Cricothyroid Muscle and Thyroarytenoid MuscleDominance in Vocal Register Control:Preliminary Results

*Karen Ann Kochis-Jennings, †,‡Eileen M. Finnegan, ‡Henry T. Hoffman, §Sanyukta Jaiswal, and †Darcey Hull,*Northridge, California, and yzIowa City, Iowa, and xWashington, District of Columbia

Summary: Hypothesis. Headmix and head registers use cricothyroid (CT) muscle dominant voicing, whereas chest

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and chestmix registers use thyroarytenoid (TA) muscle dominant voicing.Study Design. Cross-sectional study.Methods. CT and TA electromyographic data obtained from five untrained singers and two trained singers wereanalyzed to determine CT and TA muscle dominance as a function of register. Simultaneous recordings of TA andCT muscle activity and audio were obtained during production of pitch glides and a variety of midrange and upperpitches in chest, chestmix, headmix, and head registers.Results. TA dominant phonation was only observed for chest productions and headmix/head register productionsbelow 300 Hz. All phonation above 300 Hz, regardless of register, showed CT:TA muscle activity ratios that wereCT dominant or close to 1, indicating nearly equal CTand TA muscle activity. This was true for all subjects on all vocaltasks. For the subjects sampled in this study, pitch level appeared to have a greater effect on TA and CT muscle domi-nance than vocal register.Conclusion. Preliminary findings regarding CTand TA dominance and register control do not support the assumptionthat all chest and chestmix production has greater TA muscle activity than CT muscle activity or that all headmix andhead production require greater CTmuscle activity than TAmuscle activity. The data indicate that pitch level may play agreater role in determining TA and CT dominance than register.Key Words: Vocal registers–Thyroarytenoid muscle–Cricothyroid muscle–EMG.

INTRODUCTIONThe term ‘‘register’’ has been defined as a series of tones thatare perceived to be of similar vocal quality and produced ina similar physiological manner.1,2 Nonetheless, registercharacterization and terminology remain areas of muchambiguity, debate and disagreement among singers, singingteachers, and voice scientists alike. Current theories ofregister control point to registration as a primarily laryngealevent, dependent on laryngeal muscle activity, degree ofvocal fold adduction, and glottal shape.3–7 Results ofnumerous acoustic, aerodynamic, and physiological studies,such as electroglottography (EGG) and videostroboscopy,have gradually improved our understanding of three vocalregisters; chest, falsetto, and glottal fry. Among singers andsinging teachers, additional registers have been perceptuallyidentified, such as middle, mix, chestmix, and headmix.

Middle voice, or ‘‘mix,’’ is defined by Miller8 as the area ofthe female voice that lies between the primo and secundo pas-sagio. Miller further separates ‘‘mixed’’ voice into two types of

ted for publication January 29, 2014.ted at the 10th Pan-European Voice Conference; August 22 2013, Prague, Czech.he *Department of Communication Disorders and Sciences, California State Uni-orthridge, California; yDepartment of Communication Sciences and Disorders,y of Iowa, Iowa City, Iowa; zDepartment of Otolaryngology, University ofspitals and Clinics, Iowa City, Iowa; and the xDepartment of Hearing, Speechuage Sciences, Gaulladet University, Washington, District of Columbia.ss correspondence and reprint requests to Karen Ann Kochis-Jennings, Californiaiversity, 18111 Nordhoff Street, Northridge, CA 91330. E-mail: karen.nnings.32@csun.edul of Voice, Vol. -, No. -, pp. 1-9997/$36.004 The Voice Foundationx.doi.org/10.1016/j.jvoice.2014.01.017

mix, ‘‘chest mixture’’ and ‘‘head mixture,’’ stating that, for thefemale classical singer, chest mixture is the middle voice timbreencountered in the female lower middle voice and is character-ized by limited head sensation. He describes head mixture as‘‘headier’’ than chest mixture with increasing head sensationas the singer moves into the subject’s upper middle voice.The trained singer learns to transition from chest to falsetto orchest to head without an abrupt change in register and mostsingers and singing teachers agree that the transitional area isperceptually different from chest or falsetto; hence, the terms‘‘middle’’ and ‘‘mixed voice’’ have evolved in an attempt todescribe this type of phonation.

