Measuring word retrieval in narrative discourse: core lexicon in aphasia.

Background: Discourse analysis procedures are time consuming and impractical in a clinical setting. Critical to clinicians are simple and informative discourse measures that require minimal time and labour to complete. Many studies, however, have overlooked difficulties that clinicians face. We recently developed core lexicon lists for nouns, verbs, adjectives and adverbs for two narrative discourse tasks with healthy control groups. Core lexicon lists consist of important lexical items required to produce coherently meaningful discourse in response to discourse tasks. Measuring core lexicon is useful for quantifying word retrieval impairments at the discourse level in clinical populations.

Aims: To apply an age-based core lexicon list for nouns, verbs, adjectives and adverbs for the wordless picture books Good Dog Carl (1985) and Picnic (1984) and to determine how well the lists measured linguistic impairments in persons with aphasia (PWA).

Materials & Methods: Lemma forms were extracted from 470 control participants who were divided into seven age groups. Twenty-five core lexicons were identified for four word classes (nouns, verbs, adjectives and adverbs) among the seven age groups. The nouns, verbs, adjectives and adverbs for each PWA (N = 11) were then compared with the core lexicon for their respective age group. Per cent agreement was computed by comparing the number of total items within each list to the number of items that PWA produced. A Spearman's correlation coefficient was computed between the WAB-R AQ and the per cent agreement for each word type for PWA.

Outcomes & Results: The percentage of agreement for each word type among the age cohorts ranged between 56% and 96%. Of the four word types, core verbs significantly correlated with the WAB AQs for both discourse tasks. A post-hoc analysis found significant differences between fluent and non-fluent aphasia for core verbs.

Conclusions & Implications: Core lexicon analysis appears to be a practical way to capture impairments in word retrieval at the discourse level. Core verbs may be a better indicator to understand holistic language performances for PWA. Use of the core lexicon checklist can serve as an option to reconcile ecological validity with clinical usability.