Are abstract action words embodied? An fMRI investigation at the interface between language and motor cognition

Abstract

The cognitive and neural representation of abstract words is still an open question for theories of embodied cognition. Generally, it is proposed that abstract words are grounded in the activation of sensorimotor or at least experiential properties, exactly as concrete words. Further behavioral theories propose multiple representations evoked by abstract and concrete words. We conducted a functional magnetic resonance imaging (fMRI) study to investigate the neural correlates of concrete and abstract multi-word expressions in an action context. Participants were required to read simple sentences which combined each concrete noun with an adequate concrete verb and an adequate abstract verb, as well as an adequate abstract noun with either kind of verbs previously used. Thus, our experimental design included a continuum from pure concreteness to mere abstractness. As expected, comprehension of both concrete and abstract language content activated the core areas of the sensorimotor neural network namely the left lateral (precentral gyrus) and medial (supplementary motor area) premotor cortex. While the purely concrete multi-word expressions elicited activations within the left inferior frontal gyrus (pars triangularis) and two foci within the left inferior parietal cortex, the purely abstract multi-word expressions were represented in the anterior part of left middle temporal gyrus that is part of the language processing system. Although the sensorimotor neural network is engaged in both concrete and abstract language contents, the present findings show that concrete multi-word processing relies more on the sensorimotor system, and abstract multi-word processing relies more on the linguistic system.

Keywords: abstract; concrete; fMRI; language comprehension; sensorimotor cortex.

Figure 1

Experimental design with an exemplary stimuli combination (A) and trial procedure (B). Each noun referring to a graspable object, preceded by a determinative or non-determinative article, was combined with an adequate motor verb as well as an adequate non-motor verb, and an adequate noun referring to a non-graspable entity was combined with the same verbs previously used, e.g., “einen Schmetterling malen” (to draw a butterfly), CC—“einen Schmetterling bestaunen” (to marvel at a butterfly), CA—“den Sonnenuntergang malen” (to draw the sunset), AC—“den Sonnenuntergang bestaunen” (to marvel at the sunset), AA. Note that according to the German word order the noun is presented first followed by the verb. Due to the variable onset delay (jitter) the trial duration was 2500 ms at minimum to 4500 ms at maximum.

Figure 2

Absolute activations resulting from functional localizer task and experimental task. Activations from finger tapping task compared to rest (red), activations from the presentation of abstract and concrete multi-word expressions (CC+AA) in the experimental task compared to rest (blue), and overlapping areas of the functional localizer task and the experimental tasks (green) as revealed by a conjunction analysis. Images were thresholded at p < 0.05, FWE corrected for the whole brain volume, superimposed on representative sagittal, coronal and axial slices of the MNI template using the software MRIcron Version 12/2012 (http://www.mccauslandcenter.sc.edu/mricro/mricron/index.html).

Figure 3

Direct contrasts of concreteness vs. abstractness. Differences between processing concrete noun-verb combinations (top panel) compared to abstract noun-verb combinations (bottom panel) and extracted contrast values for the pure abstract, the summarized mixed conditions and the pure abstract condition from defined local maxima. Note that for visualization the statistical images were thresholded at p < 0.001, uncorrected, with an extended cluster size of ≥45 contiguous voxels (360 mm³), superimposed on the MNI template using the software MRIcron Version 12/2012 (http://www.mccauslandcenter.sc.edu/mricro/mricron/index.html). The contrast values were extracted from the individual beta images and are depicted as group mean with standard deviation of the mean. Asterisks indicate statistical differences of post-hoc paired t tests (p < 0.05, Bonferroni-corrected for multiple comparisons).