Journal of Experimental Voice Research2008, Vol. 1, n°2 : 34-39.

Role of Proprioceptive Memoryin a Professional Opera Singer's Absolute Pitch

An Experimental Pilot Study

Nicole Scotto Di Carlo

Laboratoire Parole et Langage, UMR 6057 CNRS — 29, avenue Robert Schumann13621. Aix-en-Provence Cédex 01 (France)

nicole.scotto@lpl-aix.fr

Abstract: This experiment was aimed at modifying the proprioceptivereferences of a professional soprano endowed with absolute pitch. Todo so, an osteopathic doctor changed the height of her larynx by alteringthe tension between the hyoid bone and the occipital bone. Acephalometric analysis of x-rays taken before and after themanipulations indicated that the position of the phonatory organs hadindeed been affected. The results of an acoustic analysis, and perceptiontests on the tones produced before and after manipulation providedirrefutable evidence of the influence of the laryngeal manipulations onthe tonal accuracy of the emission. This study demonstrates the criticalrole that this soprano's kinesthetic-pallesthetic memory plays in pitchrecognition, and suggests the existence of different types of absolutepitch.

Keywords: Singing voice, Laryngeal height, Tonal accuracy, Kinestheticand pallesthetic reference sensitivities, Internal tuning fork, Tuningstrategy, Absolute pitch, Proprioceptive memory.

IntroductionGiven the complexity of the topic and the difficulty of

conducting experiments in this area other than via MRI orEEG, experimental research on absolute pitch deals mainlywith the brain functioning of musicians who possess thisability (increased size of the planum temporale [1] study ofthe endogenous evoked potential [2] of P3 [3], etc). Inparallel, a few studies have attempted to discover the genesinvolved in the development of absolute pitch [4]. While all ofthese studies focus on the genesis of the phenomenon, thepresent research attempts to gain insight into how absolutepitch functions by analyzing an opera singer's tuningstrategy.

Opera singers possess an extremely precise kinestheticmemory of the positions of their phonatory organs whensinging each tone in their tessitura.

A preliminary experiment on the reproducibility ofphonatory positions in opera singing was first conducted onsix volunteer professional singers, including the sopranowho participated in the study. One or two months apart,depending on availability, two series of x-rays were taken ofthe singers as they sung the same note, on the same vowel,

in the lower register and then in the upper register, twooctaves higher. A comparison of the x-rays of each singer ineach register indicated no apparent difference over time, andthe X-ray tracings, when superimposed, were almost perfectlyaligned. Such positional precision during phonation mayseem surprising, but as we shall see in this study, althoughthe manipulated organs moved very slightly both for thelinear and the angular measures, the shifts led to fully audibledifferences in timbre and vocal quality. Given that one of thepriorities of singers is to achieve voice homogeneity, it isnormal that they strive for extreme precision in the positionsand movements of their phonatory organs.

Most of those who possess absolute pitch — that is, theability to spontaneously recognize or produce any tonewithout an external reference— utilize a strategy whichsuggests that their proprioceptive memory acts as aninternal tuning fork. It was hypothesized here that the sheerfact of changing the position of one of the phonatory organswould disrupt the proprioceptive control of tone accuracy.An experiment was conducted to test this hypothesis.

ExperimentThe professional soprano chosen for the study, who is

endowed with absolute pitch, uses a vocal technique basedon internal voice sensitivities (IVS) and involving a slightdownward shift of the larynx for singing in the lower registerand a slight upward shift for singing in the upper register,which is a characteristic of high, vocalizing voices. Theexperiment was aimed at modifying the proprioceptivereferences of this singer. This was achieved with thecollaboration of an osteopathic doctor, who performed aseries of manipulations consisting in altering the tensionbetween her hyoid and occipital bones and therebymodifying the height of the larynx.

