Poster A37, Tuesday, August 20, 2019, 10:15 am – 12:00 pm, Restaurant Hall
Here and there, what and where: investigating the role of the dorsal visuospatial stream in linguistic spatial encoding.
Roberta Rocca1,2, Marlene Staib1, Kristian Tylén1,2, Kenny Coventry3, Torben Lund4, Mikkel Wallentin1,2,4;1Department of Linguistics, Cognitive Science and Semiotics, Aarhus University, 2Interacting Minds Center, Aarhus University, 3School of Psychology, University of East Anglia, 4Center of Functionally Integrative Neuroscience, Aarhus University Hospital
INTRODUCTION: Literature on spatial language suggests that the neural underpinnings of spatial expressions and non-linguistic spatial processing overlap along dorsal visuospatial pathways. Taken together, these results might suggest that language processing is generally organized along a ventral-dorsal divide between neural substrates for semantics and spatial relations mirroring the distinction between object identification and location in vision. This hypothesis has been formulated on a theoretical basis, but the existence of a dorsal stream for language processing has never been addressed empirically. In our study, we aimed at explicitly testing this question on a naturalistic fMRI dataset with near word-level temporal resolution (TR=388ms). METHODS: We conducted a fast-fMRI experiment where 28 participants listened to a dialogue with highly frequent occurrences of wh-words (“where”, “what”, “who”) and spatial demonstratives (“here”, “there”). Demonstratives are purely spatial words, used to direct attention towards specific locations in the environment on the basis contrastive distance cues (near vs. far). Where, what, and who prime the processing of spatial information, object identity, and personal identity respectively, thus functioning as proxies to the divide between semantics and spatial relations in language. We modelled neural response to each word of interest using FIR models (20 bins, 500ms lags), which yielded 28 (participants) x 20 (time bins) x 5 (word types) beta maps. Each of these maps represented response to a specific word, at a specific time point after stimulus onset, for a specific participant. We computed Pearson’s correlation between beta maps for demonstratives and beta maps for each wh-word for each subject and time point, both at whole-brain level and in 60 AAL regions. This yielded 28 (participants) x 20 (time bins) x 6 (word combinations) correlation values representing similarity in response to each pair of words over 10s after stimulus onset. RESULTS: A linear mixed effects analysis on whole-brain similarity values showed that, as expected, topographical similarity was significantly higher between spatial demonstratives and where compared to what and who. Zooming in on local patterns, we found that higher global similarity was driven by response patterns in superior parietal and frontal areas belonging to the dorsal processing stream, thus speaking in favour of a functional specialization of the dorsal stream for linguistic spatial encoding. DISCUSSION: We interpret our results as suggestive of a functional role of the dorsal stream and related pathways in linguistic encoding of space, as opposed to ventral structures (the “what” stream) supporting semantic and conceptual processing. While a dorsal-ventral divide had been hypothesized before on theoretical grounds, our study is the first to provide direct evidence for the role of the dorsal stream in language processing. Moreover, direct involvement of the visuospatial dorsal stream in linguistic spatial encoding supports distributed accounts on the neurobiology of language processing. Rather than relying on a specialized circuitry, language engages a non-segregated architecture, where neural structures supporting perceptual tasks are dynamically recruited in a context-dependent fashion.
Themes: Meaning: Lexical Semantics, Meaning: Discourse and Pragmatics
Method: Functional Imaging