Wednesday, December 5, 2018

Web Secret 548: the free energy principle

Karl Friston is the foremost neuroscientist in the world and on a short list to eventually win the Nobel Prize in Medicine. He has published more than 1,000 academic papers since the turn of the millennium.

I had never heard of him until I read an article in the December 2019 Wired Magazine: The Genius Neuroscientist Who Might Hold the Key to True AI. Let me summarize what may be Friston's greatest contribution to human knowledge.

It's called the free energy principle and it aims to explain how the human brain works.

Friston believes that the best way to think of the brain is as a probability machine. The idea is that brains compute and perceive in a probabilistic manner, constantly making predictions and adjusting beliefs based on what the senses contribute. The brain is an “inference engine” that seeks to minimize “prediction error.”

In seeking to predict what the next wave of sensations is going to tell it—and the next, and the next—the brain is constantly making inferences and updating its beliefs based on what the senses relay back, and trying to minimize prediction-signal errors.

Free energy is the difference between the states you expect to be in and the states your sensors tell you that you are in. Or, to put it another way, when you are minimizing free energy, you are minimizing surprise.

A single-celled organism has the same imperative to reduce surprise that a brain does. According to Friston, any biological system that resists a tendency to disorder and dissolution will adhere to the free energy principle—whether it’s a protozoan or a pro basketball team.

When the brain makes a prediction that isn’t immediately borne out by what the senses relay back, it can minimize free energy in one of two ways: It can revise its prediction—absorb the surprise, concede the error, update its model of the world—or it can act to make the prediction true.

If I infer that I am touching my nose with my left index finger, but my proprioceptors tell me my arm is hanging at my side, I can minimize my brain’s raging prediction-error signals by raising that arm up and pressing a digit to the middle of my face.

Why should you care?

The free energy principle is also a theory of mental illness. When the brain assigns too little or too much weight to evidence pouring in from the senses, trouble occurs. Someone with schizophrenia, for example, may fail to update their model of the world to account for sensory input from the eyes. Where one person might see a friendly neighbor, a schizophrenic might see a demon.

If you think about psychiatric conditions, and indeed most neurological conditions, they are just broken beliefs or false inference—hallucinations and delusions,” Friston says.

So: The free energy principle offers a unifying explanation for how the mind works and a unifying explanation for how the mind malfunctions. It stands to reason, then, that it might also put us on a path toward building a mind from scratch.

And that dear reader, is where I leave you.

Read the article.

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