The experiment was conducted in accordance with ethicalstandards, and with the consent of the Head of the Adult

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Radiology Department at the Timone University Hospital inMarseilles. The most up-to-date radiology equipment wasused. At each step of the experiment, every methodologicalprecaution was taken to protect the singers from any kind ofphysical or moral harm. Moreover, the osteopathicmanipulations were pre-tested on the author, and theradiology equipment settings were pre-adjusted in such away that the singers who volunteered to take part in theexperiment would be exposed to the lowest possible level ofradiation.

Experimental SetupProfile x-rays of the head and neck in left/plate position

(distance: 3 meters, duration of exposure: 0.15 s, voltage: 120kv, current: 100 mAS) were taken before and aftermanipulation, using an antidiffusion system. The subject wasstanding and was allowed to assume a natural positionwithout any constraints (such as the use of a cephalostat, orpositioning in the Frankfort Plane by the radiologist). Inorder to be able to analyze the soprano's comments andperform the acoustic study of her voice quality before andafter manipulation, the entire session was recorded on aprofessional Nagra DR-S recorder equipped with anomnidirectional Sennheiser ME40 microphone. To avoidinfluencing her analysis of what she was feeling, she was notinformed of the true reason for the manipulations she wouldundergo.

Experimental ProcedureTo obtain reference x-rays and recordings before the

osteopathic doctor performed the manipulation, thesoprano was asked to sing her entire tessitura from thelower to the upper register, and then to sing the vowel [a] inthe lower register on Bb3 (233 Hz) and in the upper registeron Bb5 (932 Hz). A profile X-ray was taken for each of thesetwo tones, with simultaneous recording of the sound. Next,the practitioner had the subject lie down. He controlled theposition of the temporal occipital bone with one hand, andof the hyoid bone with the other. The first part of thepreparation phase required balancing the tensions. To dothis, he began by holding the occipital bone in a fixedposition and slightly drawing the hyoid bone forward; thenhe held the hyoid bone in a fixed position and slightlypushed the occipital bone backward. The second partrequired finding a point of equilibrium between these twoextremes, which relaxes the tissues and enables the properarrival of blood, lymph, and interstitial tissues. Only at thispoint can the manipulation be performed. Two approachesare possible: the practitioner can either change the hyoidbone tension relative to the occipital bone, or change theoccipital bone tension relative to the hyoid bone. Thesecond solution was chosen because it is closer tophysiological reality. In this case, the doctor acts upon theoccipital bone, either by moving the hyoid bone downwardand thereby preventing the larynx from rising, which

corresponds to the laryngeal position used by this sopranoto sing in the lower register, or by moving it upward andthereby preventing the larynx from lowering, whichcorresponds to the laryngeal position she uses to sing in theupper register.

Then the first manipulation was performed to set thesinger's larynx in the lower-register position via theanteriorization of her occipital bone. This was achieved bysliding the occipital condyle along the glenoid cavity of theatlas in such a way that the posterior surface of the odontoidapophysis of the axis came closer to the posterior part of theforamen magnum. This occipital bone position causes theanteriorization of the styloid apophysis of the temporalbone, which releases stylohyoid muscle tension and lowersthe hyoid bone and the larynx. The experiment must becompleted within the next ten minutes, after which thephonatory organs return to their initial position. In this low-larynx position, the soprano was asked to sing the vowel [a]in her upper register (on Bb5) as a profile X-ray was beingtaken and her voice was being recorded. Then she was askedto sing across her tessitura from the lower register to theupper register, and to state her impressions.

The same process was used for the second manipulation,which set the subject's larynx in the upper-register position.This time, the manipulation consisted in posteriorizing theoccipital bone relative to the atlas, in order to trigger asuperior-posterior shift of the styloid apophysis and therebyincrease the tension of the stylohyoid muscle, causing thehyoid bone to pivot upward and backward and the laryngealbox to rise.

