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Semioccluded Vocal Tract Exercises: Changes in Laryngeal and Pharyngeal Activity During Stroboscopy
Semioccluded Vocal Tract Exercises: Changes in Laryngeal and Pharyngeal Activity During Stroboscopy *Troy Clifford Dargin, †Anne DeLaunay, and ‡Jeff Searl, *Lawrence and zKansas City, Kansas, and yKansas City, Missouri Summary: Objective. The purpose of this study was to compare the changes in laryngeal activity from baseline during three different semioccluded vocal tract exercises (SOVTs). Study Design. This is a prospective case-series study. Methods. Transnasal stroboscopy was performed while four singers performed three SOVTs (straw phonation, lip trill, and tongue trill) to evaluate laryngeal changes during the execution of SOVTs. Evaluations using a modified Stroboscopy Evaluation Rating Form captured the following parameters: amplitude of vocal fold movement, mucosal wave, phase closure, glottal closure, anterior-posterior vocal tract constrictions, medial-lateral vocal tract constrictions, laryngeal ascension, and pharyngeal constriction during a pitch glide. Results. The parameters that changed from baseline, as well as the direction and magnitude of change that occurred across SOVTs, varied within and between each subject. All the singers benefited from at least one SOVT, but no single SOVT benefited all four singers. Conclusions. Although SOVTs result in endoscopic and stroboscopic changes that might be considered beneficial, the results indicate marked variability across SOVTs and singers in terms of the laryngeal and pharyngeal adjustments induced by the exercises. Singing teachers and Speech Language Pathologists (SLPs) may need to more carefully assess the impact of specific SOVTs when deciding which one(s) to prescribe as a teaching or therapeutic exercise. Key Words: Semioccluded vocal tract–Pharyngeal–Laryngeal–Stroboscopy–Singing.
INTRODUCTION Semioccluded vocal tract exercises (SOVTs) are increasingly being incorporated into vocal warm-up and training regimens for singers.1,2 Singers and singing teachers have advocated vocal warm-up before performing or working with the voice for many years,3,4 although in a recent survey, just over half of singers reported completing warm-ups.5 Reasons stated for the importance of doing vocal warm-ups in the singing community vary but include the belief that it may lessen the chance of vocal injury5 and that the singing voice is easier to produce, more versatile, and stronger following warm-ups.6 The specific type of warm-up exercise to use and the actual benefit of the exercise remain open to debate. Selection of exercises appears to be more a function of a teacher’s or singer’s personal preference and previous training. Some advocate whole body aerobic warm-ups,7 stretching and relaxation exercises for the head and neck,4 diaphragmatic breathing activities,8 and a wide range of vocal tasks. The vocal tasks typically include some version of pitch and register changes such as scales and arpeggios4,8 with a variety of goals such as increased vocal flexibility, agility, and improved transition Accepted for publication May 1, 2015. Portions of this work have been presented at The Voice Foundation, Philadelphia, PA, June 2, 2012 (‘‘Speaker Differences in Laryngeal Activity,’’ The Voice Foundation, Philadelphia, PA, June 2, 2012) and the National Center for Voice and Speech, Salt Lake City, UT, July 9, 2011 (‘‘Stroboscopic and Aerodynamic Changes Associated With Semioccluded Vocal Tract Exercises—Preliminary Data’’). From the *University of Kansas, Dole Human Development Center, Lawrence, Kansas; yUniversity of Missouri-Kansas City Conservatory of Music, Kansas City, Missouri; and the zUniversity of Kansas Medical Center, Kansas City, Kansas. Address correspondence and reprint requests to Troy Clifford Dargin, University of Kansas, 1000 Sunnyside Ave., 3001 Dole Human Development Center, office 3017, Lawrence, KS 66045-7555. E-mail: [email protected] Journal of Voice, Vol. -, No. -, pp. 1-9 0892-1997/$36.00 Ó 2015 The Voice Foundation http://dx.doi.org/10.1016/j.jvoice.2015.05.006
between registers. Phonating across a range of pitches, registers, and loudness levels while partially obstructing the vocal tract constitutes an SOVT exercise.9 In essence, SOVTs are a modified version of exercises that have historically been promoted for warm-up and training of singers. There are several types of SOVTs that have been described in the literature, and these vary along a continuum of the degree of vocal tract occlusion. From greater to lesser occlusion, a partial list of SOVTs includes phonation through a straw held between the lips, sustained voiced fricative production (such as /v/), lip trills, tongue trills, and humming (nasal /m/ consonant).10,11 Straw phonation is grounded in a long-standing practice of phonating into a tube that dates back older than 100 years but has only started to be evaluated empirically within the past 10–15 years.12 The singer holds a straw firmly between the lips while phonating across a range of pitches and intensities. Similarly, trills are produced at the lips or at the linguaalveolar ridge while sustaining phonation; both the vocal folds and the lips or tongue tip oscillate during the task. Humming and sustained voiced fricatives are done by partially occluding the vocal tract for the target consonant while phonating; in the case of the hum, the constriction orally is complete and the palate is lowered to allow phonation to be sustained with nasal sound production. Studies of the impacts of warm-up exercises in general have produced ambiguous results when assessed instrumentally, although the impacts for SOVTs in particular suggest perhaps more consistent changes. For warm-up routines that are non– SOVT-specific (but might include some trials with nasal and fricative consonants), a measure of the phonation threshold pressure (PTP) has been used most often as an index of the physiologic effect. PTP is defined as the minimum subglottal air pressure that is needed to set the vocal folds into vibration.13
2 PTP should be lowered following warm-ups if the exercises improve the function of the phonatory mechanism. That was found to be the case for soprano singers (n ¼ 10, aged 19– 21 years) who warmed up completing various ascending and descending legato scales on /zi/, staccato triads on /i/, stepwise thirds over one half octave on /trioioi/, and allegro scales on /vi/.14 However, no consistent pattern of change in PTP occurred for amateur male (n ¼ 3) and female (n ¼ 7) singers who warmed up by sustaining a variety of vowels at different pitch and loudness level and singing /mu/ on a descending pitch with some subjects even demonstrating an increase in PTP after exercise.15 In a group of eight female nonsingers who experienced vocal fatigue, warm-up exercises also did not result in a reduction of PTP.16 Of two singers who warmed up using exercises of their own choice, the men demonstrated lowering of the larynx after warming up but the women did not while epilaryngeal outlet-to-pharyngeal inlet dimensions (measured via magnetic resonance imaging [MRI]) increased for both suggesting some supraglottal alterations occurred.17 Lowering of the larynx is associated with closer spacing of the formants during sustained vowels and may contribute to generating the singer’s formant18 which is a clustering of the third, fourth, and fifth formants that helps the singer’s voice to be heard in the presence of an orchestra. The emerging data specific to SOVTs suggest that there may be predictable changes during and after the semiocclusion tasks although much remains to be evaluated. According to Titze,9 partial occlusion of the vocal tract during SOVTs increases the air pressure above (supraglottal) and between the vocal folds (intraglottal) resulting in decreased glottal resistance and slightly separated positioning of the vocal folds. Computational modeling and human study approaches have indicated that semiocclusion can result in efficient vocal fold vibration that minimizes vocal fold collision forces.12,19 By keeping collision forces low, a singer could, theoretically, warm up the voice across a range of pitches, registers, and loudness levels while limiting the likelihood of vocal fold tissue damage. Straw and tube phonation is perhaps the most studied of the SOVTs. On the basis of computational models, oral air pressure is substantially elevated during the task, resulting in the back pressure that decreases glottal resistance and slightly parts the vocal folds.20 Increasing the straw length and/or decreasing the diameter created greater resistance and higher oral air pressure in two male and one female participants (nonsingers).2 Airflow (sustained vowel and /pa/) also has been demonstrated to increase immediately after completing SOVTs and laryngeal resistance to decrease for singers completing straw phonation, lip trills, and tongue trills in four singers.21 Both Laukkanen et al17 and Guzman et al1 noted that oral cavity, pharynx, and epilarynx tube areas measured via MRI were all increased immediately after straw phonation exercises (single subjects in each study) which could have a positive impact on the singing voice. Acoustic changes are expected to occur when completing SOVTs. Singing power ratio (higher harmonic energy/lower harmonic energy) was increased in the frequency region of the singer’s formant by a male singer during and after completing straw phonation.22 Barrichelo-Lindstrom and
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Behlau23 studied 54 acting students trained to produce the Y-Buzz. The Y-Buzz is a type of SOVT produced with a combination of the consonant /j/ and the /i/ vowel. After training, there was acoustic evidence of vocal tract lengthening as indicated by lowering the first four formant frequencies for better tuning of formants. Additionally, the distance between F1 and F0 was smaller. This indicates a more efficient transference function of the vocal tract, wherein two formants or a partial and formant are close in proximity resulting in greater amplitude of those frequencies.24 Titze and Laukkanen20 found similar results through computational modeling of phonation through a resonance tube, wherein F1 was lowered from 300 to 150 Hz and the intraoral acoustic pressure tripled. The vocal tract inertive reactance at 100 Hz (f0) was doubled. In contrast, Laukkanen et al17 reported in their single subject study that there was essentially no shifting of formant frequency after completing a brief trial of straw phonation although they found MRI evidence of vocal tract area adjustments that should be favorable for the singing voice. In terms of overall voice intensity, Dargin and Searl21 found that sound pressure level immediately after completing SOVTs (straw phonation, lip trill, and tongue trill) tended to increase in a group of four singers. In addition to aerodynamic and acoustic alterations associated with SOVTs, electroglottographic (EGG) studies have also been completed. Guzman et al22 had a male singer complete straw phonation and found a decrease in the EGG contact quotient during phonation immediately after the SOVT task. This suggests less vocal fold contact as would occur with a slight parting of the vocal folds predicted to occur during SOVTs. Similar reduction in the contact quotient has been reported by Gaskill and Erickson25 for trained (n ¼ 11) and untrained (n ¼ 14) male singers producing a lip trill for 1 minute; the reduction was more prominent for the untrained singers. Hamdan et al26 also reported a reduction in the contact quotient for 10 female participants (six trained and four untrained) completing a Mediterranean tongue trill called a Zalghouta which is used in rituals at weddings and festivals. However, in contrast to Gaskill and Erickson,25 the reduction in contact quotient after the Mediterranean trill occurred only for the trained participants and not the untrained. Furthermore, one other study has reported an increase in the mean contact quotient associated with lip trill in a study of 10 professional operatic singers (five men and five women).27 Surprisingly, there are only a few studies in the literature regarding SOVT-related adjustments detectable via stroboscopy and endoscopy. Guzman et al28 looked at the effect of eight SOVT vocal tract postures on pharyngeal and laryngeal changes with nonsingers diagnosed with hyperfunctional dysphonia (19 women and nine men). They reported that all SOVTs resulted in lowering of the larynx during phonation, epilarynx narrowing, and widening of the pharynx compared with baseline non-SOVT status. Cordeiro et al27 investigated lip trill and tongue trill with five female and five male singers to see if there was a difference visually when phonating on a nonoccluded /3/ vowel. This study mainly looked at maximum vocal fold amplitude. They found that higher frequencies produced higher closed quotients during the lip trill.
