Speech motor control in fluent and dysfluent speech production of an individual with apraxia of speech and Broca's aphasia

Apraxia of speech (AOS) is typically described as a motor‐speech disorder with clinically well‐defined symptoms, but without a clear understanding of the underlying problems in motor control. A number of studies have compared the speech of subjects with AOS to the fluent speech of controls, but only a few have included speech movement data and if so, this was primarily restricted to the study of single articulators. If AOS reflects a basic neuromotor dysfunction, this should somehow be evident in the production of both dysfluent and perceptually fluent speech. The current study compared motor control strategies for the production of perceptually fluent speech between a young woman with apraxia of speech (AOS) and Broca's aphasia and a group of age‐matched control speakers using concepts and tools from articulation‐based theories. In addition, to examine the potential role of specific movement variables on gestural coordination, a second part of this study involved a comparison of fluent and dysfluent speech samples from the speaker with AOS. Movement data from the lips, jaw and tongue were acquired using the AG‐100 EMMA system during the reiterated production of multisyllabic nonwords. The findings indicated that although in general kinematic parameters of fluent speech were similar in the subject with AOS and Broca's aphasia to those of the age‐matched controls, speech task‐related differences were observed in upper lip movements and lip coordination. The comparison between fluent and dysfluent speech characteristics suggested that fluent speech was achieved through the use of specific motor control strategies, highlighting the potential association between the stability of coordinative patterns and movement range, as described in Coordination Dynamics theory.     

Linguistic impairment after right cerebellar stroke: a case report

Increasing evidence suggests the involvement of the cerebellum in non-motor functions. We describe a patient who presented speech deficits after a right cerebellar infarction without other cognitive impairments. 99mTc-HMPAO single-photon emission computed tomography showed a marked hypoperfusion in the right cerebellar hemisphere, but did not show crossed cerebellar- cerebral diaschisis. The absence of neuroradiological evidence of structural supratentorial lesions supports the cerebellar role in modulating not only the motor system, but also higher order functions.     

A kinematic investigation of anticipatory lingual movement in acquired apraxia of speech

Background: Apraxia of speech (AOS) is considered a disorder of speech planning or programming. Evidence for this stems from perceptual, acoustic, and electropalatographic investigations of articulation in AOS that revealed a delayed onset of anticipatory vowel gestures. Articulatory prolongation and syllable segregation have been attributed to a disturbance in anticipatory coarticulation.

Aims: The aim of the current study was to investigate anticipatory lingual movement for consonantal gestures in AOS, and its impact on absolute and relative speech timing.

Methods & Procedures: Tongue-tip movement and tongue-to-palate contact patterns were recorded for three speakers with AOS and a concomitant aphasia (age range?=?35–63 years; M?=?50.67 years; SD?=?14.29) and five healthy talkers (age range?=?29–65 years; M?=?52.6 years; SD?=?14.5) during the phrases “a scarlet” and “a sergeant”, using electromagnetic articulography (EMA) (AG-200 system) and electropalatography (EPG) (Reading Electropalatograph system). Anticipatory lingual movement and speech timing were analysed during the final C₁VC/C₂ syllable in each of these phrases, where C represented an alveolar or postalveolar consonant. Specifically, tongue-tip displacement was calculated from the onset of release to the end of release of C₁ to provide an indication of anticipatory lingual movement. With respect to speech timing, absolute (i.e., duration from time of maximum contact for C₁ to time of maximum contact for C₂) and relative (i.e., absolute duration expressed as a function of total syllable duration) durational measures were recorded, as was the stability of each. The results recorded for each of the participants with AOS were individually compared to those obtained by the control group.

Outcomes & Results: The EMA results indicated that two participants with AOS exhibited reduced anticipatory lingual movement (i.e., greater tongue-tip displacement) during repetitions of “sergeant”; however, all speakers produced a comparable tongue-tip displacement to that produced by the control group during the release of /l/ in “scarlet”. The EPG results indicated that absolute duration was significantly prolonged during the final syllables of both stimuli for each of the apraxic speakers. Equivocal results were reported for relative timing and temporal stability.

Conclusions: The results provide some preliminary evidence of reduced anticipatory lingual movement in AOS, and have demonstrated that this can have a significant impact on absolute speech timing. However, measures of relative timing were suggestive of either unimpaired or more extensive coarticulation. Additional research is required to resolve this issue.     

