Unravelling nonverbal cognitive performance in acquired aphasia

Background: Nonverbal cognitive constructs are not well understood in patients with acquired aphasia due to stroke. The relative contribution of aphasia, particularly receptive language impairment, to nonverbal function is rarely quantified in studies, although it is assumed to be substantial. Aims: The purpose of the present study was first to investigate the factor structure of some of the WAIS-III and WMS-III nonverbal tasks in patients with acquired aphasia due to stroke using confirmatory factor-analytic techniques. Second, we sought to determine the degree to which aphasia severity (both auditory comprehension and oral expression), as measured by the Language Competency Index (LCI) of the Boston Diagnostic Aphasia Examination (Goodglass et al., 2001), would account for variance in nonverbal cognitive task performance. Methods & Procedures: The present study investigated the factor structure of widely used nonverbal cognitive tasks in 136 patients with aphasia due to single left hemisphere stroke, and sought to determine the degree to which language impairment accounted for nonverbal skill. Outcomes & Results: A single factor model representing nonverbal (perceptual) constructs provided the best model fit to the data. The underlying factor structure of nonverbal constructs in patients with aphasia mirrors the structure observed in healthy adults. Although the correlations between language impairment measures and nonverbal skills were moderate, language competence accounted for a minority (about a quarter) of the variance in nonverbal skills. Conclusions: We conclude that impairment in nonverbal cognitive ability is not fully explained by language competence in people with aphasia.