Anil Seth - How the brain accomplishes perception

Sensory information that comes into the brain is necessarily ambiguous and noisy. In order to make sense of these signals, the brain has to combine its prior expectations about the causes of these signals.

About Anil Seth
"I'm a professor of Cognitive and Computational Neuroscience at the University of Sussex.
My research is into the brain basis of consciousness, the nature of perception, and what it means to be a self."

How the brain accomplishes perception
There's a natural way to think about how the brain accomplishes perception, which is that the brain takes in sensory signals from the world and it reads out these sensory signals in the brain. In this view, perception is a kind of bottom-up or outside-in process in which the brain is extracting information from sensory input.

But this isn't how things are. Sensory information that comes into the brain is necessarily ambiguous and noisy. Imagine that you are a brain: you’re locked inside a bony skull, you have no direct access to what's out there in the world. All you get are electrical signals, and these electrical signals don't come with labels, they just arrive at the brain.

In order to make sense of these signals, the brain has to combine its prior expectations about the causes of these signals. These are prior beliefs about what's out there in the world, and it has to combine them with sensory signals to form its best guess about what's out there in the world. This is what we consciously see – it’s a best guess about what caused the sensory signals that the brain receives.

Key Points

• The brain extracts information from sensory inputs. In order to make sense of these electrical signals, it has to combine them with its prior expectations about the causes of these signals and form its best guess about what's out there in the world.
• We have many more than five ways in which the brain senses the world. But, critically, none of these sensory channels relay the state of the world as it is. Perception in the brain is always a process of interpretation of these sensory signals.
• Time is illusory in the same way that colour is illusory – the way in which we experience time is not a direct readout of what's actually happening in the world. Our experience of time is also a construction.
• We all inhabit our own distinctive perceptual universes – we all have a unique, conscious experience of ourselves and of the world around us.This diversity is illustrated beautifully by people with synesthesia. Synesthesia means mixing of the senses.
• I like to think of perception as controlled hallucination. It's a construction, but it is controlled by what's out there in the world. What we call hallucination, when people see things that other people don't, is a form of uncontrolled perception.