event-related fNIRS investigation of Japanese word order

Japanese is a free word-order language, and allows both subject-object-verb (SOV) and object-subject-verb (OSV) orders. Our previous study using near-infrared spectroscopy (NIRS) imaging revealed that OSV sentences induce more activation in the left frontal lobe than SOV sentences. The present study develops our previous experiment: (1) by adopting an event-related design, and (2) by using sentences involving the adverb naze ‘why', which plays a prominent role in recent linguistic studies. The results of our new experiment indicated that the cerebral activation in OwhySV sentences was significantly larger than that in SwhyOV sentences, in the right anterior prefrontal region, which is consistent with the assumption that OwhySV order is derived from SwhyOV order. We speculate that the activation observed in the anterior prefrontal cortex during the processing of the sentences involving ‘why' might be due to the processing of higher-order function in the cerebral cortex.