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Changes in Laryngeal and Pharyngeal Activity
3
Some of the differences that are described in the modeling, EGG and MRI studies, as well as those predicted from the acoustic studies, might be evident in stroboscopic and endoscopic studies. Because stroboscopy is now widely available in clinics and training facilities, the stroboscopic examination could serve a valuable role in advancing SOVT research and might also be an option for training and assessing the outcomes of SOVT protocols for individual singers. At present, however, assessment of laryngeal and pharyngeal adjustments via stroboscopy completed during SOVT execution is quite limited. Lack of information about stroboscopic and endoscopic changes during or after SOVTs is one limit in the present literature. A second issue that has been largely ignored is the comparability in voice and laryngeal function outcomes across different SOVTs within a given singer. Most of the SOVT literature has focused on a specific type of SOVT. It may be the case that for an individual singer, one SOVT may cause a certain set of changes to the phonation process, but a different SOVT may create its own unique set of changes. Understanding whether all SOVTs result in similar laryngeal and pharyngeal adjustments within a singer has important implications for how teachers and clinicians prescribe SOVTs. This study had two purposes that address these two limitations in the extant literature on SOVTs. The first purpose was to gather pilot data on a range of parameters commonly rated by Speech Language Pathologists (SLPs) and researchers from stroboscopic and endoscopic examinations of the larynx. On the basis of predictions from modeling and other studies of SOVT, it was hypothesized that differences in glottal closure, mucosal wave excursion, supraglottic activity (ventricular folds and arytenoid complex epiglottis positioning), laryngeal height changes, and pharyngeal contraction would be visually detectable from stroboscopic examinations during SOVTs. The second purpose was to compare stroboscopic ratings within subject for three commonly used SOVTs: straw phonation, lip trill, and tongue trill.
Instrumentation Endoscopic and videostroboscopic examinations were completed using a flexible scope (model FNL-10RP3 with Pentax VNL-1170K camera) and KayPENTAX (Montvale, NJ) digital videostroboscopy system (model 9295). A microphone held to the neck on the thyroid cartilage was used to detect the fundamental frequency of the voice for stroboscopy.
METHODS Participants Three male tenors and one female soprano participated in this study. These four participated in the study by Dargin and Searl,21 wherein changes in aerodynamic and electroglottographic parameters after SOVTs were described. Subjects ranged in age from 25 to 35 years (mean, 28.25; standard deviation, 2.9) and all had >10 years of classical voice training. Two participants reported regular use of an SOVT (lip buzz, humming) as part of their vocal warm-up before voice lessons and private practice (tenor 1 and tenor 2); the other two did not (tenor 3 and soprano). Absence of laryngeal pathology was confirmed at the time of scoping for this study, and none reported a history of laryngeal or voice problems necessitating medical or SLP treatment with the exception of tenor 3 who had previously been on medication for reflux but was not currently. The study was approved by the institutional review board at the University of Kansas Medical Center. These four were selected because of their extensive training as singers and also their availability for participation.
For straw phonation, the subject held a short straw (7.7500 long 3 0.3000 diameter) firmly between the lips. This is a typical drinking straw, in contrast to a narrower stirring straw that has been used in some other studies. The subjects were instructed to keep the lips completely sealed around the straw as they phonated. The target was the sung vowel /i/ on a self-selected comfortable pitch and loudness although the holding of the straw precluded production of a vowel that was perceived as a distinct /i/. Study personnel observed the lip seal around the straw throughout the trials to encourage complete lip seal. If a trial was compromised by incomplete lip seal, the subject was stopped and the trial repeated. For the lip trill, the subject was instructed to ‘‘flutter’’ the lips (ie, raspberry with the lips) while phonating (a model from research personnel was provided). Again, the target phonation was a sung /i/. For the tongue trill, the subject was instructed to loosely extend the tongue between the lips while phonating to make the ‘‘raspberry.’’ As with straw phonation, subjects were instructed to produce phonation during trills on a self-selected comfortable pitch and loudness.
Procedures 1. Endoscopic/stroboscopic examinations were completed with the participant seated in an endoscopy suite. A vasoconstrictor was administered in the participant’s most patent nostril (determined by listening to nasal breathing while alternately closing one nostril then the other). A licensed and certified SLP with >15 years of experience performing laryngeal examinations completed all the endoscopies. The scope was passed through the nose and the endoscopist, using a continuous light source, obtained views of the pharynx, hypopharynx, and larynx to assess for any abnormalities in structures, tissue irregularities or color changes, and so forth. Once this structural assessment was completed, the scope was positioned to view the vocal folds, laryngeal vestibule, and hypopharynx. Subjects then completed the following: a. Sustained /i/. The vowel /i/ was sung for 10 seconds at a self-selected pitch and comfortable loudness. This was repeated three times with a short break between trials. Then, they sang /i/ on an octave scale ascending and descending from the self-selected pitch at a moderate tempo. This was repeated three times or more if needed to obtain a recording with a clear view of the larynx, pharynx, and hypopharynx. b. SOVTs: Subjects completed three trials of each of straw phonation, lip trill, and tongue trill.
4 Measures and analysis The two authors served as raters of the video recordings. One was a licensed SLP with >15 years of clinic experience in the area of voice disorders, and the other was a graduate student in speech-language pathology. A modified version of the Stroboscopy Evaluation Rating Form (SERF; Poburka, 1999) was used for making visual perceptual ratings. Four parameters from the SERF included for rating were (1) amplitude of vocal fold edge movement from midline (0 ¼ no movement– 10 ¼ greatest excursion from midline), (2) mucosal wave excursion (0–10), (3) phase closure (categorized as open/closed ratio of 90%/10%, 66%/33%, 33%/66%, 10%/90% per Poburka, 1999), and (4) glottal closure (categorized as complete, hourglass, incomplete, irregular, posterior gap, anterior gap, spindle gap, variable pattern). The SERF also rates supraglottic activity as a composite of anterior-posterior (AP) and medial-lateral (ML) constrictions (0 ¼ none to 5 ¼ complete/nearly complete constriction). For this study, we rated AP and ML constrictions separately given the possibility that someone might have different degrees of constriction for AP and ML. Two additional parameters, not part of the SERF, were added for rating. These were (1) laryngeal height elevation during pitch glide (0 ¼ none and 4 ¼ significant) and (2) pharyngeal constriction during pitch glide (0 ¼ none, 1 ¼ some, and 2 ¼ significant). These were added to allow some description of possible global changes in the larynx and pharynx during singing activity. Items from the SERF excluded from ratings were nonvibrating portion, vocal fold edge smoothness, vocal fold edge straightness, vertical height, phase symmetry, and regularity. Reasons for excluding these parameters were primarily related to rater reliability referenced by the SERF developer or reduced relevance for rating nondisordered larynges. Before making their ratings, the two raters met to review the SERF and the accompanying article that described the parameters from the SERF.29 They discussed each parameter to establish a common understanding of what each represented. Each rater independently viewed the recorded laryngeal examinations. The raters were allowed to view the examinations as many times as they wished, using regular speed playback as well as slow motion and frame-by-frame playback. They then compared ratings and resolved differences by consensus. In addition to ratings of individual parameters, the raters were required to categorize the overall impact of a given SOVT for each subject as one of the following: beneficial, no change, worse, or equivocal. For this judgment, the two raters (by consensus) looked at how many parameters changed, the direction of the change, and the magnitude of the change to come to a decision about the benefit of the SOVT for that subject. Equivocal was intended for situations in which both notable benefit and worsening occurred across the set of parameters. These decisions were intended to reflect a clinical decision that an SLP would make or a training decision that a teacher would make, in assessing the degree of benefit, if any, from each SOVT. The following guidelines for each parameter were used when helping to make this overall rating. Desirable outcomes were (1) amplitude ratings of 4–6 (one-third to half
Journal of Voice, Vol. -, No. -, 2015
the width of the visible vocal fold surface; per); (2) mucosal wave ratings of 4–6; (3) phase closure of 66/33; (4) glottal closure categorization as small posterior gap (SOVTs are expected to result in less complete closure); (5) AP constriction ratings that increase (epilarynx tube narrowing in the AP dimension is predicted to occur with SOVTs); (6) ML constriction ratings that decrease; (7) laryngeal height adjustment ratings that decrease; and (8) pharyngeal constriction ratings that decrease. Ultimately, the decision about change from a particular SOVT was a weighing of changes (or lack thereof) across the full set of parameters being judged. The data were treated as a four-case series. The consensus stroboscopy ratings were put into a table for each rating parameter in each of the voicing conditions (baseline, straw phonation, lip trill, tongue trill). Patterns of change in ratings across the voicing conditions were identified by the authors and described. Commonalities and differences in how the eight parameters changed across the four singers were then described. RESULTS Individual patterns Ratings for each subject across the four phonation conditions (non-SOVT, straw phonation, lip trill, and tongue trill) are in Table 1. Tenor 1. This singer had two visible indicators of excess phonatory tension during the non-SOVT baseline singing: moderate elevation of the larynx during pitch glide up and visible constriction of the pharynx during pitch glide up. He also had AP constriction that did not allow visualization of the true vocal folds precluding ratings of vocal fold amplitude, mucosal wave, phase closure, and glottal closure. It should be noted that he denied any voice complaints, and research personnel did not perceptually identify any concerning voice features during informal conversation or study activities. The view was similar during straw phonation with the addition of moderate ML supraglottic constriction (usually considered a negative feature). The most notable visible changes occurred during the tongue trill. The ML supraglottic constriction was eliminated; during pitch glide, pharyngeal constriction was eliminated and laryngeal height adjustment was reduced. Taken together, these observations suggested reduced phonatory effort during the tongue trill. The lip trill produced nearly identical results with the exception that minimal ML constriction was introduced where none was present in the baseline condition. Because the supraglottic constriction was eliminated in the trill conditions, the true vocal folds could be evaluated. Amplitude and mucosal wave were within an expected range (both rated 6) and phase closure was normal (66%/33%); a small posterior glottal gap was consistently present. Overall, it appeared that lip and tongue trill resulted in the most positive changes evidenced in the larynx; straw phonation did not produce beneficial results, and in fact, added ML constriction that was not present during baseline. Tenor 2. In the baseline condition, the most striking feature was a phase closure of 10%/90% which is consistent with
4
10/90
4
10/90
Post. Post. Post. Post. gap gap gap gap 1 1 1 0 1 1 1 1 1 0 0 1 No No No No Post. Post. Post. Post. gap gap gap gap 2 2 3 3 3 3 2 3 0 0 0 0 No No Yes Yes AP constriction ML constriction Larynx height Pharyngeal constriction
Glottal closure
Phase closure
Mucosal wave
5
‘‘pressed’’ phonation.29 This phase closure remained for all the SOVT conditions. A few subtle changes were noted during the SOVTs. Straw phonation ratings were identical to non-SOVT with the exception of a small, inconsistent posterior glottal gap. Lip trill was identical to the non-SOVT with the exception of a slight increase (from 4 to 6) in the amplitude and mucosal wave ratings. Tongue trill differed from non-SOVT in that a consistent posterior gap, slight ML compression, and pharyngeal constriction during the pitch glides were present. Overall, there were very few changes, and those that occurred were of limited magnitude, during the three SOVTs for this subject relative to the baseline condition.
