When you listen over headphones to your own voice through a pitch-shifter, do you find yourself mimicking the pitch shift? Or do you automatically counter the pitch shift by shifting in the opposite direction?  According to speech and hearing science professor Torrey Loucks, most people compensate by shifting in the opposite direction to correct the deviation. But there is another group who follow the pitch changes.  We don’t yet understand why these individual differences in auditory vocal responses occur.
In a recently published study, Professor Loucks and his graduate students HeeCheong Chon and Woojae Han at the University of Illinois in the department of Speech and Hearing Science utilized Kyma for real-time pitch shifting in an experiment that attempts to increase understanding of the neural mechanisms underlying stuttering.
In this study, a group of adults who stutter and typically fluent adults were asked to produce the same vowel sound while monitoring their own voices through headphones. Kyma was used to shift the pitch of the subject’s voice up or down by as much as 200 cents (2 half-steps) for a duration of 500 ms.
In most cases, the participants adapted by lowering or raising the pitch of their voices to counter (rather than mirror) the pitch-shift imposed by Kyma. In the stuttering participants, the adaptive response to the pitch-shift was significantly delayed as compared to the responses of non-stutterers. The stuttering participants also tended to have a lower magnitude of pitch shift responses.
In their report, “Audiovocal integration in adults who stutter” recently published in the International Journal of Language & Communication Disorders, the authors analyze and discuss some of the implications of this result.
One theoretical prediction is that persons who stutter rely more strongly on auditory feedback to produce speech, whereas typically fluent speakers use a more robust internal predictive model of the expected result and are less reliant on audio feedback. On the other hand, there are also studies suggesting that persons who stutter tend to have slower auditory reaction times and are less adept at pitch tracking than typically fluent speakers. Loucks et al conclude that, although their results “do not negate arguments that adults who stutter are more dependent on feedback, their dependence is not expressed through a more reactive pitch-shift response”.
In an article describing his research with the Beckman Institute’s Cognitive Science group, Professor Loucks explains some of the wide-ranging implications of research on stuttering:
Stuttering is very interesting because it appears to occur at the junction point between formulating what you want to say and actually being able to express it.
He also corrects some outdated preconceptions on the phenomenon of stuttering:
There are no predisposing events that make a person stutter that could be prevented either by being a better parent or being a different sort of child. No one is to blame for the occurrence of stuttering because it is a biological disorder.
Nonetheless, the stigma of stuttering can be reduced considerably by realizing that we need to accept communication disorders as occurring in the population. There’s nothing negative about having a communication disorder and people should know that stuttering does not affect a person’s ability to learn, to succeed academically, all of those things. It has nothing to do with intelligence and should not be in any way a barrier to a person realizing their full potential. It is a neurobiological disorder that no one could prevent, but which we can find better ways to treat and possibly cure in the future.
