Perhaps you’ve been chatting on your cell phone or Skyping with a friend when, suddenly, you hear your voice echoed on the other end. It’s a strange feeling, right?
Inexplicably, your normally flowing speech becomes choppy and forced. The feeling is not painful, of course—but you’d much rather restart the call than continue talking uncomfortably. Why do we get so flustered by the sound of our own echoing voices?
This phenomenon, called “delayed auditory feedback,” occurs when one’s voice is played back to them less than a second after speaking. This fractional difference is just enough to silence them into realizing that something is wrong.
“The reason that delayed auditory feedback causes us so much trouble is that our brains are expecting our voices to arrive at the ‘normal’ time,” says Frank Guenther, Ph.D., professor in the Departments of Speech, Language, & Hearing Sciences and Biomedical Engineering at Boston University.
Our brains monitor our voices for speech errors, or the difference between actual and expected sound. Normally, the difference is negligible, if at all; in delayed auditory feedback, however, the discrepancy is quite large.
“This big expectation mismatch can cause us to stop speaking since it sounds like we’re not doing it correctly, followed by another false start, etc.,” says Guenther.
In a 2008 study published in Neuroimage, Guenther and his research team explored the brain regions responsible for this peculiar phenomenon.
Participants were placed inside an fMRI machine and instructed to read single-syllable words (“beck,” “bet,” “deck,” “debt”) while their brains were imaged. For a subset of the trials, the researchers delayed the timing of the participants’ vocal feedback.
During these trials, fMRI imaging revealed increased activation of the superior temporal cortex, the region primarily involved in auditory perception, as well as the right prefrontal cortex, implicated in decision-making and planning.
These areas, the researchers concluded, indicate neurons (brain cells) that are more active when coding for the mismatch between actual and expected auditory signals.
Interestingly, delayed auditory feedback can be used therapeutically for people who stutter.
Speech pathologists have found that delaying a stutterer’s vocal feedback by 50 to 70 milliseconds can actually reduce stammering by nearly 70 percent without any prior training.
Given the effect of delayed auditory feedback on normal speech, this treatment seems rather … backwards, right?
Like several other therapies that aim to mask the stutterer from perceiving their own uneven speech, delayed auditory feedback tricks one’s brain into thinking that the voice they hear is not their own.
Adds Guenther, “Delayed auditory feedback can improve fluency in people who stutter…so they don’t hear themselves producing errors which might otherwise lead to ‘resets’ or reptitions of speech sounds.”
In the meantime, if you find yourself wishing to silence an annoying colleague, public cell phone abuser, or rowdy library patron, simply play back their voice at a delay.
Not surprisingly, there’s an app for that.
Jordan Gaines is a science writer and neuroscience grad student at Penn State College of Medicine. You can check out her blog, Gaines on Brains, and follow her at @GainesOnBrains.
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