Dealing with uncertainty in the brain

This post is also available in Dutch.

When we walk around we perceive the world as stable and accurate. This is actually a product of our brain performing some clever tricks to make the most of the information we receive from our senses. Sometimes, our senses can seem ambiguous and uncertain. Where does this uncertainty come from? How does our brain compensate for this uncertainty?

FedererPicture by Marianne Bevis ( CC BY-ND 2.0 license) 

The term “uncertainty” refers to how our brain is incapable of working out with certainty what the physical world around us is actually like. For example, suppose you are playing tennis, to return the serve you want to know where the ball is going to land. If you had no uncertainty in your brain or in your senses, you would perfectly know the landing position of the ball. However, this is clearly not the case; instead we can only make a good guess (an estimate) about where the ball is going to land.

Neurons activated by the motion of the ball
To understand the source of this uncertainty it’s important to know how our brain works. Our brain is composed of a larger number of cells called neurons; these neurons are capable of communicating, by exchanging electrical signals between each other. To illustrate this consider the previous example, when our eyes perceive the motion of the ball, this sends signals to the neurons responsible for detecting motion. The activity of these motion neurons depends on the direction and speed of the ball moving across the eyes. Different activity in the neurons are created depending on the ball’s motion which allows our brain to work out where the ball will land.

Source of uncertainty
Unfortunately, because neurons work in this way they are subject to a property termed noise; which is simply an unwanted addition to any signal. A common example is the sound you hear when tuning the radio. This static sound is caused by electrical noise being sent to the speakers. The same thing happens in neurons. Returning to our example of the tennis ball, even if the same ball motion is given to the eyes the landing position worked out by the brain will be different. This is because of noise altering the communication between the neurons.

How could the brain compensate for uncertainty?
Ideally, we want to be as certain as possible about our environment. We would be bad tennis players if we couldn’t predict the landing position of the ball.  Although, it is hard to estimate the landing position using our senses alone, we have another form of information – our previous experience.  Experience tells us that a ball will most likely land close to the edge of the court (it is beneficial for the opponent to aim there). Our brain could combine this knowledge with the landing position we derived from the ball motion. Combining this information would reduce the uncertainty about the balls landing position. There is growing evidence that our brain works like this; an idea termed the Bayesian brain hypothesis. Aptly named after an 18th century reverend who first proposed combing prior knowledge with current information to reduce uncertainty.

This blog is written by James Cooke. James is a PhD student at the Donders Institute and studies perception in moving environments

Edited by Romy


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