Source: Art Markman

I play the saxophone, and I have been in a few bands over the past few years. Recently, I started playing in a new band, as part of a horn section. We have learned a lot of new songs in a short period of time. One of the more frustrating experiences is when we are first learning a new song. There are times that I am aware of exactly what I am supposed to play, and yet I will still miss a cue and come in late. It is almost like there is a disconnect between my conscious sense of how the song goes and what my muscles want to do.

I was thinking of this experience when reading an interesting new paper by Frederick Verbruggen, Amy McAndrew, Gabrielle Weidemann, Tobias Stevens, and Ian McLaren in the May, 2016 issue of Psychological Science.

They found a clever way to assess this issue experimentally using a Go-No Go task. In this task, participants see one of two items on a computer screen. One item is the “Go” item. When people see that item, they are supposed to press a button as quickly as possible. The other item is the “No-Go” item. When they see this item, they should avoid pressing the button.

In this version of the task, participants were told that they would see five “Go” trials in a row followed by five “No-Go” trials. So, the sequence was completely predictable.

The researchers were interested in what happens when the trials shift from “Go” to “No-Go” and from “No-Go” to “Go.” The findings were quite interesting.

The participants clearly understood what was happening in the task. At the start of each trial, participants were asked to predict what kind of trial was going to happen next. They correctly predicted whether the next trial was going to be a “Go” or a “No-Go” trial almost all the time.

However, an interesting thing happened on the first “Go” trial after a sequence of “No-Go” trials. People took a lot longer to respond to this trial than to the next few “Go” trials. That is, even though they were expecting a “Go” trial, it still took them longer to initiate a response.

The researchers also used a clever set of measurements of readiness to make a movement. Participants were instructed to press the button with their left index finger. The researchers measured electrical activity in the muscle used to move the left index finger.

Prior to the presentation of the item on the screen as participants were preparing for the trial, a magnetic pulse was delivered through the skull using a coil. This technique, called Transcranial Magnetic Stimulation induces a small amount of electrical activity in the cortex beneath the magnet. The coil was placed over the brain area responsible for moving the left index finger. Electrical activity in the muscle was measured after the pulse.

The idea is that if the brain was already preparing to move the muscle, then the amount of electricity measured in the muscle would be larger than if the brain was not preparing to move the muscle.

On the first “Go” trial after a sequence of “No-Go” trials, there was less activity in the muscle after the pulse than on the subsequent “Go” trials. Similarly, on the first “No-Go” trial after a sequence of “Go” trials, there was more activity in the muscle after the pulse than on subsequent “No-Go” trials.

This set of findings suggests that even though people were aware of what kind of trial was coming, the brain was still preparing to make the same kind of response required for the previous trial. So, if the previous trial was a “Go” trial, then the brain prepared to execute a response. If the previous trial was a “No-Go” trial, then the brain was preparing to avoid a response.

That means that there is only a tenuous connection between what people “know” is going to happen explicitly and what their low-level motor system is preparing to do. Of course, people ultimately make the correct response. They are just slower and more prone to error when there is this mismatch between their belief and the movement being prepared.

This finding also demonstrates the value of practice. Over time, I do end up learning the right thing to play for each song. At that point, my motor system is making the correct predictions for what to do in a given song, and so my beliefs about what to do are aligned with the preparations my brain is making to play.

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