Abbreviations: Non, nonocclusion condition; Straw, straw phonation; Lip, lip trill; tongue, tongue trill; AP, anterior-posterior; ML, medial-lateral. Note: The bold values indicate ‘‘improved’’ performance; Italicized entries indicate possible ‘‘negative’’ impact. * Inconsistently present.
4
Comp Post. Comp Post. gap* gap 0 0 0 0 0 0 0 1 0 0 0 0 No No No Yes
66/33 66/33 66/33 66/33 66/33
Straw
4
Tongue Lip Straw Non
Not visible Not visible Not visible Not visible 3 0 2 Yes Amplitude
Strobe Parameter
Not 6 6 visible Not 6 6 visible Not 66/33 66/33 visible Not Post. Post. visible gap gap 3 0 0 2 1 0 2 1 1 Yes No No
Non
10/90
10/90
10/90
66/33
6 4 4 4 6
2
2
Straw
4 6
2
Tongue Lip
Non
66/33
6 8 6
6
6 6
6
Lip Straw
4 4 4
Lip
Tongue
S1 T3 T2 T1
TABLE 1. Endoscopy and Stroboscopy Ratings for Each Subject in All Conditions
Changes in Laryngeal and Pharyngeal Activity
Non
Tongue
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Tenor 3. Ratings during baseline were consistent with hyperfunction within the larynx. Phase closure was 10%/90% (pressed), amplitude and mucosal wave were dampened (ratings of 2), and ML supraglottic constriction was present. The most consistent changes during SOVTs were that phase closure shifted from 10%/90 to 66%/33% (‘‘normal’’) and the mucosal wave increased by 2–4 scale points regardless of the SOVT. Amplitude increased by 2 scale points during lip and tongue trill but not straw phonation. AP constriction increased 1 scale point from mild (2) to moderate (3) on lip and tongue trill but not straw phonation. ML constriction decreased from moderate to mild during lip trill but was unchanged during straw phonation and tongue trill. Finally, the lip and tongue trill conditions had visible pharyngeal contraction during pitch glide when none was present at baseline. Overall, straw phonation markedly improved phase closure and mucosal wave without introducing pharyngeal constriction but ML constriction remained. Lip trill improved phase closure, mucosal wave, amplitude, and ML constriction but introduced pharyngeal constriction. Tongue trill improved the same parameters as lip trill with the exceptions of unchanged ML constriction; unwanted pharyngeal constriction also occurred on the tongue trill. Soprano 1. Baseline ratings were generally within expected parameters other than mild AP and ML constrictions and mild laryngeal height adjustment. Vibration amplitude increased from a rating of 4 during non-SOVT phonation to 6 during each of the three SOVTs. Mucosal wave also increased for the straw phonation but not the trills. There was a slight shift in glottal closure during tongue trills with a small anterior glottic gap present along with the posterior gap that was consistently present in all other conditions. AP supraglottic constriction was reduced from 1 in the non-SOVT task to 0 during tongue trills. Laryngeal height adjustment was eliminated in the straw and lip trill phonation versus minimal height adjustments in non-SOVT and tongue trill. No changes occurred for phase closure (66%/33%, normal throughout) or ML supraglottic constriction (minimal throughout). Overall, there were modest positive changes in vibratory characteristics of the vocal folds and laryngeal height adjustments across all three SOVTs. Group patterns Several observations can be made from the summary information in Table 2. First, each SOVT was beneficial to at least two
6
TABLE 2. Summary of Positive and Negative Changes in Stroboscopy Parameters During Each SOVT Per Individual and Group Straw Phonation Subject
Versus Baseline
Comments [ML constriction Pharyngeal constriction persists
Lip Trill Versus Baseline Equivocal
Worse
T2
No Change
T3
Better
Improved phase closure [Mucosal wave But M/L constriction persists
S1
Better
[Amplitude Better [Mucosal wave YLaryngeal height adjustment 3 0 0 1
Benefit None Worse Equivocal
2 1 1 0
Better
Better
[ML constriction YAP constriction YLarynx height adjustment YPharyngeal constriction [Amplitude [Mucosal wave But still pressed Improved phase closure [Amplitude [Mucosal wave YML constriction But added mild pharyngeal constriction and slight decrease in AP constriction [Amplitude YLaryngeal height adjustment
Versus Baseline Better
Worse
Better
Equivocal
2 0 1 1
Comments YSupraglottic constriction YLarynx height adjustment YPharyngeal constriction [ML constriction [Pharyngeal tension Improved phase closure [Amplitude [Mucosal wave [ AP constriction But added mild pharyngeal constriction
[amplitude YAP constriction
Number of SOVTs Resulting in. Benefit None Worse Equivocal 1
0
1
1
1
1
1
0
3
0
0
0
2
0
0
1
7 1 2 2
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T1
Comments
Tongue Trill
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Changes in Laryngeal and Pharyngeal Activity
singers. Second, none of the SOVTs was beneficial for all the singers. Third, two of the SOVTs were judged to have worsened the phonatory situation for one subject apiece. Straw phonation for T1 and tongue trill for T2 each resulted in pharyngeal constriction and increased ML constriction. Lip trill did not worsen the situation for any singer but had equivocal changes for T1. Fourth, all four singers benefited from at least one SOVT. One singer (T3) benefited from all three of the SOVTs. Another (S1) benefited from two SOVTs, namely, straw phonation and lip trill. The remaining two singers each benefited from a single SOVT: for T1, the benefit was from tongue trills, and for T2, the benefit was from lip trills. Overall, if one considers 12 possible situations wherein a change in phonatory activity could occur (four singers 3 three SOVTs), benefit was noted seven times (58%), worsening two times (17%), equivocal outcomes two times (17%), and no change once (8%). DISCUSSION The purposes of this study were (1) to describe changes in laryngeal and pharyngeal activity during SOVTs relative to non-SOVT phonation, which were detectable during endoscopy/stroboscopy in four singers, and (2) to describe within-singer differences in laryngeal and pharyngeal activity occurring across three SOVTs. The main findings of this study were that a number of parameters did, in fact, change when singers were doing SOVTs but the changes were not uniform across SOVTs or across singers. Overall, potential benefits in laryngeal and pharyngeal activity during SOVTs were observed for all four of the singers, but the SOVT that was beneficial and the specific parameters that changed varied. Impact of the individual participant Singers in the present study demonstrated marked variation in whether laryngeal and pharyngeal adjustments occurred during a particular SOVT, the parameters that changed, and the extent of change. Singers T1 and T2, for example, were judged to have benefited from only one of the three SOVTs on the basis of the stroboscopic ratings that changed, and the judgment of improvement for T2 in particular during lip trill may be open to some debate. He presented with phase closure at baseline that was ‘‘pressed’’ (10/90 rating), and this persisted throughout all SOVTs, even lip trills, from which he was judged to benefit on the basis of improved vocal fold amplitude and mucosal wave ratings. Thus, it was the case that lip trill improved more than one parameter, but his most deviant baseline parameter (phase closure) was not positively changed. Also of interest for these two is that they each also demonstrated changes judged to be worse during SOVTs compared with baseline. Titze30 found that PTP changes varied substantially between singers phonating through a straw. They theorized that the singers who use more source filter tract interaction will have more ‘‘peaks and valleys’’ (p. 1071) than those who do not. Guzman et al28 found that narrower aryepiglottic opening occurred with all participants during every SOVT execution. This narrowing can be thought of as being a negative element to vocal production; however, ‘‘.a narrowed epilarynx tube
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causes some steady back pressure in the glottis . and thus leads to higher economy’’20 (p.154). The fact that some endoscopic/stroboscopic parameters may worsen during certain exercises for some singers, and may show positive changes only on specific exercises, highlights the need for more careful selection of the SOVT that they use for warm-up or training. It is interesting to note that T1 and T2 both reported regular use of SOVTs, yet they were the two singers who experienced the least amount of change from pre- to post-SOVT in this study. It may be the case that regular use of SOVTs before the study had already changed phonatory parameters for these two such that there was less room for change during the study itself. A differently designed study is needed to evaluate the long-term impacts of SOVTS on endoscopic and stroboscopic parameters. At the opposite extreme of outcomes from T1 and T2 was that from T3, who was judged to have benefited from all three SOVTs. Recall that T3 demonstrated some indications of laryngeal hyperfunction in his baseline recording including pressed phase closure, dampened amplitude and mucosal wave, and ML constriction. It may be that he had the most to gain from SOVTs. Again, further work evaluating the impact of SOVTs in individuals with evidence of hyperfunction is needed before drawing strong conclusions. Each SOVT dramatically shifted T3’s phase closure as reflected in ‘‘normal’’ judgments (66/33 ratings) by the two raters. The extent of mucosal wave excursion also increased 1–2 scale points during all three SOVTs. These changes are consistent with predictions and reports that semiocclusion should result in more efficient vocal fold vibration.31,32 Additional alterations for this singer during the trill tasks such as an increase in the amplitude of vocal fold vibration (lip and tongue trill), decreased ML constriction (lip trill), and increased AP constriction (tongue trill) also are consistent with phonation efficiency during singing. Although the weight of the evidence for T3 suggested ‘‘better’’ phonation in the trill tasks, there were some minor changes that were not desirable such as mild increase in pharyngeal constriction. Knowledge of details about the specific parameters that shift for a given SOVT for a given singer may prove meaningful in the training (or therapeutic) process depending on what issues a singer is having with the voice. Although the current results are taken from a small sample, they are intriguing because the individual subject variability31 in response to specific SOVTs suggests that singers and teachers of singers may need to more carefully select specific SOVTs for each person. Stroboscopy examinations can potentially help in the selection process. In this manner, a specific SOVT (or set of SOVTs) can be identified that provides the greatest beneficial change and those that do not clearly help and those that worsen phonatory activity can be avoided. This targeted approach to SOVT selection should result in a more efficient training process. The serial use of stroboscopy during the training could potentially serve to guide ongoing decisions about the benefits of an SOVT or the need to shift course. Impact of a specific SOVT None of the three SOVTs universally improved laryngeal and pharyngeal activity for the singers in this study. Lip trill was
