Occupational Voice: Care and Cure : Care and Cure [1 ed.] 9789062997985, 9789062991792

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Copyright © 2001. Kugler Publications. All rights reserved.

OCCUPATIONAL VOICE: CARE AND CURE

Occupational Voice: Care and Cure : Care and Cure, edited by P.H. Dejonckere, Kugler Publications, 2001. ProQuest Ebook Central,

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Copyright © 2001. Kugler Publications. All rights reserved. Occupational Voice: Care and Cure : Care and Cure, edited by P.H. Dejonckere, Kugler Publications, 2001. ProQuest Ebook Central,

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OCCUPATIONAL VOICE: CARE AND CURE

Copyright © 2001. Kugler Publications. All rights reserved.

edited by Philippe H. Dejonckere

Kugler Publications/The Hague/The Netherlands Occupational Voice: Care and Cure : Care and Cure, edited by P.H. Dejonckere, Kugler Publications, 2001. ProQuest Ebook Central,

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Copyright © 2001. Kugler Publications. All rights reserved.

ISBN 90 6299 179 3

Distributors: For the U.S.A. and Canada: Pathway Book Service 4 White Brook Road Gilsum, NH 03448 Telefax (603) 357 2073 For all other countries: Kugler Publications P.O. Box 97747 2509 GC The Hague, The Netherlands Telefax (+31.70) 3300254 Website: www.kuglerpublications.com

© Copyright 2001 Kugler Publications All rights reserved. No part of this book may be translated or reproduced in any form by print, photoprint, microfilm, or any other means without prior written permission of the publisher. Kugler Publications is an imprint of SPB Academic Publishing bv, P.O. Box 97747 2509 GC The Hague, The Netherlands

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Table of Contents

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TABLE OF CONTENTS Introduction: The concept of occupational voice disorders P.H. Dejonckere

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Criteria for occupational risk in vocalization I.R. Titze

vii

1

Gender differences in the prevalence of occupational voice disorders. Some anatomical factors that possibly contribute P.H. Dejonckere

11

Voice dosimetry R. Buekers

21

Room acoustics. How they affect vocal production and perception D.M. Howard and J.A.S. Angus

29

Phoniatric fitness examinations. Evaluation of long-term experiences W. Seidner and J. Wendler

47

Voice in the classroom. A re-evaluation V. Morton and D.R Watson

53

Air pollution and environmental factors. Their importance in the etiology of occupational voice disorders R.E. Chavez C. de Bartelt

71

Performance stress in professional voice users W.A.R. Wellens and M.J.M.C. van Opstal

81

Predictive parameters in occupational dysphonia. Myth or reality? F.I.C.R.S. de Jong, P.G.C. Kooijman and R. Orr

101

Occupational voice disorders and the Voice Handicap Index T. Murry and C.A. Rosen

113

A survey on the occupational safety and health arrangements for voice and speech professionals in Europe E. Vilkman

129

The spirit of laws on occupational diseases. Historical background and comparative overview of European legislations J. Ugeux

139

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The challenge of determining work-related voice/speech disabilities in California. A multi-disciplinary laryngology and voice pathology evaluation K. Izdebski1, E.D. Manace and J.S. Haris

149

Basic elements in voice therapy. A system for indexing and quantifying the contents of the functional approach, particularly in occupational voice disorders P.H. Dejonckere and G.H. Wieneke 155

165

Treatment outcomes in occupational voice disorders J.K. Casper

187

Medico-legal impairment and invalidity in different American and European countries P.H. Dejonckere

201

Index of authors

207

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Theoretical and practical considerations in the occupational use of voice amplification devices J.A. McGlashan and D.M. Howard

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Introduction

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INTRODUCTION The concept of occupational voice disorders Philippe H. Dejonckere

