The Concept of Regularization: Resolving the Problem of Surface Dyslexia in Semantic Variant Primary Progressive Aphasia Across Different Languages

Surface dyslexia, a diagnostic feature of the semantic variant of primary progressive aphasia (svPPA), is difficult to observe in many languages. It can be conceptualized as one manifestation of a more general "regularization" effect-that is. with semantic impairment, patients fail to recognize exceptions and revert to default rules. Objective: We predicted that, analogous to surface dyslexia in English, German patients with svPPA would regularize irregular verbs, especially those of lower frequency and in the less frequently used preterite tense. Method: Regularization was investigated in German through past-tense verb inflectional morphology in N = 10 svPPA, N = 5 PPA related to Alzheimer pathology (AB+ PPA), N = 5 patients with nonfluent variant PPA (nfvPPA), N = 12 typical (amnestic presentation) Alzheimer's disease (AD), and N = 32 healthy controls. The task involved perfect- and preterite-tense inflection of regular and irregular verbs of high and low frequency. Results: Errors in svPPA particularly involved regularization (e.g., I swim -> swimmed, I have swimmed), whereas AB+PPA made a wide range of other errors (e.g., verb agreement or tense errors). Regularization was rare in AD and controls, whereas the expected frequency effects (low worse than high) were found in svPPA. nfvPPA had profound difficulties in inflecting verbs in general. Conclusion: The study illustrates how tests tailored to a specific language can reveal the regularization effect of svPPA. For more universal diagnostic recommendations. future revisions for svPPA should consider substituting the criterion of surface dyslexia for that of a general criterion of regularization of language rules, the former being an example of the latter.