The role of the anterior left hemisphere in real-time sentence comprehension: evidence from split intransitivity.

We investigate Broca's sentence comprehension as an impairment on normal syntactic composition: the slow-syntax hypothesis (SSH). Experiment 1 examines comprehension of object-relative clauses (Wh-movement). Experiment 2 examines comprehension of sentences with unaccusative verbs (NP-movement), which like passives, base-generate their theme-argument in object position. Guided by the SSH, both experiments test the prediction that syntax-dependent effects such as "gap-filling" are observable but in a delayed fashion. Results show that whereas no priming was obtained at the point of the trace, antecedent reactivation emerged 650 and 800 ms after the verb (for Wh- and NP-movement respectively). This shows, contrary to dependency-based generalizations, that Broca's patients are able to successfully implement dependencies, albeit in a protracted manner. Given the localization value provided by Broca's aphasia, this supports the notion that the temporal implementation of syntactic structure formation (i.e., the requirement that it be fast and automatic) depends on the integrity of the anterior left hemisphere.