ACTA ACUSTICA UNITED WITH ACUSTICAVol 92 (2006) 749 ndash 755

Vocal Tract Modeling in a Prosimian PrimateThe Black and White Ruffed Lemur

Marco Gamba Cristina GiacomaDepartment of Animal and Human Biology University of Torino 10123 Torino Italy marcogambaunitoit

SummaryThe ruffed lemur (Varecia variegata variegata) like all other lemurs is endemic to Madagascar and inhabits theeastern rainforests of the island A captive breeding project for this species has been underway since the Sixtiesand lead to a relatively great population of captive ruffed lemurs Part of this population was recorded for thepurpose of this study We built a computational model of a non-human primate vocal tract deriving informationfrom a silicon cast of a cadaver and then compared the predicted acoustic response with the formant patternobserved in natural calls This analysis was performed by considering both oral and nasal tracts In fact dataabout first formants F1 and F2 derived from the phonetic analysis of V v variegata vocalizations were comparedto formant values predicted by the computational model showing a moderate percentual difference The vocalrepertoire of Varecia sp features calls showing different formant patterns that can be described by mean simpletube and multiple tube systems For the first time this paper provide vocal tract modeling of a prosimian primateand consider variation across different calls Our findings suggest that if formants in some vocal types can beeffectively predicted by mean of a uniform tube model of the oral vocal tract other vocalizations required theimplementation of nasal tract models and multi-tube vocal tract emulations

PACS no 4380Ka

1 Introduction

Living lemurs resemble primitive primates that lived mil-lions of years ago For this reason the study of livinglemurs can provide unique and highly valuable insight intoprimate evolution They are conspicuously vocal and arecapable of modifying both the shape of the airway andthe oscillation of the vocal folds [1] Previous studies haveshown lemurs of Madagascar produce a wide range of vo-calizations comprising alarm calls several contact callsmating calls and screams [1 2] The thesis that speech dif-fers from non-human primates vocal communication be-cause of the lack of a continual articulation often causedan under evaluation of non-human primates phonatoryprocesses Thus the fact that non-human primates can pro-duce important changes in the vocal tract shape and lengthhas been rarely investigated Recent evidences emergingfrom studies of various primate species demonstrate thatformants are meaningful acoustic features of non-humanprimate calls [3 4 5] and that rapid changes in vocaltract shape and length are not uniquely human as they canbe assessed from the dynamic pattern of certain acousticparameters First (F1) and second (F2) formants of non-human primates calls can distinguish when plotted dif-ferent vocal types as it happens for human vowels [6]This is particularly interesting although it has been never

Received 25 January 2006accepted 11 July 2006

investigated in lemurs If it is true that non-human pri-mates share to a certain degree with humans the abilityto act voluntary changes in vocal tract shape during vo-calisation by articulation of the tongue the mandible andthe larynx [3 7 8 9 10] lemurs could represent a simpli-fied model as lip protrusion is absent This paper providesthe first detailed description of the ruffed lemur vocal tractarea function and the first attempt to model lemur phona-tion Furthermore we compare F1 and F2 measured fromthe natural calls with the output of several vocal tract mod-els

2 Materials and Methods

Study animals were captive ruffed lemurs kept in severalinstitutions across Europe and United States We recordednatural occurring vocalization emitted by Varecia var-iegata variegata at Parco Natura Viva (Bussolengo-VrItaly) Mulhouse Zoo (France) Rheine Der Naturzoo andKoln Zoo (Germany) Apenheul (Apeldoorn The Nether-lands) St Louis Zoo (USA) Twycross Zoo DrusillasPark and Banham Zoo (UK)

The vocal repertoire of the black and white ruffed lemuris the most studied among lemurs Previous works [2 11]have recognised 16 vocal types 4 of which we consideredin this study because of their vowel like acoustic struc-ture Tape-recorded vocalizations of ruffed lemurs werecategorized by ear by visual comparison with published

copy S Hirzel Verlag middot EAA 749

ACTA ACUSTICA UNITED WITH ACUSTICA Gamba Giacoma Vocal tract modeling in lemursVol 92 (2006)

Figure 1 Sonograms of vocal types Mew (a) Shriek (b) Wail (c) and Growl-Snort (d) emitted by the ruffed lemur (Varecia varie-gata variegata) All spectrograms were generated in Praat with the following parameters time range frequency range 0ndash12000 Hzmaximum 100 dBHz dynamic range 30 dB pre-emphasis 60 dBOct dynamic compression 00

sonograms and using multivariate statistical analysis Ad-ditional video recordings were used to describe phonationmechanisms (eg presence or absence of phonatory artic-ulation)

