Bilateral eye movements reduce cortical activation asymmetries

Alternating left-right eye movements (EMs) have been shown to enhance episodic memory recall (Christman & Garvey, 2000). In turn, enhanced recall of episodic, or autobiographical, memories has been linked to increased interhemispheric interaction (Christman & Propper, 2001; Propper & Christman, 1997). Since leftward versus rightward EMs induce right versus hemisphere activation, respectively (Bakan & Svorad, 1969), bilateral EMs may facilitate interhemispheric interaction by balancing hemispheric activation levels. In other words, asymmetries in cortical activation may impair interhemispheric communication. Christman and Garvey (2000), however, demonstrated only that bilateral EMs enhance episodic memory performance; they did not directly measure hemispheric activation. To test this hypothesis directly, participants were administered two behavioral tests that are sensitive to variations in hemispheric activation. The Chimeric Faces Test (Levy, Heller, Banich, & Burton, 1983) involves mirror-image pairs of faces, with one smiling hemiface and one neutral hemiface, presented under conditions of free viewing. Participants are asked to judge which member of a pair looks happier. Right versus left hemiface biases are associated with relative increases in left versus right hemispheric activation. Line bisection tasks also tap into hemispheric activation, with leftward versus rightward bisection errors reflecting increased right versus left hemisphere activation. Bisection tasks, however, are also influenced by premotor asymmetries (e.g., Luh, 1995), and thus represent a less pure measure of hemispheric activation.

METHODS Participants performed blocks of chimeric face and line bisection trials. They then engaged in 30 seconds of alternating left-right saccades (2 eye movements per second). Participants then performed a second block of trials for both tasks.

RESULTS Results showed that behavioral asymmetries in the chimeric face task were significantly reduced after the EMs (p

Conference

English

Stehpen Christman
Kilian  Garvey

Christman, S., & Garvey, K. (2001, June). Bilateral eye movements reduce cortical activation asymmetries. Presentation at the 6th EMDR International Association Conference, Austin, TX