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Article Excerpt
Differences in the clinical and ecological manifestations of reduced intelligibility for individuals with dysarthria related to Parkinson disease (PD) have been reported in the literature. The current study explored whether a dual-task paradigm could be used during intelligibility testing to collect speech samples that were representative of functional performance. Intelligibility was calculated for four speakers with PD and four age-matched controls (CG) based on single-word, sentences, and monologue tasks recorded in single- and dual-task conditions and a spontaneous speech sample. In the dual-task condition, speakers produced the target speech sample and performed a simultaneous motor task, turning a nut on a bolt. No significant differences in intelligibility were found for the CG. For speakers with PD, differences between conditions were statistically significant for all speech tasks. Intelligibility scores in the dual-task condition were lower, with variability between tasks and speakers noted. There was a significant difference between scores for the monologue in the single-task condition and the spontaneous sample; however, there was no significant difference between the monologue in the dual-task condition and the spontaneous sample. Findings suggest that including a simple motor task during a clinical assessment may help elicit speech samples that are representative of a speaker's typical speech production.
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Speech intelligibility is an important construct in the assessment and management of clients with dysarthria. Clinically, intelligibility scores are used as an index of functional limitation, as a measure of severity of the speech disorder, as a guide for the treatment planning, and to document and monitor change during or after remediation (Yorkston, Beukelman, Strand, & Bell, 1999). Important decisions related to termination of treatment are often based, at least in part, on intelligibility scores. Because critical clinical decisions are based on intelligibility scores, the accuracy of these measures is of the utmost importance. Large differences in speech produced in a clinical or laboratory setting versus informal spontaneous situations have been reported anecdotally by clinicians as well as in the literature for speakers with PD (Keintz, Bunton, & Hoit, 2007; Sarno, 1968; Weismer, 1984). Weismer (1984), for example, reported that speakers with PD were quite intelligible when producing experimental sentences, but were significantly less intelligible during spontaneous speech. While differences in speech produced in these settings have not been well quantified, for clinicians and researchers who wish to study speech production deficits associated with PD, potential differences in clinical and ecological manifestations of the dysarthria are problematic in terms of both understanding the impairment and clinical intervention.
Speech production and its resulting speech intelligibility have been shown to be influenced by speech material, physical setting, and motivation (Hustad & Weismer, 2007). During assessment, clinicians use a number of different speech tasks in an attempt to get a sense of a speaker's production abilities. It has been questioned, however, whether a direct relation exists between intelligibility measured under highly controlled conditions and more realistic conditions (i.e., spontaneous speech) (Kent, Weismer, Kent, & Rosenbek, 1989). In a clinical setting, there are likely a number of subtle cues related to a speaker's motivation and the environment that may increase a speaker's attention to the task of speech production and thus affect her or his behavior. For example, in a clinic or research laboratory setting, speakers are keenly aware that the clinician is scrutinizing their speech production. The presence of recording and other testing equipment may also change the execution of the task (Aronson, 1990). This increased attention may lead to improved performance in production of individual phonemes, suprasegmental variables, increased amplitude of the speech signal, and possibly changes in the complexity of the message (e.g., the topic being discussed or preceding utterances), as well as nonverbal signals (e.g., gestures, postures, and facial expressions). Combined, these changes may result in higher speech intelligibility scores that are not representative of a speaker's typical production. Thus, a clinical assessment may create an unrealistic speaking situation where the speaker focuses all of her or his attention on a single task, speech production.
Everyday communication, on the other hand, can be considered a type of divided attention task where speakers are frequently required to coordinate the demands of message formulation and speech production with other daily activities such as driving, walking, preparing a meal, or watching television. In these situations, multiple stimuli compete for attentional resources (Dromey & Benson, 2003; Murray, 1999). Including a secondary task during intelligibility testing to divert some of a speaker's attention away from the primary task may be a way to create a more natural environment that will result in behaviors that are more representative of typical abilities. Performing two tasks simultaneously is an experimental procedure commonly referred to as a dual-task paradigm.
Dual-task paradigms have been widely used in research settings to examine the effects of divided attention on performance. The underlying assumption is that if attention is divided between two tasks performed simultaneously then performance on one or both will be negatively affected (Kahneman, 1973; Wickens, 1984). Several different models of attention have been used to explain changes in performance between single-and dual-task conditions. While a detailed review of these models is beyond the scope of this article and can be found elsewhere (Allport, 1993; Band, Jolicoeur, Akyurek, & Memelink, 2006; Murray, 1999; Navon & Miller, 2002; Shuster, 2004) a brief overview of the two main views is warranted to understand why performance on dual tasks may be different from performance on a single task. One view of attention models the system as capacity limited, where there is a fixed pool of attentional resources, and although the resources are limited, they can be flexibly and simultaneously allocated toward one or more activities (Kahneman, 1973; Moray, 1967; Navon & Miller, 2002; Wickens, 1984, 1989). The amount of attention directed toward a specific task relates to its demands with factors such as novelty of the task, intent to attend to a specific input, or arousal level being key factors. Failure on a task can result from a misdirection of resources or inefficiency in the allocation of resources. A second view suggests that the brain processes stimuli serially. If multiple tasks require processing concurrently, a "bottleneck" arises and completion of one task must wait or suffer (Pashler, 1984, 1990, 1994a, 1994b). In other words, conflicts among multiple tasks are related to time sharing as opposed to the sharing of resources suggested in the first view. Considerable debate exists with regard to both of these models, and performance on different types of dual-task paradigms has been used as evidence for the different models (Band et al., 2006).
The majority of the research using dual-task paradigms has evaluated performance on motor tasks that were executed concurrently with secondary tasks that varied in modality and complexity (Chang & Hammond, 1987; LaBarba, Bowers, Kingsberg, & Freeman, 1987; McLeod, 1977; Parush, 2005; Seth-Smith, Ashton, & McFarland, 1989; Simon & Sussman, 1987). In contrast, studies where changes in speech production were of primary interest have been limited to the use of motor-based secondary tasks because of concerns about single modality interference (i.e., two tasks competing for the same resources such as performance of mental arithmetic and verb-generation tasks simultaneously). Motor tasks reported in the literature range from simple manual tapping to complex visual tracking or object-assembly tasks (Bosshardt, Ballmer, & de Nil, 2002; Dromey & Benson, 2003; Ho, Iansek, & Bradshaw, 2002; Jou & Harris, 1992; Oomen & Postma, 2001). Changes reported in speech production have been shown to be related to the type of secondary task used and have included increases in the number of self-corrections in articulation, frequency of word deletion (Jou & Harris, 1992), word-shadowing errors (Elliot, Weeks, Lindley, & Jones, 1986), and changes in pause location and structure (Oomen & Postma, 2001). Others...
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