Visual half-field testing for defining cerebral hemisphere speech laterality

The purpose of this study was to investigate to what extent the noninvasive visual half-field (VHF) test can reliably determine cerebral speech dominance for the individual patient with partial epilepsy considered for surgical treatment. The present VHF test consisted of a list of 36 words presented correctly and mirrored in the lateral visual fields to 13 right-handed and 14 left-handed control subjects and to 14 right-handed and 2 left-handed patients with partial epilepsy. In the controls, it was found that all right-handed and 10 out of 14 left-handed control subjects showed a right VHF (i.e., left hemisphere) advantage. Three of the left-handed control subjects showed the opposite pattern, and one showed no visual field advantage. All of the right-handed patients showed a right VHF advantage, except one who showed no VHF advantage. The two left-handed patients had both a left VHF advantage. Intracarotid amytal speech testing documented left hemisphere speech dominance in all right-handed patients. Of the two left-handed patients, one had right-sided, the other bilateral speech representation. The results suggest that the present VHF test reliably predicts cerebral hemisphere speech in patients with epilepsy.     

Brain damage associated with apraxia of speech: evidence from case studies

ABSTRACT

The site of crucial damage that causes acquired apraxia of speech (AOS) has been debated in the literature. This study presents five in-depth cases that offer insight into the role of brain areas involved in AOS. Four of the examined participants had a primary impairment of AOS either with (n = 2) or without concomitant mild aphasia (n = 2). The fifth participant presented with a lesion relatively isolated to the left anterior insula (AIns-L), damage that is rarely reported in the literature, but without AOS. Taken together, these cases challenge the role of the AIns-L and implicate the left motor regions in AOS.     

Phonological encoding in apraxia of speech and aphasia

Background: Apraxia of speech (AOS) is considered a speech motor planning/programming disorder. While it is possible that co-occurring phonological impairments exist, the speech motor planning/programming deficit often makes it difficult to assess the phonological encoding stage directly. Studies using online methods have suggested that activation of phonological information may be protracted in AOS.

Aims: The present study was designed to investigate the integrity of the phonological encoding stage in AOS and aphasia. We tested two specific hypotheses, the Frame Hypothesis and the Segment Hypothesis. According to the Frame Hypothesis, speakers with AOS have an impairment in retrieving metrical frames (e.g., number of syllables); according to the Segment Hypothesis, speakers with AOS have an impairment in retrieving segments (e.g., consonants).

Methods & Procedures: Four individuals with AOS and varying degrees of aphasia, two speakers with aphasia, and 13 age-matched control speakers completed an online priming task in which participants name pictures in sets that do or do not share number of syllables (e.g., balcony-coconut-signature vs. balcony-carrot-sock), the initial consonant (e.g., carpenter-castle-cage vs. carpenter-beaver-sun), or both (e.g., boomerang-butterfly-bicycle vs. boomerang-sausage-cat). Error rates and reaction times were measured.

Outcomes & Results: Data for controls replicated previous literature. Reaction time data supported the Segment Hypothesis for speakers with AOS and for one speaker with aphasia without AOS, with no differences in pattern from controls for the other speaker with aphasia without AOS.

Conclusions: These results suggest that speakers with AOS may also have difficulties at the phonological encoding stage. Theoretical and clinical implications of these findings are discussed.     

An electropalatographic investigation of linguopalatal contact in participants with acquired apraxia of speech: A quantitative and qualitative analysis

The current study aimed to provide a comprehensive analysis of linguopalatal contact patterns in participants with acquired apraxia of speech (AOS). Tongue‐to‐palate contacts were recorded for three participants with AOS during consonant singletons and consonant clusters using the Reading Electropalatograph (EPG3) system. Amount and pattern of linguopalatal contact were analysed using qualitative and quantitative analysis methods and the degree of spatial variability was quantified. The results obtained for each of the apraxic speakers were individually compared to those obtained by a control group (n = 5). Misdirected articulatory gestures and distorted spatial configurations for alveolar fricatives were detected in the linguopalatal contact patterns recorded for each of the participants with AOS. Lingual overshoot, right‐side dominant contact, and increased spatial variability were also evidenced by some participants. True omission errors were absent. Overall, the combination of qualitative and quantitative analysis techniques proved valuable in providing a comprehensive analysis of linguopalatal contact in AOS. Results provided support for a motoric account of articulatory and prosodic deficits in AOS.     

Segments and syllables in the treatment of apraxia of speech: An investigation of learning and transfer effects

Background: In the treatment of severe apraxia of speech (AOS), single phonemes are often used as training targets. However, until now it remains unclear if segment production can be learned and if patients show transfer effects when a segment trained in isolation is embedded in syllables and words. Speech motor learning in normal language acquisition is based on syllabic rather than segmental learning mechanisms. The syllable is also assumed to be the basic unit of articulatory programming in normal speech.

Aims: In the present study, we investigated the effectiveness of learning single segments as compared to whole syllables in patients with AOS. Besides immediate learning effects, we were particularly interested in transfer effects on trained targets embedded into larger untrained units and in maintenance effects.

