The relationship between acoustic indices of speech motor control variability and other measures of speech performance in dysarthria

Previous studies suggested that variability indices based on information extracted from the acoustic signal are potentially useful in assessing dysarthric speech. Because of the ease of data collection, this method is especially applicable in the clinical setting. This study assessed the relationship between variability indices of sentence repetitions obtained by Functional Data Analysis with intelligibility ratings and maximum performance tasks in groups of speakers with hypokinetic dysarthria and ataxic dysarthria. The results showed significant correlations between selected parameters, which varied with dysarthria type. For the speakers with ataxic dysarthria, the variability measure mainly reflected differences in intelligibility, while for the group with hypokinetic dysarthria, there was a stronger relationship between variability indices and DDK performance. Lack of stronger correlations between variability measures and intelligibility ratings and maximum performance tasks are possibly due to heterogeneity of severity across and within speaker groups. This study provides further evidence that variability measures such as the FDA might be sensitive to speech performance of speakers with dysarthria, and can potentially differentiate between dysarthria types

Objectieve beoordeling van spraakproblemen bij sprekers met dysartrie

Research and treatment of neurogenic speech disorders benefit from the use of reliable measurements and treatment methods. In recent years, new techniques and methods are developed that can support differential diagnosis, treatment, and progress monitoring of speech disorders. In the context of applying evidence-based practice in the SLT clinic, these objective measurement methods are more than welcome. This tutorial discusses a number of methods that are widely applicable and relatively easy to use. These methods are primarily focused on dysarthria, but could also be applied in the investigation of other language and speech disorders. In this tutorial, methodologies with regard to systematic and quasi-automatic measurement of intelligibility, speech rate, articulation rate, and maximum-performance tasks are discussed. Each of these methods may be carried out by speech therapists and researchers using readily available or open-source software. In addition, this article provides an overview of a number of recently developed experimental research methodologies measuring speech variability as a quantitative assessment of speech problems. A major problem in dysarthria is the precise control of speech movements. As such, measurements of variability and stability of speech are prime targets to study speech motor control in dysarthria. Although these research methodologies still need to work with respect to technical implementation and validity, they have the potential to be a valuable tool in the SLT clinic

Assessing dysarthria using variability measures from audio recordings

Classification and characterization of motor speech disorders (MSDs) is important from the viewpoint of diagnosis and treatment. Clinical diagnosis is primarily based on auditoryperceptual characteristics of perceived speech abnormalities, but is subject to unreliable clinical judgement and quantifi cation, and diffi cult to relate to the underlying pathophysiology. In this study we investigate whether it is possible to diagnose dysarthria based on measures of speech variability by using Functional Data Analysis (FDA) (Ramsay et al.,1996). A reliable quantifi cation of variability in speech can potentially reveal underlying motor control problems, enable early detection of sub-clinical speech abnormalities, and provide sensitive and quantifi able outcome measures that aid treatment strategies. FDA has been shown to be successful in investigating variability of kinematic movements obtained by lip displacement tracking, but may also be applied to other dimensions of speech, including amplitude envelopes and pitch and formant tracks. Anderson et al. (2008) used FDA to calculate spatial and temporal variability of amplitude envelopes of sentence repetitions produced by patients with hypokinetic and ataxic dysarthria and demonstrated that variability characteristics were infl uenced by dysarthria type

Analyzing speech movement variability from audio recordings

Producing fluent and intelligible speech involves quick, precise and coordinated movements of articulators. Developmental and acquired speech motor disorders often result in an instable gestural organization of speech movements, and thus more variable speech performance. In addition, research suggest that a number of environmental factors can influence articulatory movements, including speech rate modifications, linguistic and cognitive complexity of the speech task and concurrent motor tasks. The possible interaction of internal and external factors that influence speech motor control might give more insight in the nature of different speech disorders. The spatiotemporal index (STI) (Smith et al., 1995) and Functional Data Analysis (FDA) (Ramsay et al., 1996) are techniques that have been shown to be successful in investigating variability of kinematic movements obtained by lip displacement tracking, but may also be applied to other dimensions of speech, including amplitude envelopes and pitch and formant tracks. This pilot study presents some first results on STI and FDA variability measures applied to audio recordings of young, healthy adults. The study aims to investigate whether variability measures obtained from acoustic data reflect those from kinematic data

Compensatory and adaptive responses to real-time formant shifts in adults and children

