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Vocal Tract Semi-Occlusion

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Erica Oks

on 12 May 2015

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Transcript of Vocal Tract Semi-Occlusion

Straw Phonation
Straw phonation involves holding a straw between the lips while producing a sustained vowel

The length and diameter of the straw can be altered to result in more or less resistance to air flow

Phonating through a straw increases the amount of intraoral air pressure that is generated during phonation
The increased intraoral pressure results in better impedance matching at the glottis

Phonating with a high lung pressure and high pitch during straw phonation could be completed without vocal fold trauma
The vocal fold amplitude of vibration is relatively small due to the aerodynamic changes induced by this SOVT
The acoustic energy reflected back to the vocal folds from the straw and the vocal tract aid in lowering the phonation threshold pressure (the lowest amount of lung pressure required to initiate vocal fold vibration
Semi-Occluded Vocal Tract Exercises
Semi-occluded vocal tract (SOVT) exercises narrow the vocal tract, usually near the lips or tongue tip, while voicing
singers and voice professionals ("warm-ups")
therapeutic approaches for voice disorders by speech-language pathologists

SOVTs vary from high-to-low resistance to air flow in the vocal tract
Increased resistance is created by narrowing or lengthening the vocal tract
Decreased resistance is created by opening and shortening the vocal tract

Examples of SOVTs (from higher to lower resistance) include:
phonating while holding a straw between the lips, humming, sustaining a voiced labiodental fricative, voicing during lip or tongue trill, sustaining voice alveolar or velar nasal consonants, and sustaining high tongue vowels
Lip Trills (Raspberries)
Trills and raspberries are beneficial for singers who use glottal onsets

Means of reducing tension in the tongue, jaw, and lips as an assist in "establishing legato lines"
Sound is produced smoothly and connected without intervening silence

Provides a sensation to the singer of elevated pressure within the upper vocal tract which signals them to "push less" in order to generate the voice

During the lip trill:
Flow resistance at the lips is high and time-varying
Frequency of oscillation of intraoral pressure is low causing variation in transglottal pressure
Reduced transglottal pressure results in less collision force between the vocal folds
Amplitude of vocal fold movement is reduced
Vocal Tract Semi-Occlusion Exercises and Elongation
Alexandra Kolb, Megan Lowe, Erica Oks, Amanda Ubertini
Voice disorders affect the ability to communicate and interact with others

Voice therapy is frequently used as primary treatment or as a supplement to surgical intervention

Many voice therapy techniques and programs are based on exercises that semi-occlude the vocal tract
References
Dargin & Searl (2015)
Andrade, P. A., Wood, G., Ratcliffe, P., Epstein, R., Pijper, A., & Svec, J. G. (2014).
Electroglottographic Study of Seven Semi-Occluded Exercises: LaxVox, Straw, Lip-Trill, Tongue-Trill, Humming, Hand-Over-Mouth, and Tongue-Trill Combined With Hand-Over-Mouth.
Journal of Voice
, 28(5), 589-595.
Colten, R.H., Casper, J.K., & Leonard, R. (2011). Understanding voice problems: A physiological
perspective for diagnosis and treatment, Fourth edition, MD: Lippincott Williams & Wilkins
Dargin, T. C., & Searl, J. (2015). Semi-occluded vocal tract exercises: Aerodynamic and
electroglottographic measurements in singers. Journal of Voice. 29(2), 155-164
Rosenberg, M. D. (2014). Using semi-occluded vocal tract exercises in voice therapy: the
clinician’s primer.
Perspectives on Voice and Voice Disorders
, 24(2), 71-79.
Titze, I.R. (2013). One more small step in solving the mystery of the benefits of semioccluded
vocal tract exercises.
Journal of Singing
. 69(3), 305-306
Titze, I. & Hunter, E. (2011). Feasibility of measurement of a voice range profile with a semi-
occluded vocal tract.
Logopedics Phoniatrics Vocology
. 36(1), 32-39
Dargin & Searl (2015)
Rationale
Vocalization becomes:
Easier to produce
More resonant
More centrally placed in terms of adduction and registration

Acoustic benefits
A vocal tract air column that vibrates (up & down) can create a reactive push-pull on the tissue surfaces so that vocal fold vibration is reinforced
Therefore, a vocal tract that is narrowed (semi-occluded) in some region along its length helps to produce a favorable push-pull effect

