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People With Half Their Brains Removed Do Well on Psych Tests

In a recent study, adults who had had hemispherectomies as children — to combat severe epilepsy — performed within 10% of other study subjects on face and word recognition

At Carnegie Mellon University’s Department of Psychology and Neuroscience Institute, researchers recently found that people who had had half their brains removed as children (due to serious epilepsy) “scored surprisingly well on face and word recognition tests”:

The researchers expected that those volunteers who had only their right hemisphere would do well at face recognition but not as well at word recognition, since the right hemisphere is generally used to process images while the left hemisphere processes words; they expected the opposite results for those who still had just their left hemisphere. Instead, the researchers found that both groups performed nearly equally well and both were on average 86% accurate on the tests compared to a control group consisting of people who had not undergone an hemispherectomy, with average 96% accuracy.

The researchers also conducted a nearly identical experiment in which the faces and words were shown off to the left or right; both groups still did surprisingly well—but there was one interesting difference. In comparing their results with the control group, those who had undergone a hemispherectomy did as well as the control group in identifying images or words in two instances—when a word was placed on the left side, or a face on the right.

Bob Yirka , Medical Xpress, “Adults who, as children, had half their brain removed still able to score well with face and word recognition” at MedicalXpress (August 17, 2022) The paper is open access.

In view of the claim we frequently hear that “the mind is just what the brain does,” it’s a remarkable fact that the forty study subjects who had half their brains removed are functional at all, never mind that they do less well than a control group with no similar background.

We are used to thinking of the brain as an organization with departments, some in the left brain and some in the right. But the brain may be more like an ocean so it is more complex than that.

There are many such findings out there. There are stories about people with split brains, a brain missing key components, or only half a brain, (or maybe less)

Michael Egnor

If neurosurgeon Michael Egnor is right, not only is the human mind not simply what the brain does but human consciousness, unlike a material thing, cannot be split. He should know because he must sometimes split brains, in order to improve the outlook for persons with epilepsy. He concludes, from observation,

Split-brain surgery doesn’t split the mind. People after split brain surgery remain one person, with one consciousness, one intellect, and one will. They have perceptual disabilities caused by the surgery but those disabilities are subtle and not noticed in everyday life. Their abstract intellect remains unified and the will that follows on that intellect remains unified. Split-brain surgery doesn’t split logic or mathematics or abstract reasoning or moral decisions based on abstract reasoning.

The results of split-brain surgery are strong arguments for dualism and for the immateriality of the intellect and will. – Mind Matters News

The same appears to be true of functioning with only half a brain. It’s all something to think about if we fear that lack of brainpower is holding us back in life. Maybe it’s not that after all…


You may also wish to read: Yes, split brains are weird, but not the way you think. Scientists who dismiss consciousness and free will ignore the fact that the higher faculties of the mind cannot be split even by splitting the brain in half. Patients after split-brain surgery are not split people. They feel the same, act the same, and think the same, for all intents and purposes. Materialists like Jerry Coyne focus on subtle differences and distort the big picture. (January 17, 2020)


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People With Half Their Brains Removed Do Well on Psych Tests