Frequency tagging of syntactic structure or lexical properties; a registered MEG study.

A traditional view on sentence comprehension holds that the listener parses linguistic input using hierarchical syntactic rules. Recently, physiological evidence for such a claim has been provided by Ding et al.'s (2016) MEG study that demonstrated, using a frequency-tagging paradigm, that regularly occurring syntactic constituents were spontaneously tracked by listeners. Even more recently, this study's results have been challenged as artifactual by Frank and Yang (2018) who successfully re-created Ding's results using a distributional semantic vector model that relied exclusively on lexical information and did not appeal to any hierarchical syntactic representations. The current MEG study was designed to dissociate the two interpretations of Ding et al.'s results. Taking advantage of the morphological richness of Russian, we constructed two types of sentences of different syntactic structure; critically, this was achieved by manipulating a single affix on one of the words while all other lexical roots and affixes in the sentence were kept the same. In Experiment 1, we successfully verified the intuition that due to almost complete lexical overlap the two types of sentences should yield the same activity pattern according to Frank and Yang's (2018) lexico-semantic model. In Experiment 2, we recorded Russian listeners' MEG activity while they listened to the two types of sentences. Contradicting the hierarchical syntactic account and consistent with the lexico-semantic one, we observed no difference across the conditions in the way participants tracked the stimuli properties. Corroborated by other recent evidence, our findings show that peaks interpreted by Ding et al. as reflecting higher-level syntactic constituency may stem from non-syntactic factors.