This post was written in the lead up to our upcoming Day on Neuroscience at the University of London on Sunday 29th April.
Right now, tens of billions of neurons are working together in your brain so you can read these words.
Ever wonder how this happens?
For the longest time, consciousness was life’s greatest mystery – something we thought we’d never understand.
But new research and cutting-edge experiments in neuroscience are beginning to give us a better understanding of how the brain generates our conscious experience, and the findings are nothing less than astounding.
According to one of the world’s leading researchers into the neuroscience of consciousness – Anil Seth, the reality we experience every day is a kind of ‘controlled hallucination’ by the brain.
Sounds ridiculous right?
You might think differently by the time you’re finished reading this post.
Imagine being a brain.
You’re locked inside a skull where no light or sound can get in – all you’ve got to go on are the electrical impulses in your environment.
Somehow, the brain transforms these electrical impulses into the sights we see, the sounds we hear and even what we feel.
As Professor Seth puts it in his 2017 TED talk:
‘Perception – figuring out what’s out there – is a process of informed guesswork in which the brain combines sensory signals from the environment with its prior expectations or beliefs about the way the world is, to form its best guess about what caused those signals.
‘The brain doesn’t hear sound or see light. What we perceive is its best guess of what’s out there in the world.’
In other words, you don’t see what’s ‘out there.’
What you see, is a combination of sensory signals from the environment and your brain’s best predictions about what caused those signals.
Our common sense tells us that perception is caused by signals coming into the brain from the outside world, like the image below:
However, the latest research in neuroscience is showing that what we perceive depends as much, if not more, on the brain’s predictions flowing in the opposite direction:
‘We don’t just passively perceive the world, we actively generate it. The world as we experience it, comes as much, if not more, from the inside-out, as from the outside-in.’ Anil Seth
Perception then is a creative process, in which our brain’s predictions, beliefs and prior expectations play a key role in generating our conscious experience of reality.
The rest of this post outlines three simple experiments, you can do right now, to test this out yourself.
Experiment #1 – What You See
When you look at the image below, it appears that square ‘A’ and square ‘B’ are different colours.
But if you take a closer look, and join the two squares together with a grey bar, you’ll find both squares A & B are exactly the same colour:
So what’s happening here?
The brain is using its prior expectations, which are built deeply into the circuits of the visual cortex, that a cast shadow dims the appearance of a surface, so that we see square ‘B’ as lighter than it actually is.
In other words, because the brain has past experiences that shadows dim the colours of surfaces, it automatically expects the phenomenon of a ‘cast shadow’ to dim the colour of square B, and therefore changes the colour we see.
This experiment demonstrates just how much of what we see, depends on what our brain is expecting to see – not what’s actually there.
Experiment #2 –What You Hear
Before reading any further, please press play on the below clip:
Could you make any sense of it? I’m guessing probably not. (Try again if you’re not sure.)
Next, listen to this clip:
Now, listen to the first clip again:
The first time you listened, you probably heard incoherent gibberish.
The second time, you might have heard a political statement.
So what’s going on here?
The clip was exactly the same, all that changed was your prior expectations.
This is another example of just how strongly our brain’s predictions influence our conscious experience of the present moment. So much so, that it can transform incoherent gibberish into a political statement.
The previous two experiments are about our experience of things in the outside world. But what about our experience of having a body?
Is that a kind of hallucination too?
Experiment #3 – What You Feel
According to Professor Seth, the brain is even guessing about what is, and what is not part of its own body.
And there’s a simple experiment in neuroscience that demonstrates this – all you need is a fake rubber hand and two paintbrushes.
In the experiment, the person’s real hand is hidden from view using a screen.
Next, the fake rubber hand is placed in front of the person – roughly where their normal hand would be.
Both the fake hand and real hand (which is hidden from view) are then stroked with paintbrushes, while the person stares at the fake hand.
After a while, most people in the experiment begin to sense that the fake hand is actually part of their own body, as happens in the video below (skip to 10 minutes and 50 seconds in):
Simply seeing a hand being touched, and feeling touch at the same time, is enough evidence for the brain to guess that the fake hand is actually part of its own body.
This experiment reveals that even our experience of what our own body is, is guesswork, and a kind of ‘controlled hallucination’ by the brain.
To sum up, what you see, hear, and even what you feel are not solely determined by the signals coming in from the outside world.
Hearing, seeing and feeling depend as much, if not more, on your brain’s best predictions, beliefs and prior expectations about the causes of those signals.
Perception then, and indeed consciousness itself, appears to be a creative process in which your brain takes in sensory signals from the environment – light, sound and touch, and then make its best guess about what caused those signals.
And this, according to Seth, is what creates our reality.
If you are interested in exploring the Neuroscience of Consciousness further, Professor Anil Seth will be delivering the keynote speech at our upcoming ‘Day on Neuroscience‘ on Sunday 29th April.For more information, please see the event page.