Physiological and Acoustical Analysis ResultsMethod

The four x-rays of the vowel [a], i.e., in the lower registeron Bb3 and in the upper register on Bb5, before and aftermanipulation, were analyzed using a method derived fromcephalometry [5] and adapted to the radiological study ofphonation [6]. For this analysis, 31 parameters weremeasured: head position, anterior-posterior movements ofthe cervical spine, craniocervical angle, buccal opening, labialopening, lip projection or retraction (upper and lower), lipthickness (upper and lower), lip height (upper and lower),tongue mass orientation, aperture, region of articulation,velar tension, degree of nasalization (at the pharyngo-uvularlevel) and buccalization (at the dorso-uvular level), verticaland anterior-posterior movements of the hyoid bone and itstilt, thyrohyoidian space, vertical and anterior-posteriormovements of the thyroid cartilage and its tilt, vertical andanterior-posterior movements of the cricoid cartilage and itstilt, pharyngeal cavity dimensions at its maximal constrictionpoints (at rhinopharyngeal, buccopharyngeal, and hypo-pharyngeal levels), and vocal tract length (Fig. 1).

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Figure 1

MeasuresGiven that the minute movements of the manipulatedorgans required extremely precise measures, we produced a5 x 5 mm calibrated plate of the radiographically-opaquedistortion grid under strictly identical conditions to thoseused for x-raying the soprano. The analysis of this plate gaveus scaled measures that took into account anymagnification or deformation resulting from the angle atwhich the x-rays hit the plate. Insofar as the values usedwere corrected to compensate for the rates of magnificationand distorsion inherent in the radiographic process, theresults presented in this study correspond to real values,not measured ones.

First ManipulationAnamnesis

After the first manipulation aimed at setting the larynx inthe lower-register position, the subject said that she felt"pulled downward" and was experiencing difficulty singing inthe upper register. Moreover, the acoustic analysis confirmedthese statements by revealing the poor quality of the high-pitched tones produced.

Cephalometric AnalysisA comparison of the radiographic tracings of the vowel [a]

sung in the upper register on Bb5 before and aftermanipulation pointed out:

- Phonatory positions specific to lower-register emission* anteriorization of the cervical spine (∆ = + 3.6 mm)* decrease in velar tension (∆H=H+ 1.8 mm)* anteriorization of the tongue mass (∆H=H- 3Hmm)* lowering (∆ = - 1 mm) and anteriorization

of the laryngeal box (∆ = + 7.7 mm)* less pronounced hyoid tilt (∆ = - 4°)* less pronounced thyrocricoidian tilt (∆ = - 7°)

- Phonatory positions specific to upper-register emission:* nearly identical thyrohyoidian space.

- Compensating phonatory positions* smaller labial opening (∆ = - 9 mm)* smaller buccal opening (∆ = - 2.9 mm)* slight tilt of the head (∆ = - 2°).

Physiological InterpretationThe lowering of the laryngeal box caused by the

manipulation resulted in a vocal-tract volume increase thatrequired the subject to make an acoustic adjustment inorder to sing in the upper register [7]. She achieved this byreducing the mandibular opening in order to decrease thevolume of the buccal resonator and compensate for theupper-lip spreading brought about by the considerable risein the cheeks, one of this soprano's characteristic facialexpressions for upper-register singing.

The head tilt angle with respect to the Frankfort Plane was2° after the manipulation. The singer tried to counteract theresulting occipital anteriorization by lowering her head. Thisraised and posteriorized her occipital bone and its styloidapophysis, which moved the hyoid bone upward andbackward and thereby facilitate the thyrocricoidian shiftrequired in the upper register [8]. Without thiscompensatory maneuver, which enabled her to raise the"place" of her voice, the soprano said she would have beenunable to produce this high-pitched tone. (Fig. 2a)

Figure 2 a

Sonagraphic Analysis and Acoustic InterpretationThe acoustic part of this study was based on the corpus

that was recorded while x-rays were being taken of thesoprano singing the vowel [a] in the lower and upperregisters, before and after manipulation. The followingcalculations were made for each sound: onset accuracy, holdaccuracy, the accuracy difference between the onset pitchand the target pitch (i.e., the theoretical frequency of thereference note), between the hold and the target, between

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the onset and the hold, between the onset before and aftermanipulation, and between the hold before and aftermanipulation. Timbre (spectral composition) and vibrato(amplitude, periodicity, regularity quotient, latency, andstabilization time) were also analyzed.

