Resolving the problem of surface dyslexia in Italian through inflection of irregular verbs

Surface dyslexia and dysgraphia are considered diagnostic features of semantic variant primary progressive aphasia (svPPA) and are useful signs in English, a language whose attributes afford numerous opportunities to observe these phenomena. This, however, is not the case in many languages, including Italian, that have high transparency between orthography and phonology, making surface reading and spelling errors scarce. This creates a problem in applying the diagnostic recommendations for svPPA in such languages. Surface dyslexia and dysgraphia are examples of 'regularization' errors in which semantic knowledge loss leads to a failure to recognize exceptions that do not follow standard rules of pronunciation. Another form of regularization involves the incorrect inflection of irregular verbs using the rules that govern regular verbs. Unlike irregularly pronounced words, Italian, as with many languages, has numerous irregular verbs. The Italian Verb Inflection Test (IVIT) was developed to test the hypothesis that svPPA would regularize irregular verbs when inflecting them into two Italian past tenses. Results confirmed that people with svPPA made a significantly greater proportion of regularization errors compared to people with typical Alzheimer's disease or logopenic variant PPA. Without recourse to the other diagnostic features of PPA subgroups, the IVIT on its own could separate svPPA from these other two groups with 70% sensitivity and ~ 80% specificity. Regularization of irregular verb inflection offers a solution to the problem of applying the surface dyslexia/dysgraphia criterion for svPPA diagnosis in Italian.