8 judged to help the most singers (ie, three of four) and did not worsen the situation for any singer. Straw phonation and tongue trill each helped two singers but also worsened the overall phonation situation as judged visually for one singer each. Titze30 found substantial intersubject variability with regards to average PTP and its change with F0. Tongue trills can be difficult for some individuals to execute. This could explain why some individuals do worse with tongue trills than with other SOVTs. Straw phonation is also a difficult task for some individuals to complete because there can be no air loss through the corners of the mouth or the nose. For individuals who are not acutely aware of sensations like this, they could be attempting straw phonation without actually succeeding at the task despite the best monitoring by researchers, teachers, or clinicians. Lip trills are easy for most individuals because they have past exposure to such a warm-up task. Extended practice time executing SOVT tasks may be needed to see the full benefit of the exercises. Because each individual is unique in their vocal tract shape, it is reasonable to assume that different people respond differently to individual SOVTs. This is why singing teachers should have a variety of instructional methods and exercises to use as well as the capability to assess the impact of specific SOVTs for an individual. Visually detectable changes in laryngeal status were not consistent for a specific SOVT. For example, during straw phonation, the phase closure shifted from 10/90 to 66/33 for T3 but not for T2. Similarly, amplitude of vibration increased during straw phonation for T3 and S1 but not for T2 (the glottis was not visible during straw phonation for T1 precluding description of change). ML constriction was increased during lip trill for one subject (T1), decreased in another (S1), and unchanged in the remaining two singers. Several other examples of this variability in parameter changed, and direction of change for the same SOVT is apparent in the data. This suggests there is not a universal set of parameters that change as detected in stroboscopic examinations during a particular SOVT when produced by different people. Overall, it appeared that SOVTs generally, but not universally, resulted in beneficial changes in the larynx and pharynx in these four singers. However, it will be important to determine the extent to which no change, worsening, or equivocal change occurs in a larger set of singers. When one considers that in seven of twelve situations (four singers 3 three SOVTs), beneficial changes were judged to have occurred during SOVT execution, there is generally positive support from the stroboscopic data for use of SOVTs to effect change in the larynx and pharynx. Yet, these results highlight the need to assess the impact of an SOVT for a given individual to avoid selecting one that does not clearly help. The current data suggest that such selection will have to occur on an individual basis and that stroboscopic imaging could serve a practical role for this purpose. Ratings of AP and ML supraglottic constrictions require comment. Most SLPs are likely to defend the position that supraglottic constriction is indicative of unwanted laryngeal effort, but this is open to debate. In nonsingers who are speaking rather than singing, AP narrowing has been suggested as indicative of hyper-
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functional voice production.33,34 This is traditionally how SLPs have understood the compression of the aryepiglottic tube. However, singing research suggests the situation is likely different when singing. Narrowing of the epilarynx tube in the AP dimension is what enables the singer’s formant (cluster of third, fourth, and fifth formants) to emerge.35 In order for epilarynx tube narrowing to be of benefit to the singer, only AP compression, and not ML, should occur.36 A contributor to epilarynx tube narrowing is an increase in pharyngeal cross-sectional area.20,28 Some singing teachers promote ‘‘open throat singing,’’ which is intended to widen the pharyngeal space for optimal voice efficiency. It was for these reasons that in the present study, AP constriction was considered beneficial, whereas ML constriction and pharyngeal tension were judged as detrimental to phonation by the singers. It may be the case that both AP and ML constrictions during talking in nonsingers are a sign of excess phonatory effort. A differently designed study that assesses singers and nonsingers and which includes manipulation of supraglottic constriction would be needed for further understanding of the issue. Conclusions and limitations Overall, there were changes in laryngeal and pharyngeal activity detectable by stroboscopy during execution of SOVTs for all four singers. The specific parameters that changed, the magnitude of change, and the SOVT on which changes occurred differed across participants. Although most instances of detectable change were interpreted as beneficial, there were situations wherein laryngeal and/or pharyngeal activity was considered to be worsened during an SOVT compared with that subject’s nonSOVT phonation. Pending confirmation of the current results, use of stroboscopy, and endoscopy to guide selection of specific SOVTs for an individual may be appropriate. It is not possible to make definitive statements that one SOVT exercise is more beneficial than another across all individuals. Rather, there is likely to be a specific SOVT or subset of SOVTs that is of most benefit for a particular individual, but this can vary from person to person. Guzman et al28 also reported that to be the case for the measures, they assessed in their SOVT study. There are limitations to this study. The small sample size limits the ability to broadly generalize the results. It is unknown from this study whether greater or different changes in laryngeal and pharyngeal activity would occur during SOVTs if the exercises were done on an extended basis. The results only speak to the changes that occurred during the brief period of SOVT execution during the study. It is possible that there is an evolution to the changes that occur with extended practice. This study also cannot address the important issue of whether SOVT-induced changes in phonation persist beyond the execution of the exercise itself. Acknowledgments The authors would like to acknowledge the University of Kansas Graduate School for two summer research fellowships to help with the continuing research of this topic. The authors also thank the subjects who volunteered their time on this project.
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REFERENCES
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1. Guzman M, Laukkanen A-M, Krupa P, Horacek J, Svec JG, Geneid A. Vocal tract and glottal function during and after vocal exercising with resonance tube and straw. J Voice. 2013;27:523.e519–523.e534. 2. Laukkanen A-M, Pulakka H, Alku P, et al. High-speed registration of phonation-related glottal area variation during artificial lengthening of the vocal tract. Logoped Phoniatr Vocol. 2007;32:157–164. 3. Barr S. Singing warm-ups: physiology, psychology, or placebo? Logoped Phoniatr Vocol. 2009;34:142–144. 4. Hylton JB. Comprehensive Choral Music Education. Prentice Hall; 1995. 5. Gish A, Kunduk M, Sims L, McWhorter AJ. Vocal warm-up practices and perceptions in vocalists: a pilot survey. J Voice. 2012;26:e1–e10. 6. Vintturi J, Alku P, Lauri E-R, Sala E, Sihvo M, Vilkman E. Objective analysis of vocal warm-up with special reference to ergonomic factors. J Voice. 2001;15:36–53. 7. Shear P. Sing with power, range, and control. Can Musician. 2008;30:32. 8. Miller R. Warming up the voice. NATS J. 1990;46:22–23. 9. Titze IR. Lip and tongue trills—what do they do for us? J Singing. 1996;52: 51–53. 10. Titze IR. Voice training and therapy with a semi-occluded vocal tract: rationale and scientific underpinnings. J Speech Lang Hear Res. 2006;49:448–459. 11. Nix J. Voice research and technology: semi-occluded vocal tract postures and their application in the singing voice studio. J Singing. 2008;64:339–342. 12. Story BH, Laukkanen A-M, Titze IR. Acoustic impedance of an artificially lengthened and constricted vocal tract. J Voice. 2000;14:455–469. 13. Titze IR. The physics of small-amplitude oscillation of the vocal folds. J Acoust Soc Am. 1988;83:1536–1552. 14. Motel T, Fisher KV, Leydon C. Vocal warm-up increases phonation threshold pressure in soprano singers at high pitch. J Voice. 2003;17:160–167. 15. Elliot N, Sundberg J, Gramming P. What happens during vocal warm-up? J Voice. 1995;9:37–44. 16. Milbrath RL, Solomon NP. Do vocal warm-up exercises alleviate vocal fatigue? J Speech Lang Hear Res. 2003;46. 17. Laukkanen A-M, Horacek J, Krupa P, Svec JG. The effect of phonation into a straw on the vocal tract adjustments and formant frequencies. A preliminary MRI study on a single subject completed with acoustic results. Biomed Signal Process Control. 2012;7:50–57. 18. Sundberg J. Vocal tract resonance. In: Sataloff R, ed. Vocal Health and Pedagogy. San Diego, CA: Singular Publishing; 1998:47–64. 19. Titze I, Finnegan E, Laukkanen A, Jaiswal S. Raising lung pressure and pitch in vocal warm-ups: the use of flow-resistant straws. J Singing. 2002;58:329–338.
