Interhemispheric relations in hierarchical perception: a second look.

This study reevaluates the role of interhemispheric interactions in the consistency effect (global interference with local decisions) in hierarchical perception. In an earlier study, Robertson et al. [22] (Neuropsychology, Vol. 7, pp. 325-342, 1993) tested three split-brain patients on a hierarchical perception task in which stimuli, consisting of large (global) letters made up of smaller (local) letters, were unilaterally or bilaterally presented for identification. They found that, in general, the consistency effect did not occur in split-brain patients and argued that the effect is interhemispheric and normally mediated by the corpus callosum. We repeated the experiment with new stimuli in two of the same split-brain patients. We found that both patients demonstrated evidence for global interference, implying that the neocortical commissures are not necessary for eliciting the consistency effect in hierarchical perception.