Functional neuroimaging of grammatical class: Ambiguous and unambiguous nouns and verbs

Abstract

Neuropsychological and neuroimaging studies of grammatical-class differences suggest that nouns and verbs may be associated with different brain regions. The current functional magnetic resonance imaging (fMRI) study focused on auditory grammaticality judgements of two-word stimuli consisting of noun/verb ambiguous and unambiguous nouns and verbs preceded by either “the” or “to”. The fMRI results showed effects of class ambiguity in the left inferior frontal gyrus, possibly due to greater selection demands, and effects of grammaticality (“yes” vs. “no” response) in left superior temporal gyrus, consistent with greater activation for trials with greater conflict. In addition, posterior left temporal lobe regions showed increased activity on unambiguous trials for verbs than for nouns, consistent with prior imaging studies. Thus, in a task specifically focused on the grammatical (rather than semantic) aspects of words and that used morphologically simple nouns and verbs controlled for imageability, verbs preferentially activated posterior temporal but not frontal lobe regions. However, for ambiguous trials in this same region, nouns showed greater activation than verbs, suggesting that these effects can be modulated by class ambiguity.

Keywords:

• Neuroimaging
• Neuropsychology
• Grammatical class

The support of the National Institute on Deafness and Other Communication Disorders (under Grant NIH DC R01–00262 to the University of Maryland School of Medicine) is gratefully acknowledged. We appreciate the valuable contribution of Xuanxuan Su to implementing the experimental design and data analysis. The authors are grateful to Michele Miozzo and an anonymous reviewer for helpful comments on the manuscript.

Martha W. Burton passed away in August, 2008, shortly after completing the revisions to this manuscript.

Notes

¹ In some cases, these ROIs may have underestimated the size of a cluster, as one large part of it may have been located in the left STG with a smaller part in the left MTG. As a result of this split, the MTG activation may not have emerged in the analysis. However, a check of the output of the voxelwise ANOVAs indicated that this underestimation did not fundamentally change the outcome of the study, as only small portions of a cluster were cut off in any of the ROIs.

² In addition to the ROI analyses, we also used the same ANOVA design to investigate regions outside our defined ROIs. Most of the significant activation demonstrated in this whole brain analysis occurred in medial areas not typically associated with word processing (cingulate, medial frontal gyrus, cerebellum). In particular, we found no significant activation in the left inferior temporal area, a region outside our ROIs that had been identified in previous studies.

³ We also used BA 41 and 42 as an ROI to capture primary auditory activation. Unlike the TTG ROI, some voxels in the ROI defined by Brodmann areas overlapped with the STG ROI in the main analysis. Nevertheless, whether auditory cortex activation was measured using the TTG or Brodmann area ROIs, all six conditions produced roughly the same volume of activation on average.

⁴ This interpretation was suggested by Michele Miozzo.