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Article Excerpt
Studies examining the auditory abilities of persons with aphasia typically employ novel auditory tasks and assess performance based upon means across the testing session. However, it is not clear that the manner in which performance changes within a test session is the same across individuals with and without aphasia. In the current study, performance on a variety of novel auditory tasks in background distracter noise was assessed as a function of the time course of a 1-hour session. The tasks included frequency discrimination of tones, syllable discrimination, lexical decision, and sentence plausibility. The noise was produced by a 3T MRI scanner. Despite their increased susceptibility to distraction, and possible effects of slow rise time and overload, performance of the participants with aphasia and their normal counterparts was relatively stable. However, larger increases in performance were observed in the participants with aphasia during the initial blocks of testing, indicating that the rate at which these subjects gained proficiency differed. It is concluded that large interactions between subject group and session progress are generally absent, but that special consideration should be given to the different rates at which persons with aphasia learn novel auditory tasks in background noise.
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The auditory abilities of persons with aphasia (PWA) have been the topic of a considerable amount of research. Traditional views have considered the speech-processing deficits to be constrained to a particular modality or to a particular stage of the language-processing system (cf., Moineau, Dronkers, & Bates, 2005). However, evidence exists that auditory reception of nonlinguistic materials may also be impaired. Divenyi and Robinson (1989) found disruptions in performance by PWA on tasks involving pure-tone frequency and frequency sweep discrimination. Other work has indicated that left hemisphere damage can be accompanied by impaired detection of amplitude modulation at particular rates (Fullgrabe, Maillet, Moroni, Belin, & Lorenzi, 2004; Hescott, Lorenzi, Debruille, & Camus, 2000).
Language deficits in aphasia can be exacerbated or even caused by limitations in attention or resource allocation (McNeil & Kimelman, 1986; McNeil, Odell, & Tseng, 1991). Persons with aphasia often display reduced performance relative to normal control subjects under conditions of divided attention, in which subjects attend to simultaneous messages or perform simultaneous tasks (e.g., Murray, 2000; Murray, Holland, & Beeson, 1997; Tseng, McNeil, & Milenkovic, 1993). Similarly, these individuals perform more poorly under focused-attention conditions in which an auditory signal must be processed in the presence of a distracter stimulus (e.g., Arvedson & McNeil, 1986; Murray, 2000; Murray et al., 1997). Murray et al. (1997) assessed semantic categorization and lexical decision in the presence of competing stimuli. Although performance across normal individuals and PWA was similar when the auditory tasks were presented in isolation, the PWA responded less accurately and more slowly in both focused- and divided-attention conditions. Further, all individuals demonstrated greater disruptions in auditory processing in the presence of verbal, rather than nonverbal, distracters. More recently, Kittredge, Davis, and Blumstein (2006) found that the addition of a white noise masker could reduce semantic priming in PWA, suggesting that lexical access was degraded by the addition of the competing auditory stimulus.
In a study of auditory vigilance, LaPointe and Erickson (1991) had PWA and control subjects continuously monitor for a target word interspaced among nontarget words. It was found that performance across groups did not differ during the 10-minute task, but that the PWA performed more poorly than normal when a second (divided attention) task was added. A similar pattern of results was found when the target signal was a complex tone interspaced among pure tone nontargets, indicating that the effect was not restricted to linguistic processing (Erickson, Goldinger, & LaPointe, 1996). In a similar study, Laures (2005) observed poorer performance by PWA during auditory vigilance of both speech and nonspeech stimuli, but found no difference in performance during the initial versus the final 16 minutes of the 32-minute sessions.
Although not commonly considered a focused-attention paradigm, the noise associated with fMRI can potentially serve as a distracter. It is important to understand the possible influences of scanner noise on PWA, as the use of neuroimaging as a tool to study deficits in aphasia has increased dramatically over the past several years (cf., Price & Crinion, 2005). The scanning environment is characterized by intense background noise caused by movement of the gradient coils. This noise can be as loud as 120-130 dB SPL in a 3.0 Tesla scanner (Foster, Hall, Summerfield, Palmer, & Bowtell, 2000). Although hearing protection is commonly employed, substantial levels of background noise remain. This concomitant scanner noise may physically mask portions of the auditory spectrum or it may serve as a distracter. Because PWA may be especially susceptible to auditory signals that are degraded by limiting the...
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