‘Constituent length’ effects in fMRI do not provide evidence for abstract syntactic processing

Abstract

AbstractHow are syntactically and semantically connected word sequences, or constituents, represented in the human language system? An influential fMRI study, Pallier et al. (2011, PNAS), manipulated the length of constituents in sequences of words or pseudowords. They reported that some language regions (in the anterior temporal cortex and near the temporo-parietal junction) were sensitive to constituent length only for sequences of real words but not pseudowords. In contrast, language regions in the inferior frontal and posterior temporal cortex showed the same pattern of increased response to longer constituents—and similar overall response magnitudes— for word and pseudoword sequences. Based on these results, Pallier et al. argued that the latter regions represent abstract sentence structure. Here we identify methodological and theoretical concerns with the Pallier et al. study and conduct a replication across two fMRI experiments. Our results do not support Pallier et al.’s critical claim of distinct neural specialization for abstract syntactic representations. Instead, we find that all language regions show a similar profile of sensitivity to both constituent length and lexicality (stronger responses to real-word than pseudoword stimuli). In addition, we argue that the constituent length effect in these experiments i) is not readily grounded in established theories of sentence processing, and ii) may not actually derive from syntactic structure building, but may instead reflect the temporal receptive window of the human language system.Significance StatementAn influential study (Pallier et al., 2011, PNAS) has been widely interpreted as evidence that inferior frontal and posterior temporal brain regions perform abstract syntactic processing during language comprehension, independent of lexical content. Here we identify theoretical, empirical, and methodological concerns with the original study and conduct a replication across two experiments. Contrary to Pallier et al. (2011), we find evidence that both syntactic and lexical processing are distributed throughout the human language network, consistent with prior arguments for a highly lexicalized and distributed human language processing system.