Calls were labelled according to Pereira and colleagues[2] and additional indications were derived from other pa-pers [1 11] The 4 vocal types we considered in this studywerea Mew ndash This vocalization is a tonal emission and usu-

ally shows a moderate to absent frequency modulation(Figure 1a) A slow rise in pitch is often present inadults The mew can vary in duration but it lasts onaverage 08 s All group members were seen emittingmews in relaxed context but this emission plays a keyrole in the mother-offspring communication since theearly stages after birth [11]

b Shriek ndash Shrieks and Roars are vocalizations emittedduring the Roar Shriek Chorus The roar shriek cho-ruses resemble the inter-group spacing calls of otherprimates (eg Alouatta sp [12]) Choruses are struc-turally complex and variable group call including si-multaneous contributions by all the adults in the groupThis composite vocalization lasts from 5 to 30 seconds[1] and features two distinctive emissions One is awide-band noisy sound called ldquoroarrdquo and the other isa frequency modulated narrow-band component calledldquoshriekrdquo (Figure 1b)

c Wail ndash This call denotes urgency for re- aggregation[1] It is present only at the end of the roar shriek cho-rus Wail is particularly rich in harmonic overtones andcan appear as a tonal or noisy-tonal vocalization (Fig-ure 1c)

750

Gamba Giacoma Vocal tract modeling in lemurs ACTA ACUSTICA UNITED WITH ACUSTICAVol 92 (2006)

d Growl-snort ndash This emission is very low-pitched firstportion is usually emitted with mouth closed and no de-tectable articulation (Figure 1d) It is usually elicitedby non-specific disturbance Second part is a rapid ex-pulsion of air In the present work we have measuredformants in the growling portion

Naturally occurring vocalizations belonging to vocal typesabove described were recorded and for the purpose ofconducting this research 10 calls per vocal type werechosen Recordings were made on TDK DA-RXG tapesusing a Sony TCD-D100 Digital Audio Tape recorderand a Sennheiser ME66 directional microphone with K3Upower module We do selected calls from 10 different in-dividuals per vocal type

Acoustic analyses were performed in Praat 4304 atoolkit to do phonetic analysis by computer [13] Praatuse was combined with Akustyk 176 which is a com-prehensive vowel analysis software package by B Plichta(Michigan State University) To characterize vocal tract(filter) we measured first 2-5 formants depending on thenumber of formants detectable from the spectrogram us-ing Linear Predictive Coding (LPC) Formant presets weremodified as well per type Extensive on-screen examina-tion of all the vocal types was necessary to determineintra- and inter-individual variation Formant analysis inthis study is the result of an application of the Burgrsquosmethod [14] with superimposition over the signal spec-trogram A number of autocorrelation-based LPC spec-tra was overlaid independently derived FFT spectra of thesame vocalization to ensure the goodness of the LPC anal-ysis Typical maximum formant was 12000 Hz and num-ber of formants 3ndash7 Window length was 005 s and dy-namic range 220 Hz The formant pattern fitting was in-ferred during a step-by-step monitored process where op-erator could interrupt the analysis and modify the analysisparameters A Praat script was used to automate file open-ing and editing and file saving of the measurements

Computational models of the vocal tract were built con-sidering both a uniform tube model (a system in whichthere is one tube with a certain length and constant cross-sectional area) and multi tube models (a system compris-ing a series of concatenated tubes of fixed length eachshowing a certain cross-sectional area)

Vocal tract area functions of the oral tract and the vo-cal tract of a ruffed lemurs were determined by measuringcross-sectional areas with 1 cm increment from the vocalfolds toward mouth opening and nostrils Measures weretaken over a silicon cast (Figure 2) of the entire vocaltract (glottis to lips for the oral tract and glottis to nostrilsfor the nasal tract respectively) of one cadaver of blackand white ruffed lemur (Varecia variegata variegata) Theruffed lemur cadaver belonged to the collection of deadanimals at the Parc Botanique et Zoologique Tsimbazaza(Antananarivo Madagascar) The specimen was an adultmale (labelled as A1) whose greatest length of skull was10689 mm (taken from the most anterior part of the ros-trum excluding teeth to the most posterior point of the

