Luminance-defined edges or bars are among the basic units of visual analysis: a "primitive" component of perception. We have utilized this stimulus in a psychophysical study of bar orientation discrimination in the cat before and after selective lesions in visual cortical areas. The cortices have been divided on the basis of their connectivity into three tiers. Tier I refers to areas 17 and 18, tier II includes areas that receive directly from tier I, and tier III includes those areas that receive directly from tier II. Previous studies (Vandenbussche et al.  J. Comp. Neurol. 305:632-658) have shown that the discrimination of bar orientation depends heavily upon the integrity of areas 17 and 18 (tier I). The present study indicates that several extrastriate areas in tiers II and III contribute to this discrimination task. Our data suggest that the anterior medial lateral suprasylvian, the posterior lateral lateral suprasylvian (tier II), and the anterior lateral lateral suprasylvian (tier III) areas are most likely to contribute to bar orientation discrimination.