Research Summary: looking inside the vocal tract during stuttering
Here's an example image of the vocal tract, taken using Magnetic Resonance Imaging (MRI). Here, the speaker is facing to the left. The image has been cropped to maintain confidentiality, so the eyes and the tip of the nose have been hidden.
For this study, areas of the vocal tract were defined using rectangles or circles. They are the lips (LIP), Tongue Tip (TT), Tongue Body (TB) and the soft palate or velum (VEL).
Try an example: If you run your tongue tip from behind your teeth, back across the roof of your mouth, you will hit a soft patch. This is the "soft palate" or "velum" and it moves up or down to direct air though the mouth or the nose. Try putting a finger under your nose, whilst your hum. You'll feel the air passing though your nose! This means that the velum is lowered, allowing air into the nasal cavity!
What did the study reveal?
This graph shows the amount of constriction for each sound and speech muscle. The higher the dots, the more constriction. Here, you can see that the black dots (dysfluent sounds) are more likely to be higher (more constricted) than the grey dots (fluent sounds).
3) During a stutter, this increased closure stayed the same or became stronger, but did not get less over time.
This graph shows the constriction (amount of closure) of the lips during a dysfluency. The lip muscles oscillate and the closure increases over time (arrow), before being released.
4) Stuttering was not caused by difficulties forming a combined consonant-vowel sound. When we say a sound like “ma”, with a consonant (m) and a vowel (a), our lips have to close for the “m” but at the same time, our tongue gets in the right position for the “a”. During a stutter on “m”, the tongue was forming the expected shape in preparation for the “a”. And yet, the difficulty appears to be the release of the overly constricted lips.
Try an example: Your tongue position controls vowel sounds (a, e, i, o, u).
Pretend you're about to say "Me". Pay attention to the shape of the vocal tract: your lips are closed and the tongue is quite high in the mouth. When you start to say "Me" the tongue doesn't move much - it's already in position right from the M sound!
Do the same with "Man". This time, the tongue will be low.
What were the limitations of the study?
About the Authors
Yijing Lu is a fifth-year PhD student in Linguistics at the University of Southern California.
"My primary research interest is in speech production, especially the control of speech articulators in both typical and atypical speech. Most of my research involves examining articulatory data collected using real-time MRI."
See Yijing's Website
Get in touch with Yijing here: firstname.lastname@example.org
Louis Goldstein is Yijing's PhD supervisor and is a professor at the Department of Linguistics at the University of Southern California.
This data was collected as part of the INSTEP project run by the Speech and Brain Lab at the University of Oxford. A huge thank you to all of the participants who took part in the INSTEP study, and in this case, special thanks to the participant who contributed to this work!
An interview with the lead author - Yijing Lu.