Cortical representation of the constituent structure of sentences
- aInstitut National de la Santé et de la Recherche Médicale, Cognitive Neuroimaging Unit, U992,
- bCentre National de la Recherche Scientifique, F-75794 Paris, France;
- cNeuroSpin Center, Commissariat à l'Energie Atomique, Département des Sciences de la Vie/Institut d'Imagerie Biomédicale, and
- dUniversité Paris-Sud, F-91191 Gif/Yvette, France; and
- eCollège de France, F-75005 Paris, France
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Contributed by Stanislas Dehaene, December 15, 2010 (sent for review September 23, 2010)
↵1C.P. and A.-D.D. contributed equally to this work.
Abstract
Linguistic analyses suggest that sentences are not mere strings of words but possess a hierarchical structure with constituents nested inside each other. We used functional magnetic resonance imaging (fMRI) to search for the cerebral mechanisms of this theoretical construct. We hypothesized that the neural assembly that encodes a constituent grows with its size, which can be approximately indexed by the number of words it encompasses. We therefore searched for brain regions where activation increased parametrically with the size of linguistic constituents, in response to a visual stream always comprising 12 written words or pseudowords. The results isolated a network of left-hemispheric regions that could be dissociated into two major subsets. Inferior frontal and posterior temporal regions showed constituent size effects regardless of whether actual content words were present or were replaced by pseudowords (jabberwocky stimuli). This observation suggests that these areas operate autonomously of other language areas and can extract abstract syntactic frames based on function words and morphological information alone. On the other hand, regions in the temporal pole, anterior superior temporal sulcus and temporo-parietal junction showed constituent size effect only in the presence of lexico-semantic information, suggesting that they may encode semantic constituents. In several inferior frontal and superior temporal regions, activation was delayed in response to the largest constituent structures, suggesting that nested linguistic structures take increasingly longer time to be computed and that these delays can be measured with fMRI.
Footnotes
- 2To whom correspondence may be addressed. E-mail: christophe.pallier{at}gmail.com or stanislas.dehaene{at}cea.fr.
Author contributions: C.P., A.-D.D., and S.D. designed research; C.P. and A.-D.D. performed research; C.P., A.-D.D., and S.D. analyzed data; and C.P. and S.D. wrote the paper.
The authors declare no conflict of interest.
See Commentary on page 2177.
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1018711108/-/DCSupplemental.
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