Figure 2 Photograph of the silicon cast of the vocal tract of Vare-cia variegata variegata (sketch of the dorsal airsac (A) the lar-ynx (L) the oral (O) and the nasal (N) tracts) Reference line is1 cm

skull) Total lengths of the oral tract and the nasal tractwere 10 cm and 11 cm respectively

In this study we didnrsquot modeled the role of the airsac inruffed lemurrsquos phonation because its dimensions could notbe determined due to a possible lack in the tissue elastic-ity in the dead animals we analysed For similar reasonswe were not able to provide any information about larynxmobility in the ruffed lemur

All length and dimension measurements of the castwere taken with a Mitutoyo digital caliper (accurate to001 mm) We measured an average diameter because thecross-section of the vocal tract cast was not generally cir-cular and cross-sectional areas were computed startingfrom these measures in Microsoft Excel

Cross-sectional areas were used to build the cross-sectional area function that represents the input of the vo-cal tract modeling software [7] Vocal tract modeling wasperformed using VTAR a Matlab-based computer pro-gram for vocal tract acoustic response calculation VTARis capable of simulating complex frequency-domain mod-els for the vocal-tract acoustic response where the vocaltract is decomposed into various modules such as simpletubes branching and lateral channels Even if previousapplications of VTAR included complex models of hu-man vowel sounds [15] it can generate various non-speechmodels according to operatorrsquos choices and inputs In thisstudy vocal tract is modeled as a concatenation of tubeswhere the cross-sectional areas of each segment changedaccording to calculations from the cast measurements andthe length of tubes was kept constant at 1 cm We did twoseparate models for the oral tract and the nasal tract onthe basis of the assumption that mammals produce vo-calizations through the nose or the mouth but not both[16] Models emulating vocal tract resonances in wails andshrieks were built combining vocal tract measures withthe information derived from video recordings (schema-tised in see Figure 3) Angle of mouth opening [17] duringphonation of the ruffed lemurs were calculated and then acongruent mouth opening was simulated in the dead spec-imen Measures derived from this operations were used tobuild the vocal tract area function for wails and shrieks

751

ACTA ACUSTICA UNITED WITH ACUSTICA Gamba Giacoma Vocal tract modeling in lemursVol 92 (2006)

Table I Input data for VTAR derived from segmenting the silicon cast of a cadaver and calculating estimates of mouth opening forwails and shrieks We measured cross-sectional areas at an increment of 1 cm from glottis to lips for the oral tract (O-cast) glottis tonostrils for the nasal tract (N-cast) Segment length is 1 cm segment number and its cross sectional area is reported in columns

Segment number and cross-sectional area (cm2)Model 1 2 3 4 5 6 7 8 9 10 11

O-cast 079 064 059 056 062 088 128 081 134 115 -N-cast 079 064 113 099 087 082 179 202 141 054 007Mew 079 064 059 056 062 088 128 081 134 115 -Growl-s 079 064 113 099 087 082 179 202 141 054 007Wail 079 064 059 056 135 088 139 125 197 - -Shriek 079 064 235 222 246 352 514 - - - -

Table II Acoustic response of the multi-tube models of the ruffed lemurrsquos vocal tract Formant calculations (Computed) were basedon different tube models geneted according to input values in Table 1 Formant values for ruffed lemur calls (Natural) were determinedfrom naturally occurring vocalisations

Natural Computed DifferenceModel F1 (Hz) F2 (Hz) F1 (Hz) F2 (Hz) DF1 () DF2 ()

O-cast - - 1010 2317 - -N-cast - - 467 1851 - -Mew 902 2489 1010 2317 12 7Growl-s 490 1726 467 1851 5 7Wail 1131 2473 1167 2614 3 6Shriek 1492 5183 1610 3518 8 32

Figure 3 Across the 4 vocal typeswe considered it is possible to re-cognize vocalization emitted withclear articulatory manoeuvres andother characterized by no evidentarticulation a) mew and growl (-snort) b) wail c) chatter

Comparisons between the acoustic output obtainedfrom previous models have been made with the acousticresponse of simple tube models of the same length andwith averaged cross-sectional area

3 Results

Vocal tract area functions derived from the silicon cast(see Figure 2) were used to generate computational mod-els based on the actual cast of oral and nasal tracts (seeFigures 4a and 5a) The acoustic response of these modelsshowed clear differences for the oral tract (1010 Hz andF2 at 2317 Hz) and for the nasal tract (467 Hz and F2 at1851 Hz)

