An fMRI study dissociating distance measures computed by Broca's area in movement processing: clause boundary vs. identity

Andrea Santi,Yosef Grodzinsky,Michiru Makuuchi,Angela D Friederici

doi:10.3389/fpsyg.2015.00654

Abstract

Behavioral studies of sentence comprehension suggest that processing long-distance dependencies is subject to interference effects when Noun Phrases (NP) similar to the dependency head intervene in the dependency. Neuroimaging studies converge in localizing such effects to Broca's area, showing that activity in Broca's area increases with the number of NP interveners crossed by a moved NP of the same type. To test if NP interference effects are modulated by adding an intervening clause boundary, which should by hypothesis increase the number of successive-cyclic movements, we conducted an fMRI study contrasting NP interveners with clausal (CP) interveners. Our design thus had two components: (I) the number of NP interveners crossed by movement was parametrically modulated; (II) CP-intervention was contrasted with NP-intervention. The number of NP interveners parametrically modulated a cluster straddling left BA44/45 of Broca's area, replicating earlier studies. Adding an intervening clause boundary did not significantly modulate the size of the NP interference effect in Broca's area. Yet, such an interaction effect was observed in the Superior Frontal Gyrus (SFG). Therefore, the involvement of Broca's area in processing syntactic movement is best captured by memory mechanisms affected by a grammatically instantiated type-identity (i.e., NP) intervention.

Highlights

There is extensive evidence that Broca’s area is taxed by sentences with movement both from neuropsychological studies of patients and neuroimaging studies of healthy adults (Just et al, 1996; Stromswold et al, 1996; Caplan et al, 1999; Ben-Shachar et al, 2003, 2004; Fiebach et al, 2005; Grewe et al, 2005)
The novel result that this study presents is that while Broca’s area is sensitive to the number of type-identical interveners in long distance wh-movement, this effect is not augmented by a clausal boundary
The current parametric study manipulated the number of Noun Phrases (NP) interveners in a movement dependency while manipulating the presence of a clausal boundary across such a dependency

Summary

Introduction

There is extensive evidence that Broca’s area is taxed by sentences with movement both from neuropsychological studies of patients and neuroimaging studies of healthy adults (Just et al, 1996; Stromswold et al, 1996; Caplan et al, 1999; Ben-Shachar et al, 2003, 2004; Fiebach et al, 2005; Grewe et al, 2005) Less complex relations, such as simple phrasal composition and local agreement have been shown to activate/depend on this region (Pallier et al, 2011; Carreiras et al, 2012), they have not done so as consistently across methods and populations, as movement (for lack of evidence for simple composition in imaging see Humphries et al, 2005; Brennan et al, 2012). While many theoretical positions have been put forth in accounting for this effect, we will argue for the strength of an interference-based account, where interveners are of the same syntactic/semantic type as the moved phrase (type-identical interference ), as opposed to others, for example the number of iterations of a local movement operation

Methods

Results

Discussion

Conclusion