Motor Performance of Stutterers

A continuing program of research, which is concerned with identifying brain mechanisms underlying stuttering through an analysis of manual motor control, is described. Clear evidence has been found that the neural mechanisms associated with sequential responding (and, by implication, with speech) are lateralized in stutterers as they are in nonstutterers. Although no gross or general in-coordination has been found in motor performance by most stutterers, their left hemisphere mechanisms appear to be inefficient for organizing and initiating new sequences of responses and vulnerable to interference from other neural activities. Results of research on bimanual coordination in stutterers are consistent with a model that attributes the interference, in part, to interhemispheric processes, possibly involving the supplementary motor area. One implication of the research is that the disfluency of stuttering is onfy one manifestation of a more general disfunction in motor and cognitive organization and planning.     

Concurrent task interference in stutterers: dissociating hemispheric specialization and activation

Using all four combinations of hand and foot, adult stutterers and nonstutterers performed a unimanual sequential finger tapping task together with a stimulus-contingent foot responding task. The two groups were similar in that both demonstrated more dual-task interference when using the ipsilateral than contralateral limb pairs. Contrary to a prediction based on a hypothesis that attributes stuttering to neural interference due to an ungated or unregulated activity flow between the hemispheres, stutterers did not show more interference than nonstutterers when using the contralateral limb pairs. The groups did differ, however, in terms of finger tapping interference associated with right- versus left-foot concurrent task responding. Nonstutterers showed more interference when using the left than right foot. This was interpreted in terms of the attentional demands that the foot responding task placed on a system with an inherent left-hemisphere attentional bias. The lack of a reliable difference in stutterers with respect to interference by the two feet is consistent with indications from other research that stutterers have a relatively labile system of hemispheric attention or activation. The results of the study are placed into the context of a general model of the brain mechanisms associated with stuttering.     

Sequence initiation performance by stutterers under conditions of response competition

Male stutterers and nonstutterers were compared on their performance of a task that required tapping keys as rapidly and accurately as possible to reproduce different sequences of finger movements as soon as they had been demonstrated on a visual display panel. Testing using the right hand alone confirmed previous findings that stutterers are significantly slower than nonstutterers in initiating new movement sequences and make significantly more errors on initial sequences. Subjects were also tested on this sequence reproduction task while they performed concurrently a manual task with the left hand that required turning a knob in response to signal tones. The hypothesis underlying the study was that associated with stuttering is a dysfunction in the mechanisms regulating interhemispheric communication, and it was predicted that the concurrent task would interfere more with the sequence reproduction task performance of stutterers than with that of nonstutterers. A joint analysis of the speed and accuracy aspects of performance of the two tasks confirmed the prediction. Additional research required to clarify whether the effects are in fact due to the hypothesized interhemispheric mechanisms or to a generally greater susceptibility of stutterers to interference from any concurrent motor or cognitive activity is discussed.     

Primary-school stutterers: Have attitudes changed?

How concerned are primary-school-aged stuttering children about their communication problem? What are the clinical implications of this concern?Fifteen years ago, Silverman (1970) suggested that primary-school-aged children who stuttered were not concerned about their disfluencies. A clinical implication of that report was that the interpreted lack of concern might negatively affect the children's motivation and desire for change in therapy. Scant research exists to support or refute this implication. While research is available on reactions to stuttering, pretherapeutic attitudes—especially those of children—have not been systematically reported. Guitar (1976) measured the pre-treatment attitudes of 38 adult stutterers and reported that, “those stutterers with more negative attitudes measured just prior to treatment, were most likely to have high levels of stuttering a year later, even though all subjects left therapy entirely fluent.” In related areas, research by Kolb, Winter, and Berlen (1968), McFall (1970), and McFall and Hammen (1971) has indicated that clients who are more motivated do better in behavior modification programs.Whether or not these findings may be generalized to children, in the midst of a developmental process, is purely speculative.     

发展性口吃的脑机制

口吃是一种常见的言语障碍,对此曾提出过大脑半球言语功能偏侧化异常假设。近期,发展性口吃的神经成像研究在支持这一经典假设的同时,还发现负责言语监控的颞叶系统和负责言语运动控制的额叶系统与皮层下脑结构存在功能失调,这可能损害言语产生时的精确时间控制。据此,研究者开始用神经网络的观点来解释发展性口吃产生的脑机制,认为患者可能存在由多个言语产生相关脑区构成的“双通路”网络的功能障碍     

