| Summary: | Individuals with Broca’s aphasia typically have difficulty understanding sentences containing syntactic dependencies (e.g., Wh-questions, as in “Which mailman did the policeman push___ yesterday afternoon”). Broca’s patients can compute these dependency relationships, though in a delayed fashion unlike their unimpaired counterparts (Love et al., 2008). The basis for the processing delay could be in lexical access (Ferrill et al., 2012); that is, lexical access is delayed, and so to is re-access of the displaced argument (e.g., Which mailman) at the gap. Based on these findings, we have argued for the Delayed Lexical Activation (DLA) hypothesis: lexical access is too slow for normally fast-acting syntactic operations, resulting in what appears to be syntactic comprehension deficits in participants with Broca’s aphasia.
The current study investigates this issue by using sentences containing unaccusative verbs (UA). UAs are intransitive verbs, but their single argument is base generated in object position and displaced to subject position, leaving behind a gap (Burzio, 1986) and thus creating a syntactic dependency, as in:
1. The boy disappeared <the boy> yesterday afternoon.
Friedmann et al. (2008) demonstrated that unimpaired individuals do not immediately reactivate the displaced argument at verb offset (gap), but instead 750ms downstream. This inherent delay observed with UAs in neurologically healthy participants provides an opportunity to test listeners with Broca’s aphasia. Specifically, we ask whether these participants also evince such a delay (and thus show a normal pattern), or whether the delay is pushed even further ‘downstream’ because of their inherently slow lexical activation.
Twelve adults who experienced a single unilateral left hemisphere stroke participated in the study; seven had a Broca’s aphasia with a comprehension deficit and the remaining five participants were considered LCVA controls.
We used an on-line cross-modal picture priming task. Participants listened to 32 sentences that contained UAs as in (2) below.
2. The queen with the bad temper vanished[*1] during[*2] the[*3] spectacu[*4]lar fireworks show.
During the uninterrupted temporal unfolding of each sentence, a picture representing the displaced NP (e.g., queen) or an unrelated control probe (e.g., surgeon) was briefly presented at one of four probe positions (as numbered above). Participants listened to sentences while also making a binary decision about the picture (animate/inanimate). Faster response times to the related as compared to the control probe indicate lexical priming/activation.
Similar to Friedmann et al.’s (2008) findings of normally delayed re-access of the displaced argument, the results for all 12 participants (Fig.1) revealed priming only at the downstream probe position [*2], t(11)=3.08, p=.01. In a separate subgroup analysis, the same pattern was found for the Broca group, t(6)=4.77, p=.003.
These results suggest that participants with Broca’s aphasia can take advantage of the inherent delay of unaccusatives and exhibit similar patterns of syntactic dependency linking as unimpaired individuals. We discuss these findings with reference to its generalizability across patient groups, the DLA, and the interaction between lexical and syntactic processes.
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