The interpretation of imperfective aspect in developmental dyslexia

I present the results of an experiment testing the ability of dyslexic children to interpret the Italian past tenses Imperfetto (IMPF) and Passato Prossimo (PP). The experiment is a picture selection task. Subjects hear either an IMPF sentence or a PP sentence and are then asked to match the sentence with a picture depicting either an ‘ongoing’ (matching IMPF) or a ‘complete’ (matching PP) situation. The test has been administered to a group of 9-year-old dyslexic children (DYS), a group of age-matched control children (AMC), a group of 5-year-old control children (PSC), and a group of adult controls (ADC). ADC and AMC consistently matched PP sentences with a complete situation and IMPF sentences with an ongoing situation. PSC provided chance level results both with IMPF and PP sentences, showing no mastery of either tense. DYS displayed adult-like competence of PP, consistently matching PP sentences with complete situations, but non adult-like mastery of IMPF, reflected in chance level results, which were not significantly different from the PSC. In order to explain this pattern of results, I propose that (i) reference to complete events with IMPF is excluded by pragmatic considerations, a scalar implicature, and that (ii) dyslexic children, having poor verbal short-term memory resources, often fail in building the set of alternative derivations necessary to compute the scalar implicature associated with IMPF. The proposal predicts that dyslexic children are also impaired in the comprehension of canonical scalar terms, such as disjunction sentences and existentially quantified noun-phrases. I show, drawing data from recent experimental studies, that the prediction is fulfilled.