Towards a functional neural systems model of developmental stuttering

This paper overviews recent developments in an ongoing program of brain imaging research on developmental stuttering that is being conducted at the University of Texas Health Science Center, San Antonio. This program has primarily used H₂¹⁵O PET imaging of different speaking tasks by right-handed adult male and female persistent stutterers, recovered stutterers and controls in order to isolate the neural regions that are functionally associated with stuttered speech. The principal findings have emerged from studies using condition contrasts and performance correlation techniques. The emerging findings from these studies are reviewed and referenced to a neural model of normal speech production recently proposed by Jürgens [Neurosci. Biobehav. Rev. 26 (2002) 235]. This paper will report (1) the reconfiguration of previous findings within the Jürgens Model; (2) preliminary findings of an investigation with late recovered stutterers; (3) an investigation of neural activations during a treatment procedure designed to produce a sustained improvement in fluency; and (4) an across-studies comparison that seeks to isolate neural regions within the Jürgens Model that are consistently associated with stuttering. Two regions appear to meet this criterion: right anterior insula (activated) and anterior middle and superior temporal gyri (deactivated) mainly in right hemisphere. The implications of these findings and the direction of future imaging investigations are discussed.

Educational objectives: The reader will learn about (1) recent uses of H₂¹⁵O PET imaging in stuttering research; (2) the use of a new neurological model of speech production in imaging research on stuttering; and (3) initial findings from PET imaging investigations of treated and recovered stutterers.     

Motor Performance of Stutterers and Nonstutterers on Timing and Force Control Tasks

Recently it has been suggested that speech and manual timing tasks share a common central process (Franz, Zelaznik, & Smith, 1992): Because stuttering is thought to be related to deficits in motoric processes such as timing, stutterers (n = 15) were compared with a set of age-, education-, and sex-matched nonstutterers on timing and isometric force-production tasks. In the timing tasks, subjects flexed and extended the right index finger at the metacarpophalangeal joint at cycle durations of 600, 500, 400, 300, and 200 ms. In the force-production tasks, subjects generated isometric forces to match target force levels displayed on a cathode-ray tube (CRT) screen. There were five levels of force, ranging from.11 to 7.85 newtons. Overall, there were no differences in timing and force-production performance between stutterers and nonstutterers. These results are similar to those obtained recently by Hulstijn, Summers, van Lieshout, and Peters (1992). We suggest that stuttering is not characterized by a general deficit in rhythmic timing. Instead, the motor deficit associated with stuttering should be viewed as speech specific.     

Motor Performance of Stutterers and Nonstutterers on Timing and Force Control Tasks

Recently it has been suggested that speech and manual timing tasks share a common central process (Franz, Zelaznik, & Smith, 1992). Because stuttering is thought to be related to deficits in motoric processes such as timing, stutterers (n = 15) were compared with a set of age-, education-, and sex-matched nonstutterers on timing and isometric force-production tasks. In the timing tasks, subjects flexed and extended the right index finger at the metacarpophalangeal joint at cycle durations of 600, 500, 400, 300, and 200 ms. In the force-production tasks, subjects generated isometric forces to match target force levels displayed on a cathode-ray tube (CRT) screen. There were five levels of force, ranging from .11 to 7.85 newtons. Overall, there were no differences in timing and force-production performance between stutterers and nonstutterers. These results are similar to those obtained recently by Hulstijn, Summers, van Lieshout, and Peters (1992). We suggest that stuttering is not characterized by a general deficit in rhythmic timing. Instead, the motor deficit associated with stuttering should be viewed as speech specific.     

Traits attributed to stuttering and nonstuttering children by their mothers

Traits attributed to 34 stuttering and 34 nonstuttering male children by their mothers using an adjective checklist were studied. Mothers of school-aged male stutterers were found to perceive their children as being more insecure, sensitive, anxious, withdrawn, fearful, and introverted than did mothers of nonstutterers. It was concluded that although research has not demonstrated a characteristic stuttering personality, stutterers continue to be perceived as having characteristic personality patterns.     

The effects of simulated stuttering and prolonged speech on the neural activation patterns of stuttering and nonstuttering adults

Functional magnetic resonance imaging was used to investigate the neural correlates of passive listening, habitual speech and two modified speech patterns (simulated stuttering and prolonged speech) in stuttering and nonstuttering adults. Within-group comparisons revealed increased right hemisphere biased activation of speech-related regions during the simulated stuttered and prolonged speech tasks, relative to the habitual speech task, in the stuttering group. No significant activation differences were observed within the nonstuttering participants during these speech conditions. Between-group comparisons revealed less left superior temporal gyrus activation in stutterers during habitual speech and increased right inferior frontal gyrus activation during simulated stuttering relative to nonstutterers. Stutterers were also found to have increased activation in the left middle and superior temporal gyri and right insula, primary motor cortex and supplementary motor cortex during the passive listening condition relative to nonstutterers. The results provide further evidence for the presence of functional deficiencies underlying auditory processing, motor planning and execution in people who stutter, with these differences being affected by speech manner.     

