One of the most well-established findings in human neuropsychology is the superiority of the left cerebral hemisphere for language processing. However, it has become evident that the right hemisphere is not uninvolved in language use. Research conducted in our laboratory over the past 25 years indicates that the right hemisphere makes unique contributions to linguistic processing, and that the full complement of language abilities requires both hemispheres of the brain.
Some of our most important findings are:
- When word meanings are accessed, semantically related word meanings are activated in both the left and right hemispheres. However, a broader set of related meanings remains accessible within the right hemisphere; within the left hemisphere only the most relevant meanings are maintained. This suggests that the right hemisphere is important for maintaining multiple meanings of ambiguous words, distant semantic associations of words, and broader aspects of meaning comprehension. Such functions may be important for the ability to revise initial interpretations of words or phrases, maintaining discourse coherence, and understanding multiple levels of meaning.
- The right hemisphere also contributes to the comprehension of sentences, and is sensitive to some semantic and grammatical features of sentences including sentence anomaly, number agreement, and form class expectancy.
- Both the left and right hemispheres are involved in comprehending metaphors, at least metaphors that are familiar (work of Natalie Kacinik). This includes metaphors that are conveyed using a single word, as well as phrasal metaphors.
- Some of the same right hemisphere processes that are used in comprehension, may also be used in word selection during language production. These studies utilized the verb generation task, and indicated a broader activation of potentially relevant responses when word retrieval is initiated by the right hemisphere.
- The right hemisphere may also be involved in the acquisition of meanings for newly learned words (work of Travellia Tjokro). This has been investigated by teaching participants words in a new language (“Lingo”), and exploring the extent to which the newly learned words can be primed, and prime other related meanings, within each hemisphere.
- During the earliest moments of word recognition, phonological information is available only within the left hemisphere (work of Laura Halderman). However, orthographic information is available within the right hemisphere at the earliest moments probed, and phonological information becomes available to the right hemisphere somewhat later.
This research has been funded by grants from the National Science Foundation (BCS-0079456, SBR-9729009), the U.S.-Israel Binational Science Foundation, and the National Institutes of Mental Health (MH438868). Collaborators on these studies include Dr. Miriam Faust (Bar-Ilan University), Dr. Curt Burgess (UCR), and Dr. Mark Beeman (Northwestern University).