Representations of conceptual information during automatic and active semantic access

Abstract

When we read a word or see an object, conceptual meaning is automatically accessed. However, previous research investigating non-perceptual sensitivity to semantic class has employed active tasks. In this fMRI study, we tested whether conceptual representations in regions constituting the semantic network are invoked during passive semantic access and whether these representations are modulated by the need to access deeper knowledge. Seventeen healthy subjects performed a semantically active typicality judgment task and a semantically passive phonetic decision task, in both the written and the spoken input-modalities. Stimuli consisted of one hundred forty-four concepts drawn from six semantic categories. Multivariate Pattern Analysis (MVPA) revealed that the left posterior middle temporal gyrus (pMTG), posterior ventral temporal cortex (pVTC) and pars triangularis of the left inferior frontal gyrus (IFG) showed a stronger sensitivity to semantic category when active rather than passive semantic access is required. Using a cross-task training/testing classifier, we determined that conceptual representations were not only active in these regions during passive semantic access but that the neural representation of these categories was common to both active and passive access. Collectively, these results show that while representations in the pMTG, pVTC and IFG are strongly modulated by active conceptual access, consistent representational patterns are present during active and passive conceptual access in these same regions.

Keywords: BA45; Semantic representations; Words; fMRI; pMTG; pVTC.

Figure 1

Tasks. (A) Phonetic decision task, (B) Typicality judgmental task.

Figure 2

Schematic overview of all whole-brain decoding analysis performed. For each decoding MVP analysis, the type of trials adopted during training and testing phase are provided.

Figure 3

Univariate analysis. 3D rendering of the main effect of task: (A) Typicality > Phonetic task and (B) Phonetic > Typicality task. The significance level was set at voxel-level threshold of uncorrected p < 0.001, combined with cluster-level inference of p < 0.05 corrected for the whole brain volume.

Figure 4

Amodal representations of category. 3D rendering of the whole-brain crossmodal category decoding for (A) typicality and phonetic tasks and (B) typicality task only. No significant clusters for the phonetic task only were detected. (C) Axial and (D) Sagittal slices showing binary map of the wholebrain crossmodal decoding for both tasks (red), typicality task (green) and the overlap between the two maps (yellow). The significance level was set at voxel-level threshold of uncorrected p < 0.001, combined with cluster-level inference of p < 0.05 corrected for the whole brain volume.

Figure 5

Enhanced category-sensitive for active access compared to passive access. Decoding accuracy difference (above chance) between typicality and phonetic task for each ROI derived from the searchlight decoding for both tasks. Error bars indicate standard error of the mean. * corresponds to p < .05, ** corresponds to p < .01, *** corresponds to p < .001. Abbreviations: PFC: prefrontal cortex; IPS: intraparietal sulcus; OFC: orbitofrontal cortex; VTC: ventral temporal cortex; pMTG: posterior middle temporal gyrus.

Figure 6

Task-general conceptual representations within ROIs derived from the searchlight crossmodal decoding for the typicality task only. Above chance mean decoding accuracy of a crosstask and cross-modal decoding analysis. Error bars indicate standard error of the mean. * corresponds to p < .05, ** corresponds to p < .01, *** corresponds to p < .001. Abbreviations: VTC: ventral temporal cortex; pMTG: posterior middle temporal gyrus; pSTG: posterior superior temporal gyrus.