Have you ever heard a sound inside your mind make suggestions to you when you are thinking or making a decision? I bet many of you have this kind of experience. Of course, the sound appears from no where and also disappears in seconds – all in a mysterious way. In some adventure novels, we can see the writer writes something like ‘However, there is a sound in his mind whispering ‘no, no, don’t go there’’, and most of them will explain this as character’s strong instinct. On the other side, in cartoon, the same thing usually is presented by a small image of the character itself. Like in ‘Tom & Jerry’, when Jerry is struggling whether he should do something, two small mouse (represent as angel mice and evil mice) usually will stand on his shoulders and argue with each other to let Jerry listen to their own idea. So scientifically, what is this sound and where does it come from?
Academically, the sound appears when people are thinking is called inner speech (or inner voice). And no commonly approved mechanism have already been set for this subject, which covers psychology, neuro science and cognitive science. Generally, it might be a process of self-talking as listening what you are saying to yourself. Inner speech is benefit for people’s time management, problem- solving, self-encouragement and critical thinking if they appear always properly at the right time. However, excessive inner speech will compromise people’s cognition and interpretation, even will trigger people getting depression disorder or anxiety disorder.
The research of inner speech was began at 1930 by Lev Vygotsky, an amazingly important figure to psychology. He first defined the inner speech as ‘speech began as a social medium and became internalized as inner speech, that is, verbalized thought’. However, back to those days, current technology cannot support Lev Vygotsky to further study the inner speech. Fellow researchers were able to go deeper until imagology was well-developed.
As we know, cerebral cortex can be separated as different areas based on their functions, and one of those areas which links to linguistic output is called Broca’s area.
Some researches indicated that the Broca’s area was activated when people are talking. As shown in the fMRI image, colors indicate that Broca’s area and area that controls human’s mouth are activated. So here is the problem: what will happen in our cerebral cortex when there is a sound in our head?
Like most of you guys can guess, the result of this relative research indicated that volunteers’ broca’s areas were also activated when they were doing inner speech. Then researchers went further as they stimulated volunteers’ broca’s areas, and they found both of volunteers’ speaking and inner speech were obviously affected. So they dropped the conclusion as ‘Inner speech is closely related to the activities in Broca’s area, just like talking. Furthermore, those researchers also found two other things: 1. The breathing patterns are the same when people are talking or doing inner speech; 2. The speeds are the same when people are talking or doing inner speech. So seems like those two findings also support the hypothesis above.
However, some other research also found that many stuttering volunteers believed they were not stuttering when they were doing inner speech. And more specific fMRI images pointed out that except Broca’s area, inner speech activates and uses quite different areas on the cerebral cortex with normal talking. So if I have to answer the original question, I would say the sound we heard in our mind was most likely our own sound.
Of course, there are still many scientists are studying this subject and try to answer this question. For example, PhD Mark Scott from UBC published an article on ‘Psychological science’ in 2013 talking about another explanation for the process of inner speech. He believed inner speech is caused by corollary discharge.
What is corollary discharge? It is pretty easy to explain: sometime when people scratch some part of your body, you will feel tickle and want to laugh out. However, if you scratch the exact place by yourself, you won’t have the feeling. That is because corollary discharge copy the signal before your muscle ever move to tell your brain that you are coming to scratch yourself, then you can barely feel tickle because you are ‘well-prepared’ for that.
So Mark believed corollary discharge also happens when people doing inner speech: when we are thinking to speak something, corollary discharge will send an advanced signal to our auditory system to tell the system what we are going to speak. So whether at last we are going to speak out or not, our auditory system have already gotten the information we want to say. In another word, the inner speech we are heard is actually corollary discharge. Unfortunately, we still cannot prove that corollary discharge is the origin of inner speech. But if we can prove that, then the sound of inner speech will be definitely our own sound.
Resource:
- ‘Thought as action: inner speech, self-monitoring and auditory verbal hallucinations’ – Fernyhough C.
- ‘Inner speech: nature and functions’ – Vicente A., Martinez-Manrique F.
- ‘Inner speech captures the perception of external speech’ – Scott M., Yeung H. H., Gick B. & Werker J. F.
- ‘Influence of preceding liquid on stop consonant perception’ – Mann V. A.
- ‘Corollary discharge provides the sensory content of inner speech’ – Scott M.