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Bernd J. Kröger: research

My current research topics:

Classification of normal and disordered voice quality

Production-Perception Approach (PPA): Stimuli are generated using a self-oszillating two-mass model (see: VocalTractLab)

Try to imitate the auditory stimuli, following the articulatory explanations (not for rough and instable voice)
  • pressurelow  mid  high  low2high  high2low     ... results in soft to loud voice (no or little change in voice quality)
  • tensionlow  mid  high  low2high  high2low     ... results in low to high pitch (no or little change in voice quality)
  • articulation vs. phonation:   aua(low)  aua(high)  aaa(low-high-low)  uuu(low-high-low)     ... results in changes of pitch or in changes of supralaryngeal articulation (no or little change in voice quality)
  • abduction:   low  mid  high  low2high  high2low     ... results in change of voice quality: from asthen (hypo) to strained (hyper)
  • noisy leak:   low  mid  high  low2high  high2low     ... results in change of voice quality: from no to full breathiness
  • tissueDamping4RoughVibs:   low  mid  high  low2high  high2low     ... results in change of voice quality: from full to no roughness
  • tissueDamping4InstabVibs:   low  mid  high  low2high  high2low     ... results in change of voice quality: instable voice because of low tissue damping
  • changeTension4InstabVibs:   low  mid  high  low2high  high2low     ... results in change of voice quality: instable voice because of changes in vocal fold tension

Classification of Voice Quality using GIRBAS Scale
(following: PH Dejonckere et al. 1996, Revue de Laryngolgie - Otologie - Rhinologie 117, 219-224)
(description of voice features: see also ASHA CAPE-V 2002: pdf)

four-point scale of severity: 0="normal/no", 1="slight", 2="moderate", 3="severe"

  • Overall Grade of Hoarseness (G): global, integrated impression of voice deviance (here: mean value of the next five voice features)
  • Instability (I): Fluctuation of voice quality over time and/or unstable vocal fold oscillations
  • Roughness (R): vocal fold oscillations with perceivable irregularities
  • Breathiness (B): stable vocal fold oscillations but with audible air escape / with audible additional noise
  • Asthenia (A): stable vocal fold oscillations but too weak vocal effort (i.e. hypofunction)
  • Strained Quality (S): stable vocal fold oscillations but excessive (i.e. too strong) vocal effort (i.e. hyperfunction)

Overview: research topics

Speech acquisition: Development of a mental syllabary

Generation of mono-syllables (and bisyllabic words) of Standard German using an action-based articulatory production model (using: VocalTractLab) and speaker JD3.speaker

