowed speech rate induced by DAF, but recent experiments have suggested that increasing the speech rate may also decrease stuttering under DAF. This investigation described the effect of combining a fast speech rate and DAF on the fluency of four people who stutter. Fluency of the two mildly dysfluent subjects was the same for both no DAF and DAF conditions at normal and at fast oral reading rates. In contrast, the two severely dysfluent subjects improved in fluency from the no DAF to the DAF conditions. They were found to be dysfluent at both normal and fast oral reading rates without DAF. The results of the study point to the need for further research on the relationship between speech rate and stuttering frequency under conditions of DAF and no DAF. EDUCATIONAL OBJECTIVES: Readers will learn about and be able to describe how the frequency of stuttering is affected by: (1) speech rates; (2) DAF; and (3) how stuttering severity influences such effects.     

I: Effect of delayed auditory feedback on speech and keytapping

The effects of delayed auditory feedback (DAF) on the performance of simple speech and keytapping tasks were compared. In the first experiment, each of the fourteen young adult subjects was asked to repeat the speech sound “b” in groups of three sounds. The subject heard his undelayed speech sounds through earphones. Under the delay condition, the speech sounds were delayed 244 millisec. before being returned to the subject's earphones. In the second experiment, each of the same subjects was asked to tap on a key in groups of three taps. The subjects heard an undelayed click through earphones each time they tapped on the key. Under the delay condition, the clicks were delayed 244 millisec. before being returned to the earphones. Graphic recordings were made of the time and intensity characteristics of tapping under both conditions.

The changes which occurred in speech and keytapping under DAF were qualitatively the same and consisted of increases in intensity and unit-to-unit time of both taps and speech sounds. When performing under DAF, the subjects also exhibited a tendency to repeat more sounds or to tap more times than had been requested. The percentage of change in intensity and time characteristics for speech and keytapping performances which occurred under DAF were not significantly different for the two motor systems. The amount of change in speech performance under DAF did not correlate significantly with the amount of change in keytapping performance.     

Differential levels of speech and manual dysfluency in adults who stutter during simultaneous drawing and speaking tasks

We examined the disruptive effects of stuttering on manual performance during simultaneous speaking and drawing tasks. Fifteen stuttering and fifteen non-stuttering participants drew continuous circles with a pen on a digitizer tablet under three conditions: silent (i.e., neither reading nor speaking), reading aloud, and choral reading (i.e., reading aloud in unison with another reader). We counted the frequency of stuttering events in the speaking tasks and measured pen stroke duration and pen stroke dysfluency (normalized jerk) in all three tasks. The control group was stutter-free and did not increase manual dysfluency in any condition. In the silent condition, the stuttering group performed pen movements without evidence of dysfluency, similar to the control group. However, in the reading aloud condition, the stuttering group stuttered on 12% of the syllables and showed increased manual dysfluency. In the choral reading condition stuttering was virtually eliminated (reduced by 97%), but manual dysfluency was reduced by only 47% relative to the reading aloud condition. Trials where more stuttered events were generally positively correlated with higher manual dysfluency. The results are consistent with a model in which episodes of stuttering and motor dysfluency are related to neural interconnectivity between manual and speech processes.     

Atypical central auditory speech-sound discrimination in children who stutter as indexed by the mismatch negativity

PurposeRecent theoretical conceptualizations suggest that disfluencies in stuttering may arise from several factors, one of them being atypical auditory processing. The main purpose of the present study was to investigate whether speech sound encoding and central auditory discrimination, are affected in children who stutter (CWS).MethodsParticipants were 10 CWS, and 12 typically developing children with fluent speech (TDC). Event-related potentials (ERPs) for syllables and syllable changes [consonant, vowel, vowel-duration, frequency (F0), and intensity changes], critical in speech perception and language development of CWS were compared to those of TDC.ResultsThere were no significant group differences in the amplitudes or latencies of the P1 or N2 responses elicited by the standard stimuli. However, the Mismatch Negativity (MMN) amplitude was significantly smaller in CWS than in TDC. For TDC all deviants of the linguistic multifeature paradigm elicited significant MMN amplitudes, comparable with the results found earlier with the same paradigm in 6-year-old children. In contrast, only the duration change elicited a significant MMN in CWS.ConclusionsThe results showed that central auditory speech-sound processing was typical at the level of sound encoding in CWS. In contrast, central speech-sound discrimination, as indexed by the MMN for multiple sound features (both phonetic and prosodic), was atypical in the group of CWS. Findings were linked to existing conceptualizations on stuttering etiology.Educational objectives: The reader will be able (a) to describe recent findings on central auditory speech-sound processing in individuals who stutter, (b) to describe the measurement of auditory reception and central auditory speech-sound discrimination, (c) to describe the findings of central auditory speech-sound discrimination, as indexed by the mismatch negativity (MMN), in children who stutter.     