Vocal tract area functions for mews and growl-snortswere assumed comparable with the ones derived from thecast Area functions for wails and growl-snorts were mod-ified according to the degree of articulation because boththese vocal types showed clear articulatory manoeuvres(schematized in Figure 3) The VTAR program was used

to calculate the formant frequencies (see Table I for theinput data used) Acoustic response of each multi-tubemodel and the formant values measured from the spon-taneous natural calls were then compared (see Table II)

First formant predicted for the oral tract model derivedfrom cast measures showed F1 at 1010 Hz and F2 at 2317Hz Mews are produced with the mouth closed thus themodel we considered was the one derived from the actualoral tract cast When compared with data from the pho-netic analysis of mews these values showed a moderatedifference (12 for F1 and 7 for F2)

Growl-snort is emitted with mouth closed or almostclosed and no evident articulation can be detected in thepart of the call we analyzed for the purpose of this paperGrowl components of the growl-snort were at first com-pared with the acoustic response provided by the mouth-closed vocal tract However F1 and F2 in the growl (re-spectively 490 Hz and 1726 Hz) exhibit clear differences(107 for F1 and 34 for F2)

752

Gamba Giacoma Vocal tract modeling in lemurs ACTA ACUSTICA UNITED WITH ACUSTICAVol 92 (2006)

Figure 4 Vocal tract area function (a) and acoustic response (b)of the oral vocal tract model of a ruffed lemur (Varecia variegatavariegata)

We then considered the hypothesis that filtering in thegrowl was involving mainly the nasal tract In fact differ-ences between F1 and F2 from the nasal tract computa-tional model were considerably more similar to the onesmeasured in growls Difference for the first formants is re-spectively 5 and 7

Wails are emitted with a slightly opened mouth and weobtained F1 and F2 respectively at 1167 Hz and 2614 HzThis model seems to be effective in representing the vo-cal tract configuration of the ruffed lemur when emittingwails in fact difference is 3 for F1 and 6 for F2

Shrieks are always emitted with the mouth wide openedand completely retracted corners This may causes a short-ening of the oral vocal tract up to 30ndash50 We assumedthat a plausible model should feature a shorter vocaltract than the previous ones and calculated the acousticresponse at the seventh segment Formants values were1610 Hz and 3518 Hz First formant showed impressivesimilarities with the natural one (8 difference) Howeversecond formant showed more discrepancies (32 differ-ence)

Vocal tract was then modelled in its simplest formby calculating the acoustic response of a simple losslessacoustic tube with the same length of the multi-tube sys-tems previously considered The cross-sectional area of

Figure 5 Vocal tract area function (a) and acoustic response (b)of the nasal vocal tract model of a ruffed lemur (Varecia varie-gata variegata)

the tube was averaged on the basis of the anatomical mea-sures (see Table I)

Acoustic response of each simple tube model againgenerated using VTAR and the formant values measuredfrom the spontaneous natural calls were then compared(see Table III)

The simple tube model emulating the oral tract pre-dicted F1 at 889 Hz and F2 at 2530 Hz where 814 Hz (F1)and 2304 Hz (F2) were the values given for the nasal tractThe values predicted from the simple tube model fit prop-erly with formants measured from mew (1 and 2 dif-ferences) and shriek (6 and 10 differences) vocaliza-tions However the simple tube systems failed in repro-ducing first formant of wails (22 for F1 and 2 for F2)and the vocal tract resonance of growl-snorts (66 for F1and 33 for F2) It is interesting to note that a uniformtube model of the vocal tract which could effectively pre-dict growl-snortsrsquo F1 should be much longer than the ac-tual ruffed lemur vocal tract (21ndash22 cm)

4 Discussion

Recent studies about other non-human primates showedthat a 3-segment tube model with variable diameterscould predict a more precise formant pattern for Dianamonkeyrsquos alarm calls than simple tube models did [6]

753

Gamba Giacoma Vocal tract modeling in lemurs ACTA ACUSTICA UNITED WITH ACUSTICAVol 92 (2006)

Figure 4 Vocal tract area function (a) and acoustic response (b)of the oral vocal tract model of a ruffed lemur (Varecia variegatavariegata)

We then considered the hypothesis that filtering in thegrowl was involving mainly the nasal tract In fact differ-ences between F1 and F2 from the nasal tract computa-tional model were considerably more similar to the onesmeasured in growls Difference for the first formants is re-spectively 5 and 7