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20. Titze IR, Laukkanen A-M. Can vocal economy in phonation be increased with an artificially lengthened vocal tract? A computer modeling study. Logoped Phoniatr Vocol. 2007;32:147–156. 21. Dargin TC, Searl J. Semi-occluded vocal tract exercises: aerodynamic and electroglottographic measurements in singers. J Voice. 2015;29:155–164. 22. Guzman M, Rubin A, Mu~noz D, Jackson-Menaldi C. Changes in glottal contact quotient during resonance tube phonation and phonation with vibrato. J Voice. 2013;27:305–311. 23. Barrichelo-Lindstr€om V, Behlau M. Resonant voice in acting students: perceptual and acoustic correlates of the trained Y-Buzz by Lessac. J Voice. 2009;23:603–609. 24. Carlsson G, Sundberg J. Formant frequency tuning in singing. J Voice. 1992;6:256–260. 25. Gaskill CS, Erickson ML. The effect of a voiced lip trill on estimated glottal closed quotient. J Voice. 2008;22:634–643. 26. Hamdan A-L, Nassar J, Al Zaghal Z, El-Khoury E, Bsat M, Tabri D. Glottal contact quotient in Mediterranean tongue trill. J Voice. 2012;26:669. e611–669.e615. 27. Cordeiro GF, Montagnoli AN, Nemr NK, Menezes MH, Tsuji DH. Comparative analysis of the closed quotient for lip and tongue trills in relation to the sustained vowel /ε/. J Voice. 2012;26:e17–e22. 28. Guzman M, Castro C, Testart A, Mu~noz D, Gerhard J. Laryngeal and pharyngeal activity during semioccluded vocal tract postures in subjects diagnosed with hyperfunctional dysphonia. J Voice. 2013;27:709–716. 29. Poburka BJ. A new stroboscopy rating form. J Voice. 1999;13:403–413. 30. Titze IR. Phonation threshold pressure measurement with a semi-occluded vocal tract. J Speech Lang Hear Res. 2009;52:1062–1072. 31. Maxfield L, Titze I, Hunter E, Kapsner-Smith M. Intraoral pressures produced by thirteen semi-occluded vocal tract gestures. Logoped Phoniatr Vocol. 2014;1–7. 32. Yiu EM, Chen FC, Lo G, Pang G. Vibratory and perceptual measurement of resonant voice. J Voice. 2012;26:675.e613–675.e619. 33. Stager SV, Bielamowicz SA, Regnell JR, Gupta A, Barkmeier JM. Supraglottic activity: evidence of vocal hyperfunction or laryngeal articulation? J Speech Lang Hear Res. 2000;43:229. 34. Stager SV, Bielamowicz S, Gupta A, Marullo S, Regnell JR, Barkmeier J. Quantification of static and dynamic supraglottic activity. J Speech Lang Hear Res. 2001;44:1245. 35. Sundberg J. Articulatory interpretation of the ‘‘singing formant’’. J Acoust Soc Am. 1974;55:838–844. 36. Titze IR. Acoustic interpretation of resonant voice. J Voice. 2001;15: 519–528.
INTRODUCTION Semioccluded vocal tract exercises (SOVTs) are increasingly being incorporated into vocal warm-up and training regimens for singers.1,2 Singers and singing teachers have advocated vocal warm-up before performing or working with the voice for many years,3,4 although in a recent survey, just over half of singers reported completing warm-ups.5 Reasons stated for the importance of doing vocal warm-ups in the singing community vary but include the belief that it may lessen the chance of vocal injury5 and that the singing voice is easier to produce, more versatile, and stronger following warm-ups.6 The specific type of warm-up exercise to use and the actual benefit of the exercise remain open to debate. Selection of exercises appears to be more a function of a teacher’s or singer’s personal preference and previous training. Some advocate whole body aerobic warm-ups,7 stretching and relaxation exercises for the head and neck,4 diaphragmatic breathing activities,8 and a wide range of vocal tasks. The vocal tasks typically include some version of pitch and register changes such as scales and arpeggios4,8 with a variety of goals such as increased vocal flexibility, agility, and improved transition Accepted for publication May 1, 2015. Portions of this work have been presented at The Voice Foundation, Philadelphia, PA, June 2, 2012 (‘‘Speaker Differences in Laryngeal Activity,’’ The Voice Foundation, Philadelphia, PA, June 2, 2012) and the National Center for Voice and Speech, Salt Lake City, UT, July 9, 2011 (‘‘Stroboscopic and Aerodynamic Changes Associated With Semioccluded Vocal Tract Exercises—Preliminary Data’’). From the *University of Kansas, Dole Human Development Center, Lawrence, Kansas; yUniversity of Missouri-Kansas City Conservatory of Music, Kansas City, Missouri; and the zUniversity of Kansas Medical Center, Kansas City, Kansas. Address correspondence and reprint requests to Troy Clifford Dargin, University of Kansas, 1000 Sunnyside Ave., 3001 Dole Human Development Center, office 3017, Lawrence, KS 66045-7555. E-mail: [email protected] Journal of Voice, Vol. -, No. -, pp. 1-9 0892-1997/$36.00 Ó 2015 The Voice Foundation http://dx.doi.org/10.1016/j.jvoice.2015.05.006
between registers. Phonating across a range of pitches, registers, and loudness levels while partially obstructing the vocal tract constitutes an SOVT exercise.9 In essence, SOVTs are a modified version of exercises that have historically been promoted for warm-up and training of singers. There are several types of SOVTs that have been described in the literature, and these vary along a continuum of the degree of vocal tract occlusion. From greater to lesser occlusion, a partial list of SOVTs includes phonation through a straw held between the lips, sustained voiced fricative production (such as /v/), lip trills, tongue trills, and humming (nasal /m/ consonant).10,11 Straw phonation is grounded in a long-standing practice of phonating into a tube that dates back older than 100 years but has only started to be evaluated empirically within the past 10–15 years.12 The singer holds a straw firmly between the lips while phonating across a range of pitches and intensities. Similarly, trills are produced at the lips or at the linguaalveolar ridge while sustaining phonation; both the vocal folds and the lips or tongue tip oscillate during the task. Humming and sustained voiced fricatives are done by partially occluding the vocal tract for the target consonant while phonating; in the case of the hum, the constriction orally is complete and the palate is lowered to allow phonation to be sustained with nasal sound production. Studies of the impacts of warm-up exercises in general have produced ambiguous results when assessed instrumentally, although the impacts for SOVTs in particular suggest perhaps more consistent changes. For warm-up routines that are non– SOVT-specific (but might include some trials with nasal and fricative consonants), a measure of the phonation threshold pressure (PTP) has been used most often as an index of the physiologic effect. PTP is defined as the minimum subglottal air pressure that is needed to set the vocal folds into vibration.13
2 PTP should be lowered following warm-ups if the exercises improve the function of the phonatory mechanism. That was found to be the case for soprano singers (n ¼ 10, aged 19– 21 years) who warmed up completing various ascending and descending legato scales on /zi/, staccato triads on /i/, stepwise thirds over one half octave on /trioioi/, and allegro scales on /vi/.14 However, no consistent pattern of change in PTP occurred for amateur male (n ¼ 3) and female (n ¼ 7) singers who warmed up by sustaining a variety of vowels at different pitch and loudness level and singing /mu/ on a descending pitch with some subjects even demonstrating an increase in PTP after exercise.15 In a group of eight female nonsingers who experienced vocal fatigue, warm-up exercises also did not result in a reduction of PTP.16 Of two singers who warmed up using exercises of their own choice, the men demonstrated lowering of the larynx after warming up but the women did not while epilaryngeal outlet-to-pharyngeal inlet dimensions (measured via magnetic resonance imaging [MRI]) increased for both suggesting some supraglottal alterations occurred.17 Lowering of the larynx is associated with closer spacing of the formants during sustained vowels and may contribute to generating the singer’s formant18 which is a clustering of the third, fourth, and fifth formants that helps the singer’s voice to be heard in the presence of an orchestra. The emerging data specific to SOVTs suggest that there may be predictable changes during and after the semiocclusion tasks although much remains to be evaluated. According to Titze,9 partial occlusion of the vocal tract during SOVTs increases the air pressure above (supraglottal) and between the vocal folds (intraglottal) resulting in decreased glottal resistance and slightly separated positioning of the vocal folds. Computational modeling and human study approaches have indicated that semiocclusion can result in efficient vocal fold vibration that minimizes vocal fold collision forces.12,19 By keeping collision forces low, a singer could, theoretically, warm up the voice across a range of pitches, registers, and loudness levels while limiting the likelihood of vocal fold tissue damage. Straw and tube phonation is perhaps the most studied of the SOVTs. On the basis of computational models, oral air pressure is substantially elevated during the task, resulting in the back pressure that decreases glottal resistance and slightly parts the vocal folds.20 Increasing the straw length and/or decreasing the diameter created greater resistance and higher oral air pressure in two male and one female participants (nonsingers).2 Airflow (sustained vowel and /pa/) also has been demonstrated to increase immediately after completing SOVTs and laryngeal resistance to decrease for singers completing straw phonation, lip trills, and tongue trills in four singers.21 Both Laukkanen et al17 and Guzman et al1 noted that oral cavity, pharynx, and epilarynx tube areas measured via MRI were all increased immediately after straw phonation exercises (single subjects in each study) which could have a positive impact on the singing voice. Acoustic changes are expected to occur when completing SOVTs. Singing power ratio (higher harmonic energy/lower harmonic energy) was increased in the frequency region of the singer’s formant by a male singer during and after completing straw phonation.22 Barrichelo-Lindstrom and