The perceptual quality of the transitional area often seemsdifferent for the female classical singer than for the femalecontemporary commercial music (CCM) singer; thus, the termshead dominant mix and chest dominant mix have come into useto differentiate type of middle voice. More recently, the terms‘‘Thyroarytenoid (TA) dominant’’ and ‘‘Cricothyroid (CT)dominant’’ have also been used when referring to vocal quali-ties that are perceived as more chest-like or head-like in theirtimbre.9–12 The definition of ‘‘dominant,’’ as it applies tophysical anatomy, is that one member of a pair of bodilystructures is more effective or predominant in action than theother member (Merrium Webster, 2014).13 The underlyingassumption in the usage of the terms TA dominant and CTdominant is that chest and chestmix productions have moreTA muscle activity than CT muscle activity and thus are TAdominant, whereas head and headmix productions have moreCT muscle activity than TA muscle activity and are thus CTdominant. Yet, empirical laryngeal muscle activity data thatsupport this assumption are lacking. There are very few studies

Journal of Voice, Vol. -, No. -, 20142

of laryngeal muscle activity in trained male and female singers.Those that exist are primarily descriptive and reported only in-dividual laryngeal muscle activity by register. They do notdirectly compare TA and CT muscle activity levels or calculateCT:TAmuscle activity ratios to determine TA or CT dominanceby register.

The few electromyographic (EMG) studies that examinevocal registration in trained singers have shown that TA muscleactivity is greatest for chest, then mixed and middle registersand least for head and falsetto; CT muscle activity, however,was shown to have little relationship to register.14,15 Hiranoet al14 measured CT, lateral cricoarytenoid (LCA), and TAmus-cle activity in four classically trained singers (two males andtwo females) during same pitch phonation in chest, middle,head, and falsetto and rank ordered the level of individual laryn-geal muscle activity by register. They reported that TA and LCAmuscle activity was greatest in chest, then middle, then head,and least in falsetto. CT activity was greatest in chest for twosubjects, showed similar activity levels across all registers forthe third subject, and showed similar activity in head and chestfor the remaining subject. Actual laryngeal muscle activitylevels, however, were not reported. Kochis-Jennings et al15

measured the mean percent of maximum CTand TAmuscle ac-tivity in five trained and two untrained female CCM singersduring same pitch phonation across 3–5 semitones in thesingers’ middle to upper frequency range. Results showedthat TA muscle activity was generally greatest in chest, thenchestmix, then headmix, and then head. At the lowest of thesefrequencies (294–350 Hz), TA activity was often similar forchest and chestmix productions or chestmix and headmix, de-pending on the subject. CT muscle activity was reported forthree of the subjects. The first subject showed greater CT mus-cle activity for chest than chestmix, but similar CT activity forchestmix and head. The second and third subjects producedonly headmix and head phonation. The second subject showedgreater CTactivity for headmix than for head, whereas the thirdsubject showed similar levels of CT activity for both registers.Neither Hirano et al14 nor Kochis-Jennings et al15 investigatedor reported on TA and CT dominance in register control. Thefinding that TA muscle activity is greater in chest and chestmixthan middle, headmix and head does not necessarily mean thatthese registers are TA dominant, that is, have greater TAmuscleactivity than CT muscle activity. To obtain data on TA and CTdominance in register control, one must directly measure TAand CT muscle activity during same pitch phonation acrossdifferent vocal registers or during glissandos traversing at leasttwo vocal registers and calculate CT:TA muscle activationratios.

Studies investigating laryngeal muscle activity in untrainedmales have also reported greater TA and CT muscle activityfor chest than falsetto.16,17 Gay et al16 measured TA and CTac-tivity in five untrained males during same pitch sustainedphonation and reported that TA and CT muscle activity weregreater for chest than falsetto. Baer et al17 measured TA andCT muscle activity in one untrained male during same pitchphonation at three frequencies (220, 330, and 440 Hz) in chestand falsetto. They also reported greater TA and CT activity for

chest than falsetto. However, neither of these studies reportedCT:TA muscle activity ratios nor did they comment on TAand CT muscle dominance in vocal register control.Existing data do not point toward TA or CT dominance as a

register control mechanism. Although existing studies haveclearly shown that TA and LCA muscle activity are greater forchest productions than falsetto or head, no studies have formallyexamined the relationship between CT and TA muscle activitylevels as a function of vocal register to establish TA and CTdominance for register control. Although evidence from acous-tic, aerodynamic, and physiological studies using EGG indicatethat heavier registers, such as chest, chestmix, and middle, havegreater vocal fold adduction than lighter registers, such as head-mix, head, and falsetto, these findings neither indicate nor canthey indicate that heavy registers have more TA muscle activitythan CT muscle activity. Although greater vocal fold adductionmay be suggestive of greater TA muscle activity for heavy reg-isters, it should not be assumed that this finding indicates greaterTAmuscle activity than CTmuscle activity. The presence of TAor CT dominance in vocal register production can only be deter-mined by usingEMG tomeasure the levels of TA andCTmuscleactivity and calculating CT:TA muscle activation ratios. Thishas not been done. Furthermore, much of the data that existfor trained singers are primarily descriptive in nature.The purpose of this study was to test the hypothesis that chest

and chestmix registers are TA dominant and show greater TAmuscle activity than CT muscle activity and that headmix andhead registers are CT dominant and show greater CTmuscle ac-tivity than TAmuscle activity. To do this, we analyzed both newEMGCTand TAmuscle activation data and reanalyzed a subsetof previously published data to calculate CT:TA muscle activa-tion ratios by register.

