Can a brain scan show whether people are already producing their language response while their conversation partner is still speaking?

answered by Sara Bögels (Radboud University)

editor: Fleur Zeldenrust

Short answer

With some types of brain scans (which measure electrical signals from the brain), you can immediately see what's happening in the brain when people are, for example, in a conversation. In such a scan, we observed a brain signal in someone about to answer a question, already a few seconds before the question was finished. We think this signal indeed indicates that the response planning has already begun.

Longer answer

Different types of brain scans

In conversations, people usually take turns. We know that people can switch turns very quickly, often with no more than a small part of a second of silence between them. Planning such a turn often takes much longer. Therefore, like the person who asked this question, we were curious whether people might already start planning their turn while their conversation partner is still talking. To investigate this, we needed to find a way to see what’s happening in their minds (a “brain scan”) while they are still listening. Some types of brain scans (such as fMRI, functional magnetic resonance imaging) are too slow to investigate this. While they can show which parts of the brain are active during a particular task, they can’t tell exactly when. What we could use, however, was EEG (electroencephalography), which measures electrical signals from the brain at the moment they arise. 

Figure 1: The measured EEG signal during response preparation. Source: see research below at ‘further reading’. 

Two types of study

Participants in the study had to answer quiz questions, such as “Which character, also known as 007, appears in the famous movies?” When they heard the word “007,” participants could already start planning their answer (James Bond). Around that moment, we saw an electrical signal in their brains. In a second study in which participants heard the same quiz questions but didn’t have to answer them, we didn’t see this signal, or it was much weaker. Therefore, we think this signal means that people have indeed already started thinking about and planning their answer while their conversation partner is still talking. So we think it’s indeed possible to use EEG to see whether people are already planning their response while their conversation partner is still talking.

Further reading