Objectives: Mental rotation is the brain's visuospatial understanding of what objects are and where they belong. Previous research indicated that deaf signers showed behavioral enhancement for nonlinguistic visual tasks, including mental rotation. In this study, we investigated the neural difference of mental rotation processing between deaf signers and hearing nonsigners using blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI).
Design: The participants performed a block-designed experiment, consisting of alternating blocks of comparison and rotation periods, separated by a baseline or fixation period. Mental rotation tasks were performed using three-dimensional figures. fMRI images were acquired during the entire experiment, and the fMRI data were analyzed with Analysis of Functional NeuroImages. A factorial design analysis of variance was designed for fMRI analyses. The differences of activation were analyzed for the main effects of group and task, as well as for the interaction of group by task.
Results: The study showed differences in activated areas between deaf signers and hearing nonsigners on the mental rotation of three-dimensional figures. Subtracting activations of fixation from activations of rotation, both groups showed consistent activation in bilateral occipital lobe, bilateral parietal lobe, and bilateral posterior temporal lobe. There were different main effects of task (rotation versus comparison) with significant activation clusters in the bilateral precuneus, the right middle frontal gyrus, the bilateral medial frontal gyrus, the right interior frontal gyrus, the right superior frontal gyrus, the right anterior cingulate, and the bilateral posterior cingulate. There were significant interaction effects of group by task in the bilateral anterior cingulate, the right inferior frontal gyrus, the left superior frontal gyrus, the left posterior cingulate, the left middle temporal gyrus, and the right inferior parietal lobe. In simple effects of deaf and hearing groups with rotation minus comparison, deaf signers mainly showed activity in the right hemisphere, while hearing nonsigners showed bilateral activity. In the simple effects of rotation task, decreased activities were shown for deaf signers compared with hearing nonsigners throughout several regions, including the bilateral parahippocampal gyrus, the left posterior cingulate cortex, the right anterior cingulate cortex, and the right inferior parietal lobe.
Conclusion: Decreased activations in several brain regions of deaf signers when compared to hearing nonsigners reflected increased neural efficiency and a precise functional circuitry, which was generated through long-term experience with sign language processing. In addition, we inferred tentatively that there may be a lateralization pattern to the right hemisphere for deaf signers when performing mental rotation tasks.