[V] 01: V = long vowel, diphtong (incl. vowel plus vocalic /r/),
      triphthong(= diphthong plus vocalic /r/)
well-timed speech actions: vocalic, glottal abduction, lung pressure action;
two actions for intonation were added;
the utterence ends with last lung pressure action
long: i: e: E: a: o: u: y: 2: @:
diphthong: aI aU OI
long+voc/r/: i:6 e:6 E:6 a:6 o:6 u:6 y:6 2:6
triphthong: aI6 aU6 OI6
articulation: V01_ges.zip
[V] 02: from V = long to V = short vowel and reduced vowel:
compared to V01: shorten vowel;
end of utterance is determined by last lung pressure action (0Pa); function of this action is like consonantal closure in syllable offset!
short and reduced vowel only occurr in CV context (see below; figure shows [d@])
audios for variation of V in /CV/: see above and below;
V = long, short, reduced
[CV] 01: from V to VC with C = voiced plosive, lateral, or /r/ as fricative realization:
compared to V01/V02: in addition: consonantal obstruction action
long: ba: da: ga: la: ra: bu: du: gu: lu: ru: bi: di: gi: li: ri:
diphthong: baI baU daU daI gaU gaI gOI laU raU rOI raI
long+voc/r/: bi:6 bE:6 di:6 dE:6 gi:6 le:6 ru:6
triphthong: baU6 baI6 raI6
short: ba da ga la ra
reduced: b@ d@ g@ l@ r@
words: ga:b@ ga:d@ la:g@ ba:r@ gal@ gar@
articulation: CV01_ges.zip
[CV] 02: from C = lateral to C = nasal:
compared to VC01: add a velopharyngeal opening action
long: ma: na: mi: ni: mu: nu:
diphthong: maU naU maI naI mOI nOI
long+voc/r/: mi:6 me:6 mE:6 mo:6 nE:6 na:6 nu:6
triphthong: maU6 maI6
short: ma na
reduced: m@ n@
words: da:m@ pan@
articulation: CV02_ges.zip
[CV] 03: from C = voiced to C = voiceless plosive:
compared to CV01: shift of consonantal obstruction action to the left in order to allow VOT;
add a gottal abduction action (logner duration of initial glottal opening action)
long: pa: ta: ka: pi: ti: ki: pu: tu: ku:
diphthong: paI paU pOI taI taU tOI kaI kaU kOI
long+voc/r/: pi:6 pu:6 ti:6 ty:6 te:6 to:6 tu:6 ke:6 ko:6 ku:6
triphthong: paU6 taU6 tOI6
short: pa ta ka
reduced: p@ t@ k@
words: kap@ pa:t@ bak@
articulation: CV03_ges.zip
[CV] 04: from C = voiceless plosive to C = voiceless fricative:
compared to CV03: longer duration of glottal opening action over whole consonatal obstruction;
slightly right shift of consonantal obstruction action (more temporal overlap with vocalic action)
long: fa: sa: Sa: ci: xa:
diphthong: faU faI SaU SaI SOI
long+voc/r/: fi:r fy:r fE:r fo:r fu:r Si:r Sy:r SE:r Sa:r So:r Su:r
triphtong: faIr fOIr SaUr
short: fa sa Sa ca xa
reduced: f@ s@ S@ c@ x@
words: ?af@ kas@ laS@ kYc@ la:x@
articulation: CV04_ges.zip
[CV] 05: from C = voiceless to C = voiced fricative:
compared to CV04: add a glottal adduction action (here called "breathy"),
leading to phonation and a leak in order to generate enough air flow
for frication noise during production of voiced fricative
long: va: za: Za: ja:
diphthong: vaU vaI zaU zaI jaU
triphtong: vaIr zaUr
short: va za Za ja reduced: v@ z@ Z@ j@
words: m2:v@ va:z@ ga:z@ ko:j@
articulation: CV05_ges.zip
[CV] 06: from V CV with C = glottal stop /?/:
