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Tingting Liu, Sheng He, Peng Zhang, Gordon Legge; Different tactile stimuli produce different activation patterns in occipitotemporal cortex. Journal of Vision 2011;11(11):781. doi: 10.1167/11.11.781.
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Activity in visual cortex with tactile perception has been observed in people with normal or impaired vision. The functional significance of this activity is unclear. In this fMRI study, we ask whether different tactile stimuli produce distinguishable multi-voxel activation patterns in occipitotemporal cortex, and whether these patterns differ for normally sighted and visually impaired subjects. In separate block-designed scans, three types of tactile stimuli were presented to contrast shapes (“X” vs. “O”), spatial configuration (two dots placed in quadrants 1, 3 vs. 2, 4 defined by a “plus”), and orientation (horizontal vs. vertical bars). Subjects performed tactile shape, distance, and orientation tasks for these three types of stimuli with their eyes closed. Preliminary data from four normally sighted subjects and one low vision subject revealed activation in somatosensory and motor cortex and multiple regions of visual cortex, including primary visual cortex, lateral occipital cortex (LOC) and inferior temporal cortex (IT). Seven regions of cortex were selected as regions of interest (ROIs): foveal representation near the occipital pole, LOC, IT from each hemisphere and the left somatosensory cortex representing the right index finger. Spatial patterns of voxel activity were extracted for each type of stimulus from these ROIs. Correlations were computed between these patterns from the same stimulus category (e.g. X-X) versus different stimulus categories (e.g. X-O). In the LOC and IT, there is evidence of higher within-category correlations than across-category correlations in the shape discrimination experiment, consistent with their multimodal function in processing shapes. In the fovea ROI, the correlations were higher in the spatial configuration experiment than in the shape experiment (0.44 vs. 0.26), perhaps indicating that retinotopic cortex is more involved with tactile configuration than shape. The correlation analysis did not reveal a definitive difference between our low vision subject and the normally sighted subjects.
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