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Anthony Cate, Xiaojian Kang, Timothy Herron, David Woods; Part-whole integration of 2D shapes in the hippocampus and the basal ganglia. Journal of Vision 2011;11(11):1094. doi: https://doi.org/10.1167/11.11.1094.
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Subcortical structures including the hippocampus and the basal ganglia support learning and memory for specific spatial or temporal configurations of discrete items. This fMRI study (N = 18) found that this role extends to online perceptual representation of configurations of local parts of 2D planar shapes. Stimuli for passive viewing consisted of one set of shape parts, which were combined differently in different epochs to create different numbers of unique whole shapes. Parts forming the top and bottom of an abstract shape were joined by a convex region to promote perceptual unitization. Stimuli were presented sequentially at 2 Hz during 16-second epochs. There were three kinds of stimulus sets: a set with 4 unique shapes created from a set of 4 parts (two unique top parts, two unique bottom parts); 4 shapes from 8 parts; and 16 shapes from 8 parts. All parts and whole shapes appeared with equal frequency in all conditions. We analyzed activation corresponding to two independent measures of part/whole sensitivity: 1) sensitivity to greater diversity of either parts or whole shapes in an epoch; 2) sensitivity to greater frequency of 1-back repetition of parts or wholes within an epoch. Greater diversity of whole shapes, but not parts, activated the hippocampus and caudate nucleus bilaterally. The body of the caudate, but not the hippocampus, was positively activated by 1-back repetition of the same part in the context of two different wholes. No such effects were seen for repetitions of whole shapes. Together these results show that 1) the hippocampus is preferentially active during passive viewing of sets of simple shapes that have component parts in common, and which are distinguished only by the specific configurations of the parts; 2) the basal ganglia network plays a role in supporting perceptual representations of objects composed of distinct subunits.
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