METHODS

SubjectsSeven subjects participated in this study; two trained femalesingers, four untrained female singers, and one untrainedmale singer. Subjects’ age ranged from 21 to 47 years. Subjectcharacteristics for the trained singers are listed in Table 1. Thesubjects were interviewed to ensure they had no history of voiceor speech disorders, bleeding problems, allergy to subcutaneousanesthetic agents, or history of smoking. All subjects werecautioned against the use of aspirin or Coumadin within14 days before the experiment day. Each subject received alaryngeal examination performed by the participating laryngol-ogist on the day of the experiment to ensure that the laryngealanatomy and gross movement of the vocal folds were withinnormal limits.

ProcedureSimultaneous recordings of TA and CT muscle activity andaudio were obtained from each subject.

Laryngeal EMG. Each subject was seated upright in a chair.A reference electrode was placed on the forehead of the subject.A small amount (0.5 cc) of 2% lidocaine with 1:100 000epinephrine was injected just below the surface of the skin

TABLE 1.Subject Characteristics for F5 and F6

Subject Age Years of Training Type of Training Styles of Music Level

F5 47 12 y of private training Nonclassical Jazz, pop, and R&B Soloist Professional singer andsinging teacher

F6 26 2 y of private training Classical Pop, Christian Pop, andCountry—Solo and Choir

Avocational singer

Karen Ann Kochis-Jennings, et al CT and TA Dominance in Vocal Register Control 3

overlaying the CT ligament before electrode insertion. Stainlesssteel bipolar hooked-wire electrodes (0.0003 inch) were theninserted percutaneously through a 25-gauge needle bilaterallyinto the TA and CT muscles. Placement of the hooked-wireelectrodes into the TA and CT muscles was judged correct ifthere was EMG activity associated with the verification tasksand if the CT membrane was pierced during insertion.

Typically, the patient experienced a sense of pressure or mi-nor discomfort when the hooked-wire electrodes were inserted.However, once the needle that was used to insert the wires waswithdrawn, the patient did not feel the wires. Occasionally, ifthe wire electrodes were inserted close to the mucosa, wherethere is greater sensitivity, the participant might continue toexperience discomfort even after the insertion needle was with-drawn. If this were the case, those wires would be removed andthen new wire electrodes would be inserted more laterally intothe TA muscle. Typically, any discomfort experienced by theparticipant occurred during insertion and during removal ofthe hooked-wire electrodes but not during data acquisition.

The bipolar hooked-wire electrodes and ground electrodewere connected to a preamplifier (B466; Bioengineering, TheUniversity of Iowa). Output from the preamplifier was directedto a bioamp speech physiology system (Bioengineering, TheUniversity of Iowa) and high-pass filtered at 300 Hz. EMGsignal output from the bioamp was then low-pass filtered at5 kHz via a Dual High/Low-Pass Filter (Wavetek Rockland432; Wavetek, San Diego, CA). EMG signals were thendirected to an analog to digital converter (DI-205; Dataq Instru-ments, Akron, OH), which was connected to a portable two-channel parallel port I/O Module (DI-720; Dataq Instruments,Akron, OH), which allowed the signals to be recorded onto alaptop computer (Dell Latitude) via waveform acquisition soft-ware (Windaq Pro+ Data Acquisition Software; Dataq Instru-ments, Akron, OH). Sampling rate for the EMG dataacquisition was 10000 samples per second per channel.

A simultaneous audio recording used for audio reference andchatter was recorded directly into the Windaq data acquisitionprogram via laptop computer (Dell Latitude) by connecting ahead-mounted condenser microphone (AKG, C42; AKG byHarmon, Los Angeles, CA) directly into the analog to digitalconverter (DI-205; Dataq Instruments).

Audio signal. Audio signals of the subjects’ vocalizations tobe used for acoustic analysis were recorded via DAT recorder(Sony PCM-M1; Sony, Tokyo, Japan) at a sampling rate of41100 samples/s. Microphones used to acquire the audio signalsincluded two condenser microphones (Sony Electret ECM-MS907 Condenser Microphone and Sony Dynamic Omni-

Directional F-VS3; Sony, Tokyo, Japan). Audio recordingswere then digitized with audio editing software (Sonic SoundForge; Sonic Foundry, Madison, WI) at a sampling rate of44100 samples/s and edited into sample tokens for perceptualrating and acoustic analysis.

