Sensitivity to effective relational complexity in the occipitoparietal lobe

Previous work identified bilateral regions in the occipitoparietal lobe sensitive to the complexity of relational information [Phillips, S., Niki, K., 2003. Increased bilateral occipitoparietal activity for retention of binary versus unary indexed lists in pair recognition. NeuroImage 20 (2), 1226–1235]. Here, we investigate the effect of learning on sensitivity to relational complexity. Eight subjects were scanned on a pair recognition task before, during and after a 2-week training period when subjects learned to recognize a set of shape pairs. For each trial of the pair recognition task, subjects determined whether a probe pair appeared in a list of learned or novel pairs. In the low/high relational complexity condition, every pair in list AB CD EF/AB AD CB was uniquely identifiable by an item in either/both the first or/and second position. Whole-brain and region of interest contrasts revealed a significant interaction between complexity and learning in the occipitoparietal lobe. The increase in activity for the retention of high versus low complexity lists was greater for learned than novel pair lists. Subjects were more likely to respond to low complexity lists as though they were high complexity prior to training. The results suggest that this region provides a window into effective relational complexity, that is, complexity of relational information as processed by the subject, not as presumed by task design.