CONCEPT
The Left-Hemisphere Interpreter
Michael Gazzaniga and Roger Sperry’s name for the brain’s narrative faculty—lodged primarily in the left hemisphere—that maintains a coherent first-person story by manufacturing confident reasons for behaviors it did not cause and cannot introspect, proving that fluent self-explanation is not reliable self-knowledge.
The left-hemisphere interpreter is the human prototype of the most dangerous failure mode in AI: the confident confabulation of reasons that are coherent, plausible, and false.
Roger Sperry’s split-brain experiments, extended by his collaborator Michael Gazzaniga into a full theory, showed that the left hemisphere runs a continuous narrative process whose job is to maintain a story of a unified, rational self—and that this process fabricates explanations rather than admitting ignorance when the real cause of a behavior is inaccessible to it. In the classic demonstration, a split-brain patient whose right hemisphere had seen a snow scene directed the left hand to point at a shovel. When asked why, the left hemisphere—which had seen only a chicken claw—explained that you need a shovel to clean out the chicken shed. The explanation was invented on the spot, delivered with complete sincerity, and believed by the patient. The faculty that generates the explanation is