Varieties of vision: from blind responses to conscious recognition.

Lesions in consecutive parts of the visual system cause visual deficits that spare increasingly complex residual functions. Patients with lesions up to and including primary visual cortex can show neuroendocrine, reflexive, implicit and forced-choice responses to visual stimulation but no conscious vision. In contrast, patients with lesions in higher visual cortical areas have conscious vision. Its lowest level is that of phenomenal vision, followed by object vision and recognition. These levels are dissociable. They require the integrity of different parts of the system.