Cutting the corpus callosum (split-brain) broadly disrupts functional integration across perception and attention, but some processes like action control remain unified. The key unresolved question is whether split-brain patients have split or unified consciousness. Current evidence is insufficient to decide, and future studies may need to consider intermediate conceptualizations beyond a simple yes or no.
A critical evaluation of recent split-brain experiments argues that claims of unified consciousness in patient D.D.C. are premature. Two distinct conceptions of unity of consciousness are distinguished: agency-based and experience-based. Whether the behavioral data demonstrate unity of agency remains an open question, depending on both the mechanisms underlying split-brain behavior and what constitutes a single agent. Even if agency-based unity is established, the data are difficult to reconcile with full unity of consciousness in the experience-based sense.
Split-brain subjects may have two distinct subjects of experience, one per hemisphere, because consciousness is unified within each hemisphere but not across them. The empirical basis is that elements of experience are present in both hemispheres yet are not integrated between them. This suggests each hemisphere has its own subjective perspective, making it impossible for a single subject to have multiple perspectives in the same way another subject has one. Therefore, the two hemispheres likely correspond to separate subjects of experience, each related to its perspective as a normal person is to theirs.