Carolyn D. Gershman¹ (), Ted Supalla^1,2, Anna Seydell-Greenwald^1,2, Barbara Landau^1,3, Elissa L. Newport^1,2; ¹Center for Brain Plasticity and Recovery, Georgetown University Medical Center, ²MedStar National Rehabilitation Hospital, ³Johns Hopkins University, Department of Cognitive Science

Native signers have life-long expertise with a visual-gestural language that is produced by movements of the hands through space and constrained by spatial features, such as orientation, movement path, location, and handshape. Because language is typically lateralized to the brain’s left hemisphere, lifelong processing of visual-spatial linguistic features might also result in left-lateralized processing of non-linguistic visual-spatial materials in native signers. Consistent with this hypothesis, behavioral studies have reported enhanced motion, velocity, and orientation discrimination among signers when stimuli are presented in the right visual field, and one fMRI study found a leftward shift in activation of motion processing area MT-MST for native signers viewing moving flow fields. However, few other imaging studies have investigated MT-MST lateralization in signers, and heterogeneous subject samples make interpretation difficult. Here we used fMRI to investigate lateralization for processing coherent motion in 19 deaf native signers and 19 hearing non-signers, contrasting a coherent motion direction judgment task with viewing of static dots (control). Group-level activation maps revealed bilateral MT-MST activation in both deaf and hearing participants and no significant group differences in lateralization (p=0.80). Compared to hearing participants, deaf subjects showed significant activation in auditory motion regions (p=0.002), which was lateralized to the right hemisphere. These results align with auditory deprivation research showing cross-modal changes in the deaf, with RH dominance in auditory motion regions for processing coherent motion. However, the findings do not support previous reports on LH lateralization for visual processing due to life-long sign exposure.