Pause time and phonation time in stuttering and cluttering

This study examined the potential usefulness of automated analysis of on-off speech patterns in the differentiation of stuttering from cluttering. Two groups of fifteen persons who had been previously classified as stutterers and clutterers served as subjects for this investigation. The data indicate that stutterers tend to have greater mean pause times and lower mean phonation times than clutterers. This result corresponds to the clinically observable characteristics of these groups. It is concluded that automated analysis of on-off speech patterns provides some basis for the differential diagnosis of stuttering from cluttering.Supported, in part, by a general research support grant from NIMH to the Research Foundation for Mental Hygiene, Inc.     

School-age children's perceptions of a person who stutters

The present study examined the perceptions school-age children have of stutterers. Four groups of fourth and fifth grade students viewed a videotape with either the speaker stuttering or not stuttering while reading a poem. A semantic differential scale of bi-polar adjective pairs was used to rate the speaker on intelligence and personality traits. The current study found that there is a significant difference between school-age children's perceptions of stutterers and nonstutterers with the ratings for the disfluent speaker more negative than the ratings for the fluent speaker. It was found that children did not rate personality and intelligence related traits differently. This information can be used to validate the need for education regarding stuttering for children and those who work with children. EDUCATIONAL OBJECTIVES: The reader will learn about and be able to (1). identify perceptions of stutterers by a variety of groups; (2). discuss the implications of research on perceptions of stutterers; and (3). compare/contrast children and adults and their perceptions.     

Bridging the divide between laboratory and "real world" in stuttering

Stutterers stutter significantly less in the laboratory and the clinic than in everyday speaking situations. This paper reviews pertinent literature to show that, in the outside world, stutterers have a stake in what they say and therefore message content and interpersonal dynamics command attention-relegating speech-motor planning and execution to an automatic, memory-based process called speech concatenation. In the laboratory and the clinic, content of communication and interpersonal dynamics are less important, allowing stutterers to concentrate on the motor planning of articulation and prosody. Evidence reviewed here suggests that speech construction (real time preparation of an utterance motor plan) is incompatible with stuttering. Evidence also suggests that a slight delay in retrieving motor plans from memory during speech concatenation is the immediate source of stuttering.     

Effects of subgrouping in stuttering research

The most frequently utilized research design in stuttering research compares stutterers to nonstutterers, with the assumption that stutterers represent a homogeneous group. The present study examines the effects of subgrouping stuttering subjects. Sample populations were randomly selected from a pool of stuttering children, successively increasing the stringency of selection criteria for group membership. The groups were contrasted across five dependent variables. The results indicated that the performance differences between the groups increased as the selection criteria became more stringent. The findings were interpreted as supporting the need to more closely examine the individual differences of stutterers, deviating from the traditional research paradigm.     

An evaluation of the effects of supplemental “fluency” training during maintenance

The voice onset time (VOT) of two groups of treated stutterers and a normal-speaking group was assessed by spectrographic analysis. Both groups of stutterers had significantly slower VOT than the normal speakers. The experimental group of stutterers was given 8 wk of “fluency” training designed to remediate characteristics of speech identified as related to “tenuous” fluency. The control group of stutterers received ongoing maintenance therapy. Posttreatment VOT was assessed. The experimental stuttering group had significantly decreased their VOT in the direction of the normal-speaking group, whereas the control group of stutterers had a greater VOT between pre- and posttreatment. The implication of these results for the maintenance of fluency are discussed.     

Features Resembling Tourette''s Syndrome in Developmental Stutterers

Developmental stuttering (DS) may be related to the extrapyramidal motor system and shares many clinical similarities with Tourette's syndrome (TS), which is widely believed to be associated with extrapyramidal dysfunction. Twenty-two stutterers were examined for neuropsychiatric features commonly seen in TS, including tics, obsessive-compulsive behaviors (OCB), and attention deficit disorders. Eleven stutterers displayed motor tics, and symptoms of OCB were observed at rates similar to those seen in persons with TS. Few stutterers demonstrated significant attentional deficits. Findings are consistent with models suggesting extrapyramidal involvement in DS and raise the possibility that DS and TS are pathogenetically related.     

Perceptual evaluation of the speech before and after fluency shaping stuttering therapy

An often-cited criterion for assessing the effect of a stuttering therapy is the ability of the stutterers to produce normally fluent speech. Many modern stuttering therapies use special techniques that may produce stutter-free speech that does not sound completely normal. The present study investigates this problem in the framework of the Dutch adaptation of the Precision Fluency Shaping Program.