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“People using their voice professionally are at risk for occupational voice diseases, and require specific prevention and treatment” was the topic focused on by the third Pan European Voice Conference, organized in August 1999 at Utrecht University. The present book includes the main tutorial lectures, with reviews of the most relevant research data and opinions regarding this specific area of concern. Occupational voice users include not only singers and actors, but also teachers, politicians, lawyers, clergymen, telephone operators, etc. 1. The pathogenesis of voice disorders in such patients can be primarily related to their occupation, and thus, after adequate differential diagnosis, these need to be recognized as true occupational diseases, in the same way as, for example, occupational hearing loss2. A surfeit of information is available on the potential damage from exposure to excessive noise levels3,4. Noise-induced hearing loss is generally recognized as a typical occupational disease. The relationship between dose and effect is clear, as is documented in publications by the International Organization of Standardization (ISO)5. The dose combines intensity and duration, and therefore, the concept of dosimetry is of major importance. Also of importance is the definition of the safe limits for exposure to noise. However, factors regarding individual susceptibility to noise and the reversibility of early effects also have to be considered, as well as possible preventive indices of noise-induced hearing loss6. In some – but not all – respects, noise-induced hearing loss may be considered as a useful model for occupational voice disorders. Epidemiology Titze7 compared the percentage of the US working population and of the voiceclinic load for different occupation categories: for example, telephone marketers constitute only 0.78% of the total workforce, but 2.3% of the clinic load; teachers represent 4.2% of the US workforce and 20% of the voice-clinic load. Studies based on questionnaires have suggested that teachers and aerobic instructors are at high risk for disabilities from voice disorders, and that these health problems may have significant work-related and economic effects8,9. For example, Russel et al.10 investigated the prevalence of self-reported voice problems in teachers: 16% of teachers reported voice problems on the day of

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the survey, 20% during the current teaching year, and 19% at some time during their career. Roughly speaking, we can conclude from the several studies published during the 1990s that about 20% of teachers experience voice disorders11.

Voice dosimetry Objective measurement of vocal use and vocal load is necessary for the identification of activities and working conditions that are at risk. Voice dosimeters can provide information on the total vocalization time and sound pressure level over a whole working day, in a real life situation12-14. Just as noise dosimeters define acceptable levels of noise exposure, voice dosimeters help to define the average acceptable limits for vocal load.

Hyperphonation

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Repeated mechanical vibrations transmitted to the body tissues by engines or machines are known to be able of eliciting – in certain conditions – specific kinds of pathology, which are also considered to be occupational diseases 15,16. The vibration may involve the whole body (e.g., in a vehicle) or mainly the hand, wrist, elbow, or shoulder (hand-held power tools). There are standards in the field of occupational health that stipulate the acceptable limits for tissue acceleration values, depending on the frequency17. Titze’s calculations suggest that the risk of damage from tissue vibration is exceeded by occupational vocalists, such as telephone marketers and teachers18. In the last few years, much new and important information has materialized on the dangers of ‘hyperphonation’, i.e., loud and prolonged phonation beyond the physiological range. Laboratory experiments on canine larynges, hyperphonated in vivo under anesthesia, demonstrated obvious damage to vocal fold epithelia19. The basement membrane shows early lesions and seems to be particularly sensitive20. A clinical study by Mann et al.21 in drill sergeants, demonstrated significant increases in vocal fold edema, erythema and edge irregularity, and decreases in vocal fold mucosal wave and amplitude of excursion, following a five-day training period.

Voice fatigue, relief and recovery According to Titze18, two different aspects must be considered: 1. Muscle fatigue: the muscle chemistry needs to be reset for the following contractions.

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2. Epithelial cells may die and be shed, due to repeated traumata. New cells have to develop underneath. Collagen and elastin fibers may have separated from the structural matrix of the lamina propria, and have to be removed and replaced by the fibroblasts. Detached protein debris will be removed and re-used by the fibroblasts to make new protein fibers that will support the connective tissue structure. Therefore, minor destruction and repair is continuous. Can the regenerative processes keep up with the destructive process, and what are the physiological time constants in these processes? When there is damage to the joints, ligaments, tendons, or other connective tissue, the recovery time will be proportional to the amount of localized tissue injury that has occurred. If muscle fatigue is the only complaint, the recovery period required will probably be shorter. Hypothetical curves for tissue injury and the recovery period for human phonation have been suggested by Titze18. Nevertheless, vocal fatigue is still difficult to identify in practical and clinical situations, and Buekers has questioned the clinical relevance of voice endurance tests13,14.