compared to V01/V02: add a glottal stop action (strong adduction);
slightly later onset of lung pressure action (1000Pa)
long: ?i: ?a: ?u: ?y:
diphthong: ?aI ?OI ?aU
short/reduced: ?I ?a ?U ?Y ?@
articulation: CV06_ges.zip
[CV] 07: from /?V/ to /hV/ with /h/ = glottal voiceless fricative:
compared to CV04 (oral voiceless fricative): delete the oral consonantal obstruction action;
just: long glottal abduction action (voiceless) plus synchronous lung pressure action (1000Pa)
V=long: hi: ha: hu: hy:
diphthong: haI hOI haU
V=short/reduced: hI ha hU hY h@
words: ?e:(h)@ my:(h)@
articulation: CV07_ges.zip
[CCV] 01: from CV (CV01-CV03) to CCV01
with C1 = plosives and C2 = lateral, nasal, or /r/ as fricative realization:
mainly add one consonantal obstruction action;
other changes of velic, glottal, F0 and lung actions similar as in CV01-CV03
V=[a:]: bla: bra: gla: gna: gra: pla: pra: kla: kna: kra:
V=[i:]: bli: bri: gli: gni: gri: pli: pri: kli: kni: kri:
V=[u:]: blu: bru: glu: gnu: gru: plu: klu: knu: kru:
articulation: CCV01_ges.zip
[CCV] 02: from CCV01 to CCV02 with C1 = voiceless fricative or C1C2 are both voiceless:
changes of actions similar to CV01-CV05
V=[a:]: fla: Sla: Sna: pfa: Spa: Sta:
V=[i:]: fli: Sli: Sni: pfi: Spi: Sti:
V=[u:]: flu: Slu: Snu: pfu: Spu: Stu:
articulation: CCV02_ges.zip
[CVC] 01: from CV01...CV09 to CVC01 with C(final) = nasal or lateral:
overlap of consonantal closure action with last part of preceding vowel
and co-occurring velopharyngeal opening action in case of nasal
from CV01: ba:n da:m ga:n la:m ga:b@n ga:r@n gal@n ban bal dam dIl gan lam ran da:m@n pan@n m2:b@l
from CV02: mo:n ma:l man mOl na:m nIm
from CV03: pa:n pa:l kan kal ka:m tIm tEl
from CV04: faIn fal Sal SaUm ?af@n vaf@l lax@n vax@n vaf@n la:x@n ?a:x@n
from CV05: va:m va:n va:l van val vIl vOl jan m2:v@n va:z@n ko:j@n
from CV07: ?i:m ?Im ?i:n ?In ?a:m ?a:l ?am ?a:n ?an ?al
from CV08: ha:n hu:n ho:l ham hIm han hal hIn ?e:(h)@n my:(h)@n
articulation: CVC01_ges.zip
[CVC] 02: from CV01...CV09 to CVC02 with C(final) = voiceless plosive:
overlap of consonantal closure action with last part of preceding vowel
and co-occurring glottal opening action
from CV01: ba:t ba:k bak bu:k bu:p lo:t lo:p ra:t rUk
from CV02: ma:t mat na:t nEp
from CV03: pak kap pat
from CV04: fIt SIk SOk
from CV05: za:t zak zat vat jUp jUk
from CV07: ?a:t ?Et ?Ek ?ap
from CV08: ha:t hu:t hat hIk hak
articulation: CVC02_ges.zip
[CVC] 03: from CV01...CV09 to CVC02 with C(final) = voiceless fricative:
overlap of consonantal obstruction action with last part of preceding vowel
and co-occurring glottal opening action
from CV01: ga:s la:s laUs laIc das bas dax dOx lax rax laS raS ri:f raIf rIf dIc daIc rIc raIc lIc
from CV02: ma:s nas naS na:x mi:f mUf mUs mIc
from CV03: pas paS kES kEs tax tIS tu:x taIc ki:s
from CV04: fu:s fi:s fas fIS fES fUS Sax SaIc Si:f SIf
from CV05: vaIc vas vaS vax vIS vu:S zax zIc
from CV07: ?a:s ?aUf ?aIs ?aUs ?as ?ax ?aS ?uf ?Ox
from CV08: has haf huX haS haIs haUs hOIs hi:s
articulation: CVC03_ges.zip

