Able to name, unable to compare

Abstract
A patient with a lesion of the posterior half of the corpus callosum correctly named simple (e.g. colors) and complex (e.g. faces) stimuli whether presented to one or both hemi-fields. Although proficient at these tasks, and also able to make same/different judgements for stimuli within an hemifield, he failed dramatically when required to compare stimuli between the two hemifields. These results indicate that, while the posterior portion of the corpus callosum may not be essential for naming visual stimuli, it is essential for comparing stimuli between the two visual fields.