Environmental factors

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The relative humidity of the air affects vocal function: the most common subjective complaints of teachers with regard to their working environment are the dryness and dustiness of the air. Professional singers note that singing is more difficult in a dry environment: dry air puts an increased strain on the phonatory apparatus and raises the demands on its efficacious and appropriate use 22. The human voice is very sensitive to decreases in the relative humidity of inhaled air because, in experimental conditions, even after short provocation, a significant increase in perturbation measures has been found23. Noise is also a very common and relatively well-known risk factor in the working environment of professional voice users. It has been observed that the sound level of the speaking voice significantly increases in ambient noise levels starting from 40 dB (A) (about 3 dB for each 10 dB increase in ambient noise), due to the Lombard effect24,25. In kindergartens, for example, noise levels have been found to vary between 75 and 80 dB (A)26,27.

Effects of stress Mendoza and Carballo investigated the effects of experimentally induced stress on voice characteristics28. In conditions of stress, induced by means of a stressful environment and cognitive workload tasks, they observed: 1. an increase in Fo with respect to baseline; 2. a decrease in pitch perturbation quotient and in amplitude perturbation quotient;

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3. a lower presence of turbulent noise in the spectral zone in which the existence of harmonic components is not expected (2800-5800 Hz), with respect to harmonic energy in the 70-4500 Hz range; 4. an increase in harmonic energy in the 1600-4500 Hz range with respect to harmonic energy in the 70-1600 Hz range. The increase in Fo seems to be considered a universal indicator of stress and of cognitive workload, as is the lowering of Fo perturbation. The response to a stressful stimulus demands a high level of activation, which in turn produces elevated ergotropic arousal that would cause an increase in the tension of the vocal muscles, producing a higher and more tense voice. Mattiske et al.29 report that teachers seem to experience a significant degree of stress during their work30, and there is some research evidence that anxiety and stress are associated with the development of voice problems31. Marks32 compares teachers’ voices with those of nurses, and finds that psychological stress is reported more frequently by teachers. There are indications that stress, psychological tension, personality, and other psychological factors, may play an important role in voicing problems among teachers30,33,34.

Vocal fold lesions

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Phonotrauma may result in typical vocal fold lesions, to be interpreted as a direct consequence of mechanical stress and/or as tissue reaction to that stress. Vocal fold nodules and polyps are classical examples35,36, but also contact ulcerations/granulomas of the vocal processes35,36,37, if not induced by acid reflux. Vocal fold hemorrhage is generally consecutive to acute phonotrauma35. Depending on reversibility and context, microsurgery may become indicated as an important element of the treatment38,39.

Care and cure Patients with occupational voice disorders should benefit from specific medical and paramedical treatments, as well as from technical aids, with respect to their particular pathogenesis. There are major economical aspects at stake, and occupational rehabilitation plays an important role. In a few cases, compensation and professional re-orientation is necessary. Outcomes of the various possible treatment strategies have still to be investigated. However, prevention is still essential. There are indications that vocal hygiene education programs could improve the voice by reducing vocal abuse in daily life and by practising specific strategies to maintain classroom order and to reduce the use of the voice during teaching40. Further research is needed to demonstrate the usefulness of prevention strategies on the incidence of actual voice disorders.