Wails are emitted with a slightly opened mouth and weobtained F1 and F2 respectively at 1167 Hz and 2614 HzThis model seems to be effective in representing the vo-cal tract configuration of the ruffed lemur when emittingwails in fact difference is 3 for F1 and 6 for F2

Shrieks are always emitted with the mouth wide openedand completely retracted corners This may causes a short-ening of the oral vocal tract up to 30ndash50 We assumedthat a plausible model should feature a shorter vocaltract than the previous ones and calculated the acousticresponse at the seventh segment Formants values were1610 Hz and 3518 Hz First formant showed impressivesimilarities with the natural one (8 difference) Howeversecond formant showed more discrepancies (32 differ-ence)

Vocal tract was then modelled in its simplest formby calculating the acoustic response of a simple losslessacoustic tube with the same length of the multi-tube sys-tems previously considered The cross-sectional area of

Figure 5 Vocal tract area function (a) and acoustic response (b)of the nasal vocal tract model of a ruffed lemur (Varecia varie-gata variegata)

the tube was averaged on the basis of the anatomical mea-sures (see Table I)

Acoustic response of each simple tube model againgenerated using VTAR and the formant values measuredfrom the spontaneous natural calls were then compared(see Table III)

The simple tube model emulating the oral tract pre-dicted F1 at 889 Hz and F2 at 2530 Hz where 814 Hz (F1)and 2304 Hz (F2) were the values given for the nasal tractThe values predicted from the simple tube model fit prop-erly with formants measured from mew (1 and 2 dif-ferences) and shriek (6 and 10 differences) vocaliza-tions However the simple tube systems failed in repro-ducing first formant of wails (22 for F1 and 2 for F2)and the vocal tract resonance of growl-snorts (66 for F1and 33 for F2) It is interesting to note that a uniformtube model of the vocal tract which could effectively pre-dict growl-snortsrsquo F1 should be much longer than the ac-tual ruffed lemur vocal tract (21ndash22 cm)

4 Discussion

Recent studies about other non-human primates showedthat a 3-segment tube model with variable diameterscould predict a more precise formant pattern for Dianamonkeyrsquos alarm calls than simple tube models did [6]

753

ACTA ACUSTICA UNITED WITH ACUSTICA Gamba Giacoma Vocal tract modeling in lemursVol 92 (2006)

Table III Acoustic response of the uniform tube models of the ruffed lemurrsquos vocal tract First two colums show length of the tube andaveraged cross sectional area (see Table for original values) We reported only one formant calculation (Computed) per model as theemulation using the actual vocal tract length usually provide the best fit to formant values measured in ruffed lemurs calls (Natural)

Tube Av c-s- a Natural Computed DifferenceModel l (Hz) (cm2) F1 (Hz) F2 (Hz) F1 (Hz) F2 (Hz) DF1 () DF2 ()

O-cast 100 086 - - 889 2530 - -N-cast 110 100 - - 814 2304 - -Mew 100 086 902 2489 889 2530 1 2Growl-s 110 100 490 1726 814 2304 66 33Wail 90 104 1131 2473 881 2518 22 2Shriek 50 169 1492 5183 1577 4680 6 10

In this work we obtained a vocal tract silicon cast ofa ruffed lemur which allowed measuring details of thestructure of a non-human primate vocal tract The oral andnasal tract morphologies were subsequently used to modelthe acoustic characteristics of the ruffed lemur filter sys-tem These measurements have been supplemented by es-timates of the cross-sectional area of ruffed lemur emittingsome typical vowel-like vocalizations (wails and shrieks)

The acoustic response generated by VTAR when webuilt a multi-tube model of the oral tract and the nasal tractshowed distinct results

This is important when observed in the light of lemurphonation processes In fact ruffed lemurs emit calls bothwith open mouth and closed mouth

Formants measured in naturally produced utterancesmatched reasonably formant values obtained by the com-putational multi-tube models at least for 3 vocal types(mews growl-snorts and wails) But whereas mews andwails could be effectively modelled using the oral tractcross-sectional area estimates the model considering con-catenated tubes emulating the nasal tract showed a muchmore congruent fit

The question that may arise at this point whether weneed to consider multi-tube models to describe ruffedlemur vocal tract resonance or we can rely on the simpletube models suggested by previous studies [18 19]