Tasks. After electrode placement in the target muscle, verifi-cation tasks were performed to confirm electrode placement inthe target muscle. To confirm CT placement, subjects wereasked to produce (a) a sustained high pitch, (b) an ascendingpitch glide, and (c) a chin press. To confirm TA muscle place-ment, subjects were asked to (a) produce hard glottal attacks,(b) perform a valsalva maneuver, (c) sustain phonation at acomfortable pitch, and (d) swallow. Each TA and CT verifica-tion task was performed three times pre- and post-experiment.To obtain levels of maximum muscle activity, the subjects per-formed five tasks that are commonly used to elicit maximumTA and CT muscle activity; a swallow, a valsalva maneuver, ahard adduction, and a loud high-pitched phonation.

Experimental tasks for the trained subjects consisted of sus-tained phonation on /i/ or /ne/ at three to five frequencies be-tween Eb4 and Bb4 (depending on voice type) produced inchest, chestmix, headmix, and head. Sustained phonation taskswere repeated five times per frequency per register. The trainedsingers were also asked to produce a song phrase in those samevocal registers and produced at least three repetitions in eachregister. All trained and untrained subjects were asked toperform ascending pitch glides on /i/, starting at a comfortablepitch and gliding as high as comfortable for the subject.

Measurement

Perceptual judgment of register. To determinewhich reg-isters were elicited from the trained subjects, the singing tokenswere perceptually rated as chest, chestmix, headmix, or headvoice by two trained judges. The judges were two professionalCCM singing teachers with 15 and 8 years of experience. Eachjudge was provided with a CDwith recorded samples of singingproduced in the chest, chestmix, headmix, and head registers byprofessional female singers and consisted of song phrase seg-ments that exemplified (a) high frequency chest production(belting), (b) chestmix, (c) headmix, and (d) head voice. Thejudges were asked to listen to the CD before rating the subjects’singing tokens and to refer to the CD for recalibration asneeded. The audio recordings of the subjects’ singing tokenswere randomized and presented to the judges for categorization.Perceptual identification of the chest to falsetto/head registertransition during the ascending pitch glides was performed by

Journal of Voice, Vol. -, No. -, 20144

the primary investigator and then verified via acoustic analysis.In the majority of cases, the chest to head and chest to falsettoregister transitions were abrupt and perceptually obvious.

Laryngeal EMG. Measurements of TA and CT muscle activ-ity were obtained for all singing tasks using Windaq signalprocessing and analysis software. All EMG signals were in-spected visually and aurally for artifact. Areas of maximumCT and TA muscle activity were then identified and themaximum root mean square values during a 20-millisecondwindow were recorded for each muscle. The EMG signalswere then rectified and smoothed by obtaining a movingaverage from the digitized signal (with a 50-millisecond win-dow using a smoothing factor of 250). The mean TA and CTmuscle activity for each sustained phonation singing tokenwas obtained by measuring mean TA and CT muscle activityat the middle 1/3 or middle 2/4 of the token to avoid muscle ac-tivity onset and offset bursts. For song phrases, muscle activitywas measured only during the vowel portions of syllables. Forthe pitch glides, TA and CT muscle activity and frequency werecalculated in 50-millisecond increments.

Measurements of mean maximum TA and CT muscleactivity were used to calculate the percent of mean maximumactivity for the TA and CT muscle activity obtained for eachsinging task. Normalization of the data in this manner allowedfor comparison of TA and CT muscle activity within and acrosssubjects. TA and CT muscle activation ratios were then calcu-lated by dividing the mean percent of maximum CT muscleactivity by the mean percent of maximum TA muscle activity.

Audio signals. Fast Fourier transforms (FFTs) were per-formed on the DAT audio recordings of sustained phonationand vowel portions of the song phrases to measure the ampli-tude of the fundamental frequency with a software analysisprogram (Windaq Pro+ Data Analysis Software). In addition,the mean amplitudes of the harmonics in the singer’s formantand speaker’s formant clusters were also measured. For the pur-poses of this study, the singer’s and speaker’s formants aredefined as a clustering of formants for which the amplitudesare noticeably increased in comparison with the surroundingharmonics, resulting in prominent peaks of energy in the 2–3 kHz (singer’s formant) and 3.5–5 kHz (speaker’s formant)ranges. The audio signal acoustic data were then comparedacross registers and with the judges’ perceptual ratings. Toverify the location of the chest to falsetto register transition dur-ing pitch glides, FFTs were performed at four frequency pointsbefore and after the perceptually identified register transition.Amplitude of the fundamental frequency and the mean energyof the harmonics in the singer’s formant and speaker’s formantclusters were compared for the chest and falsetto frequencies.

