The challenge of variability for syntactic accounts of agrammatism: A study on feature dissimilarity in Italian relatives

This study explores syntactic processing in ten Italian-speaking individuals with agrammatism, testing predictions from two competing linguistic accounts: the Trace Deletion Hypothesis and Generalized Minimality. We examined subject, object and passive relatives in comprehension (sentence-to-picture matching task) and production (sentence priming task), manipulating number mismatch as a possible facilitation factor. According to Generalized Minimality, mismatch should reduce intervention effects in object relatives, while the Trace Deletion Hypothesis predicts uniform impairment of derived structures. Comprehension results showed an overall subject advantage, with mismatch-related facilitation observed in a subset of participants. However, high interindividual variability challenged strong generalisations. No clear performance pattern emerged in production, possibly due to concurring deficits and task-related limitations. Passive relatives, expected to be easier in line with studies on language acquisition, were as impaired as object relatives, supporting a specific deficit with passives in agrammatism. Linguistic theory played a central role in accounting for the variability observed, with Generalized Minimality emerging as the most explanatory, yet not unchallenged account.