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Behlau23 studied 54 acting students trained to produce the Y-Buzz. The Y-Buzz is a type of SOVT produced with a combination of the consonant /j/ and the /i/ vowel. After training, there was acoustic evidence of vocal tract lengthening as indicated by lowering the first four formant frequencies for better tuning of formants. Additionally, the distance between F1 and F0 was smaller. This indicates a more efficient transference function of the vocal tract, wherein two formants or a partial and formant are close in proximity resulting in greater amplitude of those frequencies.24 Titze and Laukkanen20 found similar results through computational modeling of phonation through a resonance tube, wherein F1 was lowered from 300 to 150 Hz and the intraoral acoustic pressure tripled. The vocal tract inertive reactance at 100 Hz (f0) was doubled. In contrast, Laukkanen et al17 reported in their single subject study that there was essentially no shifting of formant frequency after completing a brief trial of straw phonation although they found MRI evidence of vocal tract area adjustments that should be favorable for the singing voice. In terms of overall voice intensity, Dargin and Searl21 found that sound pressure level immediately after completing SOVTs (straw phonation, lip trill, and tongue trill) tended to increase in a group of four singers. In addition to aerodynamic and acoustic alterations associated with SOVTs, electroglottographic (EGG) studies have also been completed. Guzman et al22 had a male singer complete straw phonation and found a decrease in the EGG contact quotient during phonation immediately after the SOVT task. This suggests less vocal fold contact as would occur with a slight parting of the vocal folds predicted to occur during SOVTs. Similar reduction in the contact quotient has been reported by Gaskill and Erickson25 for trained (n ¼ 11) and untrained (n ¼ 14) male singers producing a lip trill for 1 minute; the reduction was more prominent for the untrained singers. Hamdan et al26 also reported a reduction in the contact quotient for 10 female participants (six trained and four untrained) completing a Mediterranean tongue trill called a Zalghouta which is used in rituals at weddings and festivals. However, in contrast to Gaskill and Erickson,25 the reduction in contact quotient after the Mediterranean trill occurred only for the trained participants and not the untrained. Furthermore, one other study has reported an increase in the mean contact quotient associated with lip trill in a study of 10 professional operatic singers (five men and five women).27 Surprisingly, there are only a few studies in the literature regarding SOVT-related adjustments detectable via stroboscopy and endoscopy. Guzman et al28 looked at the effect of eight SOVT vocal tract postures on pharyngeal and laryngeal changes with nonsingers diagnosed with hyperfunctional dysphonia (19 women and nine men). They reported that all SOVTs resulted in lowering of the larynx during phonation, epilarynx narrowing, and widening of the pharynx compared with baseline non-SOVT status. Cordeiro et al27 investigated lip trill and tongue trill with five female and five male singers to see if there was a difference visually when phonating on a nonoccluded /3/ vowel. This study mainly looked at maximum vocal fold amplitude. They found that higher frequencies produced higher closed quotients during the lip trill.
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Some of the differences that are described in the modeling, EGG and MRI studies, as well as those predicted from the acoustic studies, might be evident in stroboscopic and endoscopic studies. Because stroboscopy is now widely available in clinics and training facilities, the stroboscopic examination could serve a valuable role in advancing SOVT research and might also be an option for training and assessing the outcomes of SOVT protocols for individual singers. At present, however, assessment of laryngeal and pharyngeal adjustments via stroboscopy completed during SOVT execution is quite limited. Lack of information about stroboscopic and endoscopic changes during or after SOVTs is one limit in the present literature. A second issue that has been largely ignored is the comparability in voice and laryngeal function outcomes across different SOVTs within a given singer. Most of the SOVT literature has focused on a specific type of SOVT. It may be the case that for an individual singer, one SOVT may cause a certain set of changes to the phonation process, but a different SOVT may create its own unique set of changes. Understanding whether all SOVTs result in similar laryngeal and pharyngeal adjustments within a singer has important implications for how teachers and clinicians prescribe SOVTs. This study had two purposes that address these two limitations in the extant literature on SOVTs. The first purpose was to gather pilot data on a range of parameters commonly rated by Speech Language Pathologists (SLPs) and researchers from stroboscopic and endoscopic examinations of the larynx. On the basis of predictions from modeling and other studies of SOVT, it was hypothesized that differences in glottal closure, mucosal wave excursion, supraglottic activity (ventricular folds and arytenoid complex epiglottis positioning), laryngeal height changes, and pharyngeal contraction would be visually detectable from stroboscopic examinations during SOVTs. The second purpose was to compare stroboscopic ratings within subject for three commonly used SOVTs: straw phonation, lip trill, and tongue trill.
Instrumentation Endoscopic and videostroboscopic examinations were completed using a flexible scope (model FNL-10RP3 with Pentax VNL-1170K camera) and KayPENTAX (Montvale, NJ) digital videostroboscopy system (model 9295). A microphone held to the neck on the thyroid cartilage was used to detect the fundamental frequency of the voice for stroboscopy.
METHODS Participants Three male tenors and one female soprano participated in this study. These four participated in the study by Dargin and Searl,21 wherein changes in aerodynamic and electroglottographic parameters after SOVTs were described. Subjects ranged in age from 25 to 35 years (mean, 28.25; standard deviation, 2.9) and all had >10 years of classical voice training. Two participants reported regular use of an SOVT (lip buzz, humming) as part of their vocal warm-up before voice lessons and private practice (tenor 1 and tenor 2); the other two did not (tenor 3 and soprano). Absence of laryngeal pathology was confirmed at the time of scoping for this study, and none reported a history of laryngeal or voice problems necessitating medical or SLP treatment with the exception of tenor 3 who had previously been on medication for reflux but was not currently. The study was approved by the institutional review board at the University of Kansas Medical Center. These four were selected because of their extensive training as singers and also their availability for participation.
For straw phonation, the subject held a short straw (7.7500 long 3 0.3000 diameter) firmly between the lips. This is a typical drinking straw, in contrast to a narrower stirring straw that has been used in some other studies. The subjects were instructed to keep the lips completely sealed around the straw as they phonated. The target was the sung vowel /i/ on a self-selected comfortable pitch and loudness although the holding of the straw precluded production of a vowel that was perceived as a distinct /i/. Study personnel observed the lip seal around the straw throughout the trials to encourage complete lip seal. If a trial was compromised by incomplete lip seal, the subject was stopped and the trial repeated. For the lip trill, the subject was instructed to ‘‘flutter’’ the lips (ie, raspberry with the lips) while phonating (a model from research personnel was provided). Again, the target phonation was a sung /i/. For the tongue trill, the subject was instructed to loosely extend the tongue between the lips while phonating to make the ‘‘raspberry.’’ As with straw phonation, subjects were instructed to produce phonation during trills on a self-selected comfortable pitch and loudness.
Procedures 1. Endoscopic/stroboscopic examinations were completed with the participant seated in an endoscopy suite. A vasoconstrictor was administered in the participant’s most patent nostril (determined by listening to nasal breathing while alternately closing one nostril then the other). A licensed and certified SLP with >15 years of experience performing laryngeal examinations completed all the endoscopies. The scope was passed through the nose and the endoscopist, using a continuous light source, obtained views of the pharynx, hypopharynx, and larynx to assess for any abnormalities in structures, tissue irregularities or color changes, and so forth. Once this structural assessment was completed, the scope was positioned to view the vocal folds, laryngeal vestibule, and hypopharynx. Subjects then completed the following: a. Sustained /i/. The vowel /i/ was sung for 10 seconds at a self-selected pitch and comfortable loudness. This was repeated three times with a short break between trials. Then, they sang /i/ on an octave scale ascending and descending from the self-selected pitch at a moderate tempo. This was repeated three times or more if needed to obtain a recording with a clear view of the larynx, pharynx, and hypopharynx. b. SOVTs: Subjects completed three trials of each of straw phonation, lip trill, and tongue trill.