RESULTSVerified CT and TA muscle electrode insertions were obtainedfor all subjects. Perceptual ratings and acoustic analysis of theaudio signals for vocal register for the trained and untrainedsubjects during pitch glides showed that all subjects transi-tioned from chest to head or chest to falsetto at some point dur-ing the ascending pitch glide. Transitions from chest to head or

chest to falsetto were marked by significantly increased energyin the fundamental frequency and a marked decrease in energyin the singer’s and speaker’s formant clusters. Four of the sevensubjects exhibited abrupt register transitions from chest to heador chest to falsetto that were perceptually obvious. Three of theseven subjects exhibited smoother register transitions.Perceptual rating and acoustic analysis of the audio signals

for vocal register for the trained subjects’ sustained phonationand song phrases confirmed that subject F5 was able to producechest, chestmix, and head on five pitches and chestmix and headon four pitches. Subject F6 was able to produce only headmixand head over the vocal range sampled, D4–D5. Singingsamples for which rater agreement could not be obtainedwere discarded and not included in the analysis. Results fromthe acoustic analysis for the trained singers showed statisticallysignificant differences in the energy of the fundamental fre-quency and singers’ and speakers’ formant between the targetregisters and have been detailed in a previous publication andwill not be discussed here.15

ElectromyographyFigures 1 and 2 show CT:TAmuscle activation ratios during theproduction of two ascending pitch glides for the untrainedsingers, subjects F1–F4 and M1, and the trained singers, sub-jects F5 and F6. Subject F5 was asked to produce two pitchglides, the first with a late register transition (higher pitch)and the second with an early register transition (lower pitch).Ratios that fall on the horizontal line (ratio ¼ 1) of the graphshave equal CT and TA muscle activity. Ratios that fall abovethe line show greater CT muscle activity than TA muscle activ-ity and indicate CT dominant phonation. Ratios that fall belowthe line have greater TAmuscle activity than CTmuscle activityand indicate TA dominant phonation.

Pitch glide resultsAll subjects produced two ascending pitch glides starting inchest and transitioning to head or falsetto. Subjects producedpitch glides over a pitch range of 1.5–3 octaves.There are a number of observations to be made from these

data.First, TAdominant phonationwas observedduring theproduc-

tion of the pitch glides in five of the seven subjects but occurredonly when the fundamental frequency was below 200–300 Hz(B3–Eb4). Two of the subjects, F1 and F5, never used TA domi-nant phonation evenwhenproducing chest pitches below300Hz.Figures 1 and 2 show the CT:TA muscle activation ratios duringthe production of ascending pitch glides for the singers and non-singers. Subjects F2, F3, F4, F6, and M1 show TA dominantphonation below 200–300 Hz as indicated by ratio values lessthan 1 (data below the horizontal line). These subjects showed to-tal chest phonation ranges of 6–14 semitones and used TA domi-nant phonation over the lower 42–57% of their chest range.Second, CT dominant phonation was observed during the

pitch glides in all subjects for chest, head, and falsetto phona-tion above 200–300 Hz. CT dominant phonation was observedeven for higher chest productions at 400–430 Hz (Figures 1and 2). Subjects F1 and F5 used CT dominant phonation for

FIGURE 1. CT:TA muscle activity for subjects F1 through F4 and M1 during two ascending pitch glides. Squares ¼ chest, circles ¼ head,triangles ¼ transitional area.

Karen Ann Kochis-Jennings, et al CT and TA Dominance in Vocal Register Control 5

all chest and head productions regardless of pitch. Subjects F2,F3, F4, F6, and M1 used CT dominant phonation for chest pro-ductions in the upper 43–58% of their chest range. CT dominantphonation, as indicated by ratio values greater than 1, fallsabove the horizontal line (Figures 1 and 2).

Third, the highest CT:TA ratios, indicating high CT domi-nance, did not always correspond to the highest head or falsettopitches (Figures 1 and 2). For two subjects (F4, F6), the CT:TAmuscle activation ratios were greatest for high-pitch head pro-ductions. For other subjects (F1, F5), the highest CT:TA ratiosoccurred during high-pitch chest productions. The remainingsubjects showed CT:TA ratios that were sometimes highestfor high head or falsetto phonation and sometimes highest forhigh-pitch chest phonation.

Fourth, although all register transitions occurred during CTdominant phonation (CT:TA ratios > 1), a noticeable decreasein the CT:TA muscle activity ratio was observed before or dur-ing the register transition during at least one of the pitch glidetokens for all but one subject, indicating a change or adjustmentin CT and TA muscle activity before or during the register tran-sition (Figures 1 and 2). However, the phonation remained CTdominant. Subject F6, a trained singer, showed no such changein CT:TA muscle activation ratios and was perceived to have avery ‘‘smooth’’ register transition from chest to head.

Fifth, CT:TA ratios of 1 (equal CT and TA muscle activity)were observed for all but two subjects and typically occurredin the lower 20–50% of the chest pitch range (Figures 1 and2). Subjects F1 and F5 produced only CT dominant phonation

FIGURE 2. CTand TA muscle activation ratios during ascending pitch glides for subjects F5 (top) and F6 (bottom), the trained singers. The hor-izontal line marks a ratio of 1. Values above the line indicate relatively greater CT muscle activity (CT dominant phonation) and below the line

relatively greater TA muscle activity (TA dominant phonation).