We built a set of uniform tube models varying lengthand averaging cross-sectional areas according to anatomi-cal measurements When we compare formants predictedby the best fitting simple tube models with formants de-rived from the natural calls

The uniform tube model showed a more precise predic-tion than the concatenated tubes ones for the formant pat-tern of both mews and shrieks However it fails in predict-ing a plausible F1 for wails and seems far from being ableto describe vocal tract resonance of the growl componentof growl-snorts

Recent claims about the need to consider complex tubemodel to describe non-human primate formant patterns arestill in debate [6 20]

The pioneering works of Lieberman and colleagues[18 7] demonstrated that non-human primates possess alimited vowel space due to the limitation imposed by theirvocal tract anatomy that differs from the one of humans

Tongue position and the impossibility to create abruptchanges in the oral tract cross sectional area are supposedto be the 2 main candidates limiting non-human primatesphonation abilities [20 21]

Lemurs share these limitations with the other non-human primates [12 22 23] and our findings support thefact that part of their phonation could effectively beingmodelled through the uniform tube model

However assuming that the single dead animalrsquos vocaltract we measured is representative for this species multi-tube modelling based on anatomical measures offered twointeresting insights into these prosimians phonation abili-ties

If the physiological basis for the ruffed lemur formantfrequencies resides in their vocal tract and not in acces-sory structures (eg air sacs not modelled in this paper)closed-mouth sounds as the growl-snort could be the resultof the column of air passing by the nasal tract instead ofthe oral tract This could be an important factor to be con-sidered in future studies when phonation processes are ap-proached across the entire vocal repertoire of non-humanprimate species

A second point is represented by the fact that complexmodels could predict prosimian formant patterns betterthan the uniform tube model at least for 2 of the vocaltypes we analyzed (growl-snort and wail) This may sug-gest the need to re-consider some of the some of the basicassumptions about non-human primate phonation abilitieswhere oral tract phonation is very often the only one con-sidered [6] Extensive investigation of formant variationin non-human primate vocalizations and its interpretationusing computational models based on anatomical mea-surements could represent an important basis to increaseknowledge about these speciesrsquo phonation abilities Possi-bly more complex models including resonance in both thenasal tract and the oral tract could provide a better fit tonatural formant values Vocal sacs should be taken in ac-count as well Understanding their position and dimensioncan be crucial to describe of the role they play in modify-ing the acoustic signal

In these attempts to decode phonation mechanismacross different vocal types in lemurs we showed evidenceof the ability in these species to modify vocal tract lengthat least between different vocal types As reported from

754

Gamba Giacoma Vocal tract modeling in lemurs ACTA ACUSTICA UNITED WITH ACUSTICAVol 92 (2006)

studies in human and in non-human primates there couldbe a functional value in providing information on vocalizerbody size (reduced actual or even exaggerated) throughacoustic features of vocalization [16 24 25]

As it happens in humans opening the vocal tract raisesthe F1 formant and this can be also obtained by articula-tory maneuvers Even if ruffed lemurs are not capable oflip protrusion as humans and other primates mouth open-ing and lips retraction can act to shorten the vocal tract

5 Conclusion

The vocal repertoire of the ruffed lemurs shows theseprosimians possess the ability to change the configurationof the vocal tract Measures taken over the vocal tract castof a ruffed lemur cadaver were collected and used to buildseveral computational models including uniform tube andmulti-tube models The uniform tube model of the oraltract seems to explain properly formant patterns in someof the vocalisations emitted by ruffed lemurs but fails inother vocalizations For these calls a better prediction wasobtained by complex models of either the oral tract aloneor the vocal tract alone

Prosimian primates diverged from the anthropoidbranch (monkeys apes and humans) more than 60 millionyears ago and these results suggest that even in lemursonly the use of both uniform tubes models and complextubes models can provide valid predictions of the lemurformant patterns when investigated across the vocal reper-toire

Acknowledgement

This research was supported by the Universitagrave degli Studidi Torino and by grants to MG from the Parco NaturaViva ndash Centro Tutela Specie Minacciate We thank for theirhelp and supervision Dr Gilbert Rakotoarisoa Chef duDept Faune and Jules Medard at the Parc Botanique eZoologique de Tsimbazaza Antananarivo Madagascar

References

[1] J M Macedonia K F Stanger Phylogeny of the Lemuri-dae revisited Evidence from communication signals FoliaPrimatol 63 (1994) 1ndash43

