Improving speech intelligibility in dysarthric patients is considered the primary goal of therapeutic intervention.
This study aimed at examining factors affecting speech intelligibility in four Arabic-speaking dysarthric groups using perceptual and instrumental techniques in order to gain a better understanding of the important factors contributing to reduced speech clarity in these patients.
Methods and procedures
Participants included 30 male Egyptian dysarthric patients (patient group) and 30 male age-matched healthy individuals (control group). The patient group was subdivided–on the basis of the neurological examination and investigation that had been carried out previously at the Neurology Department, Kasr el Aini Hospital–into four subgroups; spastic, ataxic, flaccid, and hypokinetic (having Parkinsonism). Speech samples consisting of spontaneous speech and a standard reading passage (that the participants were asked to repeat after the assessor) were used to obtain the following variables: speech rate (number of words per minute), Speech Intelligibility Score, number of nonintelligible words per minute, dysphonia grade, percent of consonants correct, percent of vowels correct, Nasalance Score, fundamental frequency, jitter, shimmer, harmonic-to-noise ratio, duration of /a/, first and second formant frequency values for three corner vowels /a/, /i/, and /u/, voice onset time of /b/, /t/, /k/, stop gap of /t/, /t/, /d/, /d/, and duration of /s/ and /∫/. The study examined the differences between the healthy control group and the different dysarthric groups for each variable as well as the correlation between speech intelligibility and each variable within each dysarthric subgroup.
Outcomes and results
The Speech Intelligibility Score was the highest for flaccid dysarthria and the lowest for ataxic. Results revealed significant differences between the control group and each of the patient groups studied for all subjective measures as well as most of the instrumental measures that were included in the study. A significant positive correlation was found between speech rate and speech intelligibility in patients with ataxic and flaccid dysarthria. However, a negative correlation was found between speech rate and speech intelligibility in patients with hypokinetic dysarthria. A significant negative correlation was found between speech intelligibility and jitter, F1 and F2 of /u/, stop gap of /t/, /t/, /d/, and /d/, and /s/ duration in spastic, ataxic, and flaccid groups. In addition, a significant negative correlation was found between shimmer and speech intelligibility in the ataxic group and between Nasalance Score and speech intelligibility in the flaccid group.
Conclusion and implications
Factors contributing to reduced speech intelligibility vary from one type of dysarthria to the other.