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in chest and head and showed no CT:TA ratios of 1 during pitchglides.

Sixth, CT:TA muscle activity ratios showed variable patternsas pitch was increased in falsetto and head (Figures 1 and 2).Subjects F1 and F2 showed flat, unchanging CT:TA ratios aspitch increased in head. Subjects F3 and F6 showed increasingCT:TA ratios in head with increased pitch that then decreased orremained the same as pitch further increased. Subject F5showed decreasing CT:TA ratios with increasing pitch inhead and subject F4 showed unchanging CT:TA ratios withincreased pitch that either increased or decreased when thehighest head pitch was obtained. Increasing ratios are indicativeof increasing CT activity or decreasing TA activity, whereasdecreasing ratios are indicative of decreasing CT activity orincreasing TA activity.

Finally, CT:TA muscle activity ratios for chest and headphonation were sometimes similar or the same (Figures 1 and2). For example, subjects F1, F2, and F5 showed CT:TA ratiosfor high chest pitches and head phonation that were the same orsimilar. In addition, subjects with the greatest pitch ranges didnot necessarily show the widest ranges of CT:TA muscle activ-ity ratios. For example, subject F6 phonated over 36 semitones(3 octaves) and showed a CT:TA muscle activity ratio range ofonly 0.75–1.75, whereas subject F3 phonated over a range of 14semitones and showed a CT:TA muscle activity ratio range of0.5–7.75.

Sustained phonation and song phrase resultsThe trained singer subjects, F5 and F6, differed in their abilityto produce all vocal tasks in the target vocal registers. For sus-tained phonation and song phrases, F5 produced five pitches(Eb4–G4) in chest register and nine pitches (Eb4–D5) in thechestmix and head registers. F6 did not produce any phonationin chest or chestmix register. The subject produced thirteenpitches (D4–D5) in the headmix and head registers. Figure 3shows the CT:TA muscle activation ratios for the sustainedphonation and song phrase productions. Figure 4 shows CTand TA muscle activation plots (MAPs) for the trained singers,subject F5 (top) and F6 (bottom), during the production of sus-tained phonation and song phrases. The CT:TA muscle activityratios in Figure 3 were calculated from the mean percent ofmaximum TA and CT muscle activity values shown inFigure 4. In the MAPs, CT and TA muscle activity is shownas the mean percent of maximum CT and TA muscle activity.CT:TA muscle activity ratio results for subjects F5 and F6 forsustained phonation and song phrases were similar to those ob-tained for these subjects during pitch glides. However, a numberof interesting observations were made.First, TA dominant phonation was observed for subject F6

but not for subject F5 (Figure 3). Subject F6 showed TA domi-nant phonation for headmix and head productions in the lowerand middle portion of the subject’s pitch range (220–350 Hz).

FIGURE 3. The ratio of CT muscle activity to TA muscle activity asa function of frequency and register for subjects F5 and F6, the trained

singers, during sustained phonation and song phrases. The horizontal

line marks a ratio of 1. Values above the line indicate relatively greater

CT muscle activity (CT dominant phonation) and below the line rela-

tively greater TA muscle activity (TA dominant phonation).

FIGURE 4. MAPs showing mean percent of maximum TA and CTmuscle activity by register and frequency for F5 and F5. The dotted

lines indicate the quadrants described by Titze.18 The solid diagonal

line indicates equal activation of the TA and CT muscles. Data points

above the line identify tones produced with greater CT activity (CT

dominant phonation) and those below the line tones produced with

relatively greater TA muscle activity (TA dominant phonation). Modi-

fication of a figure previously published in Kochis-Jennings, et al J

Voice. 2012; 26 (2): 182–193. Used with permission from Journal of

Voice.

Karen Ann Kochis-Jennings, et al CT and TA Dominance in Vocal Register Control 7

TA dominance during headmix and head phonation was unex-pected. For subject F6, head phonation between 294 and350 Hz was less TA dominant (0.87–0.93) than for same pitchphonation in headmix (0.78–0.81).

Second, the use of CT dominant phonation varied for subjectsF5 and F6 (Figure 3). Subject F5 showed CT dominant phona-tion for all productions regardless of pitch or register. However,the degree of CT dominance varied by register and pitch for F5.For example, subject F5 showed the lowest CT dominant ratiosand narrowest range of ratios (1.15–1.5) for chestmix produc-tions from 311 to 588 Hz. The greatest CT:TA ratios (2.75–3.37) for subject F5 were observed for head phonation between440 and 588 Hz. CT:TA ratios for F5 for chest production be-tween 294 and 392 Hz fell between those for chestmix andhead, 1.15–2.06. Subject F6 showed CT dominant phonationfor headmix and head from 450 to 588 Hz.