Overview: research topics

Neural model of speech production, perception, and acquisition (theoretical neuroscience, systemic neuroscience)

See also: Wikipedia: Neurocomputational Speech Processing

1 ) A conventional connectionist SOM and GSOM neural model for production, perception and acqusition of speech is developed on the basis of two different articulatory-acoustic models

  • Kröger BJ, Cao M (2015) The emergence of phonetic-phonological features in a biologically inspired model of speech processing. Journal of Phonetics 53:88-100 (doi, pdf)
  • Kröger BJ, Kannampuzha J, Kaufmann E (2014) Associative learning and self-organization as basic principles for simulating speech acquisition, speech production, and speech perception. EPJ Nonlinear Biomedical Physics 2:2 (doi, pdf) (Fig8_large, Fig9_large, Fig10_large)
  • Kröger BJ, Heim S (2013) How could a self-organizing associative speech action repository (SAR) be represented in the brain? Hallesche Schriften zur Sprechwissenschaft und Phonetik 45: 61-68 (doi, pdf)
  • Kröger BJ, Kannampuzha J, Eckers C, Heim S, Kaufmann E, Neuschaefer-Rube C (2012) The neurophonetic model of speech processing ACT: structure, knowledge acquisition, and function modes. In: Esposito A, Esposito AM, Vinciarelli A, Hoffmann R, Müller VC (eds.) Cognitive Behavioural Systems, LNCS 7403 (Springer, Heidelberg, Berlin), pp. 398-404 (pdf)
  • Kröger BJ, Birkholz P, Kannampuzha J, Kaufmann E, Neuschaefer-Rube C (2011) Towards the acquisition of a sensorimotor vocal tract action repository within a neural model of speech processing. In: Esposito A, Vinciarelli A, Vicsi K, Pelachaud C, Nijholt A (eds.) Analysis of Verbal and Nonverbal Communication and Enactment: The Processing Issues. LNCS 6800 (Springer, Berlin), pp. 287-293 (pdf)
  • Kröger BJ, Birkholz P, Neuschaefer-Rube C (2011) Towards an articulation-based developmental robotics approach for word processing in face-to-face communication. PALADYN Journal of Behavioral Robotics 2: 82-93 (pdf, doi)
  • Kröger BJ, Miller N, Lowit A, Neuschaefer-Rube C. (2011) Defective neural motor speech mappings as a source for apraxia of speech: Evidence from a quantitative neural model of speech processing. In: Lowit A, Kent R (eds.) Assessment of Motor Speech Disorders. (Plural Publishing, San Diego, CA) pp. 325-346 (pdf)
  • Kröger BJ, Kannampuzha J, Neuschaefer-Rube C (2009) Towards a neurocomputational model of speech production and perception. Speech Communication 51: 793-809 (pdf, doi)
2 ) A time-explicit spiking neuron model for speech production is under development using the NENGO neural modeling framework (see: www.nengo.ca)
  • Papers on this topic started in 2014 (see publications and references below)
  • Video of syllable sequencing task (6 syllables; syllable duration of 100ms; normal dopamine level): youtube_syllable_sequencing; see Senft et al. (2016)
  • Senft V, Stewart TC, Bekolay T, Eliasmith C, Kröger BJ (2016) Reduction of dopamine in basal ganglia and its effects on syllable sequencing in speech: A computer simulation study. Basal Ganglia 6: 7-17 (doi, pdf)
  • Kröger BJ, Bekolay T, Blouw P (2016) Modeling motor planning in speech processing using the Neural Engineering Framework. In: Jokisch O (Ed.) Studientexte zur Sprachkommunikation: Elektronische Sprachsignalverarbeitung 2016 (TUDpress, Dresden, Germany), pp. 15-22 (ISBN: 978-3-95908-040-8) (pdf)
  • Kröger BJ, Bekolay T, Eliasmith C (2014) Modeling speech production using the Neural Engineering Framework. Proceedings of CogInfoCom 2014 (Vetri sul Mare, Italy) pp. 203-208 (ISBN: 978-1-4799-7279-1) and IEEE Xplore Digital Library DOI=10.1109/CogInfoCom.2014.7020446 (doi, pdf)

Overview: research topics

Articulatory-acoustic synthesis of speech and singing

1 ) A fast 2D-articulatory-acoustic speech synthesizer using the vocal tract action control concept (Kröger et al. 2010, Cognitive Processing 11: 187-205, pdf) and based on our earlier geometrical model (Kröger et al. 2005, ZASPiL 40: 79-94, pdf) has been reprogrammed in Python. Currently we work on integration of this fast speech synthesizer into a neuroscience-based model of speech learning.
An older version of the synthesizer was based on a simple Köln articulatory model, but used the same acoustic model. (see: Kröger et al. 1993 Journal Phonetica, Kröger 1998 Habil.-Thesis)

Video examples:

  • Generation of area function from Köln articulatory model for sentence "Das ist mein Haus": am.avi
  • Generation of acoustic speech signal from area function for sentence "Das ist mein Haus": ar.avi
  • Visualization of air flow and pressure within vocal tract for vowel /a/: one glottal period: as.avi
  • Visualization glottal area, glottal flow, its time derivative, and mouth radiated sound pressure for sentence "Das ist mein Haus": re.avi
Audio examples:
  • Sentence "Guten Tag, .... " (synthesis by minimal rules, no prosody): gtag.wav
  • Example for Reduction in German Sentence "mit dem Boot" to "mim Boot" (see Kröger 1993 Journal Phonetica): boot.wav
  • Intonation contours (synthetic fist, natural is following) (copy synthesis using two mass model): bababa2.wav

2 ) A 3D-articulatory-acoustic synthesizer including a gestural control concept has been developed for high quality synthesis of speech and singing.
Currently the model is capable of synthesizing unrestricted text including all sound types (vowels, plosives, fricatives, ...) and unrestricted songs for untrained male and female voices. (Birkholz & Kröger 2007: Abstracts of PEVOC, Groningen, Poster).
Examples: a) Video and sound example for speech: Naechster Halt Hamburg; b) Sound example for singing: Dona Nobis Pacem; c) Test: Synthesis of Singing Challenge (during INTERSPEECH 2007, Antwerp): Contest of 6 singing synthesis systems: 2nd place for the Birkholz 3D-articulatory-acoustic model

