In the experiment, the researchers asked participants to repeat meaningless sounds out loud (“blah-blah-blah”) while performing visual and sound tasks. Because we cannot say two things at the same time, muttering these sounds made participants unable to tell themselves what to do in each task. Under these circumstances, humans behaved like monkeys do, activating separate visual and sound areas of the brain for each task.
This study elegantly showed that talking to ourselves is probably not the only way to control our behaviour, but it is the one that we prefer and use by default. But this doesn’t mean that we can always control what we say.
Indeed, there are many situations in which our inner talk can become problematic. When talking to ourselves at 3am, we typically really try to stop thinking so we can go back to sleep. But telling yourself not to think only sends your mind wandering, activating all kinds of thoughts — including inner talk — in an almost random way.