4 Measures and analysis The two authors served as raters of the video recordings. One was a licensed SLP with >15 years of clinic experience in the area of voice disorders, and the other was a graduate student in speech-language pathology. A modified version of the Stroboscopy Evaluation Rating Form (SERF; Poburka, 1999) was used for making visual perceptual ratings. Four parameters from the SERF included for rating were (1) amplitude of vocal fold edge movement from midline (0 ¼ no movement– 10 ¼ greatest excursion from midline), (2) mucosal wave excursion (0–10), (3) phase closure (categorized as open/closed ratio of 90%/10%, 66%/33%, 33%/66%, 10%/90% per Poburka, 1999), and (4) glottal closure (categorized as complete, hourglass, incomplete, irregular, posterior gap, anterior gap, spindle gap, variable pattern). The SERF also rates supraglottic activity as a composite of anterior-posterior (AP) and medial-lateral (ML) constrictions (0 ¼ none to 5 ¼ complete/nearly complete constriction). For this study, we rated AP and ML constrictions separately given the possibility that someone might have different degrees of constriction for AP and ML. Two additional parameters, not part of the SERF, were added for rating. These were (1) laryngeal height elevation during pitch glide (0 ¼ none and 4 ¼ significant) and (2) pharyngeal constriction during pitch glide (0 ¼ none, 1 ¼ some, and 2 ¼ significant). These were added to allow some description of possible global changes in the larynx and pharynx during singing activity. Items from the SERF excluded from ratings were nonvibrating portion, vocal fold edge smoothness, vocal fold edge straightness, vertical height, phase symmetry, and regularity. Reasons for excluding these parameters were primarily related to rater reliability referenced by the SERF developer or reduced relevance for rating nondisordered larynges. Before making their ratings, the two raters met to review the SERF and the accompanying article that described the parameters from the SERF.29 They discussed each parameter to establish a common understanding of what each represented. Each rater independently viewed the recorded laryngeal examinations. The raters were allowed to view the examinations as many times as they wished, using regular speed playback as well as slow motion and frame-by-frame playback. They then compared ratings and resolved differences by consensus. In addition to ratings of individual parameters, the raters were required to categorize the overall impact of a given SOVT for each subject as one of the following: beneficial, no change, worse, or equivocal. For this judgment, the two raters (by consensus) looked at how many parameters changed, the direction of the change, and the magnitude of the change to come to a decision about the benefit of the SOVT for that subject. Equivocal was intended for situations in which both notable benefit and worsening occurred across the set of parameters. These decisions were intended to reflect a clinical decision that an SLP would make or a training decision that a teacher would make, in assessing the degree of benefit, if any, from each SOVT. The following guidelines for each parameter were used when helping to make this overall rating. Desirable outcomes were (1) amplitude ratings of 4–6 (one-third to half
Journal of Voice, Vol. -, No. -, 2015
the width of the visible vocal fold surface; per); (2) mucosal wave ratings of 4–6; (3) phase closure of 66/33; (4) glottal closure categorization as small posterior gap (SOVTs are expected to result in less complete closure); (5) AP constriction ratings that increase (epilarynx tube narrowing in the AP dimension is predicted to occur with SOVTs); (6) ML constriction ratings that decrease; (7) laryngeal height adjustment ratings that decrease; and (8) pharyngeal constriction ratings that decrease. Ultimately, the decision about change from a particular SOVT was a weighing of changes (or lack thereof) across the full set of parameters being judged. The data were treated as a four-case series. The consensus stroboscopy ratings were put into a table for each rating parameter in each of the voicing conditions (baseline, straw phonation, lip trill, tongue trill). Patterns of change in ratings across the voicing conditions were identified by the authors and described. Commonalities and differences in how the eight parameters changed across the four singers were then described. RESULTS Individual patterns Ratings for each subject across the four phonation conditions (non-SOVT, straw phonation, lip trill, and tongue trill) are in Table 1. Tenor 1. This singer had two visible indicators of excess phonatory tension during the non-SOVT baseline singing: moderate elevation of the larynx during pitch glide up and visible constriction of the pharynx during pitch glide up. He also had AP constriction that did not allow visualization of the true vocal folds precluding ratings of vocal fold amplitude, mucosal wave, phase closure, and glottal closure. It should be noted that he denied any voice complaints, and research personnel did not perceptually identify any concerning voice features during informal conversation or study activities. The view was similar during straw phonation with the addition of moderate ML supraglottic constriction (usually considered a negative feature). The most notable visible changes occurred during the tongue trill. The ML supraglottic constriction was eliminated; during pitch glide, pharyngeal constriction was eliminated and laryngeal height adjustment was reduced. Taken together, these observations suggested reduced phonatory effort during the tongue trill. The lip trill produced nearly identical results with the exception that minimal ML constriction was introduced where none was present in the baseline condition. Because the supraglottic constriction was eliminated in the trill conditions, the true vocal folds could be evaluated. Amplitude and mucosal wave were within an expected range (both rated 6) and phase closure was normal (66%/33%); a small posterior glottal gap was consistently present. Overall, it appeared that lip and tongue trill resulted in the most positive changes evidenced in the larynx; straw phonation did not produce beneficial results, and in fact, added ML constriction that was not present during baseline. Tenor 2. In the baseline condition, the most striking feature was a phase closure of 10%/90% which is consistent with
4
10/90
4
10/90
Post. Post. Post. Post. gap gap gap gap 1 1 1 0 1 1 1 1 1 0 0 1 No No No No Post. Post. Post. Post. gap gap gap gap 2 2 3 3 3 3 2 3 0 0 0 0 No No Yes Yes AP constriction ML constriction Larynx height Pharyngeal constriction
Glottal closure
Phase closure
Mucosal wave
5
‘‘pressed’’ phonation.29 This phase closure remained for all the SOVT conditions. A few subtle changes were noted during the SOVTs. Straw phonation ratings were identical to non-SOVT with the exception of a small, inconsistent posterior glottal gap. Lip trill was identical to the non-SOVT with the exception of a slight increase (from 4 to 6) in the amplitude and mucosal wave ratings. Tongue trill differed from non-SOVT in that a consistent posterior gap, slight ML compression, and pharyngeal constriction during the pitch glides were present. Overall, there were very few changes, and those that occurred were of limited magnitude, during the three SOVTs for this subject relative to the baseline condition.
Abbreviations: Non, nonocclusion condition; Straw, straw phonation; Lip, lip trill; tongue, tongue trill; AP, anterior-posterior; ML, medial-lateral. Note: The bold values indicate ‘‘improved’’ performance; Italicized entries indicate possible ‘‘negative’’ impact. * Inconsistently present.
4
Comp Post. Comp Post. gap* gap 0 0 0 0 0 0 0 1 0 0 0 0 No No No Yes
66/33 66/33 66/33 66/33 66/33
Straw
4
Tongue Lip Straw Non
Not visible Not visible Not visible Not visible 3 0 2 Yes Amplitude
Strobe Parameter
Not 6 6 visible Not 6 6 visible Not 66/33 66/33 visible Not Post. Post. visible gap gap 3 0 0 2 1 0 2 1 1 Yes No No
Non
10/90
10/90
10/90
66/33
6 4 4 4 6
2
2
Straw
4 6
2
Tongue Lip
Non
66/33
6 8 6
6
6 6
6
Lip Straw
4 4 4
Lip
Tongue
S1 T3 T2 T1
TABLE 1. Endoscopy and Stroboscopy Ratings for Each Subject in All Conditions
Changes in Laryngeal and Pharyngeal Activity
Non
Tongue
Troy Clifford Dargin, et al
Tenor 3. Ratings during baseline were consistent with hyperfunction within the larynx. Phase closure was 10%/90% (pressed), amplitude and mucosal wave were dampened (ratings of 2), and ML supraglottic constriction was present. The most consistent changes during SOVTs were that phase closure shifted from 10%/90 to 66%/33% (‘‘normal’’) and the mucosal wave increased by 2–4 scale points regardless of the SOVT. Amplitude increased by 2 scale points during lip and tongue trill but not straw phonation. AP constriction increased 1 scale point from mild (2) to moderate (3) on lip and tongue trill but not straw phonation. ML constriction decreased from moderate to mild during lip trill but was unchanged during straw phonation and tongue trill. Finally, the lip and tongue trill conditions had visible pharyngeal contraction during pitch glide when none was present at baseline. Overall, straw phonation markedly improved phase closure and mucosal wave without introducing pharyngeal constriction but ML constriction remained. Lip trill improved phase closure, mucosal wave, amplitude, and ML constriction but introduced pharyngeal constriction. Tongue trill improved the same parameters as lip trill with the exceptions of unchanged ML constriction; unwanted pharyngeal constriction also occurred on the tongue trill. Soprano 1. Baseline ratings were generally within expected parameters other than mild AP and ML constrictions and mild laryngeal height adjustment. Vibration amplitude increased from a rating of 4 during non-SOVT phonation to 6 during each of the three SOVTs. Mucosal wave also increased for the straw phonation but not the trills. There was a slight shift in glottal closure during tongue trills with a small anterior glottic gap present along with the posterior gap that was consistently present in all other conditions. AP supraglottic constriction was reduced from 1 in the non-SOVT task to 0 during tongue trills. Laryngeal height adjustment was eliminated in the straw and lip trill phonation versus minimal height adjustments in non-SOVT and tongue trill. No changes occurred for phase closure (66%/33%, normal throughout) or ML supraglottic constriction (minimal throughout). Overall, there were modest positive changes in vibratory characteristics of the vocal folds and laryngeal height adjustments across all three SOVTs. Group patterns Several observations can be made from the summary information in Table 2. First, each SOVT was beneficial to at least two
6
TABLE 2. Summary of Positive and Negative Changes in Stroboscopy Parameters During Each SOVT Per Individual and Group Straw Phonation Subject
Versus Baseline
Comments [ML constriction Pharyngeal constriction persists
Lip Trill Versus Baseline Equivocal
Worse
T2
No Change
T3
Better
Improved phase closure [Mucosal wave But M/L constriction persists
S1
Better
[Amplitude Better [Mucosal wave YLaryngeal height adjustment 3 0 0 1
Benefit None Worse Equivocal
2 1 1 0
Better
Better
[ML constriction YAP constriction YLarynx height adjustment YPharyngeal constriction [Amplitude [Mucosal wave But still pressed Improved phase closure [Amplitude [Mucosal wave YML constriction But added mild pharyngeal constriction and slight decrease in AP constriction [Amplitude YLaryngeal height adjustment
Versus Baseline Better
Worse
Better
Equivocal
2 0 1 1
Comments YSupraglottic constriction YLarynx height adjustment YPharyngeal constriction [ML constriction [Pharyngeal tension Improved phase closure [Amplitude [Mucosal wave [ AP constriction But added mild pharyngeal constriction
[amplitude YAP constriction
Number of SOVTs Resulting in. Benefit None Worse Equivocal 1
0
1
1
1
1
1
0
3
0
0
0
2
0
0
1
7 1 2 2
Journal of Voice, Vol. -, No. -, 2015
T1
Comments
Tongue Trill
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Changes in Laryngeal and Pharyngeal Activity
