Hemispheric asymmetry in event knowledge activation during incremental language comprehension: A visual half-field ERP study

Abstract

During incremental language comprehension, the brain activates knowledge of described events, including knowledge elements that constitute semantic anomalies in their linguistic context. The present study investigates hemispheric asymmetries in this process, with the aim of advancing our understanding of the neural basis and functional properties of event knowledge activation during incremental comprehension. In a visual half-field event-related brain potential (ERP) experiment, participants read brief discourses in which the third sentence contained a word that was either highly expected, semantically anomalous but related to the described event (Event-Related), or semantically anomalous but unrelated to the described event (Event-Unrelated). For both visual fields of target word presentation, semantically anomalous words elicited N400 ERP components of greater amplitude than did expected words. Crucially, Event-Related anomalous words elicited a reduced N400 relative to Event-Unrelated anomalous words only with left visual field/right hemisphere presentation. This result suggests that right hemisphere processes are critical to the activation of event knowledge elements that violate the linguistic context, and in doing so informs existing theories of hemispheric asymmetries in semantic processing during language comprehension. Additionally, this finding coincides with past research suggesting a crucial role for the right hemisphere in elaborative inference generation, raises interesting questions regarding hemispheric coordination in generating event-specific linguistic expectancies, and more generally highlights the possibility of functional dissociation of event knowledge activation for the generation of elaborative inferences and for linguistic expectancies.

Keywords: ERP; Event knowledge; Event-related brain potentials; Hemispheric asymmetry; Language; N400.

Figure 1

Grand average ERPs at the 26 scalp electrodes for the three target word types, for both right visual field / left hemisphere (RVF/LH) and left visual field / right hemisphere (LVF/RH) presentation. Ticks on the x-axis represent 200ms intervals. Negative voltage is plotted up. A diagram of scalp electrode placement is provided. Channels included in analysis of N400 effect amplitudes are underlined. Channels included in the analysis of N400 effect scalp distribution are darkened.

Figure 2

Grand average ERPs at the midline parietal electrode for the three target word types, for both RVF/LH and LVF/RH presentation.

Figure 3

Scalp topographies of mean ERP amplitude from 200–500ms post-stimulus onset. (A) Topographies for target word ERPs. (B) Topographies for the difference ERPs representing the N400 effects for Event-Related and Event-Unrelated target words.

Figure 4

Raster plots representing the results of the mass univariate tests conducted in the 500–900ms window. Time is represented on the x-axis with ticks at 100ms intervals. Electrodes are split into three groups along the y-axis: left hemisphere (top group), midline (middle group) and right hemisphere (bottom group). Electrodes in each group are listed in order of anteriority, with prefrontal at group top and occipital at group bottom. Darkened cells indicate a statistically significant negative deviation from zero in the indicated difference ERP, after FDR control.