Language comprehension: The interplay between form and content

Language Comprehension: The Interplay between Form and Content Vasiliki Folia a,b,c (vasiliki.folia@fcdonders.ru.nl) Christian Forkstam a,b,c (christian.forkstam@ki.se) Peter Hagoort a,c (peter.hagoort@fcdonders.ru.nl) Karl Magnus Petersson a,b,c,d (karl-magnus.petersson@mpi.nl) a Max Planck Institute for Psycholinguistics, Nijmegen, the Netherlands b Stockholm Brain Institute, Karolinska Institutet, Stockholm, Sweden c Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen, the Netherlands d Cognitive Neuroscience Research Group, Universidade do Algarve, Faro, Portugal Abstract In a 2x2 event-related FMRI study we find support for the idea that the inferior frontal cortex, centered on Broca’s region and its homologue, is involved in constructive unification operations during the structure-building process in parsing for comprehension. Tentatively, we provide evidence for a role of the dorsolateral prefrontal cortex centered on BA 9/46 in the control component of the language system. Finally, the left temporo-parietal cortex, in the vicinity of Wernicke’s region, supports the interaction between the syntax of gender agreement and sentence-level semantics. Keywords: FMRI; syntax; semantics; language comprehension; Broca’s region; Wernicke’s region; inferior parietal region Introduction Humans encounter many new and unexpected sentences in everyday life and typically interpret them without cognitive effort. This ability is grounded in a peculiar biological system, part of the human brain, called the faculty of language. Most current models of language processing agree that different types of constraints are rapidly utilized in on- line sentence processing (Hagoort, 2005). Constraints on how words can be structurally combined operate interactively and in parallel with qualitatively distinct constraints on the combination of word meanings, the grouping of words into phonological phrases, and their referential binding in discourse models (Jackendoff, 2007). Most models make a distinction between retrieval and combinatorial/compositional processes, implying that sentences have internal structure. Retrieval entails lexical selection from the mental lexicon, a specific long-term memory store. Lexical representations include knowledge about lexical form, syntactic properties (e.g., constituent class, syntactic gender etc.), and lexical meaning. The creative aspect of language is in part captured by its generative structure-building processes which create sentence-internal structure that represents for example who did what to whom and how. A recent trend in theoretical linguistics suggests that the separation between lexical items and traditional rules of grammar is fading and increasing support for these so-called lexicalized models have accumulated. In lexicalized models of parsing, the properties of words needed for sentence level integration are retrieved from the mental lexicon in the form of structured primitive representations (e.g., treelet) and only relatively generic structure building operations like unification (Vosse & Kempen, 2000), unify-pieces (Culicover & Jackendoff, 2005), or merge (Chomsky, 2005) are necessary to complete the on-line combinatorial integration process. Vosse and Kempen (2000) proposed a computationally explicit lexicalist unification space model that accounts for a large range of empirical findings in the parsing- and neuropsychological aphasia literature. According to this unification space model, every incoming word retrieves lexical frames (elementary syntactic trees) that specify possible structural environments for input words. When retrieved, these lexical frames enter the unification space in a sequential fashion and are integrated interactively and in parallel in a unification process in which lexical frames are dynamically linked and various constraints, like agreement and linear order constraints, are applied (Kempen & Harbusch, 2002). A key question in our understanding of language is whether and where in the human brain the different levels are localized and processed as well as whether and where they interact. Understanding where, how, and when the linguistic subcomponents are interacting in order to provide a coherent interpretation is a fundamental challenge in the neurobiological study of the language faculty (Chomsky, 2005). It is well-accepted that large regions within the frontal, temporal, and temporo-parietal cortices are involved in language processing. The temporal and temporo-parietal cortices play a central role in both short-term verbal memory (e.g., Petersson et al., 2009), storage and retrieval of lexical information, that has been encoded during language acquisition (Indefrey & Cutler, 2005). Based on a meta-analysis of syntactic processing (Indefrey, 2004), Hagoort (2005) suggested that the left posterior temporal cortex is involved in the retrieval of lexical frames that form the building blocks for syntactic unification, which he argued, is supported by the left inferior frontal cortex (LIFC). Functional magnetic resonance imaging (FMRI) evidence support the role of the LIFC in the unification operations that are performed at the structural/syntactic (Petersson et al., 2004; Snijders et al., 2008) and