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References

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1. Irving RM, Epstein R, Harries MLL: Care of the professional voice. Clin Otolaryngol 22:202205, 1997 2. Dejonckere PH: The concept of ‘occupational voice’. In: Dejonckere PH, Peters H (eds) Communication and its Disorders: A Science in Progress, Proceedings of the 24th IALP Congress Amsterdam, 1998, Vol 1, pp 177-178. Nijmegen, NL: Nijmegen University Press 1999 3. Sataloff RT, Sataloff J: Occupational Hearing Loss, 2nd Edn. New York, NY: Marcel Dekker 1993 4. Kryter KD: The Handbook of Hearing and the Effects of Noise. New York, NY: Academic Press 1994 5. ISO-1999: Acoustics: determination of occupational noise exposure and estimation of noiseinduced hearing impairment. Geneva: International Organization of Standardization 1990 6. Chon KM, Roh HJ, Goh EK, Wang SG: Noise induced hearing loss and the individual susceptibility to the noise. Int Tinnitus J 2:73–82, 1996 7. Titze IR: Populations in the US workforce who rely on voice as a primary tool of trade: a preliminary report. J Voice 11:254-259, 1997 8. Smith E, Lemke J, Taylor M, Kirchner HL, Hoffman H: Frequency of voice problems among teachers and other occupations. J Voice 12:480-488, 1998 9. Newman C, Kersner M: Voice problems of aerobics instructors: implications for preventative training. Log Phon Vocol 23:177-180, 1998 10. Russel A, Oates J, Greenwood KM: Prevalence of voice problems in teachers. J Voice 12:467-479, 1998 11. Simberg S, Laine A, Sala E, Rönnema AM: Prevalence of voice disorders among future teachers. J Voice 14:231-135, 2000 12. Masuda T, Yoshimitu I, Manako H, Komiyama S: Analysis of vocal abuse: fluctuations in phonation time and intensity in 4 groups of speakers. Acta Otolaryngol (Stockh) 113:547552, 1993 13. Buekers R: Voice Performances in Relation to Demands and Capacity. PhD Thesis, Maastricht 1998 14. Buekers R: Voice endurance tests and vocal fatigue. Clin Otolaryngol 23:533-538, 1998 15. ILO (International Labour Office): Encyclopedia of Occupational Health and Safety, 3rd Edn. Geneva: Luigi Parmeggiani Ed 1983 16. Dejonckere PH: Occupational voice disorders. In: ILO Encyclopedia of Occupational Health and Safety, 3rd Edn. Geneva: Luigi Parmeggiani Ed 1983 17. Griffin MJ: Handbook of Human Vibration. San Diego, CA: Academic Press 1990 18. Titze IR: Toward occupational safety criteria for vocalization. Log Phon Vocol 24:49-54, 1999 19. Gray SD, Titze IR, Lusk RP: Electron microscopy of hyperphonated vocal cords. J Voice 1:109-115, 1987 20. Gray SD: Basement membrane zone injury in vocal nodules. In: Gauffin J, Hammarberg B (eds) Vocal Fold Physiology. San Diego, CA: Singular Publishing Group Inc 1991 21. Mann EA, McClean MD, Gurevich-Uvena J, Barkmeier J, McKenzie-Garner P, Paffrath J, Patow C: The effects of excessive vocalization on acoustic and videostroboscopic measures of vocal fold condition. J Voice 13:294-302, 1999 22. Sundberg J: The Science of the Singing Voice. De Kalb, IL: Northern Illinois University Press 1986 23. Hemler R, Wieneke G, Dejonckere PH: The effect of relative humidity of inhaled air on acoustic parameters of voice in normal subjects. J Voice 11:295-300, 1997 24. Van Heusden E, Plomp R, Pols LCW: Effect of ambient noise on the vocal output and the preferred listening level of conversational speech. Appl Acoust 12:31-43, 1979

