A Spanish grammaticality judgment task for neurodegenerative diseases: inflectional, transitivity, and word order comprehension in PPA and Alzheimer's Disease

Impairment in the comprehension of morphosyntactic and transitivity information does not feature in current diagnostic guidelines for primary progressive aphasia (PPA) or Alzheimer's Disease (AD), despite research reporting delayed sensitivity or insensitivity of these clinical populations to these linguistic domains. Moreover, studies rarely compare all three PPA variants and AD within a single design, and the literature is weighted toward English, whose reduced morphology may not capture the full range of comprehension difficulties these populations experience. We developed a computer-based acceptability judgment task covering comprehension of the nominal and verbal inflection paradigm in Spanish, transitivity and word order. We recruited Spanish-speaking patients diagnosed with non-fluent/agrammatic, logopenic and semantic variants of PPA and typical AD. Psychometric evaluation confirmed good sensitivity, internal consistency and moderate correlation of task accuracy with language and neuropsychological measures. The four clinical groups retained the ability to endorse grammatical sentences but showed selective difficulty rejecting unacceptable ones. AD and the three PPA variants showed impaired comprehension of inflectional and transitivity information, whereas sensitivity to word order was comparatively preserved. Exploratory analyses revealed that short-term memory, working memory, and verbal semantics were differentially associated with sentence evaluation performance within and across groups. VBM analyses identified the left posterior temporal cortex as the main neuroanatomical correlate of grammaticality judgment performance. These findings extend prior English-language research to Spanish, demonstrating that morphosyntactic and transitivity deficits are a robust and cross-linguistically consistent feature of neurodegenerative language decline, and highlighting the importance of developing language-sensitive assessment tools for underrepresented linguistic populations.