Pre-, post-, and -year follow-up therapy speech samples of 32 severe stutterers who were treated in a four-week intensive therapy are compared with comparable samples of 20 nonstutterers. For that aim the samples were rated on 14 bipolar scales by groups of about 20 listeners. The results show that the speech of the stutterers in all three conditions differs significantly from the speech of the nonstutterers. The pretherapy speech takes an extreme position on a Distorted Speech dimension, due to the large proportion of disfluencies. The posttherapy speech has extremely low scores on a Dynamics/Prosody dimension, a‘1 while the follow-up therapy speech differs from the normal speech on both dimensions, but now the distances are smaller. These results are discussed in relation to the severity of the stuttering problem in the group of treated stutterers. Finally, implications for future research on therapy evaluation are discussed.     

Subtyping stuttering I: a review

A reliable and practical subtype system of stuttering should enhance all related scientific work concerned with this disorder. Although a fair number of classification systems have been offered, to date, none has received wide recognition or has been routinely applied in research or clinical spheres. Whereas progress has been made in understanding and treating the disorder, for the most part stuttering continues to be viewed and addressed as a unitary problem. The objectives of the current article are to (a) highlight the motivation for identifying sub-types of stuttering, (b) outline the issues involved in researching subtypes, and (c) address the question of whether or not subtyping is plausible for this disorder. Toward these ends, a broad-based review of past concepts regarding subtypes of stuttering and stutterers is presented according to seven categories that reflect the various authors' conceptual or experimental approaches. Selected studies for each category are also presented to illustrate the research problems and challenges. It is concluded that islands of progress can be identified in subtype research, particularly in studies of children. It is recommended that future studies include multiple factors or domains in the data collection process, especially with young children during the formative years of the disorder, when substantial overlap in the development of several speech/language domains occurs. EDUCATIONAL OBJECTIVES: (a) Readers will be able to describe the theory and research concerning the numerous attempts to subtype stuttering, particularly during the past 50 years; (b) Readers will be able to explain the general issues that need to be resolved in order to identify subtypes as well as current and future research strategies aimed at achieving these goals.     

Visuoperceptual and visuomotor deficits in developmental stutterers: an exploratory study

Although the cause of stuttering is unknown, there is strong evidence for it being a neuromotor disorder characterised by an abnormality of higher control encompassing not only speech but other motor systems. The aim of this exploratory study was to look for the presence of non-speech/language deficits--in particular, visuomotor and visuoperceptual deficits--in persons who stutter. Twelve moderate to severe developmental stutterers were compared with a group of fluent speakers, matched for age and sex, on a range of computerized sensory-motor tasks. These tasks covered various aspects of visuomotor function--ballistic movement, dynamic steadiness, and several types of tracking--and visuoperceptual function--acuity, static perception, and dynamic perception. A novel technique was used to remove the visuospatial component from tracking performance. Stutterers had slower reaction times, less accurate random tracking, and impaired dynamic visual perception. Severity of stuttering correlated with reaction time and dynamic perception. Removal of the visuoperceptual component from tracking performance indicated that the impaired tracking in the stutterers was predominantly due to reduced dynamic perception. This is the first study to provide preliminary evidence for the presence of non-linguistic visuoperceptual and upper-limb visuomotor tracking deficits in people with moderate to severe stuttering. These findings support a neurogenic aetiology for stuttering and are compatible with evidence of an overactive dopamine system in stutterers.     

Assessment of stuttering in a familiar versus an unfamiliar language

The present study investigated how well individuals knowledgeable about stuttering are able to make disfluency judgments in clients who speak another language than their own. Fourteen native speakers of Brazilian Portuguese identified and judged stuttering in Dutch speakers and in Portuguese speakers. Fourteen native speakers of Dutch identified and judged stuttering in Brazilian Portuguese speakers and in Dutch speakers. It was found that judges can make similar level of judgment in a native and a foreign language, and that native and foreign judges can make similar level of judgment irrespective of native/foreign differences. It was also found, however, that the Dutch judges performed significantly better in identifying native stutterers than foreign stutterers. And for the identification of nonstutterers, both panels performed better in their native language than in the foreign language, and in their native language they both performed better than the other panel. Both the Brazilian Portuguese and the Dutch speaking panel were generally also less confident, and found identification of stuttering more difficult in the foreign language than in the native language. In addition, when asked for the characteristics that helped them identify stutterers, they provided more detail in the native language than in the foreign language. Also a number of differences were found between the two panels which may be due to differences in training or cultural background. The implications of the findings for clinical practice and for future research in this area are discussed. EDUCATIONAL OBJECTIVES: The reader will be able to: (1) describe how language influences the identification of a speech disorder such as stuttering, and (2) list, and (3) define behaviors that help to identify stuttering in a foreign language.