Impact of cognitive function and dysarthria on spoken language and perceived speech severity in multiple sclerosis
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Purpose : The current study sought to investigate the separate effects of dysarthria and cognitive status on global speech timing, speech hesitation, and linguistic complexity characteristics and how these speech behaviors impose on listener impressions for three connected speech tasks presumed to differ in cognitive-linguistic demand for four carefully defined speaker groups; 1) MS with cognitive deficits (MSCI), 2) MS with clinically diagnosed dysarthria and intact cognition (MSDYS), 3) MS without dysarthria or cognitive deficits (MS), and 4) healthy talkers (CON). The relationship between neuropsychological test scores and speech-language production and perceptual variables for speakers with cognitive deficits was also explored. Methods : 48 speakers, including 36 individuals reporting a neurological diagnosis of MS and 12 healthy talkers participated. The three MS groups and control group each contained 12 speakers (8 women and 4 men). Cognitive function was quantified using standard clinical tests of memory, information processing speed, and executive function. A standard z-score of ≤ −1.50 indicated deficits in a given cognitive domain. Three certified speech-language pathologists determined the clinical diagnosis of dysarthria for speakers with MS. Experimental speech tasks of interest included audio-recordings of an oral reading of the Grandfather passage and two spontaneous speech samples in the form of Familiar and Unfamiliar descriptive discourse. Various measures of spoken language were of interest. Suprasegmental acoustic measures included speech and articulatory rate. Linguistic speech hesitation measures included pause frequency (i.e., silent and filled pauses), mean silent pause duration, grammatical appropriateness of pauses, and interjection frequency. For the two discourse samples, three standard measures of language complexity were obtained including subordination index, inter-sentence cohesion adequacy, and lexical diversity. Ten listeners judged each speech sample using the perceptual construct of Speech Severity using a visual analog scale. Additional measures obtained to describe participants included the Sentence Intelligibility Test (SIT), the 10-item Communication Participation Item Bank (CPIB), and standard biopsychosocial measures of depression ( Beck Depression Inventory-Fast Screen ; BDI-FS), fatigue ( Fatigue Severity Scale ; FSS), and overall disease severity ( Expanded Disability Status Scale ; EDSS). Healthy controls completed all measures, with the exception of the CPIB and EDSS. All data were analyzed using standard, descriptive and parametric statistics. For the MSCI group, the relationship between neuropsychological test scores and speech-language variables were explored for each speech task using Pearson correlations. The relationship between neuropsychological test scores and Speech Severity also was explored. Results and Discussion : Topic familiarity for descriptive discourse did not strongly influence speech production or perceptual variables; however, results indicated predicted task-related differences for some spoken language measures. With the exception of the MSCI group, all speaker groups produced the same or slower global speech timing (i.e., speech and articulatory rates), more silent and filled pauses, more grammatical and longer silent pause durations in spontaneous discourse compared to reading aloud. Results revealed no appreciable task differences for linguistic complexity measures. Results indicated group differences for speech rate. The MSCI group produced significantly faster speech rates compared to the MSDYS group. Both the MSDYS and the MSCI groups were judged to have significantly poorer perceived Speech Severity compared to typically aging adults. The Task x Group interaction was only significant for the number of silent pauses. The MSDYS group produced fewer silent pauses in spontaneous speech and more silent pauses in the reading task compared to other groups. Finally, correlation analysis revealed moderate relationships between neuropsychological test scores and speech hesitation measures, within the MSCI group. Slower information processing and poorer memory were significantly correlated with more silent pauses and poorer executive function was associated with fewer filled pauses in the Unfamiliar discourse task. Results have both clinical and theoretical implications. Overall, clinicians should demonstrate caution when interpreting global measures of speech timing and perceptual measures in the absence of information about cognitive ability. Results also have implications for a comprehensive model of spoken language incorporating cognitive, linguistic, and motor variables.