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25. Dejonckere PH, Pépin F: Study of the Lombard effect by measuring equivalent sound level. Fol Phoniat 35:310-315, 1983 26. Truchon-Cagnon C, Hétu R: Noise in day-care centers for children. J Noise Control Engin 30:57-64, 1988 27. Vilkman E: Occupational risk factors and voice disorders. Log Phon Vocol 21:137-141, 1996 28. Mendoza E, Carballo G: Acoustic analysis of induced vocal stress by means of cognitive workload tasks. J Voice 12:263-273, 1998 29. Mattiske JA, Oates J, Greenwood KM: Vocal problems among teachers: a review of prevalence, causes, prevention and treatment. J Voice 12:489-499, 1998 30. Russel DW, Altmaier E, Van Velzen D: Job related stress, social support and burnout among classroom teachers. J Appl Psychol 72:269-274, 1987 31. Green G: Psycho-behavioral characteristics of children with vocal nodules: WPBIC ratings. J Speech Hear Disord 54:306-312, 1989 32. Marks JB: A Comparative Study of Voice Problems among Teachers and Civil Service Workers. Thesis. The University of Minnesota 1985 33. Calas M, Verhulst J, Lecoq M, Dalleas B, Seilhean M: Vocal pathology of teachers. Rev Laryngol (Bordeaux) 110:397-406, 1989 34. Cooper M: Vocal suicide in teachers. Peabody J Educ 47:334-337, 1970 35. Gould WJ, Rubin JS, Yanagisawa E: Benign vocal fold pathology through the eyes of the laryngologist. In: Rubin JS, Sataloff RT, Korovin GS, Gould WJ (eds) Diagnosis and treatment of voice disorders. New York, NY: Igaku-Shoin 1995 36. Titze IR: Principles of Voice Production. Englewood Cliffs, NJ: Prentice Hall 1994 37. Nagata K, Kurita S, Yasumoto S, Maeda T, Kawasaki H, Hirano M: Vocal fold polyps and nodules. Auris Nasus Larynx 10 (Suppl):37-45, 1983 38. Bouchayer M, Cornut G: Microsurgical treatment of benign vocal fold lesions: indications, techniques, results. Folia Phoniatr 44:155-184, 1992 39. Cornut G, Bouchayer M: Phonosurgery for singers. J Voice 3:269-276, 1989 40. Chan RWK: Does the voice improve with vocal hygiene education? A study of some instrumental voice measures in a group of kindergarten teachers. J Voice 8:279-291, 1994

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Criteria for occupational risk in vocalization

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CRITERIA FOR OCCUPATIONAL RISK IN VOCALIZATION Ingo R. Titze National Center for Voice & Speech, Department of Speech Pathology & Audiology, The University of Iowa, Iowa City, IA, USA

Introduction Much is known about the damage excessive exposure to sound can do to the hearing mechanism1. However, comparatively little is known about the dangers of self-induced vibration in body tissues such as the vocal folds. It is generally understood by clinicians that excessively loud phonation, or prolonged periods of phonation, can lead to voice disorders such as vocal nodules, chronic inflammation, or vocal fatigue. But can ‘excessive’ and ‘prolonged’ be quantified? Those who vocalize for the purpose of recreation and meditation claim that self-induced vibrations from vocalization can have a healing and stressrelieving effect. If this is true, at what point does a healing remedy become a threat to one’s health? The answer is the same as for any health-promoting activity, including exercise and food consumption: when the rate of absorption, elimination, or regeneration of biological material required to accommodate the activity is exceeded. In this chapter, we address the absorption of vibration in terms of energy and acceleration.

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Key factors for risk in vocalization The effect that vibration can have on human body tissues has been summarized in the Handbook of Human Vibration2. The general topic is divided into two subtopics: 1. whole-body vibration; and 2. hand-transmitted vibration. The first applies to people who are subjected to vibration in vehicles, on floors, or against surfaces that shake the entire body. The second applies to people who are working with power tools. Of the two subtopics, the latter (hand-transmitted vibration)

Address for correspondence: Ingo R. Titze, National Center for Voice & Speech, Department of Speech Pathology & Audiology, The University of Iowa, Iowa City, IA 52242, USA Occupational voice – care and cure, pp. 1–10 edited by P.H. Dejonckere © 2001 Kugler Publications, The Hague, The Netherlands