  • Kröger BJ, Birkholz P, Kannampuzha J, Neuschaefer-Rube C (2010) Modeling different voice qualities for female and male talkers using a geometric-kinematic articulatory voice source model: preliminary results. In: S Fuchs, P Hoole, C Mooshammer, M Zygis (eds.) Between the regular and the particular speech and language. (Peter Lang, Frankfurt) pp. 97-124 (pdf)
  • Kröger BJ, Birkholz P (2009) Articulatory Synthesis of Speech and Singing: State of the Art and Suggestions for Future Research. In: Esposito A, Hussain A, Marinaro M (eds) Multimodal Signals: Cognitive and Algorithmic Issues. LNAI 5398 (Springer, Berlin), pp. 306-319 (pdf)
  • Kröger BJ, Birkholz P (2007) A gesture-based concept for speech movement control in articulatory speech synthesis. In: Esposito A, Faundez-Zanuy M, Keller E, Marinaro M (eds.) Verbal and Nonverbal Communication Behaviours, LNAI 4775 (Springer Verlag, Berlin, Heidelberg) pp. 174-189 (pdf, doi)
  • Birkholz P, Jackel D, Kröger BJ (2007) Simulation of losses due to turbulence in the time-varying vocal system. IEEE Transactions on Audio, Speech, and Language Processing 15: 1218-1225 (pdf, doi)
  • Birkholz P, Jackel D, Kröger BJ (2006) Construction and control of a three-dimensional vocal tract model. Proceedings of the International Conference on Acoustics, Speech, and Signal Processing (ICASSP 2006) (Toulouse, France) pp. 873-876 (pdf)
  • Kröger BJ (1997) On the quantitative relationship between subglottal pressure, vocal cord tension, and glottal adduction in singing. Proceedings of the Institute of Acoustics 19 (5): 479-484 (ISMA97) (pdf)
  • Kröger BJ (1996) Artikulatorische Sprachsynthese (Eingeladener Vortrag) In: Fortschritte der Akustik: Plenarvorträge und Fachbeiträge der 22. Deutschen Jahrestagung für Akustik, DAGA '96. (DEGA, Oldenburg) pp. 96-100 (pdf)
  • Kröger BJ (1993) A gestural approach for controlling an articulatory speech synthesizer. Proceedings of Eurospeech 1993 (Berlin, Germany), pp. 1903-1906 (pdf)
  • Kröger BJ (1992) Minimal rules for articulatory speech synthesis. In: J Vandewalle, R Boite, M Moonen, A Oosterlinck (Hrsg.) Signal Processing VI: Theories and Applications Amsterdam, Elsevier) pp. 331-334 (pdf)
  • Kröger BJ (1991) Zur Auswirkung der Glottis-Sprechtrakt-Kopplung auf die Stimmreinheit. Sprache-Stimme-Gehör 15:139-142 (pdf)
  • Kröger BJ (1989) Die Synthese der weiblichen Stimme unter besonderer Berücksichtigung der Phonation. Unveröffentlichte Dissertation. Universität zu Köln. (pdf)

Overview: research topics

Apraxia of Speech (AOS) and Childhood Apraxia of Speech (CAS):

see pdf of an introductory lecture: AOS: The poorly understood speech disorder
Papers on motor planning by using speech action units started in 2010 (see publications)


  • Becker-Redding U, Kirchner M, Kröger BJ (2015) Kindliche Sprechapraxie und KoArt – eine Evaluationsstudie zur Therapieeffektivität. In: Abstractband 44. Jahreskongress des dbl (Düsseldorf) p. 23 (pdf)
  • Schulz S, Heim S, Willmes K, Kröger BJ (2014) Analyse sprechapraktischer Fehler im System artikulatorischer Gesten. Sprache Stimme Gehör 38: Se7–Se8 (doi)
  • Kröger BJ, Becker-Redding U (2013) Wann ist Therapieresistenz bei kindlichen Sprechstörungen ein Hinweis auf kindliche Sprechapraxie? Proceedings of DGPP 2013 (Bochum, Germany) (pdf)
  • Kröger BJ, Miller N, Lowit A, Neuschaefer-Rube C. (2011) Defective neural motor speech mappings as a source for apraxia of speech: Evidence from a quantitative neural model of speech processing. In: Lowit A, Kent R (eds.) Assessment of Motor Speech Disorders. (Plural Publishing, San Diego, CA) pp. 325-346 (pdf)
  • Kröger BJ (2010) Computersimulation sprechapraktischer Symptome aufgrund funktioneller Defekte. Sprache-Stimme-Gehör 34: 139-145 (pdf)

