Segmentation and selection contribute to local processing in hierarchical analysis.

The present study examined the role of segmentation and selection processes when we respond to local elements in hierarchical stimuli. The ease of segmentation and selection of an individual local element from hierarchical patterns was manipulated by making one local element substantially distinct from the others in colour. Experiment 1 showed that, when attention was spread across the global and local levels in a divided attention task, the introduction of the local red element speeded responses to local targets but slowed responses when targets appeared at the global level. Experiment 2 used a selective attention task in which subjects responded only to the local or the global shapes across a block of trials. Under these circumstances, the local red element reduced global-to-local interference in addition to speeding local responses. The results suggest that the efficiency with which local elements are segmented and selected affects responses to local aspects of hierarchical patterns; furthermore, the effect of local pop-out on global processing is contingent on top-down attentional control settings.