Hemispheric differences in processing dichotic meaningful and non-meaningful words.

Classic dichotic-listening paradigms reveal a right-ear advantage (REA) for speech sounds as compared to non-speech sounds. This REA is assumed to be associated with a left-hemisphere dominance for meaningful speech processing. This study objectively probed the relationship between ear advantage and hemispheric dominance in a dichotic-listening situation, using event-related potentials (ERPs). The mismatch negativity (MMN) and a late negativity (LN) were measured for bisyllabic meaningful words and non-meaningful pseudowords, which differed in their second syllable. Eighteen normal-hearing listeners were presented with a repeating diotic standard ([beI-gi:] or [leI-gi:]) and an occasional dichotic deviant (a standard presented to one ear and a deviant [beI-bi:], [beI-di:], [leI-bi:] or [leI-di:] presented to the opposite ear). As predicted there was a REA for meaningful words compared to non-meaningful words. Also, dipole source analysis suggested that dipole strength was stronger in the left than the right cortical region for meaningful words. However, there were differences in response within meaningful words as well as between meaningful and non-meaningful words which may be explained by the characteristics of embedded words and the position-specific probability of phoneme occurrence in words.