Some of those predictions involve sequences that are predictable. Anyone who has listened to a CD (or record, cassette, or 8-track) often knows that you start to hear the first few notes of the next song on the album after a song ends. Even though you did not try to learn what was coming next, your brain naturally helps you to make this prediction.

Other predictions involve actions. When you press down on the turn signal in your car to make a left turn, you expect to hear the repeated click of the turn signal. If you don't hear the sound after you engage the turn signal, you might look at the dashboard to make sure that the turn signal is actually on. You are able to do this, because you have made a mental connection between an action and an outcome.

One question of interest to researchers was whether people could also learn to predict what would happen when they made the choice not to act. One the one hand, choosing not to do something is still a choice, and so there is some information about that decision in the brain that could be used as the basis of the prediction. On the other hand, choosing not to act means that there is no information about a specific action that could be used to help the brain predict what is going to happen.

The problem with studying a question like this is that you need to have something to measure. Traditional measurements in psychology involve actions, which makes it hard to study what people do when they are choosing not to act.

To address this problem, Simone Kuhn and Marcel Brass turned to brain imaging in a study published in the December, 2010 issue of Cognitive, Affective, and Behavioral Neurosciences.

In this paper the researchers first trained people about what would happen both when they acted and when they did not act. In this study, people sat in front of a computer. Periodically, an orange dot would flash on the screen. When this happened, people had to make the choice either to press buttons in front of them with each hand or not to press the buttons. (People were asked to use both hands because that would ease the interpretation of the later part of the experiment in which images of their brains were taken.) The participants were asked to press the button on about half the trials, but to make the choice as randomly as possible. In this training part of the study, every time participants pressed the buttons, they heard a high tone as feedback. Every time they chose not to press the button, they heard a low tone as feedback.

After this training, people were put in an fMRI scanner. The scanner allows researchers to measure changes in blood flow to different parts of the brain over time. Because areas of the brain that are active require a lot of energy, lots of blood will flow to regions that are very active when a particular task is being performed. This blood flow brings the nutrients needed for the brain to stay active.

The researchers first confirmed that when people listened to tones, that the areas of their brain that normally respond to tones (the auditory cortex) would show increased blood flow. Then, they looked at what happened in auditory cortex in the other tasks. When people pressed the button in response to the red dot, then auditory cortex was also active, but when people did not act in response to the yellow dot, auditory cortex was not active. This result shows that when people are responding based on some event in the world, then they do not predict what might have happened if they did not respond.

The interesting result came when people chose either to respond or not to respond to the orange dot. In this case, auditory cortex was active both when people decided to respond and when they did not. That is, the practice session of the experiment led people to predict that when they chose not to respond that they would hear a tone.

There are a few interesting aspects to these findings.

On the scientific side, these results demonstrate how brain imaging can be used to study something that would be difficult to study otherwise. It is hard to get people to state reliably whether they are imagining a particular sound. Having a more objective measure (like activity in the brain) helps to measure things that would be hard to detect otherwise.

On the practical side, these findings show that your brain treats your choice not to respond to something as if it was an action. That is useful. There are many situations in life where the right thing to do is to refrain from acting in a situation. If someone cuts you off on the road, for example, then it is a healthy thing not to yell at them or to make some kind of gesture. Happily, your brain has mechanisms in it that allow you to make good predictions about what will happen in those situations when you choose not to act.

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