Neural Correlates of Implicit and Explicit Metaphors: An ERP Study
Dr. Gwenda Schmidt, Hope College
Due to the often unfamiliar nature of metaphors as well as the greater semantic distance between the two concepts being linked, many have hypothesized that figurative language is processed in the right hemisphere (RH) (Jung-Beeman, 2005; Schmidtet al., 2007). However, there have been many contradictory findings in this regard. One factor not previously considered is the existence of different type of metaphors such as implicit metaphors (IM) and explicit metaphors (EM). Our goal was to examine how EM (The veteran professor was a fossil) differ from IM (The teenagers could not relate to the fossil) in their neural processing. Understanding the implicit meaning of a sentence may draw on additional cognitive resources, thereby affecting the difficulty, and perhaps neural pathways involved in processing these sentences. We also wanted determine if the RH is specialized for metaphor processing. We used event-related potentials (ERP) in conjunction with divided visual field presentation to measure the N400 for each sentence as presented to each hemisphere of the brain. ERPs are derived from electroencephalographic (EEG) recordings from the scalp. The N400 is a peak of negative brain activity occurring approximately 400ms after a word, which indexes the ease of semantic processing. We can measure differences in neural processing by observing differences in N400 amplitude across visual field presentation. We conducted an ANOVA with factors of figurativeness, implicitness, and side of presentation using the N400 amplitude as the dependent measure. When IM were presented to the RH, the N400s measured by the parietal lobe electrodes were about the same as those for EM. The left hemisphere (LH) presentation showed much larger N400s for IM than for EM. This suggests that the LH is less efficient at processing IM in comparison to EM while the RH can do both equally well.
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