Methods & Procedures: Four patients with severe AOS participated in this study. Target segments and target syllables were trained in two separate phases. To examine learning effects, we presented trained and untrained items in isolation immediately before and after a learning phase. Transfer effects of the segmental learning were examined by presenting syllables which contained the target and control phonemes. The transfer of syllabic learning was assessed on the basis of two-syllabic words containing the target and control syllables.

Main Contributions: In the segmental condition, only one patient showed a significant learning effect. Transfer effects onto untrained syllables containing the trained consonants were missing in all patients. After the syllabic training, three patients produced significantly lower error rates on the trained, but not on the control syllables. In two of them, the improvements were still maintained when the syllables were embedded in two-syllabic words.

Conclusions: The lack of segmental learning effects in three patients may be due to the fact that single consonants are artificial speech units we normally do not produce in isolation. The complete absence of transfer effects suggests that intrasyllabic coarticulation is part of the phonetic plan and cannot be mastered by speech apraxic patients without extra exercise. The observed learning effects after the syllabic learning confirm that syllables constitute more natural speech motor units which are easier to re-acquire than single consonants. Furthermore, the embedding of learned monosyllables into unlearned two-syllabic words requires less extra speech motor planning than the embedding of a trained segment into the coarticulated context of a syllable.     

Word-level prosodic measures and the differential diagnosis of apraxia of speech

Impaired production of prosody is considered a primary diagnostic criterion for apraxia of speech. In this study, we examined diagnostic relevance for five word-level prosody measures. Seven speakers with AOS, nine with aphasia and no AOS, and 19 age-matched neurotypical controls produced nine words consisting of three or four syllables. Lexical stress indices were computed based on relative values for duration, fundamental frequency, and intensity across pairs of unstressed-stressed syllables with varying intrinsic vowel duration contrast patterns. A simple average syllable duration measure was also obtained. AOS speakers differed from the other two groups on three metrics that were solely or primarily derived from duration measures. The degree of diagnostic overlap was smallest for the syllable duration metric, which also showed the strongest inter-observer reliability and most complete overlap between neurotypical speakers and speakers with aphasia and no AOS. Vowel intrinsic durational properties affected lexical stress metrics significantly, indicating a need to select word targets purposefully. Based on these results, it appears that the average syllable duration metric is a more stable and informative alternative for differential diagnostic purposes. The results will, however, need to be replicated in a larger sample.     

Clinical and imaging progression over 10 years in a patient with primary progressive apraxia of speech and autopsy-confirmed corticobasal degeneration

Primary progressive apraxia of speech (PPAOS) is a neurodegenerative disorder in which AOS is the sole presenting complaint. We report clinical and neuroimaging data spanning 10 years from disease onset-to-death in a 49 year-old male PPAOS patient, DY, who died with corticobasal degeneration. He presented with AOS with normal neuroimaging. Abnormalities in the caudate nucleus, supplementary motor area, cingulate, insula, and Broca’s area were observed after five years, with involvement of motor cortex and development of agrammatism, Parkinsonism, and dysarthria three years later. Cognitive impairment and temporoparietal atrophy were late features. This data provides important insight into disease progression of corticobasal degeneration when presenting as PPAOS.     

An EMA analysis of the effect of increasing word length on consonant production in apraxia of speech: A case study

The effect of increasing word length on the articulatory dynamics (i.e. duration, distance, maximum acceleration, maximum deceleration, and maximum velocity) of consonant production in acquired apraxia of speech was investigated using electromagnetic articulography (EMA). Tongue‐tip and tongue‐back movement of one apraxic patient was recorded using the AG‐200 EMA system during word‐initial consonant productions in one, two, and three syllable words. Significantly deviant articulatory parameters were recorded for each of the target consonants during one, two, and three syllables words. Word length effects were most evident during the release phase of target consonant productions. The results are discussed with respect to theories of speech motor control as they relate to AOS.     

Understanding and management of acquired apraxia of speech: Contribution of the Department of Veterans Affairs

Background: Acquired apraxia of speech (AOS) is a neurogenic disorder involving the ability to plan and/or program speech production. Our understanding of the characteristics, nature, and treatment of AOS has been in a continual state of evolution. Significant inroads have been made concerning our knowledge of AOS and its management and the Department of Veterans Affairs (DVA) has played a substantial role in adding to that knowledge base.

Aims: The Department of Veterans Affairs has been a long‐standing source of support for research involving neurogenic speech and language disorders. The purpose of this article is to highlight the contributions made by the DVA and its investigators to our understanding and treatment of AOS.

Methods & Procedures: Searches of electronic databases were conducted to identify DVA authors of AOS research reports. Additionally, records of DVA, Rehabilitation Research and Development grant funding were reviewed to determine DVA investigators who had conducted research pertinent to AOS.