Auditory feedback plays an important role in speech motor learning. Previous studies investigating auditory feedback in speech development suggest that crucial steps are made in the development of auditory-motor integration around the age of 4. The present study investigated compensatory and adaptive responses to auditory perturbation in 4 to 9 year-old children compared to young adults (aged 19 – 29 years). Auditory feedback was perturbed by real-time shifting the first and second formant (F1 and F2) of the vowel /e:/ during the production of CVC words in a fivestep paradigm (familiarization; baseline; ramp; hold; release). Results showed that the children were able to compensate and adapt in a similar or larger degree compared to the young adults, even though the proportion of speakers displaying a consistent compensatory response was higher in the group of adults. In contrast to previous reports, results did not show differences in token-to-token variability between children and adults

Auditory feedback perturbation in adults and children

Auditory feedback plays an important role in speech motor learning. Experimental paradigms where auditory feedback is perturbed during speech production of children might give valuable insights in the role of auditory feedback in the acquisition of speech motor programs throughout development. Studies investigating auditory feedback in speech development suggest that crucial steps are made in the development of auditory-motor integration between the ages of 4 – 9 years, but thus far direct comparisons between different age groups are absent. In the present study, we investigated to what extent Dutch speaking children in this age span were able to compensate for and adapt to auditory feedback perturbations. Auditory feedback was perturbed by real-time shifting the first and second formant of the vowel /e/ during the production of CVC words. Preliminary results indicate that age is an important factor in the presence of stable compensation and adaptation effects. When comparing groups, both children and adults were able to compensate for perturbed auditory feedback, but the proportion of subjects displaying this effect was greater in the adult group. Furthermore, we will discuss experimental considerations and limitations of measuring on-line and off-line compensation for perturbed auditory feedback with very young speakers

Articulation in children with developmental speech disorders

A central issue in studies on developmental speech disorders, especially with regard to childhood apraxia of speech (CAS) and phonological disorder (PD) is the distinction between phonological and motoric processes. Acoustic studies suggest that children with CAS produce incorrect realizations of correctly selected phonemes, whereas the opposite is postulated for children with PD. Thus conceived, the underlying impairment is located at different levels of speech production in these two groups of children

Acoustic characterization of dysarthria in children with cerebral palsy : exploring age-related effects

The speech of children with dysarthria and cerebral palsy (CP) is characterized by respiratory, phonatory and articulatory difficulties. Whilst, traditionally, speech deviations were described perceptually, the focus has recently shifted to acoustic measures to quantify the children’s speech changes more objectively and systematically. This study investigated the role of age in acoustically characterizing dysarthria in children with CP. Speech samples of eight children were analyzed using various acoustic measures and compared to those of typically-developing peers. Results showed overall group differences for several acoustic measures. Additionally, the degree to which acoustic measures may differentiate children with CP and their peers is influenced by age, with various measures found to be more suitable in differentiating older affected and unaffected children (13-18 years) compared to younger ones (7-8 years). This finding suggests that age is important when selecting acoustic markers of dysarthria, with some markers constituting more sensitive measures than others

Rate-related kinematic changes in younger and older adults

This study aimed to investigate the effects of speech rate changes on kinematic characteristics and stability of speech movements in younger and older speakers using electromagnetic midsagittal articulography (EMMA). Eight young adults and eight older adults engaged in a series of syllable repetition tasks of /pa, /sa/ and /ta/ obtained at self-paced slow, habitual and fast speech rates, as well as in a series of metronome guided speech rates, ranging from 2 to 4 syllables per second. The kinematic parameters duration, amplitude and peak velocity were obtained for opening and closing movements. Older speakers were able to increase speech rate to the same degree or higher compared to younger speakers in both pacing conditions. Kinematic data show that older adults increased duration and decreased peak velocity in closing movements of alveolar constrictions at slower rates more prominently than younger adults. The results on movement stability revealed no differences between age groups. The results suggest that an age-related difference in speed-accuracy trade-off can be ruled out. Differences in kinematic characteristics point towards the possibility that older adults aimed to facilitate a closed loop control system to maintain movement stability at slower speech rates

Stability and composition of functional synergies for speech movements in children and adults

The consistency and composition of functional synergies for speech movements were investigated in 7 year-old children and adults in a reiterated speech task using electromagnetic articulography (EMA). Results showed higher variability in children for tongue tip and jaw, but not for lower lip movement trajectories. Furthermore, the relative contribution to the oral closure of lower lip was smaller in children compared to adults, whereas in this respect no difference was found for tongue tip. These results support and extend findings of non-linearity in speech motor development and illustrate the importance of a multi-measures approach in studying speech motor development