Markov blanket

Chapter 1 - Our Worldview

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The structure of a Markov blanket. Is the Free-Energy Principle a Formal Theory of Semantics? From Variational Density Dynamics to Neural and Phenotypic Representations - Karl Friston

What is a Markov blanket?

Distinction.

When you are talking about something, you are not talking about anything else. This distinction is important because if this distinction didn't exist, nothing would exist because everything would be part of 'the same'.

The distinction exists on every scale, between the world and land, land and business, business and employee, employee and its brain, …

Everything inside a 'distinction' is called a Markov blanket: a coherent system that can be separated from 'the rest' of the world.

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How a Markov blanket exists over time.

As a starter, think about a drop of ink falling into a water-filled vase. If the ink dispersed, you would not think of it as a living thing. But on the contrary, if the ink would open up a little bit and then shrink again into a drop and do that over and over again, you would think about it differently.

For the entropy principle, the second description is remarkable. This means that living systems tend to – opposite to entropy – move inwards. They don't disperse as entropy would predict, but they follow the rules of their proper Markov blanket model.

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How can we think about our brain as a Markov blanket?

First, with every action, you create movement in the world. Your brain tries to maximise the evidence for your model of that world with every move. The first direction is inside-out.
Secondly, by the senses and the internal sensory states, the brain is busy maximising its own model's validity. So the second direction is outside-in and inside-in.

Think about a fresh born animal jumping around on the lawn or a baby with stomping feet. These first actions are necessary to experience in what sense the world changes when they do the first thing they can do.

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Two clear-cut actions

This ‘distinct system’ has only two simple states

The active states are NOT influenced directly by external conditions. They depend upon the internal states. They do affect the external situation.
1. Their direction is from inside to outside.
The sensory states do NOT influence the externality. They do affect the internal condition.
1. Their direction is from outside to inside or from inside to inside.

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Evidence of existence

In summary, you are always maximising the gathering of evidence of your own existence.

Let's take the principle of a Markov blanket to understand the principle in itself. What can we think of as not being evidence of existence? The principle truly becomes convincing when you think about mental illness. People with schizophrenia, for example, fail to update their account of the world upon taking in sensory input.

The free energy principle is the opposite of entropy. Where entropy is about opening up, minimising free energy is about creating relationships and coherence between at least two elements.

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