Comparison of the sonagrams of the vowel [a] sung in theupper register on Bb5 before and after manipulation revealeda drop of 14.87HSvt (≈ 1/4 of a tone) on the Bb5 onset aftermanipulation. The mean pitch calculated on the totalduration of the hold decreased by 10.56HSvt (≈ 2 commas).This was caused by lowering of the laryngeal box, along witha less pronounced crico-thyroidian shift. The low laryngealposition also had an impact both on the note's timbre,which was darker due to the paucity of the high-frequencyharmonics (attenuation of harmonics starting at H4), and onthe placement of the sound, which was less cephalized, less"in the head" than the reference sound.

The manipulation had little effect on the vibrato. Itsperiodicity went from 6.72 to 6.30 Pv/s and its amplitude,from 47.75 to 38HSvt. The mean regularity quotient wasvirtually identical before (22.22%) and after (23.30%)manipulation. In both cases, the vibrato was irregular. Thevibrato latency and stabilization time were significantlylonger than in the reference sound, since they practicallydoubled in duration. Latency rose from 22.50Hcs to 32.10Hcsand stabilization time, from 63Hcs to 135Hcs, indicating thatfollowing manipulation, the soprano had trouble finding thecorrect pitch of the sound (Fig. 2b)

Figure 2 b

In summary, the Bb5 after manipulation was two commaslower than the one sung before. It also was "placed lower",was less of a head tone, and had a slightly darker timbrethan the reference sound.

Second ManipulationAnamnesis

After the second manipulation aimed at setting the larynx inthe upper-register position, the singer said that the high-pitched tones were easier to produce, although sheexperienced no additional difficulty with lower-register ones.The acoustic analysis confirmed an excellent vocal qualityacross the lower-to upper-register range.

Cephalometrics AnalysisThe comparison between the radiographic tracings of the

vowel [a] sung in the lower register on Bb3 before and aftermanipulation pointed out:- Phonatory positions specific to upper-register emission

* slight posteriorization of the cervical spine (∆ = - 0,1 mm)* posteriorization (∆ = - 0.7 mm), elevation (∆ = + 1.6 mm), and verticalization of the hyoid bone (∆ = + 4°)* rise of the laryngeal box (∆ = + 3 mm)* decrease in the thyrohyoidian space (∆ = - 0,2 mm)* greater thyrocricoidian shift (∆ = + 3°)* wider pharyngo-uvular space (∆ = + 2 mm),* slightly less labialization (∆ = - 1 mm)* shortening of the vocal tract (∆ = - 5 mm)

- Phonatory positions specific to lower-register emission* nearly identical tongue position* nearly identical velum position

- Compensating phonatory positions* smaller buccal opening (∆ = - 1,4 mm)* smaller labial opening (∆ = - 3.8 mm),

Physiological InterpretationBecause lower-register emission does not require

mobilization of the phonatory organs as much as upper-register emission, the soprano did not have any majorproblems singing in the lower register with her larynxpositioned for the upper register. This accounts for why hercompensating phonatory positions were limited to anattempt to correct the vowel's timbre by reducing the buccalopening and the labial opening. Indeed, the smaller vocal-tract volume resulting from the second manipulationrequired an acoustic adjustment aimed at darkening thetimbre in the lower register. To do this, the vocal tract couldbe lengthened by substantial labial projection and its volumecould be decreased by reducing the buccal opening. Whilethe buccal opening was not as great as it was on thereference sound, it was not narrow enough to meet acousticrequirements. Concerning labial projection, its extent wasalmost identical here to that used before the manipulation,most likely because this position is the singer's physiologicallimit. The soprano attempted to compensate for theinsufficient labialization and the inappropriate buccalopening by reducing her labial opening (Fig. 3a)

Sonagraphic Analysis and Acoustic InterpretationAfter manipulation, the Bb3 onset was 57.04HSvt higher

(more than one tone). The hold was up 25.98HSvt (1/2 tone)compared to the control tone. This can be explained by therise of the laryngeal box and a more pronounced crico-thyroidian shift. Moreover, this laryngeal position had animpact on timbre, which was clearer due to its rich high-frequency harmonics (reinforcement of H7, H8, H10, H13,H15, and H16), and on the placement of the sound, whichwas less of a chest tone than the reference [9].

