Selective attention to global and local levels in the comparison of hierarchical patterns

Selective attention to the global and the local levels of hierarchical patterns was studied, using a simultaneous comparison task. Subjects were asked to determine whether two simultaneously presented patterns were the same or different at the designated level. On half of the trials the comparison outputs on the two levels were compatible, and on the other half they were incompatible. With patterns composed of many relatively small elements, global and local sameness and difference were detected equally fast in the compatible trials. When incompatible output was present, irrelevant global sameness and difference interfered with "same"/'different" judgments on the local elements and on texture, but not vice versa. With patterns composed of a few relatively large elements, global dominance was observed in the compatible trials. In the incompatible trials the interference from conflicting irrelevant output was mutual and affected mostly "same" judgments. These results are discussed in terms of the interaction between the separability and integrality of the dimensions involved and task demands. It is proposed that dimensional analysis is necessary but not sufficient for successful selective attention to a stimulus dimension.