Figure 4 shows CTand TA percent of mean maximumMAPsfor subjects F5 (top) and F6 (bottom). The dotted lines divide

the MAP into four quadrants described by Titze,18 where A isthe speech quadrant, B is the falsetto quadrant, C is the high-pitch chest quadrant, and D is the pressed phonation quadrant.The diagonal line indicates equal activation of the TA and CTmuscles. Data points above the line indicate pitches producedwith CT dominant voicing (ie, with greater CT muscle activityin comparison with TA muscle activity). Data points below thediagonal line indicate pitches produced with TA dominant voic-ing (greater TA muscle activity than CT muscle activity). Inthese MAPs, any phonation in the D quadrant would be TA

Journal of Voice, Vol. -, No. -, 20148

dominant, any phonation in the B quadrant would be CT domi-nant and those in quadrants A and C could be either TA or CTdominant depending on whether the phonation fell above (CTdominant) or below (TA dominant) the horizontal line.

For subjects F5 and F6, the data were not grouped by vocalregister in the predicted manner (Figure 4). For F5, most phona-tions fell within the A quadrant above the diagonal line and inthe B quadrant, indicating CT dominant phonation. For F5, allhead phonation from Eb4 to D5, all chestmix phonation fromEb4 to A4 and Eb4 chest phonation was located above the hor-izontal line in quadrant A, indicating CT dominant phonation.Chest phonation from E4 to G4 fell in the quadrant B, the fal-setto or CT dominant quadrant, and this was unexpected.High chestmix phonation (B4, C5, D5) was near the center ofthe MAP (50% of maximum CT and TA muscle activity) andin quadrant C, fairly close to the diagonal line, indicating nearlyequal CT and TA muscle activity. For F6, all the phonations,which were produced in head and headmix registers, fell withinthe A quadrant, but both above and below the diagonal line,indicating TA dominant phonation for the lower pitches andCT dominant phonation for the higher pitches. There were nophonations for either subject in the D ‘‘pressed phonation’’ orTA dominant quadrant (ie, greater than 50% activation of TAmuscle, with less than 50% activation of the CT muscle).

Although both singers increased CT muscle activity relativeto TA muscle activity to increase pitch in all registers, subjectF5 decreased the CT:TA ratio while increasing pitch in chest-mix by increasing TA activity (Figure 4). F5 produced thepitches B4–D5 in only chestmix and head. In head, F5 increasedthe CT:TA ratio with increased pitch. In chestmix, F5 increasedboth CT (45–77%) and TA (33–63%) muscle activity as thesubject increased pitch, resulting in ratios that were onlyslightly CT dominant (1–1.5) (Figures 3 and 4). Of interest isF5’s CT:TA muscle activity ratios for the B4–D5 chestmixproductions in comparison with the subject’s CT:TA muscleactivity ratios for the F4–G4 chest productions. F5 used equalor greater TA activity but less CT activity for high pitch chest-mix than for mid-range chest pitches, E4–G4. The lower levelsof CT activity for B4–D5 in chestmix as compared with CTactivity for F4–G4 in chest were unexpected because B4–D5are significantly higher than F4–G4 and TA muscle activity inchestmix was equal or greater than for chest (Figure 4). F6increased CT muscle activity to increase pitch in head andheadmix above G4, whereas TA muscle activity showed littlechange with pitch, resulting in CT dominant ratios for allpitches above G4 (Figures 3 and 4). However, F6 exhibitedTA dominant voicing in both headmix and head from D3 toF4, despite increasing CT activity with pitch. This was unex-pected for headmix and head phonation.

DISCUSSIONThe purpose of this study was to test the hypothesis that chestand chestmix register phonation uses TA muscle dominantvoicing, whereas headmix and head register phonation usesCT muscle dominant voicing. Findings regarding the CT:TAmuscle activity ratios and the MAPs are discussed below.

In vocal pedagogy, a trend has emerged where particularvocal qualities or registers are referred to as TA dominant orCT dominant.11,12,18 However, these terms have not evolvedfrom the direct measurement of laryngeal muscle activityduring singing but from perceptual judgment based onpedagogical experience and physiological measurements thatprovide only indirect measurements of laryngeal function.Although the terms TA dominant and CT dominant seemlogical, laryngeal muscle activity data for singers are sparseat best and the role of laryngeal muscle activity in the controlof mixed registers is poorly understood. When the CT and TAmuscle activity ratios for the trained and untrained subjectswere examined, interesting muscle activity patterns emerged.Our expectation was that all chest and chestmix phonation

