Today starts part three of our series on the speech mechanism-we’ve discussed air flow from the lungs in Part 1 and creating voicing in the larynx in Part 2. This discussion focuses on a couple of new areas that many of us may not consider when with think of speech: our resonators!
We know from our previous discussions that sound is created when the air stream from our lungs passes through the larynx and vibrates our vocal folds-we even call the larynx our “voice box” because of this. If we separated our larynx from the other parts of our vocal tract, we would sound more like kazoos than anything else! That is where resonators come into play. These are the air-filled cavities of our throat, mouth, and nasal cavity that act together to enhance some frequencies and attenuate (or dampen) others.
Let’s break that down a bit more. When we are speaking with our natural voice in a conversation, our vocal cords buzz at what we call a fundamental frequency, which is somewhere between 98 Hz and 262 Hz for most people. Furthermore, that frequency is a complex sound that contains several harmonics or overtones. This mix of sound is propagated through the air and structures in our vocal tract (the throat, mouth, and nose). You can think of them much like a tuning fork-if you were to play a 200 Hz sound next to a 200 Hz tuning fork, it would begin to vibrate and further strengthen the sound in the room. Our vocal tract structures and their overall length function much the same way they tend to vibrate best at certain frequencies and will thus enhance them, creating a unique tone. This is what contributes to making your voice, in particular, sound like “you.”
For the most part, this aspect of resonance is not of major concern for people with dyspraxia-these structures have a more passive role on speech than aspects such as breath control or changing pitch at the vocal fold level and are usually interrupted only by structural differences (for example, cleft palate or large tonsils). However, resonance isn’t only about creating your unique voice but also plays a role in clearly producing some speech sounds. Let’s define and describe the three main resonators in more detail to explore this:
This is the mouth or oral cavity, which is the most variable resonator and is responsible for shaping the majority of our speech sounds through the act of articulation (formation of sounds). We’ll spend significant time on this in part 4 of the series.
Also known as the throat, this is the semi-rigid structure that extends from the top of the trachea and esophagus up to our soft palate, or velum (the flap that the “dangly” thing at the back of your mouth hangs from). It is part of the digestive and respiratory systems as both food and air pass through it, and it can change its shape to a small degree to affect the sound.
This is the bony space of our sinuses behind our nose and above the velum, also called the nasal cavity. It is constant in shape and size.
The interplay between the air stream and the velum is the next big contributor to resonance and is typically where dyspraxia can cause disruptions. Almost every language has a mix of oral sounds (i.e. when the air stream flows out of the mouth) and nasal sounds (i.e. when the air flows through the nasal cavity). For example, in English, we have oral consonants like /b/, /d/, or /k/ and our nasal consonants are /m/, /n/, or /ng/ as in “king”. We achieve “normal” resonance by balancing the movement of air between these cavities so that the listener clearly perceives the intended sound.
In order to do so, our velum has to move up or relax down to either close or open the velopharyngeal port, or the opening between the nasal cavity and the throat. In connected speech, this has to happen rapidly-for example; the velum may need to be up to produce “ba”, drop down for the “n,” and then immediately close again for “dy” in the word “bandy”. In the case of a person with apraxia of speech, this timing can be tricky and result in errors like:
Hypernasality: When the velum remains down and air flows through the nasal cavity on oral sounds. For example, the speaker may pronounce “Ban” more like “Man”.
Hyponasality: When the velum remains lifted so that air is directed through the oral cavity on nasal sounds. For example, “Might” could sound more like “Bite”.
Mixed Resonance: When both hyper- and hyponasality are present at different times during speech.
This timing issue can quickly hijack speech and make an “easy” skill like producing a clear /m/ sound much more difficult! In fact, this is why mixed resonance is common in people with speech apraxia. If you are a person with minimal or unreliable speech, it makes sense why sounds or words may come out clearly one time and then seem completely garbled the next-you are completing a highly complex fine motor skill just to change your resonance!
I hope that Part 3 of this series has given you more tools and information to understand the complexity of speech whether you are a nonspeaking person, family member, or professional. Of course, we are not at the end yet. Keep your eyes open for the final part of this series, articulation, coming soon!
Living in Atlanta and supporting non-speakers in Georgia and Nashville, Tennessee, Bryana Williams is a Speech-Language Pathologist and registered Spelling to Communicate Practitioner. She owns her own private practice and has, for the past two years, worked as part of the I-ASC S2C Professional Training Course as a mentor, Cohort Captain and continues to support I-ASC’s practitioner and CRP training initiatives through the development and improvement of training protocols. Bryana was introduced to Spelling to Communicate in 2014 during an outreach in Atlanta: “I immediately saw, over the course of just a few hours, students demonstrating their knowledge and communicative skills at a level that my traditional training had never allowed them to reach. I knew then that I had to change everything.” She subsequently has focused her career on learning from and with neurodiverse individuals, bringing her interests in teaching and communication to her current role as a member of I-ASC Leadership in expanding the professional training course and developing content.