If you are listening to a particularly boring speaker, it may actually be your own voice you are “hearing.”

Dr Bo Yao of the University of Glasgow’s Institute of Neuroscience conducted a study into what’s loosely called the inner voice. It’s the experience you get when reading printed material and “hearing” the words on the page. Previous study has suggested one of the reasons the brain does this is to give added emphasis to direct speech quotations. This helps make up for the way that quotation marks don’t necessarily provide enough contrast between description and dialog.

In the new study, Dr Yao’s team performed MRI scans on 18 participants who were listening to audio clips of stories that included speech. The direct speech passages were deliberately read in either a dramatic and lively manner, or in an intentionally dull and monotonous tone.

The testing showed that when the participants heard the dull version, there was an increase in activity in their auditory cortex (pictured), which processes speech and other sounds. Yao believes that although the participants were hearing the quotations read out loud, their brains were using the inner voice to repackage them as more engaging and lively speech.

Colleague Professor Christoph Scheepers noted that the increase in activity seemed to come only with direct speech (“No, I am your father”) rather than with indirect speech (“Vader told Luke he was his father.”)

One possible explanation is that the brain associates direct speech in real life with a wide range of stimuli aside from the words themselves, such as the voice and tone of the speaker along with facial expressions and gestures. Because of this, it may automatically switch focus during direct speech in preparation to deal with the increase in information to process. When this doesn’t materialize, the inner voice may automatically fill in the gaps and artificially create the information.