The mean (s.d.) d′
in the post-run test was 2.56 (0.74), suggesting that the participants were attentive to the stimuli during the scans. We first describe the fMRI results for the contrasts between the three main conditions, Lit, Met and Abs. The results are displayed on an inflated brain surface using Caret (Van Essen et al., 2001
). A complete listing of the activated areas with coordinates is provided in the Supplemental Material (Part I)
Literal - Abstract
The areas activated to a greater extent by the Lit condition relative to the Abs condition included the left anterior inferior parietal lobule (aIPL; including supramarginal gyrus and postcentral sulcus), left parahippocampal and fusiform gyrus, left precuneus, left posterior middle and inferior temporal gyrus and lateral occipital gyrus, left superior frontal gyrus, left orbitofrontal cortex, bilateral cerebellum and thalamus, as well as the right hippocampus and fusiform gyrus ().
Areas activated by condition contrasts. Yellow-orange scale shows greater activation for the first condition; blue-cyan scale shows greater activation for the second condition in the contrast. L = left hemisphere, R = right hemisphere.
Abs sentences activated the left superior temporal sulcus and the anterior superior temporal gyrus, cuneus, as well as the right angular gyrus.
Metaphor - Abstract
The Met condition activated left aIPL, Rolandic operculum, superior parietal gyrus, and the superior frontal gyrus. The cerebellum and thalamus were activated bilaterally. The right aIPL, parietal operculum, insula, and parahippocampal gyrus were also activated (). No areas were activated to a greater extent for the Abs sentences.
Metaphor - Literal
Compared to Lit sentences, the Met sentences activated the left anterior and posterior cingulate gyrus, cuneus, superior temporal sulcus, and the temporal pole. In the right hemisphere, the aIPL, parietal operculum and the superior parietal gyrus were activated ().
The Lit condition activated the left parahippocampal and fusiform gyrus relative to the Met sentences.
Correlations with Familiarity
To assess the effects of sentence familiarity on the activation, we used the Familiarity Rating as a condition-wise regressor in the analysis. Correlations with familiarity can pinpoint areas involved in the semantic processing, but also areas modulated due to general processing difficulty. To isolate, to the extent possible, activation modulation due to semantic factors, we computed Familiarity × Condition interactions. The regions responding only to general difficulty and task load effects should be modulated similarly in all three conditions and therefore would not show interactions. Indeed, middle and inferior frontal lobe regions, commonly associated with task difficulty effects, were negatively correlated with familiarity in each condition (see Supplemental Material, Part II
) and were absent from the interaction maps. In addition, because our hypotheses concern correlations with Lit or Met familiarity, we applied a mask to the interaction maps that included only voxels that showed a significant correlation with familiarity in Lit or Met conditions.
Literal-Abs × Familiarity
All the regions in this interaction showed negative correlation with familiarity for Lit sentences, and greater negative correlation for Lit than for Abs sentences (cyan and green in ). They included the left anterior inferior frontal gyrus, central sulcus, superior parietal gyrus, and posterior superior temporal sulcus; the right aIPL; and bilateral posterior middle and inferior temporal gyrus, parietal operculum, and SMA.
Figure 3 The overlap of condition contrasts, condition x familiarity interactions, and the motor localizer. Interactions in (a) and (b) show greater negative correlation to familiarity for Lit and Met conditions respectively. Talairach y coordinates are indicated (more ...)
Metaphor-Abstract × Familiarity
Similar to the previous interaction, all areas here showed negative correlations for Met sentences, and greater negative correlations for Met than for Abs sentences. These areas included the left posterior superior temporal sulcus and bilateral central sulcus, SMA, lingual gyrus, and cuneus (cyan and green in ).
Metaphor-Literal × Familiarity
The right supramarginal gyrus and the left superior parietal gyrus showed a significant interaction. The right supramarginal gyrus showed a positive correlation with familiarity for Met, while the left superior parietal gyrus was negatively correlated in the Lit condition (cyan and green in ).
Identical analyses were also carried out using RTs, rather than familiarity ratings, as regressors. No Condition × RT interactions in sensory-motor regions were found after identical application of corrections for multiple comparisons. This suggests that these interactions are unlikely to be due to differences only in the length of action simulations or some form of pre-response motor readiness (although the latter is unexpected in any case because no responses were made during scanning).
Overlap with Localizer
also shows the overlap of the areas activated by the hand localizer task, the condition contrasts, and the Condition × Familiarity interactions. Activations in the central sulcus, aIPL, posterior superior temporal sulcus, posterior middle and inferior temporal gyrus, opercular regions, SMA, thalamus, and cerebellum overlapped the localizer activation (magenta, cyan and white colors). In contrast, activations in the dorsomedial prefrontal region, parahippocampal and fusiform gyrus, middle superior temporal sulcus, and posterior cingulate did not overlap the localizer (red and green colors), and occipital regions partly overlapped. The left posterior middle/inferior temporal region was the only area to show an overlap between the condition contrasts and the familiarity interactions (white color).
A summary of the main results is presented in , where areas commonly and differentially activated between the contrasts and familiarity interactions can be seen.
A summary of the main results. ‘×’ indicates regions that are activated or correlated with familiarity, or overlap with the localizer activation.