In the 1960s, two researchers, Roger Sperry and Michael Gazzaniga, began studying patients whose corpus callosum had been severed.
Think of the corpus callosum as a bridge between the two halves of your brain, joining them into a focused whole.
The researchers hoped they could find a cure for epilepsy. But these 'split-brain' patients revealed more than they anticipated: an unsettling window into the reality of consciousness.
You see: your left hemisphere controls the right side of your body and is language-dominant. Meanwhile, your right hemisphere controls the left side and excels at spatial reasoning but has limited language capability.
Each hemisphere only sees half the world - the left hemisphere sees the right visual field, the right hemisphere sees the left.
Researchers realised they could exploit this.
You could flash an image to only the right hemisphere, and show the word “WALK” to the left visual field. The patient stands up and walks. And when you ask them why they’re walking, they would confidently explain, “I’m going to get a Coke” or “I needed to stretch.”
The participants would fabricate an excuse for the action they just took – because they didn’t know why they acted.
Here’s what was happening:
The right hemisphere saw “WALK” and executed the command. The left hemisphere - the one producing speech - never saw the instruction. It has no idea why the person is walking. But it doesn’t say “I don’t know.” It instantly generates a plausible explanation that feels completely true to the patient.
Gazzaniga called the left hemisphere “the interpreter.”
It creates coherent narratives from incomplete information. It confabulates constantly, spawning stories about your behaviour after the fact, then convinces you those stories are your actual reasoning.
This is how your brain normally operates.
In another experiment, researchers show an object to the right hemisphere only. They ask the patient to reach out with their left hand (controlled by the right hemisphere) and grab an object from several options. The left hand picks up the correct object - the one the right hemisphere saw.
“Why did you pick that up?”The left hemisphere, which never saw the image and has no control over the left hand, doesn’t hesitate. It immediately fabricates an explanation: “Well, it’s the most useful one” or “I thought it matched better.” Complete fairy tale.
But the participants weren’t intentionally lying. They genuinely believed the explanation for an action their left hemisphere had no part in making.
So here’s the question:
If half of your brain is constantly reacting to stimuli that the other half sees, and making up convincing cover stories, what else might your brain be lying to you about?
Neuroscientist Benjamin Libet measured brain activity while people decided to take a small action, like moving their finger.
The brain showed “readiness potential” - decision activity - 350 milliseconds before conscious awareness of the decision. Your brain decides, then tells you that you decided. The experience of conscious choice arrives after the choice has already been made.
Priming studies subliminally showed participants images of money. They become measurably less helpful afterwards. But if you ask them why they weren’t helpful, they give rational explanations completely unrelated to money. They genuinely don’t know they were primed. Their interpreter generated a story that felt true.
Post-hypnotic suggestion works the same way.
We like to think we know ourselves. That we understand our motivations, our reasons, our choices. But the split-brain studies reveal that when we’re not fully cognisant of our actions, we’re usually guessing, then believing our guesses.
The life trap
Why did you choose your career? Your partner? That meal? Your political beliefs?
You may well have a confident explanation for your reasoning. And I don’t have brain probes to tell you otherwise.
But how much of that explanation is the interpreter doing what it does – weaving a coherent story from incomplete information, filling gaps with plausible narrative, then convincing you that narrative was your actual thought process?
The gap between “why you actually did something” and “the story you tell about why you did it” is often much larger than you think. So think twice.
