Psychology › Brain & biology › Brain regions and localization of function
Split-brain experiments (Sperry, Gazzaniga)
1962; Nobel 1981· Finding or experiment
Well replicatedStrong, repeated evidence.
Patients whose brain halves were surgically disconnected showed that each hemisphere can perceive and act on its own.
See it on the Psychology map →What it says
To control severe epilepsy, surgeons cut the corpus callosum, the cable linking the two hemispheres. From 1962 Roger Sperry and his student Michael Gazzaniga flashed images to one side of vision at a time. A picture seen only by the right hemisphere could not be named, since speech usually sits in the left, yet the left hand, run by the right hemisphere, could pick out the matching object. The left hemisphere often invented confident reasons for actions it had not started: Gazzaniga's 'interpreter'.
Why it matters
It showed the hemispheres specialize, and that the talking mind can fabricate reasons for behavior, an idea echoed in later research on how people explain their own choices.
The evidence
Status: well replicated for the core findings, from a few dozen patients studied for decades. Pop ideas of logical 'left-brained' and creative 'right-brained' people are not supported; a 2013 Utah study of over 1,000 brain scans found no such types.
Open questions
Whether a split brain holds two minds or one: a 2017 Dutch study found patients could report items in either visual field with either hand, challenging the classic picture.
Connections (2)
▸Split-brain experiments (Sperry, Gazzaniga) showed hemisphere specialization in Brain regions and localization of functionWell replicated
The connection
Split-brain patients showed that the two hemispheres, normally sharing information instantly, have different strengths. The left usually handles speech and grammar; the right is better at faces, spatial layout and some emotional cues. Cutting the link exposed this division of labor, extending the localization story that began with Broca's speech area.
Who showed it and when
California Institute of Technology, Pasadena, from 1962: Roger Sperry and Michael Gazzaniga, with surgeons Joseph Bogen and Philip Vogel, studying epilepsy patients.
The evidence
Repeated tests on a few dozen patients over decades, Sperry's 1981 Nobel Prize, and matching results from brain imaging and from numbing one hemisphere at a time (the Wada test).
Open questions
Specialization is relative: both hemispheres contribute to most abilities, and some left-handers have language on the right or both sides.
▸Perception: how the brain builds what we see was split between hemispheres in Split-brain experiments (Sperry, Gazzaniga)Well replicated
The connection
When surgeons cut the nerve bundle linking the two hemispheres to treat severe epilepsy, each half perceives separately. A picture flashed to the left visual field reaches only the right hemisphere: patients cannot name it, since speech usually sits on the left, yet their left hand can pick out the matching object.
Who showed it and when
Caltech, from 1962: Roger Sperry and Michael Gazzaniga tested patients of surgeons Philip Vogel and Joseph Bogen; Sperry shared the 1981 Nobel Prize.
The evidence
Carefully controlled tests flashing images to one visual field, repeated in many patients over decades and published from 1962.
Open questions
Whether a split brain holds two conscious minds is debated; a 2017 study found some patients' awareness surprisingly unified despite divided perception.