Abstract representations in temporal cortex support generative linguistic processing

Abstract

Generativity, the ability to create and evaluate novel constructions, is a fundamental property of human language and cognition. The productivity of generative processes is determined by the scope of the representations they engage. Here we examine the neural representation of reduplication, a productive phonological process that can create novel forms through patterned syllable copying (e.g. ba-mih → ba-ba-mih, ba-mih-mih, or ba-mih-ba). Using MRI-constrained source estimates of combined MEG/EEG data collected during an auditory artificial grammar task, we identified localized cortical activity associated with syllable reduplication pattern contrasts in novel trisyllabic nonwords. Neural decoding analyses identified a set of predominantly right hemisphere temporal lobe regions whose activity reliably discriminated reduplication patterns evoked by untrained, novel stimuli. Effective connectivity analyses suggested that sensitivity to abstracted reduplication patterns was propagated between these temporal regions. These results suggest that localized temporal lobe activity patterns function as abstract representations that support linguistic generativity.

Keywords: abstraction; effective connectivity; language; magnetoencephalography; neural decoding; phonology; representation; variable.

Fig. 1:. Event-related cortical activation and regions of interest (ROIs).

(A) Spatial distribution of estimated activity, averaged across all conditions and subjects for the interval of 100-500 ms after the stimulus onset. The activity is visualized on the lateral view of averaged inflated cortical surfaces. The color scale indicates the percentile of the activation magnitude among all source locations. (B) ROIs identified based on the estimated spatiotemporal patterns of activity. Color coding indicates regions that in subsequent analyses showed reliable activation differences (green), successful decoding (yellow), or both (magenta, region L-STG₁) across all reduplication pattern contrasts. The other regions (pale blue) showed neither activation differences nor decoding. Descriptive names and locations of the ROIs are given in Fig. S1 and Table S1.

Fig. 2:. Time courses of pairwise activation contrasts and decoding accuracy between conditions with different reduplication patterns.

(A) Activation differences (t-values) between the experimental conditions for all ROIs as a function of time. Dotted vertical lines indicate the onset time of a repeated syllables. The cortical lobes where the ROI resided are indicated by colors in the column at left; names of the ROIs can be found in Fig. S2. (B) Pairwise decoding accuracy (t-values) between conditions. (C) Decoding accuracy (blue: %-correct; yellow: t-values) for the 8 ROIs that reliably supported decoding of reduplication contrasts, shown for the AAB versus ABB comparison. Shaded regions mark the results of cluster-based permutation test for statistically significant decoding accuracy across the subjects (p < 0.05).

Fig. 3:. Cortical information flow associated with reduplication.

Effective connectivity between the 8 ROIs that supported reliable decoding of reduplication contrasts in the interval of 100-250 ms after the onset of the second syllable in which reduplication of the second syllable (A) created stronger information flow (solid lines) or (B) weaker information flow (dashed lines). Line color reflects the source of information flow. In both cases, only those connections are depicted that showed significant differences between conditions in both AAB-ABA and AAB-ABB contrasts, as measured by Granger causality analysis (p < 0.05, FDR-corrected).