JCPSLP vol 14 no 3 2012

www.fon.hum.uva.nl/praat). PRAAT was first released in 1995 and is regularly maintained by its developers (P. Boersma and D. Weeninck, University of Amsterdam). It has been used extensively for analysis of both healthy and impaired speakers. Comprehensive manual and tutorials on the website provide guidelines for checking for errors in measurement that can occur more frequently with the more variable speech of dysarthria. Aims The aim of this study was to demonstrate the use of a small number of easy-to-collect acoustic measures using a free software program, PRAAT (Boersma & Weenink, 2010), for three prototypical dysarthria cases: one spastic, one ataxic, and one flaccid dysarthria case. The list of measures presented here is by no means comprehensive, but rather provides an introduction to using the PRAAT software and perhaps an incentive to explore it more fully. We report the results of these acoustic analyses, compare them with available normative data, and how they relate to perceptual judgements. We predicted that the individuals with spastic or flaccid dysarthria would demonstrate abnormal vocal quality measures (e.g., jitter, shimmer, HNR), associated with perceived abnormal vocal quality. The individual with ataxic dysarthria and notable pitch breaks and vocal tremor was expected to show high variability of f0 during sustained ah production. We expected that all would demonstrate reduced speech rate in diadochokinetic and connected speech tasks. Further, the individuals with spastic and ataxic dysarthria would deviate from normal on objective measures of prosody (i.e., relative duration, f0 and/or intensity across syllables in connected speech as measured by the PVI), reflecting the perception of equal stress or scanning speech, respectively. Perception of monopitch or monoloudness should be reflected as lower PVI values for f0 and dB (PVI_ f0 , PVI_dB), respectively.

Yumoto & Gould, 1982). Of note, software programs have different algorithms for calculating these measures which may yield differing results (Maryn, Corthals, De Bodt, Van Cauwenberge, & Deliyski, 2009). It is best to use norms generated by the selected software and standardise data collection methods to achieve highly reliable measurement over time. Further, the software may generate some erroneous f0 measurements (e.g., excessively high values at the edges of vowels) that distort maximum and average measures. Care is taken to omit these from the selection used for calculations (see Figure 1). Analysis of prosody also involves measuring frequency and intensity, as well as segment or syllable durations, but at word or connected speech level. English is a stress- timed language that generally alternates stressed and unstressed syllables in a word or sentence. One measure proving useful for capturing this pattern is the pairwise variability index (PVI), which is a normalised measure of relative duration, f0 , or intensity over a word or speech sample (Ballard, Robin, McCabe, & McDonald, 2010; Courson, Ballard, Canault, & Gentil, 2012; Low, Grabe, & Nolan, 2000; Vergis & Ballard, 2012). Specifically, one calculates the difference in duration (or f0 or intensity) over two consecutive vowels and divides the difference by their average. This calculation is done pairwise for the whole sample and the average PVI value used as an index of stress variability. Low et al. (2000) reported that in British-English average PVI for vowel duration (PVI_Dur) in sentences containing all stressed words (100% stressed) is ~30 and rises to ~78 for sentences with alternating stressed and unstressed words (50% stressed). The Grandfather passage (Darley, Aronson, & Brown, 1975) contains about 60% stressed words so PVI values below 30 indicate equal and excess stress. Most of the recommended acoustic measures of speech can be made using free downloadable speech acquisition and analysis programs, such as PRAAT (http://

Audrey McCarry (top), and Kirrie J. Ballard

Table 1. Demographic and injury data for the three participants with dysarthria and three age- and gender-matched control participants Participant Age Sex PTA (months) CT results TPO Injury Dysarthria ASSIDS Participant 1 39 M 3.5 Large left SAH and SDH and 10 mm midline shift, craniotomy and evacuation of haemorrhage 3 Fall Mild- moderate Spastic 84% (single words) 94% (sentences) Control 1 41 M Participant 2 27 F 1 Left occipital penetrating wound with bullet 18

Moderate Ataxic

86% (single words) 95% (sentences)

Focal open head injury

fragmentation and swelling of bilateral cerebellar hemispheres, SAH and SDH surrounding occipital lobes and cerebellar hemispheres, left parietal craniectomy and debridement of foreign body EDH, left SDH, base of skull, temporal and sphenoid fracture, left cerebellar haematoma, bilateral craniotomy, hydrocephalus and meningitis, CSF drainage and ventriculoperitoneal shunt

Control 2 30 F Participant 3 26 M 6

Severe Flaccid

26% (single words) Sentences not attempted

15 Motor vehicle

accident

Control 3 25 M Note: PTA: post-traumatic amnesia; TPO: time post-onset; ASSIDS: Assessment of Intelligibility for Dysarthric Speech (Yorkston, Beukelman & Traynor, 1984); SAH: subarachnoid haemorrhage; SDH: subdural haemorrhage; EDH: extradural haemorrhage; CSF: cerebrospinal fluid.

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JCPSLP Volume 14, Number 3 2012

Journal of Clinical Practice in Speech-Language Pathology