[2] M E Pereira M L Seeligson J M Macedonia Thebehavioral repertoire of the black-and-white ruffed lemurVarecia variegata variegata (Primates Lemuridae) FoliaPrimatol 51 (1988) 1ndash32

[3] W T Fitch Vocal tract length and formant frequency dis-persion correlate with body size in rhesus macaques JAcoust Soc Am 102 (1997) 1213ndash1222

[4] T Riede K Zuberbuehler Pulse register phonation in Di-ana monkey alarm calls J Acoust Soc Am 113 (2003)2919ndash2926

[5] T Riede K Zuberbuehler The relationship between acous-tic structure and semantic information in Diana monkeyalarm vocalization J Acoust Soc Am 114 (2003) 1132

[6] T Riede E Bronson H Hatzikirou K Zuberbuehler Vo-cal production mechanisms in a non-human primate mor-phological data and a model Journ Hum Evol 48 (2005)85ndash96

[7] P Lieberman D H Klatt W H Wilson Vocal tract limita-tions on the vowel repertoires of rhesus monkeys and othernonhuman primates Science 164 (1969) 1185ndash1187

[8] M D Hauser C S Evans P Marler The role of articula-tion in the production of rhesus monkey (Macaca mulatta)vocalizations Anim Behav 45 (1993) 423ndash433

[9] W T Fitch M D Hauser Unpacking ldquohonestyrdquo verte-brate vocal production and the evolution of acoustic sig-nals ndash In Acoustic Communication Vol 16 A M Sim-mons R F Fay A Popper (eds) Springer New York2002 65ndash137

[10] W T Fitch M D Hauser Vocal production in nonhumanprimates Acoustics physiology and functional constraintson ldquohonestrdquo advertisement Am Journ Primatol 37 (1995)191ndash219

[11] M Gamba C Giacoma C A Zaborra Monitoring the vo-cal behaviour of ruffed lemurs in the nest-box Eaza News43 (2003) 28ndash29

[12] R V Drubbel J P Gautier On the occurence of nocturnaland diurnal loud calls differing in structure and duration inRed Howlers of French Guiana Folia Primatol 60 (1993)195ndash209

[13] P Boersma Praat a system for doing phonetics by com-puter Glot International 5 (2001) 341ndash345

[14] D G Childers Modern spectrum analysis IEEE Press(1978) 252ndash255

[15] Z Zhang C Y Espy-Wilson A vocal tract model forAmerican English l J Acoust Soc Am 115 (2004)1274

[16] W T Fitch The phonetic potential of nonhuman vocaltracts comparative cineradiographic observations of vocal-izing animals Phonetica 57 (2000) 205ndash218

[17] P U Dijkstra L G de Bont B Stegenga G Boering An-gle of mouth opening measurement reliability of a tech-nique for temporomandibular joint mobility assessment JOral Rehabil 22 (1995) 263ndash8

[18] P Lieberman Primate vocalization and human linguisticability J Acoust Soc Am 44 (1968) 1574ndash1584

[19] M J Owren R M Seyfarth D L Cheney The acous-tic features of vowel-like grunt calls in chacma baboons(Papio cyncephalus ursinus) Implications for productionprocesses and functions J Acoust Soc Am 101 (1997)2951ndash2963

[20] P Lieberman Limits on tongue deformation ndash Diana mon-key formants and the impossible vocal tract shapes pro-posed by Riede et al (2005) Journ Hum Evol 50 (2006)219ndash21

[21] T Nishimura A Mikami J Suzuki T Matsuzawa De-scent of the larynx in chimpanzee infants Proc Natl AcadSci 100 (2003) 6930ndash6933

[22] M Kollmann L Papin Etudes sur les lemuriens I Le lar-ynx et le pharynx Anatomie comparee et anatomie micro-scopique Annales des Sciences Naturelles 19 (1914) 227ndash317

[23] J Jordan Quelques remarques sur la situation du larynxchez les leacutemuriens et les singes Acta Biol Med 4 (39-51)1960

[24] W T Fitch Comparative vocal production and the evolu-tion of speech Reinterpreting the descent of the larynx ndashIn The Transition to Language A Wray (ed) OxfordUniversity Press Oxford 2002

[25] D Rendall S Kollias C Ney P Lloyd Pitch (F0) andformant profiles of human vowels and vowel-like baboongrunts The role of vocalizer body size and voice-acousticallometry J Acoust Soc Am 117 (2005) 944ndash955

755