The locative alternation: distinguishing linguistic processing cost from error signals in Broca's region

The left inferior frontal gyrus (LIFG) is known to be involved in the processing of syntactic complexity, such as word order variation. It is also known to be involved in semantic interpretation in studies of various types of semantic and pragmatic anomalies. Across neuroimaging studies of language processing, two main approaches can be found, one that contrasts anomalous and well-formed words or sentences in order to yield an error response and one that contrasts two well-formed syntactic structures differing in complexity, investigating effects of increased integration costs. The present fMRI study aimed at disentangling the error signal from the processing cost signal in LIFG. To do so, we examined the so-called Locative Alternation, which involves the contrast between the Content-Locative construction, e.g. He sprays paint on the wall, and the Container-Locative construction, e.g. He sprays the wall with paint, which have been argued to differ in processing. By including asymmetric verbs, e.g. He blocks the road with rocks vs. *He blocks rocks on the road, we were able to study the contrast between well formed and anomalous constructions. Participants performed an acceptability judgment task during fMRI. The results showed that increased syntactic integration costs yielded both increased response time as well as LIFG activation. Anomalous sentences yielded low acceptability rating but no increase in response time, yet they also evoked increased LIFG activation. Thus, the processing cost and the error signal were found to be functionally independent, but spatially overlapping in the brain.