Overview: research topics

Treatment of speech disorders using SpeechTrainer

SpeechTrainer is a software-package for 2D-visualisation of speech movements (download SpeTra). SpeechTrainer can be used as a visual stimulation technique in treatment of different types of speech disorders. (see Funk_2006, Kröger_2005 )

  • Use of SpeTra in treatment of articulation disorders:
  • Use of SpeTra in treatment of apraxia of speech:
  • Kröger BJ (2009) Visuelle Animation der Artikulation als Therapiehilfe bei Spechstörungen: Eine neurophonetische Begründung. Sprache-Stimme-Gehör 33: 179-185 (pdf)
  • Funk J, Montanus S, Kröger BJ (2006) Therapie von neurogenen und kindlichen Sprechstörungen mit dem Programm SpeechTrainer. Forum Logopädie 20 (2): 6-13 (pdf)
  • Kröger BJ, Gotto J, Albert S, Neuschaefer-Rube C (2005) A visual articulatory model and ist application to therapy of speech disorders: a pilot study. In: S Fuchs, P Perrier, B Pompino-Marschall (Hrsg.) Speech production and perception: Experimental analyses and models. ZASPiL 40: 79-94. (pdf)

Overview: research topics

Acoustic and perceptual methods in diagnosis of speech disorders

Phonetically oriented methods in diagnosis of speech disorders are mainly perceptually based. The main drawback of these methods is its subjectivity. Thus acoustically based methods could be advantageous. But the main problem of acoustically based methods in diagnosis of speech disorders is to extract meaningful or significant acoustic parameters.
Different phonetically oriented measures were tested for improving or refining the diagnosis of speech disorders.

  • Kukla H, Kleiser N, Kröger BJ (2014) Episodische Dysarthrie bei Hirnstammkompression: akustisch-phonetische und auditiv-perzeptuelle Analyse. In: Hoffmann R (ed.) Studientexte zur Sprachkommunikation: Elektronische Sprachsignalverarbeitung 2014 (TUDpress, Dresden, Germany), pp. 169-176
  • Jäckel R, Strecha G, Hoffmann R, Kröger BJ (2014) Untersuchung segmentaler und suprasegmentaler Charakteristiken des Sprechsignals bei Morbus Parkinson. In: Hoffmann R (ed.) Studientexte zur Sprachkommunikation: Elektronische Sprachsignalverarbeitung 2014 (TUDpress, Dresden, Germany), pp. 161-168
  • Ziethe A, Springer L, Willmes K, Kröger BJ (2013) Untersuchung zur Kernsymptomatik bei Kindern mit einer kindlichen Sprechapraxie im Alter von 4-7 Jahren. Sprache - Stimme - Gehör, in press (doi)
  • Mühlhaus J, Vorwerk W, Kröger BJ (2007) Zur Diagnostik der Auditiven Verarbeitungs- und Wahrnehmungsstörungen (AVWS) – zwei Verfahren zur Identifikation und Diskrimination ambivalenter akustischer Stimuli im Vergleich. Die Sprachheilarbeit 5: 205-212(pdf)
  • Franz, E, Willmes K, Neuschaefer-Rube C, Kröger BJ (2006) Acoustical and perceptive analyses of vowels in suspected developmental apraxia of speech: a pilot study. Abstracts of 5th International Conference of Speech Motor Control (Nijmegen, Netherlands). Also: Stem-, Spraak- en Taalpathologie 14, Suppl. p. 89. (pdf)
  • Kröger BJ, Siegert M, Neuschaefer-Rube C (2005) Phonatorisch-artikulatorische Kompensation bei einem ALS-Patienten mit schwerer dysarthrischer Sprechstörung. In: Fortschritte der Akustik: 31. Deutsche Jahrestagung für Akustik, DAGA '05. DEGA, Berlin, pp. 75-76. (pdf)
  • Kröger BJ, Diem A, Siegert M (2003) Artikulatorische und akustische Methoden in der Diagnostik und Therapie von Sprechstörungen. In: Fortschritte der Akustik: 29. Deutsche Jahrestagung für Akustik, DAGA '03. DEGA, Oldenburg, pp. 754-755. (pdf)

Overview: research topics


Bernd J. Kröger, January 2018