In the present study, we targeted Kaqchikel, a Mayan language spoken in Guatemala, in which subjects and objects are unmarked, while person (1st, 2nd, 3rd) and number (singular and plural) agreement for both objects and subjects are obligatorily expressed on a verb. Kaqchikel allows various scrambled word orders, such as SVO, VSO, and OVS, which are all grammatical. We hypothesize that activations in the left inferior frontal gyrus (L. IFG) are more enhanced for OVS than SVO, as well as for VSO than SVO, which should be observed by functional magnetic resonance imaging (fMRI). As Kaqchikel is typologically differed from other well-studied languages, this study would be ideal to examine the universal role of the L. IFG in syntactic processing.
We recruited eight right-handed native Kaqchikel speakers (aged 22-38), whose linguistic knowledge included the agreement markers on the verb, as confirmed by a discrimination test. We used a picture-sentence matching task, in which the participants listened to a sentence [Ri säq xeroyoj ri taq käq, The white (person) called the red (persons)] and judged whether the action depicted in a picture matched the meaning of the sentence. We used 3.0 T MRI system (Signa HDxt, GE Healthcare), and analyzed the fMRI data with fixed effects analyses.
The accuracy for OVS were significantly lower than that for VSO and SVO, and the reaction times for OVS and VSO were significantly longer than that for SVO (p ≤ 0.002), indicating that OVS and VSO were more demanding word orders. To exclude any general effects due to task difficulty, the accuracy was used as a nuisance variable for the fMRI analyses. To examine the effect of scrambling between word orders with a verb in the middle position (OVS and SVO), we tested the OVS – SVO contrast, which resulted in localized activation in the L. IFG and lateral premotor cortex (L. LPMC) (corrected p < 0.05). Moreover, we tested the most stringent contrast of VSO – SVO. We found clearly localized activation in the L. IFG, suggesting that VSO has more complex syntactic structures than SVO. The modulation of activations in the L. IFG and the L. LPMC thus indicates a sensitive indicator of word orders in any natural languages.