singers. Second, none of the SOVTs was beneficial for all the singers. Third, two of the SOVTs were judged to have worsened the phonatory situation for one subject apiece. Straw phonation for T1 and tongue trill for T2 each resulted in pharyngeal constriction and increased ML constriction. Lip trill did not worsen the situation for any singer but had equivocal changes for T1. Fourth, all four singers benefited from at least one SOVT. One singer (T3) benefited from all three of the SOVTs. Another (S1) benefited from two SOVTs, namely, straw phonation and lip trill. The remaining two singers each benefited from a single SOVT: for T1, the benefit was from tongue trills, and for T2, the benefit was from lip trills. Overall, if one considers 12 possible situations wherein a change in phonatory activity could occur (four singers 3 three SOVTs), benefit was noted seven times (58%), worsening two times (17%), equivocal outcomes two times (17%), and no change once (8%). DISCUSSION The purposes of this study were (1) to describe changes in laryngeal and pharyngeal activity during SOVTs relative to non-SOVT phonation, which were detectable during endoscopy/stroboscopy in four singers, and (2) to describe within-singer differences in laryngeal and pharyngeal activity occurring across three SOVTs. The main findings of this study were that a number of parameters did, in fact, change when singers were doing SOVTs but the changes were not uniform across SOVTs or across singers. Overall, potential benefits in laryngeal and pharyngeal activity during SOVTs were observed for all four of the singers, but the SOVT that was beneficial and the specific parameters that changed varied. Impact of the individual participant Singers in the present study demonstrated marked variation in whether laryngeal and pharyngeal adjustments occurred during a particular SOVT, the parameters that changed, and the extent of change. Singers T1 and T2, for example, were judged to have benefited from only one of the three SOVTs on the basis of the stroboscopic ratings that changed, and the judgment of improvement for T2 in particular during lip trill may be open to some debate. He presented with phase closure at baseline that was ‘‘pressed’’ (10/90 rating), and this persisted throughout all SOVTs, even lip trills, from which he was judged to benefit on the basis of improved vocal fold amplitude and mucosal wave ratings. Thus, it was the case that lip trill improved more than one parameter, but his most deviant baseline parameter (phase closure) was not positively changed. Also of interest for these two is that they each also demonstrated changes judged to be worse during SOVTs compared with baseline. Titze30 found that PTP changes varied substantially between singers phonating through a straw. They theorized that the singers who use more source filter tract interaction will have more ‘‘peaks and valleys’’ (p. 1071) than those who do not. Guzman et al28 found that narrower aryepiglottic opening occurred with all participants during every SOVT execution. This narrowing can be thought of as being a negative element to vocal production; however, ‘‘.a narrowed epilarynx tube
7
causes some steady back pressure in the glottis . and thus leads to higher economy’’20 (p.154). The fact that some endoscopic/stroboscopic parameters may worsen during certain exercises for some singers, and may show positive changes only on specific exercises, highlights the need for more careful selection of the SOVT that they use for warm-up or training. It is interesting to note that T1 and T2 both reported regular use of SOVTs, yet they were the two singers who experienced the least amount of change from pre- to post-SOVT in this study. It may be the case that regular use of SOVTs before the study had already changed phonatory parameters for these two such that there was less room for change during the study itself. A differently designed study is needed to evaluate the long-term impacts of SOVTS on endoscopic and stroboscopic parameters. At the opposite extreme of outcomes from T1 and T2 was that from T3, who was judged to have benefited from all three SOVTs. Recall that T3 demonstrated some indications of laryngeal hyperfunction in his baseline recording including pressed phase closure, dampened amplitude and mucosal wave, and ML constriction. It may be that he had the most to gain from SOVTs. Again, further work evaluating the impact of SOVTs in individuals with evidence of hyperfunction is needed before drawing strong conclusions. Each SOVT dramatically shifted T3’s phase closure as reflected in ‘‘normal’’ judgments (66/33 ratings) by the two raters. The extent of mucosal wave excursion also increased 1–2 scale points during all three SOVTs. These changes are consistent with predictions and reports that semiocclusion should result in more efficient vocal fold vibration.31,32 Additional alterations for this singer during the trill tasks such as an increase in the amplitude of vocal fold vibration (lip and tongue trill), decreased ML constriction (lip trill), and increased AP constriction (tongue trill) also are consistent with phonation efficiency during singing. Although the weight of the evidence for T3 suggested ‘‘better’’ phonation in the trill tasks, there were some minor changes that were not desirable such as mild increase in pharyngeal constriction. Knowledge of details about the specific parameters that shift for a given SOVT for a given singer may prove meaningful in the training (or therapeutic) process depending on what issues a singer is having with the voice. Although the current results are taken from a small sample, they are intriguing because the individual subject variability31 in response to specific SOVTs suggests that singers and teachers of singers may need to more carefully select specific SOVTs for each person. Stroboscopy examinations can potentially help in the selection process. In this manner, a specific SOVT (or set of SOVTs) can be identified that provides the greatest beneficial change and those that do not clearly help and those that worsen phonatory activity can be avoided. This targeted approach to SOVT selection should result in a more efficient training process. The serial use of stroboscopy during the training could potentially serve to guide ongoing decisions about the benefits of an SOVT or the need to shift course. Impact of a specific SOVT None of the three SOVTs universally improved laryngeal and pharyngeal activity for the singers in this study. Lip trill was
8 judged to help the most singers (ie, three of four) and did not worsen the situation for any singer. Straw phonation and tongue trill each helped two singers but also worsened the overall phonation situation as judged visually for one singer each. Titze30 found substantial intersubject variability with regards to average PTP and its change with F0. Tongue trills can be difficult for some individuals to execute. This could explain why some individuals do worse with tongue trills than with other SOVTs. Straw phonation is also a difficult task for some individuals to complete because there can be no air loss through the corners of the mouth or the nose. For individuals who are not acutely aware of sensations like this, they could be attempting straw phonation without actually succeeding at the task despite the best monitoring by researchers, teachers, or clinicians. Lip trills are easy for most individuals because they have past exposure to such a warm-up task. Extended practice time executing SOVT tasks may be needed to see the full benefit of the exercises. Because each individual is unique in their vocal tract shape, it is reasonable to assume that different people respond differently to individual SOVTs. This is why singing teachers should have a variety of instructional methods and exercises to use as well as the capability to assess the impact of specific SOVTs for an individual. Visually detectable changes in laryngeal status were not consistent for a specific SOVT. For example, during straw phonation, the phase closure shifted from 10/90 to 66/33 for T3 but not for T2. Similarly, amplitude of vibration increased during straw phonation for T3 and S1 but not for T2 (the glottis was not visible during straw phonation for T1 precluding description of change). ML constriction was increased during lip trill for one subject (T1), decreased in another (S1), and unchanged in the remaining two singers. Several other examples of this variability in parameter changed, and direction of change for the same SOVT is apparent in the data. This suggests there is not a universal set of parameters that change as detected in stroboscopic examinations during a particular SOVT when produced by different people. Overall, it appeared that SOVTs generally, but not universally, resulted in beneficial changes in the larynx and pharynx in these four singers. However, it will be important to determine the extent to which no change, worsening, or equivocal change occurs in a larger set of singers. When one considers that in seven of twelve situations (four singers 3 three SOVTs), beneficial changes were judged to have occurred during SOVT execution, there is generally positive support from the stroboscopic data for use of SOVTs to effect change in the larynx and pharynx. Yet, these results highlight the need to assess the impact of an SOVT for a given individual to avoid selecting one that does not clearly help. The current data suggest that such selection will have to occur on an individual basis and that stroboscopic imaging could serve a practical role for this purpose. Ratings of AP and ML supraglottic constrictions require comment. Most SLPs are likely to defend the position that supraglottic constriction is indicative of unwanted laryngeal effort, but this is open to debate. In nonsingers who are speaking rather than singing, AP narrowing has been suggested as indicative of hyper-
Journal of Voice, Vol. -, No. -, 2015
functional voice production.33,34 This is traditionally how SLPs have understood the compression of the aryepiglottic tube. However, singing research suggests the situation is likely different when singing. Narrowing of the epilarynx tube in the AP dimension is what enables the singer’s formant (cluster of third, fourth, and fifth formants) to emerge.35 In order for epilarynx tube narrowing to be of benefit to the singer, only AP compression, and not ML, should occur.36 A contributor to epilarynx tube narrowing is an increase in pharyngeal cross-sectional area.20,28 Some singing teachers promote ‘‘open throat singing,’’ which is intended to widen the pharyngeal space for optimal voice efficiency. It was for these reasons that in the present study, AP constriction was considered beneficial, whereas ML constriction and pharyngeal tension were judged as detrimental to phonation by the singers. It may be the case that both AP and ML constrictions during talking in nonsingers are a sign of excess phonatory effort. A differently designed study that assesses singers and nonsingers and which includes manipulation of supraglottic constriction would be needed for further understanding of the issue. Conclusions and limitations Overall, there were changes in laryngeal and pharyngeal activity detectable by stroboscopy during execution of SOVTs for all four singers. The specific parameters that changed, the magnitude of change, and the SOVT on which changes occurred differed across participants. Although most instances of detectable change were interpreted as beneficial, there were situations wherein laryngeal and/or pharyngeal activity was considered to be worsened during an SOVT compared with that subject’s nonSOVT phonation. Pending confirmation of the current results, use of stroboscopy, and endoscopy to guide selection of specific SOVTs for an individual may be appropriate. It is not possible to make definitive statements that one SOVT exercise is more beneficial than another across all individuals. Rather, there is likely to be a specific SOVT or subset of SOVTs that is of most benefit for a particular individual, but this can vary from person to person. Guzman et al28 also reported that to be the case for the measures, they assessed in their SOVT study. There are limitations to this study. The small sample size limits the ability to broadly generalize the results. It is unknown from this study whether greater or different changes in laryngeal and pharyngeal activity would occur during SOVTs if the exercises were done on an extended basis. The results only speak to the changes that occurred during the brief period of SOVT execution during the study. It is possible that there is an evolution to the changes that occur with extended practice. This study also cannot address the important issue of whether SOVT-induced changes in phonation persist beyond the execution of the exercise itself. Acknowledgments The authors would like to acknowledge the University of Kansas Graduate School for two summer research fellowships to help with the continuing research of this topic. The authors also thank the subjects who volunteered their time on this project.
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