One cat, Two cats, Red cat, Blue cats: Eliciting morphemes from individuals with primary progressive aphasia

Abstract

Background: Progressive neurodegenerative impairment with central language features, primary progressive aphasia (PPA), can be further distinguished for many individuals into one of three variants: semantic, non-fluent/agrammatic, and logopenic variant PPA. Variants differ in their relative preservation and deficits of language skills, particularly in word finding and grammar. The majority of elicited language assessments used in this population focus on single noun and verb production, while modifiers and inflectional morphemes are far less commonly examined.

Aims: The purpose of the present study is to determine whether there was an interaction between PPA variant and production of high-frequency nouns, proper names, modifiers, and bound inflectional morphemes to better understand how the variants differ.

Methods & procedures: Forty-six people with PPA and 47 individuals with no known neurological diagnoses completed a morphosyntactic generation assessment designed to target differential production of high-frequency nouns, proper names, modifiers (number, size, color), and bound inflectional morphemes (plural -s and possessive 's), the Morphosyntactic Generation test (MorGen). Performance is averaged for each of the seven morphosyntactic targets independently, resulting in seven separate performance scores.

Outcomes & results: Individuals with PPA performed significantly more poorly than controls on the assessed morphemes in a repeated-measures analysis of variance, as well as on each morpheme considered independently via t-test.In a multivariable analysis of variance among PPA variants, the interaction of morpheme and PPA variant was significant, suggesting different variants produced the morphemes with a significantly different pattern of success. When morphemes were considered independently, only production of colour resulted in a significant difference between variants, driven by the performance of individuals with nfavPPA, who performed near-ceiling. When MorGen performance was used to predict PPA variant in a multinomial logistic regression the model was significant, with age, plural -s, noun, and number contributing significantly to the prediction. In a discriminate function analysis, classification of cases was best for agrammatic variant with 70% accuracy.

Conclusions: Individuals with PPA, particularly semantic and logopenic variants, demonstrated difficulty on the MorGen compared to controls. The MorGen proved useful in predicting PPA variant. These findings highlight the potential benefit of examining a broader range of morphemes, particularly bound morphemes and modifiers, in addition to the more frequently investigated classes of nouns and verbs when understanding PPA.

Keywords: aphasia; dementia; modifiers; plural; production.

Figure 1:. Example stimuli from the MorGen task.

Target responses are shown in quotations.

Figure 2:. Contrasting profiles of relative success in modifiers by PPA variant

Error bars represent +/− 1 standard error. lvPPA=logopenic variant, nfavPPA=non-fluent/agrammatic variant, svPPA=semantic variant.