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is probably more applicable to vocal fold tissue vibration. The variables of concern are duration of exposure, acceleration of the tissues, and frequency of the vibration. In hand-transmitted vibration, the exposure is localized and generally intermittent, as in phonation. The two most important disorders that have been linked to hand-transmitted vibration are neuromuscular disorders (e.g., numbing of the hands) and vascular disorders (e.g., white-finger, or blanching, which is the consequence of a reduction in circulation). Since duration is a key variable in disorders resulting from excessive localized vibration, it is logical to ask if duration of vocalization plays a major role in voice disorders. In a recent study on populations in the US workforce who rely on voice as a primary tool of trade3, we found that classroom teachers, who comprise about 4% of the workforce, typically make up about 20% of the patient load in voice clinics. Both Sapir et al.4 and Smith et al.5 surveyed teachers and found that one-third to one-half reported having voice problems. Among the symptoms were hoarseness, difficulty with high pitches, a tired voice, too low a speaking voice, a weak voice, and effortful production. Many teachers reported direct physical discomfort (a burning or raw feeling in the throat) after prolonged daily speaking. Elementary and secondary school teachers, for example, were 32 times more likely to report these symptoms than a random sample of people in other occupations6. Since frequency of vibration is another key variable in hand-transmitted vibration, it is again logical to ask if evidence exists that those who speak with higher pitches (females and children) are more likely to report disorders than those who speak with lower pitches (adult males). In a follow-up study by Smith et al.7 on the teacher population, the symptoms reported by teachers were parsed out by gender. In a corpus of 274 male and 280 female teachers surveyed, 38% of the females reported voice problems while only 26% of the males reported voice problems. For every type of subject taught (English, science, physical education, etc.), women had the higher probability of reporting voice problems than men. The odds ratio was about 2:1. This is a particularly interesting ratio in view of the fact that the fundamental frequency ratio between females and males is also about 1.7:1. Children, who also speak at higher fundamental frequencies, are known to develop vocal nodules during the ages of four to ten years if they are vocally hyperactive in playgrounds8. Interestingly, the female/male odds ratio is 1.0 for these ages, presumably because the fundamental frequency gender ratio is also 1.0 for young children9. The root-mean-square (RMS) value of the acceleration is the third variable of importance for safety criteria set forth in the Handbook of Human Vibration. It is again logical to ask if vocal loudness (which relates to amplitude of vibration and tissue acceleration) is a factor in reported voice disorders. Over two decades ago, Holbrook10 reported that a physical education instructor phonated loudly (>75 dBA at 10 cm from the mouth) for an average of 47 minutes per day, compared to an average of 21 minutes across all teachers in the study. Smith et al.6 found that physical education teachers had almost four times the

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likelihood of having a voice problem (odds ratio of 3.7:1) than teachers who taught other subjects exclusively. Since physical education instruction involves communication over longer distances (gymnasiums, playing fields, courts, etc.), often with the intent to ‘urge on’, a louder voice is generally used. In a recent study by Buekers et al.11, sports instructors phonated in excess of 72 dB at 30 cm (equivalent to about 79 dB at 10 cm) about half their total occupational phonation time. This is both louder and longer than the earlier estimates of Holbrook. It is worthwhile to consider an analogy between vibration exposure and radiation exposure from the sun. Radiation exposure is also measured by intensity (e.g., angle of incidence of the sun rays, amount of attenuation by the atmosphere), by frequency (ultraviolet rays versus less penetrating visible light or heat), and by duration. The analogy is particularly useful because in both cases the individual is often unaware, during exposure, of the cellular and extracellular tissue damage that is being done. Humans have few sensors for radiation (other than heat); humans do have mechanoreceptors for touch, stretch, and motion in the larynx, but laboratory studies have shown that some may be inhibited during vocal fold vibration to avoid perpetual gagging or coughing when the vocal folds collide12. The magnitude of the injury is thus felt only in the repair phase. For sun radiation, maximum inflammation of the skin occurs a few hours after termination of exposure, which is also the onset of most of the pain. Subsequently, edema builds up in the form of blisters. Finally, dead skin cells are shed, and new skin cells are formed in a period of several days. In this healing process, which we call the recovery period, the individual determines how much exposure has taken place. Unfortunately, it is a retrospective analysis; the damage has already been done. The clever person uses his/her experience to predict how many minutes, or hours, of exposure are permissible on a certain day, at a certain altitude, and at a certain orientation to the sun rays. But what about the manner of phonation? Is there a habilitative component that allows the vocalist to become more economic (efficient) in his or her production, thereby being able to increase dosage and reduce recovery times? Current approaches to voice therapy have focused on improved resonance in the voice 13,14, more effective use of the respiratory and phonatory musculature, as in the accent method15, or vocal function exercises16, optimization of pitch17, and optimization of adduction18,19. Collectively, these approaches aim to provide the loudest and aesthetically most pleasing voice for the least amount of effort or ‘cost’ to the vocal mechanism. We have recently begun to theorize about a vocal economy index13,20, which we believe will guide vocal therapy in the future. It is likely that electronic amplification or improved room acoustics can also reduce vibration dose, namely in terms of the magnitude of tissue acceleration (as reflected in vocal loudness). But the possibility also exists that amplification may actually exacerbate poor vocal habits by permitting vocal ‘laziness’