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Figure 3 a

Looking now at the vibrato, although its amplitudedecreased slightly (-3HSvt) after manipulation, its periodicityhardly changed (5.84 instead of 5.82 Pv/s). On the otherhand, it lost its regularity, with the mean regularity quotientrising from 12.5% for the control tone (regular vibrato) to29% for the post-manipulation tone (irregular vibrato).Curiously, the pre-manipulation latency of 37.20Hcs droppedto 19.95Hcs afterwards. The time taken by the vibrato to setin here was twice as short after manipulation, even thoughthe "destabilized" soprano should have taken more time tofind the right pitch before beginning to make the soundvibrate. It is no doubt because of this abnormally shortlatency that she needed four times as much time to stabilizeher vibrato. Indeed, her stabilization time, which was37.20Hcs for the control tone, rose as high as 172.50Hcs aftermanipulation (Fig. 3b).

Figure 3 b

In summary, the Bb3 sung after the manipulation was asemi-tone higher than beforehand. Moreover, it sounded lesslike a chest tone and thus possessed a much lighter timbrethan a low-pitched tone produced by this soprano undernormal conditions.

Results of the Perception StudySelecting Listeners

A perceptual study of the Bb3 and Bb5 sung before andafter manipulation was conducted on 10 musicians (GI) whorated only accuracy, and on 5 singing teachers and 5

professional singers (GII) who rated accuracy as well as voiceplacement. The soprano who had undergone themanipulations eight months earlier was also asked to rateher own productions, although without being told whatexperiment was at stake (GIII). All subjects selected (GI, GII,and GIII) underwent a preliminary audition test aimed atmeasuring their pitch differential threshold. Whereas for puresounds this threshold is about 1.3HSvt (0.26 commas) innon-musicians, in the musicians tested, it was about 0.12HSvt(0.0028 commas), their pitch threshold being 0.7HSvt (0.14commas) for straight sounds and 4.6HSvt (0.92 commas) forvibrated sounds with an amplitude of 25HSvt (1/2 tone) orless [10].

TestingThe listeners were presented with two pairs of tones:

LRBM vs. LRAM (lower register before manipulation vs. lowerregister after manipulation), and URBM vs. URAM (upperregister before manipulation vs. upper register aftermanipulation). In addition, the second terms of the pairswere interchanged to obtain pairs LRAM vs. LRBM and URAMvs. URBM). The instructions were to compare the secondtone to the first one in each pair in terms of accuracy, i.e.,they had to judge whether the second tone was higher than,equal to, or lower than the reference tone. The stimuli wereassembled loops containing ten randomly orderedrepetitions. All 20 listeners who judged tonal accuracyresponded unanimously (i.e., all on-key tones wereunanimously judged to be on-key and all off-key tones werejudged to have the same tonal deviation relative to the targettone). The ten listeners in Group 2 and the listener in Group3 also responded unanimously regarding voice placement,except for a few minor differences in wording. The listenersalso performed a frequency-tuning test consisting of using afrequency generator to equate the different tones recorded.This enabled them to more precisely quantify the tonalinaccuracies they had noted during the first part of the test.

Additional TestThe soprano who had served as the subject was given an

additional test consisting in evaluating her own productionsby ear (by naming the tone heard). The tones to be judgedwere assembled on tape in random order and interspersedwith ten tones from the reference recording made before themanipulations. There were no repetitions and the subjectwas tested once. All the tones produced after manipulationwere judged to be "horribly" off-key by the soprano.

