Lingraphica Co-founder and Chief Scientist, Dr. Richard Steele, summarizes findings of Dutch researchers regarding the retrieval of nouns and verbs in persons with aphasia (PWA) based on four factors: word class, age of acquisition, imageability, and word frequency. The goals were to refine and extend findings from previously published studies of factors influencing word retrieval performance in aphasia.
Fifty-four Dutch-speaking PWA were administered four tests that probed retrieval of: (a) citation forms of nouns in isolation, (b) citation forms of verbs in isolation, (c) infinitive forms of verbs in grammatical context, and (d) conjugated forms of verbs in grammatical context. The researchers statistically analyzed data to determine influence of word class, age of acquisition, and imageability on item retrieval success. Analysts then tested for significant differences between retrieval success rates in production of verb citation forms in isolation vs.: (a) noun citation forms in isolation; (b) infinitives in grammatical context; and (c) finite verbal forms in grammatical context. Finally, the influence of frequency on retrieval success rates was statistically analyzed for: (a) verb citation forms in isolation; (b) noun citation forms in isolation; (c) infinitive verb forms in grammatical context; and (d) conjugated verb forms in grammatical context.
The first set of analyses corroborates findings from previous research that: nouns are retrieved more successfully than verbs, items acquired at an early age are retrieved more successfully than those acquired later in life, and high-imageability items are retrieved more successfully than low-imageability items. Their second set of comparisons establishes that there is a significant difference between retrieval of nouns vs. verbs in citation forms, but not between the latter vs. verb forms in grammatical contexts. The final comparisons show a significant positive correlation between higher frequency and greater retrieval success for the citation forms of nouns, but not for the citation forms of verbs.
This research corroborates and broadens understandings of factors influencing retrieval success rates by persons with aphasia of noun and verb forms. It examines the influence of presence or absence of grammatically embedding contexts on verb form retrieval, and in so doing it advances a framework for even broader investigations in future studies.
For further reading: R. Bastiaanse, M. Wieling, N. Wolthuis, 2016. The role of frequency in the retrieval of nouns and verbs in aphasia. Aphasiology, 30(11):1221–1239.