Aerodynamic benefits
A steady back pressure in the vocal tract can help stabilize vocal fold adduction
As the vocal tract is semi-occluded, a steady pressure is maintained
This pressure helps to balance an always strong pressure below the vocal folds
Titze (2013)
Dargin & Searl (2015)
Rationale
Straws/tubes have been used to elongate the vocal tract and produce easy and effortless phonation

SOVT tasks require individuals to sustain phonation of selected stimuli and to focus on coordination of respiration, phonation, ease of production, and of sensations associated with these productions

These strategies have been termed "Impedance Matching"
The optimization of impedance in the vocal tract with impedance of the vibratory source
When the vocal tract is elongated (i.e. with a straw) the larynx lowers and the laryngeal and pharyngeal muscles relax
As intraglottal pressure increases, more thyroarytenoid muscle activity occurs
The glottis becomes more rectangular in shape, the vocal folds thicken, and the phonation threshold pressure decreases
Glottal economy and efficiency (ratio of oral radiated power to aerodynamic power) increases
Colten, Casper, & Leonard (2011)
Semi-Occluded Vocal Tract Exercises
1. Steady
-
Examples
: hand-over-mouth, humming, and straw
- Single source of vibration into the vocal tract (i.e., vocal folds)
- Steady electroglottography contact quotient (CQ), contact quotient range (CQr), and fundamental frequency (Fo)
- Lower F1 - F0 values ( theoretically higher positive vocal tract reactance, promoting an easy phonation)

2. Fluctauting
-
Examples
: tongue-trill, lip-trill, and Lax-Vox
- Secondary source of vibration into the vocal tract
- Massage effect: Varying supraglottal pressure
- Fluctuating CQ and Fo
- The exercises show higher F1 - Fo (theoretically lower positive vocal tract reactance making the phonation less easy)

3. Mixing SOVTE between the groups
-
Example
: tongue-trill (fluctuating exercise) with hand-over-mouth (steady exercise)
- Massage effect
- F1 - Fo difference became smaller (promoting an easier phonation)
Andrade, Wood, Ratcliffe, Epstein, Pijper, & Svec (2014)
Rationale
Individuals with normal voices present clearer, brighter, and more sonorous voices after performing semi-occluded exercises

Effective reinforcement of the vocal fold vibration via proper phasing of supraglottal acoustic pressures due to vocal tract resonance

The vocal tract length or cross section is altered
Causing an impedance match between the vocal tract and vocal folds
Feeds energy back to the glottis as it produces an in-phase velocity between the supraglottal pressure and airflow

Supraglottal acoustic changes cause lowering of the first vocal tract formant (F1)
Allowing the fundamental frequency (Fo) of speech to be closer to F1
Increasing inertive reactance of the vocal tract and producing a more efficient vocal fold vibration pattern
Andrade, Wood, Ratcliffe, Epstein, Pijper, & Svec (2014)
Perceptual Characteristics of the Voice being Targeted
Voice quality that is neither breathy nor pressed

Reduce excessive tension on the vocal tract

Facilitate resonant voice quality

Reduction in the cross-sectional area of the distal part of the vocal tract that alters the acoustic vocal tract impedance in relation to the glottis impedance
Andrade, Wood, Ratcliffe, Epstein, Pijper, & Svec (2014)
Voice Therapy Plan
Recommended for Professional voice users
Engaging the breathing mechanism during warm-ups before performances

Recommended for vocal pathologies like vocal fatigue, recurrent laryngeal nerve paresis, and nodules

Frequency and length of techniques are variable based on client
Andrade, Wood, Ratcliffe, Epstein, Pijper, & Svec (2014)
Feedback
Many variations of SOVT exercises provide for opportunity to direct the patient to external, kinesthetic feedback
Patient senses friction or "buzzing" on his/her face and within the oral cavity
Results in better long-term acquisition of the skill/technique
Rosenberg (2014)
Titze & Hunter (2011) utilized the Voice Range Profile (VRP) also known as the phonetogram
Display of sound intensity range in a voice over a range of fundamental frequencies.
Two boundaries
Low-intensity: threshold for voicing
High-intensity: maximum safe vocal intensity (self-percieved)
Valuable for documenting changes in voice characteristics over time
Maps out pitch and loudness
Can be designed to display some elements of irregularity
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