Neurophysiological and behavioral correlates of language processing and hemispheric specialization

The purpose of this study was to examine language organization in the brain by using a series of three tasks concurrent with event-related potentials (ERPs) to investigate both hemispheric differences and interhemispheric interactions. Experiment 1 was a lexical decision task with semantic priming with four conditions for unilaterally-presented targets: (1) primed words (2) unprimed words (3) pronounceable non-words and (4) non-pronounceable non-words. Participants determined whether the target was a word. ERPs, including the late positive component (LPC) and the N400, were measured to examine neurophysiological correlates of cognitive processes that occurred during the tasks. Experiment 2 addressed methodological concerns by changing the task from primed lexical decision to primed delayed matching, where participants determined whether a second target stimulus matched the first. By delaying the decision-making process, component overlap between the LPC and N400 should be reduced. Experiment 3 used only word stimuli in a primed delayed matching task with bilateral presentations of redundant or non-identical targets to further explore interhemispheric effects.; A total of 49 undergraduates participated in one of three experiments. Behavioral and ERP results illustrate the facilitative effects of semantic priming for both hemispheres. An overall right visual field (RVF) advantage emerged for behavioral, but not ERP, measures indicating left hemisphere (LH) superiority for these language tasks. Both Experiments 1 and 2 revealed a strong hemispheric difference in N400 amplitudes for processing of pronounceable versus non-pronounceable non-words, consistent with previous behavioral findings supporting LH capability and right hemisphere (RH) inability for grapheme-to-phoneme processing. Experiment 2 reduced component overlap, but also changed the pattern of ERP findings for the four conditions. Behavioral priming effects were clearly indicated with bilateral different presentations in Experiment 3, while ERP evidence appeared to support interhemispheric cooperation.; Overall, the findings from this study support a relative rather than absolute hemispheric specialization for language processing. Despite an overall RVF (LH) advantage, both hemispheres were capable of performing the tasks and benefited from semantic priming.