Chapter 4 compares brain activations in response to Kaqchikel sentences with the VOS and SVO orders, obtained using functional magnetic resonance imaging (fMRI). It is known that the left inferior frontal gyrus (IFG) of the brain exhibits enhanced activation in response to grammatically complex, demanding sentences. The fMRI experiment we conducted with Kaqchikel speakers revealed that cortical activation in the left IFG was significantly higher in response to SVO sentences than VOS sentences, which clearly shows that it is the grammatical features of individual languages, and not universal human cognitive features, that primarily modulate brain activation and determine sentence processing load.

Chapter 3 reports behavioral experiments with a sentence plausibility judgment task in Kaqchikel to test predictions by the Individual Grammar View and the Universal Cognition View. In this task, Kaqchikel sentences in one of the three commonly used orders (VOS, SVO, and VOS) were presented in a random order to participants through headsets. The participants were asked to judge whether each sentence was semantically plausible and to push a YES button for correct sentences or a NO button for incorrect sentences as quickly and accurately as possible. The time from the beginning of each stimulus sentence until a button was pressed was measured as the reaction time. Semantically natural sentences were processed faster in the VOS order than in the SVO or VSO orders, which suggests that VOS is easier to process than SVO or VSO. These results are compatible with the prediction of the IGV, but not with the prediction of the UCV, showing that the SO preference in sentence comprehension is not fully grounded in the universal properties of human cognition; rather, processing preference may be language-specific to some extent, reflecting syntactic differences in individual languages.