Functional involvement of subcortical structures in global-local processing.

The present study examined the involvement of subcortical structures in the processing of global and local information. To this end, we used a stereoscope to present hierarchical stimuli (global shapes composed of local elements) in a dichoptic or a monocular fashion, such that global and local information was either presented to the same eye (same-eye condition) or segregated between the eyes (different-eyes condition). In Experiment 1, the typical global advantage and global-to-local interference were observed for the same-eye presentation condition. On the other hand, no indication of a global advantage or of global-to-local interference emerged in the different-eyes presentation condition. In Experiment 2 we replicated these results, ruling out a possible alternative explanation that the pattern of results observed for the different-eyes presentation condition resulted merely from segregation of the stimulus between the eyes. Rather, the experiment demonstrated that the global-to-local interference was eliminated only when global and local information was segregated between the eyes. Taken together, these findings suggest that processing the global aspect of hierarchical stimuli involves subcortical regions indexed by monocular portions of the visual system.