What Causes Your Inner Voice?

by Katy Edgington
How can we ‘hear’ ourselves speak even when we are not speaking aloud? Research published this month suggests that the same mechanism that means we cannot tickle ourselves is responsible…

The study, which appeared in the Association for Psychological Science’s journal Psychological Science, involved two experiments aimed at testing the role of corollary discharge in participants’ experiences of inner speech.

We are all familiar with the phenomenon of hearing our own voice inside our head despite not saying words out loud, but it has gone largely unexamined and unexplained until recently. ScienceOmega.com asked the paper’s author, Dr Mark Scott, why he thinks this has been the case.

"I suspect inner speech has not been a popular research topic for several reasons," Dr Scott began. "First, it can be hard to investigate because it is an internal experience. This connects to the second reason: the lingering influence of Behaviourism, which looked with suspicion on topics associated with an internal mental life. Lastly, I think there's an element of ‘hiding in plain sight’. Inner speech is such an everyday experience that it becomes background to our lives and so escapes our notice."

Preventing confusion
 

Dr Scott, who is now a postdoctoral fellow in the Japan Society for the Promotion of Science at Kobe Shoin Women’s University, explained the importance of corollary discharge.

"Corollary discharge plays a central role in our motor system," he said. "It allows us to correct motor errors before we have committed them and it allows us to prevent confusion between self- and externally-caused sensory events."

The evidence indicates that corollary discharge provides an internal prediction of the sound of your voice, which usually functions as a means of filtering out self-caused sounds from our auditory perception.

"The idea that corollary discharge underlies the ‘voice in our head’ is not new," explained Dr Scott, who carried out this work while at the University of British Columbia. "Several researchers have proposed variations on this idea for quite a while. Once the concept of corollary discharge is clear, the similarity to inner speech seems obvious: both are internal renditions of the sound of one's voice."

Dr Scott thus hypothesised that an inner voice can be formulated even in the absence of external sound stimuli. To test this theory, he carried out an experiment designed to find out whether a sound produced externally would cancel out the internal signal generated by the brain if the two sounds matched.

Development of consciousness?
 

Sure enough, participants showed a reduced response when exposed to a syllable matching that which they ‘said’ simultaneously in their head. When the syllables were mismatched, on the other hand, their performance was not affected. There are many theories as to why such a mechanism may be useful and beneficial to us.

"It allows us to rehearse information to keep it in short-term memory, it allows us to practice future conversations (or arguments), and it allows us to silently use language to help govern our own behaviour (as when we give instructions to ourselves when we practice a sport)," Dr Scott related. "The modern philosopher Daniel Dennett has even speculated on the role of inner speech in the development of consciousness."

Although Dr Scott does not see any immediate applications for these findings on the basic mechanisms of speech motor control, there is the possibility that they could shed light on certain conditions in future.

"There are several questions that I will be looking at in future research, though I don't know where exactly that research will lead," he concluded. "That’s part of the fun of doing research."