Impact of Clear, Loud, and Slow Speech on Scaled Intelligibility and Speech Severity in Parkinson's Disease and Multiple Sclerosis

Abstract

Purpose The perceptual consequences of rate reduction, increased vocal intensity, and clear speech were studied in speakers with multiple sclerosis (MS), Parkinson’s disease (PD), and healthy controls. Method Seventy-eight speakers read sentences in habitual, clear, loud, and slow conditions. Sentences were equated for peak amplitude and mixed with multitalker babble for presentation to listeners. Using a computerized visual analog scale, listeners judged intelligibility or speech severity as operationally defined in Sussman and Tjaden (2012). Results Loud and clear but not slow conditions improved intelligibility relative to the habitual condition. With the exception of the loud condition for the PD group, speech severity did not improve above habitual and was reduced relative to habitual in some instances. Intelligibility and speech severity were strongly related, but relationships for disordered speakers were weaker in clear and slow conditions versus habitual. Conclusions Both clear and loud speech show promise for improving intelligibility and maintaining or improving speech severity in multitalker babble for speakers with mild dysarthria secondary to MS or PD, at least as these perceptual constructs were defined and measured in this study. Although scaled intelligibility and speech severity overlap, the metrics further appear to have some separate value in documenting treatment-related speech changes.

Comparison of Intelligibility Measures for Adults With Parkinson's Disease, Adults With Multiple Sclerosis, and Healthy Controls

“…Each sentence contained between seven and nine words, and five key words (e.g., nouns, verbs, adjectives, and adverbs). An in-depth description of recording procedures was presented in Tjaden, Sussman, and Wilding (2014).…”

“…A VAS involves listeners choosing a point on a continuous line that does not contain any ticks or intervals to represent their judgment of a given speech sample (Kent & Kim, 2011). For example, Tjaden, Sussman, and Wilding (2014) recently used a computerized VAS task in which listeners judged intelligibility. Listeners were presented with a continuous 150-mm vertical-oriented scale on a computer monitor, with endpoints of the scale labeled "understand everything" and "cannot understand anything.…”

“…Toward this end, sentences read by speakers with multiple sclerosis (MS) and Parkinson's disease (PD) as well as healthy controls were orthographically transcribed for comparison to VAS judgments of sentence intelligibility reported in Tjaden, Sussman, and Wilding (2014). Sentences in the VAS study were produced in a speaker's typical manner of talking (e.g., habitual condition) as well as in speaking conditions used therapeutically to maximize intelligibility in dysarthria, including clear, loud, and slow.…”

“…Intelligibility has also been described or defined as how effective one is in his or her communication (Cannito et al, 2012), the ease with which the acoustic speech signal is understood (Kim & Kuo, 2012), or the extent to which the acoustic signal is understood (Tjaden, Sussman, & Wilding, 2014). Intelligibility should be distinguished further from the perceptual construct of comprehensibility (Yorkston, Strand, & Kennedy, 1996).…”

Altered resting‐state functional connectivity of the putamen and internal globus pallidus is related to speech impairment in Parkinson's disease

“…Problems with internal cueing have been well documented in PD (Jahanshahi et al., 1995; Siegert, Harper, Cameron, & Abernethy, 2002) and are thought to play a role in PD dysarthria (Sapir, 2014). Compared to habitual (internally cued) speech, measures of speech function and intelligibility improve when PD subjects are prompted (externally cued) to speak more loudly, clearly, or slowly (Dromey & Ramig, 1998; Ho, Bradshaw, Iansek, & Alfredson, 1999; Sapir, 2014; Tjaden, Sussman, & Wilding, 2014). As motor preparatory activity in PMd is biased toward the planning and execution of movements that are externally cued (Halsband, Matsuzaka, & Tanji, 1994; Halsband & Passingham, 1982; Lu, Arai, Tsai, & Ziemann, 2012; Mushiake, Inase, & Tanji, 1991), increased connectivity with GPi could reflect a mechanism for compensatory reliance on external cues during speech production in PD.…”