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How the Split Brain Emphasizes the Reality of the Mind

Fascinating research following up Roger Sperry’s work — which showed that the mind is not split when the brain is — has confirmed and extended his findings

Neurosurgeon Michael Egnor did a recent podcast with Arjuna Das at Theology Unleashed, “where Eastern theology meets Western skepticism.”

In the previous segment, they discuss the significance of the fact that there are aspects of the human mind that cannot be split into parts — as demonstrated by the work of Nobelist Roger Sperry (1913–1994). In this segment, they discuss the neuroscientists who followed up on and extended Sperry’s work — one of whom met a tragic end:

Here is a partial transcript and notes for the 1 hour 6 minute mark through the 1 hour 12 minute mark:

Michael Egnor: There has been some absolutely intriguing work done since Sperry that I think very clearly shows the existence of an immaterial aspect of the mind. Or, at least, it shows that the mind is, in fundamental ways, not splittable; it’s not material.

The first kind was done by Justine Sergent (1950–1994), a neuroscientist working at McGill University in Canada. Sergent extended Sperry’s work in the 1980s and what she did was absolutely brilliant. (01:05:54)

She took patients who had had split brain surgery and she would show either consonants or vowels in their visual fields. She would flash a k or an a — or a p or an i — in their visual fields. And she would ask them to push a button when they saw a vowel or a consonant.

So a patient would be sitting there and she’d be flashing consonants and vowels in different visual fields. She would ask them: When you see a vowel anywhere, left or right, push a button. So she’d do it a thousand times. (01:06:28)

She understood that, in people who had had a corpus callosotomy [severing the two halves of the brain], the right visual field was connected to the right arm and the left visual field was connected to the left arm … but there was no connection between the two hemispheres (halves) that control opposite sides of the body.

So a person pushing a button with the right hand had to be pushing the button — at least from a material standpoint –- based on what the left hemisphere had seen. That is what was in the right visual field. The right hand had no way of knowing what was in the left visual field because it was a disconnected hemisphere.

She found that, if she asked them, “Whenever you see a vowel anywhere, in either hemisphere, push this button with your right hand,” the right hand would push the button. Whether the vowel was seen by the right hemisphere or the left hemisphere. Even though the hemispheres were not capable of material connection with one another. (01:07:13)

So, she said, somehow the right hand knew what it was not connected to materially. If the vowel was put in the left visual field, the right hand had no way, metaphorically, to see it. But it still knew it. That happened with the other hand too. The left hand could respond to stimuli in the right visual field, even though there was no material connection that would allow information to get to the left hand from the right visual field. (01:08:15)

Note: Sergent, a highly productive researcher at the Montreal Neurological Institute at McGill University met an untimely end. She and her husband Yves committed suicide in 1994, after her name was dragged through the mud in the popular media for alleged research misconduct. An anonymous letter to the media had linked her work to a case of scientific fraud in an unrelated matter involving breast cancer research.

In “The Academic Mob and Its Fatal Toll,” (Quillette, March 2, 2018), Brad Cran notes that, in her suicide note, she wrote “I had a rich and intense life, but there comes a point when one can no longer fight and one needs a rest.” Research misconduct was never established; it appears to have been an administrative matter involving permissions, blown out of all proportion.

On March 20, 1997, the university shut down the inquiry into the matter. It wrapped up inconclusively, with the MNI research director announcing, “I think the one thing that everyone would agree on is that whoever wrote the anonymous letter acted in a totally indefensible way. We’ll probably never know who wrote that letter.” It seems odd, in a comparatively small field, that it proved impossible to find out who wrote that letter and why.

No evidence of actual research fraud turned up.

Michael Egnor: Her work has been extended by Yair Pinto. She had called the behavior she observed “perceptual disconnection with conscious unity.” There was a consciousness to these people that was not disconnected when you cut the brain in half. Now, the researchers didn’t offer dualist interpretations because they weren’t really into the philosophical perspectives. But obviously this fits the Thomistic dualist view very nicely, that perception is a material process in the brain but intellectual concepts are immaterial and do not arise from the material brain. (01:08:43)

Our understanding of what a vowel is, is not connected to a part of the brain. It’s an immaterial power. So Sergeant’s and Pinto’s work — which is an extension of Sperry’s work — is a beautiful refutation of materialism in neuroscience. And frankly, a beautiful confirmation of Thomistic dualism. (01:09:28)

