The role of LIFG-based executive control in sentence comprehension

Prior research has shown that patients with damage to the left inferior frontal gyrus (LIFG) can have difficulties in executive control as well as understanding syntactic garden-paths, that is, sentences with a temporary syntactic ambiguity that resolve towards a less preferred interpretation. The present study tested two LIFG patients on object/subject garden path and matched syntactically unambiguous sentences. Besides syntactic ambiguity, support for the preferred but ultimately inappropriate interpretation was manipulated via verb bias, using verbs that were neutral between alternative analyses and verbs that were biased towards the context-inappropriate option. The LIFG patients, a non-LIFG patient, and healthy controls were tested on a sentence interpretation task (Experiment 1) and grammaticality judgement (Experiment 2). In contrast to the non-LIFG patient and controls, the LIFG patients showed impaired thematic role assignment across garden-path as well as unambiguous sentences, which tended to be worse with biased verbs. The results argue for a role of executive control in overcoming verb bias across diverse sentence processing situations, including, but not limited to, garden-path revision.