Shave, shear, shred, or cut: PPA variant differentially impacts erroneous responses produced in a confrontation naming test of verbs

Background: All common variants of primary progressive aphasia (PPA) exhibit naming deficits. Variants are distinguished by relative deficits in repetition (logopenic; lvPPA), object knowledge (semantic; svPPA), and agrammatism or articulation (non-fluent/agrammatic; nfavPPA; Gorno-Tempini et al., 2011). The Hopkins Action Naming Assessment (HANA) is a 30-item verb naming task that can distinguish between variants (Stockbridge et al., 2021). Item-level accuracy is driven by target verb frequency, semantic information density, and conceptual concreteness of the target word (Stockbridge, Venezia, et al., 2022). Aims: In this investigation, we examined whether word frequency, semantic density, concreteness, and age of acquisition (AoA) also shaped the incorrect responses patients provided. We hypothesised that error responses would vary in these dimensions as a function of PPA variant. Methods & Procedures: The HANA was administered to 271 participants with PPA, resulting in 443 total administrations and 4,529 analysable error responses. Standardised differences between error and target responses for frequency, density, concreteness, and AoA were calculated and averaged for each patient. Analysis of variance (ANOVA) for correlated samples was used to compare variants and planned post-hoc analyses examined the effect of variant on each response quality. Outcomes & Results: Participants were similar in age, sex, handedness, and education. There was a significant interaction between PPA variant and the standardised mean differences in lexical qualities (Pillai’s Trace = 0.11, F(9, 747) = 3.19, p < 0.001). Univariate ANOVAs revealed significant differences in the semantic density of error responses relative to the target (F(3) = 7.91, p < 0.001, η_P²= 0.09), as individuals with lvPPA tended to produce error responses with greater semantic density than the target when compared to the words produced by individuals with nfavPPA (mean difference = 1.45, 95%CI = [0.60,2.29], p < 0.001; Figure 1). PPA variants also differed in the concreteness of their error responses relative to the target (F(3) = 5.99, p<0.001, η_P² = 0.07), as error responses produced by individuals with nfavPPA were significantly more concrete than those with lvPPA (mean difference = 0.08, 95%CI = [0.02,0.13], p = 0.003) or svPPA (mean difference=0.08, 95%CI = [0.02,0.14], p = 0.007). Variants did not differ significantly in AoA or frequency of responses relative to their targets. All variants tended to produce more frequent words with a lower AoA than the target verb. Conclusions: Error responses tended to be more semantically dense, more concrete, higher frequency, and younger AoA than the target verb. However, PPA variants differed significantly in the extent to which these broader trends held true. These distinct patterns may be included as part of a larger diagnostic picture that to distinguish among PPA variants.