Note: Dutch investigator Yair Pinto and colleagues published a paper in 2017 on the paradoxical unity of the mind despite the splitting of the brain, observing that “Across a wide variety of tasks, split-brain patients with a complete and radiologically confirmed transection of the corpus callosum showed full awareness of presence, and well above chance-level recognition of location, orientation and identity of stimuli throughout the entire visual field, irrespective of response type (left hand, right hand, or verbally).” (Brain)

In another paper, Pinto et al note, “Both the patients and the people nearest to them claim that consciousness is still unified in the patient. Moreover, their everyday behavior confirms this. Thus, the claim of destroyed conscious unity is extraordinary, and requires extraordinary evidence.” (Trends in Cognitive Sciences)

Arjuna Das: Why would it be that the person could push the button with one hand, despite it being in a different visual field but they couldn’t say the letter?

Michael Egnor: Because saying the letter is still a material process. Language is still a material thing. You can disconnect material things but you can’t disconnect concepts. The concepts get across, but the material ability doesn’t get across. That is, the left hemisphere can’t make the right hemisphere speak but information in the left hemisphere of a conceptual nature can easily get across without a material connection. (01:10:07)

Arjuna Das: So, how would you make it a conceptual versus a material perception? What exactly is the difference? Why can’t a letter be interpreted as a conceptual concept and then you could pick out the letter? (01:10:39)

colorful letters

Michael Egnor: The difference is between a universal and a particular. Conceptual things deal with universals, and particulars deal with individual things. For example, if I look at the letter a and realize that it’s a vowel, two different mental processes are going on. The perceptual process is that I see the letter a and it looks like an a, it’s got the shape, it’s made in a certain color, a certain size. The intellectual process is that I understand that it’s a vowel. Understanding that it’s a vowel is not a perception, it’s intellectual. The perception is actually seeing the letter. (01:10:52)

Arjuna Das: So, the person who’s pushing the button when they see a vowel, if it’s from a different hemisphere than their arm, they wouldn’t be able to select which letter it is. They could just say that it is a vowel?

Michael Egnor: Correct. They might not be able to tell you which vowel, but they can push the button that there is a vowel there. (01:11:49)

Arjuna Das: Right. So does that seem to prove that there’s a unified experience going on? (01:11:55)

Michael Egnor: Precisely. And what Pinto argues now and what Sergent argued… is that the best interpretation of split brain research is that perception is split and consciousness is unified. And by consciousness they mean abstract thought — which is exactly what Aristotle said. (01:12:00)

Next: The brain does not create the mind; it constrains it.

Here are transcripts and notes for the first hour and six minutes:

The brain can be split but the mind can’t. Neuroscientist Roger Sperry found that splitting the brain in half does not split consciousness in half. It just gives you a rather interesting, but very subtle set of perceptual disabilities.
Neurosurgeon Michael Egnor has split patients’ brains, while treating serious epilepsy, and the results are not at all what a materialist might expect.

How philosopher John Locke turned reality into theatre His “little theater in the mind” concept means that you can’t even know that nature exists. It may just be a movie that’s being played in front of your eyes.
Aristotle and Aquinas’s traditional philosophical approach, Michael Egnor argues, offers more assurance that we can truly perceive reality.

How did Descartes come to make such a mess of dualism? Mathematician René Descartes strictly separated mind and matter in a way that left the mind very vulnerable. After Descartes started the idea that only minds have experiences, materialist philosophers dispensed with mind, then puzzled over how matter has experiences.

What’s the best option for understanding the mind and the brain? Theories that attempt to show that the mind does not really exist clearly don’t work and never did. Neurosurgeon Michael Egnor reviews the mind-brain theories for East Meets West: Theology Unleashed. He think dualism makes the best sense of the evidence.

How we can know mental states are real?
Mental states are always “about” something; physical states are not “about” anything. Michael Egnor argues that doing science as a physicalist (a materialist) is like driving a car with the parking brake on; it’s a major impediment to science.

Why neurosurgeon Mike Egnor stopped being a materialist atheist. He found that materialism is just not working out in science. Most propositions in basic science are based on mathematics and mathematics is not a material thing.


How science points to meaning in life. The earliest philosopher of science, Aristotle, pioneered a way of understanding it. Neurosurgeon Michael Egnor talks about the four causes of the events in our world, from the material to the mind.

You may also wish to read: Why the universe itself can’t be the most fundamental thing. Atheist biology professor Jerry Coyne is mistaken in dismissing my observation that proofs of God’s existence follow the same logical structure as any other scientific theory. (Michael Egnor)

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How the Split Brain Emphasizes the Reality of the Mind