Further evaluation of self and peer judgements of speech with delayed auditory feedback

Fifteen undergraduate students recorded a standard reading passage under simultaneous auditory feedback (SAF) and delayed auditory feedback (DAF, 210 ms). These pairs were rated for articulation and fluency differences, reading rate differences, pitch differences, loudness differences, and overall differences in quality of speech by the fifteen speakers and by ten peer judges. Results suggest that naive speakers under DAF form a self-impression of the effects of DAF upon their speech that is not different from the qualitative ratings of independent peer judges. The hypothesis that there was no overall difference between self and peer ratings was not rejected. Implications for the use of DAF as a research or treatment modality, or as both, are discussed.     

Effects of different attention tasks on concurrent speech in adults who stutter and fluent controls

Purpose: Motor theories indicate that focusing attention on well-practiced movements interferes with skilled performance; however, specific forms of attention (alerting vs. orienting vs. executive control) associated with this effect are not well understood. The present study explored this question in relation to stuttering, and examined whether dual task conditions that engaged sustained attention or working memory (WM) affected speech fluency in different ways. We also considered whether fluency changes were associated with changes in speech rate and language.Methods: Nineteen adults who stutter (AWS) and 20 controls produced spontaneous speech under a baseline condition and two dual task conditions: one involving a sustained attention task, the other involving WM demands.Results: Both groups produced fewer stutter-like disfluencies under dual task relative to baseline conditions and this reduction did not differ between the two dual tasks (attention vs. WM). Speech rate and language variables, which were potentially influenced by attention conditions, were not affected by dual tasks in the same way as disfluencies, and appeared to be unassociated with fluency results.Conclusions: Findings indicate that atypical disfluencies decrease when attention is divided, even when secondary task demands are minimal, as they were in the sustained attention task. For simple secondary tasks, fluency changes do not appear to be a byproduct of slowed rate and are not accompanied by observable changes in language. These results demonstrate that simple manipulations of attention can induce measurable effects on aspects of speech production, and may be a useful tool for facilitating fluency in clinical intervention.     

Effect of different delayed auditory feedback intervals on a music performance task

The effects of 12 different delay intervals were studied in a musical task involving performance on an electronic organ. Disruption was found to occur to a degree comparable to similar studies involving verbal and rhythmic tasks under DAF. Maximal disruption was found with a delay of 0.27 sec, a value rather greater than that typically found to be most disruptive in speech. Three of the 12 Ss showed speeded performance under part of the range of DAF intervals, as compared with performance under immediate feedback; however, their performance also reached a peak of slowing at a delay of about 0.27 sec. No significant differences were found between male and female Ss’ performance. These findings were discussed without the context of control processes operating in music performance, and compared with the possibly analogous mechanisms of speech.     

The relationship of self-conception to perceived stuttering severity in children and adults who stutter

This explorative study addresses differences in the experience history with stuttering of children and adults who stutter. One-hundred persons, 40 elementary school children, and 60 adults, were administered a Communication Situation Scale to indicate perceived severity of their stuttering, and the Comprehensive System for the Rorschach Inkblot Test to indicate the degree to which their self-conception might be based on participation within social interactions. The findings showed a positive relationship between these two variables for children, especially with regard to interactions in dyads (pairs) and strangers, and a negative relationship for adults in dyads. The findings also showed that the relationship between these two variables was significantly inverse between children and adults, especially with regard to interactions in the above situations.     

The role of temporal speech cues in facilitating the fluency of adults who stutter

PurposeAdults who stutter speak more fluently during choral speech contexts than they do during solo speech contexts. The underlying mechanisms for this effect remain unclear, however. In this study, we examined the extent to which the choral speech effect depended on presentation of intact temporal speech cues. We also examined whether speakers who stutter followed choral signals more closely than typical speakers did.Method8 adults who stuttered and 8 adults who did not stutter read 60 sentences aloud during a solo speaking condition and three choral speaking conditions (240 total sentences), two of which featured either temporally altered or indeterminate word duration patterns. Effects of these manipulations on speech fluency, rate, and temporal entrainment with the choral speech signal were assessed.ResultsAdults who stutter spoke more fluently in all choral speaking conditions than they did when speaking solo. They also spoke slower and exhibited closer temporal entrainment with the choral signal during the mid- to late-stages of sentence production than the adults who did not stutter. Both groups entrained more closely with unaltered choral signals than they did with altered choral signals.ConclusionsFindings suggest that adults who stutter make greater use of speech-related information in choral signals when talking than adults with typical fluency do. The presence of fluency facilitation during temporally altered choral speech and conversation babble, however, suggests that temporal/gestural cueing alone cannot account for fluency facilitation in speakers who stutter. Other potential fluency enhancing mechanisms are discussed.Educational Objectives: The reader will be able to (a) summarize competing views on stuttering as a speech timing disorder, (b) describe the extent to which adults who stutter depend on an accurate rendering of temporal information in order to benefit from choral speech, and (c) discuss possible explanations for fluency facilitation in the presence of inaccurate or indeterminate temporal cues.