Evaluation of Vibrated Tone AccuracyAll subjects tested — including the soprano — estimated

the low-pitched tone (Bb3) to be a quarter tone too high andthe high-pitched tone (Bb5), one comma too low. Yet theresults of the acoustic analysis on these two notes showedthat after manipulation, the Bb3 was a semi-tone high andthe Bb5 was two commas low. The subjects thus correctlyperceived the accuracy errors but underestimated them. This

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lack of accuracy in pitch assessment, which may seemsurprising for professional musicians endowed with anexcellent musical ear, is due to the fact that the stimuli theyheard were vibrated. Indeed, vocal vibrato consists ofperiodic frequency variations around a target note. Thesevariations, which range between a quarter tone and threequarters of a tone for a normal voice and may reach or evensurpass a whole tone for pathological voices, constitute theamplitude of the vibrato. The greater this amplitude, themore difficult it is for the ear to make a tone judgement [10].This is why, on the pitch differential threshold tests, themusicians' score fell from 0.12HSvt for pure sounds to 4.6HSvtfor vibrated sounds less than or equal to 25HSvt (1/2-toneamplitude). The pre- and post-manipulation stimulipresented to the musicians ranged in amplitude between 38and 45.75HSvt, so all of these tones had an amplitude above asemi-tone. This accounts for the incorrect tonal-accuracyestimates.

ConclusionThis study showed, firstly, that vocal technique is the

result of powerful reflex conditioning, insofar as the height ofthe laryngeal box automatically determines the singer'sphonatory positions. This means, for example, that when thelarynx is positioned for singing in the lower register, theorgans take on the phonatory positions specific to thatregister, even during the emission of high-pitched tones andvice versa. This study also pointed out the important rolethat proprioceptive memory plays in pitch recognition forthe subject studied here, and thus suggested the existenceof different types of absolute pitch. This soprano is endowedwith a form of absolute pitch which, unlike that of mostinstrumentalists, does not call upon auditory memory.Instead, she relies on kinesthetic memory (memory formuscle movements) which is highly developed in operasingers, and thus on pallesthetic memory (memory ofvibratory sensations) since differences in the position of thelarynx induce different pallesthetic sensations. It is herkinesthetic-pallesthetic memory that enables this singer —via the mental positioning of her phonatory organs — to findthe exact pitch of the tones she must recognize or sing. If forany reason the position of these organs is disrupted, sheloses her ability to correctly assess pitch and can no longercontrol the tonal accuracy of the notes she produces.

Absolute pitch is currently considered to rely on a highlyexceptional auditory memory. The predominant role ofproprioceptive memory shown in this study suggests thatother sensory references may be at play in the mechanismsunderlying this ability, a topic worth investigating in futureresearch.

Acknowledgments

I would like to express my gratitude to the cantatrice MadyMesplé who kindly agreed to act as the subject in thisexperiment. Thanks are also extended to Bruno Fadié,osteopathic doctor, without whom this study could nothave been conducted, and to Doctor Patrick Sarrat,radiologist and Patrice Napoletano, X-ray technician at theTimone Hospital in Marseille, France, for their assistance.Special thanks to Vivian Waltz, scientific translator, for theEnglish version of this text.

In memoriam

In memory of my cousin Félix Fabre (1913 - 2001) who, byopening my eyes as a child to the wonders of the world andthe mysteries of life, aroused in me the curiosity of the mind,the driving need to learn, to understand, and to explain,which led me to my vocation as a researcher.

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[3] Klein M, Colas MGA. People with Absolute Pitch[Process Tones without Producing a P300. Science,1984; 223: 1306-1309.

[4] Baharloo S. Absolute Pitch: An Approach for Identifica-tion of Genetic and Nongenetic Components. Amer J.Hum Genet, 2000; 67: 755-758.

[5] Muller L. Céphalométrie et Orthodontie. Editions S.P.M.D, Paris, 1973.

[6] Scotto Di Carlo N. Application des méthodescéphalométriques à l'étude radiologique de la voixchantée. Editions P.U.P, Aix-en-Provence; 1976.

[7] Scotto Di Carlo N. La voix chantée. La Recherche,1991; 22, 235: 1016-1025.

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Dr. Nicole SCOTTO DI CARLO,CNRS Research DirectorLPL - UMR 6057 - CNRS*

* National Center For Scientific Research