would be TA dominant or nearly so and that all headmix orhead phonation would be CT dominant. However, this wasnot always the case. TA dominant phonation was only observedfor chest productions and headmix/head register productionsbelow 300–350 Hz. All phonation above 300–350 Hz, regard-less of register, showed CT:TA muscle activity ratios thatwere CT dominant or close to 1, indicating nearly equal CTand TA muscle activity. This was true for all subjects on allvocal tasks. For the subjects sampled in this study, pitch levelappeared to have a greater effect on TA and CT muscle domi-nance than vocal register.Titze7,18 has stated that as singers increase frequency in chest

register, they must either gradually separate the vocal processesand/or gradually decrease TA muscle activity as they increaseCT muscle activity if an abrupt register transition from chestto falsetto is to be avoided. He theorized that theseadjustments might begin around C4 and continue through F4to avoid an involuntary chest to falsetto register transition.Recall that all subjects that used TA dominant phonation inthe lower portion of their chest range transitioned from TAdominant phonation to CT dominant phonation between 200and 350 Hz (G3–F4). Perhaps some of our subjects were usingthis strategy as they increased pitch in chest during theascending pitch glides and this may account for the observedCT dominance in the upper 50% of the chest range.Data on laryngeal muscle activity in trained singers is sparse

and much of that data are descriptive or involve only gross in-terpretations of laryngeal muscle activity. Little is known aboutlaryngeal muscle co-contraction activity during singing. Forexample, five of seven subjects showed a transition to CT domi-nant phonation at the 40–50% point of their chest range, re-mained in CT dominant phonation throughout the remaining40–50% of their chest range and yet exhibited an abrupt registertransition although they were in CT dominant phonation at thetime of the transition. The trained singer, subject F5, producedonly CT dominant phonation but still showed an abrupt registertransition and a significant change in the CT:TAmuscle activityratio during the transition while in CT dominant phonation.More detailed studies of laryngeal muscle activity are neededto understand laryngeal muscle co-contraction activity duringsinging.Studies investigating laryngeal muscle activity in middle and

mixed registers are few. In this study, we found that, for subject

Karen Ann Kochis-Jennings, et al CT and TA Dominance in Vocal Register Control 9

F5, chestmix phonation showed lower CT:TA muscle activityratios than for same pitch phonation in chest and head. Like-wise, subject F6 showed lower CT:TA muscle activity ratiosfor headmix below 350 Hz than for same pitch phonation inhead. However, intensity, as measured by changes in theRMS of the audio signal, was greater in chestmix and headmixthan in head or chest. Thus, it cannot be entirely ruled out thatlower CT:TA muscle activation ratios were not a result ofincreased intensity. Yet, subject F5 showed CT dominantphonation across all registers, despite increased intensity inchestmix. In a previous study, we reported that TA and CTmus-cle activity during sustained same pitch phonation and songphrases were generally greater for chestmix than for headmixand head but less than for chest.15 Hirano et al14 reported laryn-geal muscle activity for middle voice to be less than for chestbut greater than for head in two female classical singers.

Other studies investigating mixed registers via EGG reportconflicting results. Bourne and Garnier19 recently reported dif-ferences in the EGG open and closed quotients for belt, mix,and legit in three trained musical theater singers and foundEGG values for mix that were intermediary to chest and legit.Conversely, Henrich et al6 found no difference in open andclosed quotients for classical singers in mix 1 (chestmix) andmix 2 (headmix) that differentiated these from chest or falsetto.They did observe differences in intensity for mix 1 (chestmix)and mix 2 (headmix). Mix 1 showed a decrease in intensitywhen transitioning from chest to falsetto and mix 2 showedan increase in intensity when transitioning from head to fal-setto. The authors suggest that adjusting intensity in chest orfalsetto equalizes the sonority of the sound and results in theperception of a mix and register equalization. The primarydifference between the two studies is the subjects; Bourneand Garnier19 investigated musical theater singers, whereasHenrich et al6 investigated classical singers. It is not yet knownwhether differences in type of vocal training result in differ-ences in laryngeal muscle activity and hence implied glottalconfiguration as measured by EGG. More research is neededto investigate laryngeal muscle activity in singers with CCMtraining and singers with classical training. The differences inthe CT:TA muscle activity ratios observed in this study for sub-jects F5 and F6 may be related to type and length of singingtraining (Table 1). F5 had 12 years of private CCM trainingand over 25 years of professional CCM performance experi-ence, whereas F6 had 2 years of private classical training and6 years of avocational CCM performance experience.

In summary, our preliminary findings regarding CT and TAdominance and register control do not support the assumption

that all chest and chestmix production has greater TA activitythan CTactivity or that all headmix and head production requiregreater CT muscle activity than TA activity. Instead, the dataindicate that pitch level may play a greater role in determiningTA and CT dominance than register. At this time, too little isknown about laryngeal muscle co-contraction and regulationduring singing and more data are needed.

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