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Poster E22, Saturday, August 18, 3:00 – 4:45 pm, Room 2000AB

Asymmetrical connectivity underlying the right visual field advantage in lateralized lexical decision

Jed Meltzer1,2, Ronald Chu1,2;1Baycrest Hospital, 2University of Toronto

The well established right visual field / left-hemisphere (RVF-lh) advantage in word recognition is commonly attributed to the typical left hemisphere dominance in language; words presented to the LVF-rh are processed less efficiently due to the need for transcallosal transfer from the right to left hemisphere. The exact stage for this hemispheric transfer is currently unsettled. Some studies suggest that transfer occurs at very early stages between primary visual regions, while other studies suggest that transfer occurs between the left visual word form area and its right hemisphere homologue. Other accounts suggest independent processing of LVF words within the right hemisphere. The current study explores these conflicting accounts and finds electrophysiological signatures for all of these interactions. Participants conducted a lateralized lexical decision task with both unilateral and bilateral display conditions. Connectivity analyses were conducted from MEG signals that were localized to the: left middle occipital gyrus (LMOG), right middle occipital gyrus (RMOG), left visual word form area (LVWFA) and right visual word form area (RVWA). Results from unilateral trials showed that early information from LVF-rh words is transferred from RMOG to LMOG, and also proceeds intrahemispherically to RVWA. Later waves of connectivity transfer information symmetrically between the two VWFA homologues. Furthermore, bilateral presentations led to reduced interhemispheric connectivity between both homologous ROI pairs. Together, these results suggest that lateralized word recognition involves multiple stages of interhemispheric interactions and that these interactions are reduced when both hemispheres must process their own stimuli simultaneously.

Topic Area: Perception: Orthographic and Other Visual Processes