Outcomes & Results: Numerous DVA investigators have been involved in AOS research and several DVA researchers have been leaders in this area of inquiry. Research by DVA investigators has significantly advanced the state of our knowledge of AOS.

Conclusion: The current AOS knowledge base rests heavily on research conducted by investigators affiliated with the DVA.     

The influence of visual and auditory information on the perception of speech and non‐speech oral movements in patients with left hemisphere lesions

Patients with lesions of the left hemisphere often suffer from oral‐facial apraxia, apraxia of speech, and aphasia. In these patients, visual features often play a critical role in speech and language therapy, when pictured lip shapes or the therapist's visible mouth movements are used to facilitate speech production and articulation. This demands audiovisual processing both in speech and language treatment and in the diagnosis of oral‐facial apraxia. The purpose of this study was to investigate differences in audiovisual perception of speech as compared to non‐speech oral gestures. Bimodal and unimodal speech and non‐speech items were used and additionally discordant stimuli constructed, which were presented for imitation. This study examined a group of healthy volunteers and a group of patients with lesions of the left hemisphere. Patients made substantially more errors than controls, but the factors influencing imitation accuracy were more or less the same in both groups. Error analyses in both groups suggested different types of representations for speech as compared to the non‐speech domain, with speech having a stronger weight on the auditory modality and non‐speech processing on the visual modality. Additionally, this study was able to show that the McGurk effect is not limited to speech.     

Lateral preferences and cerebral speech dominance

Four types of lateral preference (hand, foot, eye, ear) were measured in 73 patients, who underwent sodium Amytal speech testing. In 63 cases, speech was on the left side whereas in 10, speech was on the right. All of the patients with right hemisphere lesions had speech represented in the left hemisphere. Only a third of the patients with left hemisphere damage prior to the end of the first year of life continued to have speech on the left side. By contrast, 82% of those with left hemisphere damage after this sensitive period had speech exclusively mediated by the left hemisphere. In short, the occurrence of right hemisphere speech dominance without an early lesion to the left hemisphere is rare. The majority of patients with right-sided motor and sense organ preferences had speech represented in the left hemisphere, independent of location or age of onset of the damage. By contrast, in individuals with a clinical history of early left hemisphere injury, left-sided motor and sense organ preferences were linked to right hemisphere speech dominance. In those cases without evidence of early cerebral damage, most of the non-right-sided individuals had speech in the left hemisphere. However, the proportion of unilateral, left hemisphere speech representation in the right-handed and right-footed was higher than that observed in the left-handed and left-footed, even when those with early onset of damage were excluded from analysis. It was suggested that in the normal population, handedness and footedness are relevant factors in predicting cerebral speech dominance. Knowledge of eye and ear preference may be of little predictive value. Further, in a neurological population the overall congruency across the four patterns of lateral preference may provide useful information regarding cerebral speech dominance. A small group (5) of patients with bilateral representation of speech was also examined. Contrary to the experience at the Montreal Neurological Institute, most of these patients preferred the right limb and sense organ. Differences in investigative approach may account for the conflicting observations.     

Segmental and prosodic variability on repeated polysyllabic word production in acquired apraxia of speech plus aphasia

Background: McNeil and colleagues argued that individuals with pure apraxia of speech (AOS) have low variability of speech error type and error location within repeated multisyllabic words, compared to individuals with conduction aphasia. While this concept has been challenged, subsequent studies have varied in the stimuli and tasks used.

Aims: Our aim was to re-examine the variability of segmental errors, as well as lexical prosodic errors, using the same stimuli and tasks as used by McNeil and colleagues in a sample of individuals with AOS plus aphasia or aphasia alone. This sample is considered to be clinically relevant given the high concomitance of these disorders.

Methods & Procedures: Participants were 20 individuals with stroke-related AOS plus aphasia and 21 with aphasia alone (APH), with diagnosis based on expert judgments using published criteria. Three consecutive repetitions of 10 polysyllabic words were elicited and variability of error type, error location, and durational stress contrast was measured.

Outcome & Results: Errors were significantly more variable in type and more consistent in location within word for the AOS group than the APH group. The AOS group showed a greater number of errors overall, were less likely to improve production over the three repetition trials, and produced no clear difference in vowel duration across the first two syllables (i.e., durational stress contrast) across repetitions. The measure of durational stress contrast was a stronger predictor of AOS presence than the measures of error variability.

Conclusions: The divergence of our findings from previous work likely reflects the more complex profile of the AOS plus aphasia cases in the current study. While durational stress contrast was sufficient to predict diagnostic group, error variability measures were significantly associated with AOS and can contribute to developing targeted intervention goals.