Inner speech speaks volumes about the brain

July 16, 2013

Whether you're reading the paper or thinking through your schedule for the day, chances are that you're hearing yourself speak even if you're not saying words out loud. This internal speech—the monologue you "hear" inside your head—is a ubiquitous but largely unexamined phenomenon. A new study looks at a possible brain mechanism that could explain how we hear this inner voice in the absence of actual sound.

In two experiments, researcher Mark Scott of the University of British Columbia found evidence that a called corollary discharge—a signal that helps us distinguish the sensory experiences we produce ourselves from those produced by —plays an important role in our experiences of internal speech.

The findings from the two experiments are published in Psychological Science, a journal of the Association for Psychological Science.

Corollary discharge is a kind of predictive signal generated by the brain that helps to explain, for example, why other people can tickle us but we can't tickle ourselves. The signal predicts our own movements and effectively cancels out the tickle .

And the same mechanism plays a role in how our auditory system processes speech. When we speak, an internal copy of the sound of our voice is generated in parallel with the external sound we hear.

"We spend a lot of time speaking and that can swamp our , making it difficult for us to hear other sounds when we are speaking," Scott explains. "By attenuating the impact our own voice has on our hearing—using the 'corollary discharge' prediction—our hearing can remain sensitive to other sounds."

Scott speculated that the internal copy of our voice produced by corollary discharge can be generated even when there isn't any external sound, meaning that the sound we hear when we talk inside our heads is actually the internal prediction of the sound of our own voice.

If corollary discharge does in fact underlie our experiences of inner speech, he hypothesized, then the sensory information coming from the outside world should be cancelled out by the internal copy produced by our brains if the two sets of information match, just like when we try to tickle ourselves.

And this is precisely what the data showed. The impact of an external sound was significantly reduced when participants said a syllable in their heads that matched the external sound. Their performance was not significantly affected, however, when the syllable they said in their head didn't match the one they heard.

These findings provide evidence that internal speech makes use of a system that is primarily involved in processing external speech, and may help shed light on certain pathological conditions.

"This work is important because this theory of internal speech is closely related to theories of the auditory hallucinations associated with schizophrenia," Scott concludes.

Explore further: Study of vocal impersonations reveals how we manipulate our voices

Related Stories

Study of vocal impersonations reveals how we manipulate our voices

June 19, 2013
A study of vocal impersonations has shown for the first time how speech production and voice perception systems in the brain interact to influence the way our voices sound. The research, supported by the Wellcome Trust, marks ...

Study shows how bilinguals switch between languages

May 20, 2013
(Medical Xpress)—Individuals who learn two languages at an early age seem to switch back and forth between separate "sound systems" for each language, according to new research conducted at the University of Arizona.

Designing better hearing aids using brain-inspired speech enhance

March 7, 2013
New research is aiming to produce hearing aids which can distinguish better between speech and background noise and benefit the lives of the six million people in the UK with hearing impairments.

New research to enhance speech recognition technology

January 17, 2012
New research is hoping to understand how the human brain hears sound to help develop improved hearing aids and automatic speech recognition systems.

Recommended for you

Study finds gene variant increases risk for depression

July 20, 2017
A University of Central Florida study has found that a gene variant, thought to be carried by nearly 25 percent of the population, increases the odds of developing depression.

Study examines effects of stopping psychiatric medication

July 20, 2017
Despite numerous obstacles and severe withdrawal effects, long-term users of psychiatric drugs can stop taking them if they choose, and mental health care professionals could be more helpful to such individuals, according ...

In making decisions, are you an ant or a grasshopper?

July 20, 2017
In one of Aesop's famous fables, we are introduced to the grasshopper and the ant, whose decisions about how to spend their time affect their lives and future. The jovial grasshopper has a blast all summer singing and playing, ...

Perceiving oneself as less physically active than peers is linked to a shorter lifespan

July 20, 2017
Would you say that you are physically more active, less active, or about equally active as other people your age?

New study suggests that reduced insurance coverage for mental health treatment increases costs for the seriously ill

July 19, 2017
Higher out-of-pocket costs for mental health care could have the unintended consequence of increasing the use of acute and involuntary mental health care among those suffering from the most debilitating disorders, a Harvard ...

Old antibiotic could form new depression treatment

July 19, 2017
An antibiotic used mostly to treat acne has been found to improve the quality of life for people with major depression, in a world-first clinical trial conducted at Deakin University.

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

beleg
not rated yet Jul 20, 2013
You forgot to poll the people born deaf.
The deaf are not pathological.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.