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(e.g., too low a pitch; use of creaky, rough, or breathy voice; monotone speech). Also, the speech of teachers and lecturers may become less captivating, or less expressive if no emphasis is placed on developing a variety of vocal skills. It is hoped that voice habilitation will do more than amplify the voice. Rather, it should serve to make teachers a bit more like performers. Perhaps only then can the resource expenditure for therapy be justified vis à vis pure amplification.

Definitions of terms

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To continue with a more technical discussion, we offer the following definitions of terms that have previously led to some confusion: Vocal fatigue is a combination of muscle fatigue in the speech organs and mechanical (molecular) fatigue of the vocal fold lamina propria. Muscle fatigue is a reduction in force produced by a muscle at constant vocal effort, or an increase in effort required to maintain a constant force. Mechanical fatigue is a change in the viscoelastic properties of a material as a result of repeated mechanical stress and deformation, which includes vibration. Muscle recovery time is the time for self-perceived muscular effort to reduce (exponentially) to 37% of its peak value after performance. Lamina propria recovery time is the time for self-perceived loss of soft phonation to reduce (exponentially) to 37% of its peak value after performance. Performance time is the daily time involved in occupational vocal activities. Vibration dose is the accumulated energy or acceleration absorbed by the vocal folds due to vibration. Vocal dose (also called vocal load) is the acoustic vocal power integrated over time. Thus, the daily occupational vocal dose is the acoustic vocal power integrated over the performance time. Vocal economy is the ratio of voiced acoustic speech power to the vibration power absorbed by the vocal folds (tentative definition). These definitions may not yet be rigorous, but they serve to differentiate the key variables discussed in this chapter.

Some calculations of vocal dose For simplicity in the mathematical content of this overview, we assume sinusoidal tissue vibration of the form A sin (ω t) for the vocal folds, where A is the amplitude of vibration and ω=2πFo is the angular frequency (Fo is the fundamental frequency in Hz). We recognize that vocal fold motion is generally not sinusoidal, especially when there is vocal fold collision, but much of what we discuss here can be extended to complex motions with Fourier analysis, or nonlinear analysis with computational models.

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For sinusoidal motion, the acceleration is a=–ω2Asin(ωt),

(1)

the second derivative of the displacement with respect to time. According to Titze 21, the power dissipated in the vocal folds due to such vibration is pd=cηω2A2

(2)

where c is a constant based on vocal fold geometry, and η is the tissue viscosity. Note that this expression includes two of the three key variables in hand-transmitted vibration, amplitude and frequency. Chan and Titze22 showed that vocal fold tissue viscosity is inversely proportional to frequency, a phenomenon called ‘shear thinning’, which is characteristic of many biological materials. This reduces the frequency dependence to the first power. To include the third key variable, duration, we integrate over time to get the vibration energy dose De as follows: tp

tp

De =∫ pd dt = c' ∫ ω A2 dt 0

(3)

0

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where c' is a new constant (after shear thinning is applied) and tp is the phonation time. This definition of vibration dose assumes that frictional energy, converted into heat, damages the molecular structures of the tissue. As in the repeated backand-forth bending of a wire, the temperature rises locally, which thermally agitates the random motion of the molecules, which weakens their bonds, which leads to mechanical fatigue and, ultimately, rupture. Cooper and Titze23 have shown that the temperature of vibrating vocal folds does rise due to this viscous energy dissipation, but the effect of cooling by blood circulation was not able to be assessed because the larynges were excised from the body. Blood circulation does remove heat, but if this circulation is reduced by vibration, as the Handbook of Human Vibration clearly asserts, then the ‘burning’ sensation sometimes accompanying prolonged phonation may actually be the consequence of a small temperature rise. But, alternate explanations need to be sought. It is also possible that large instantaneous forces, brought about by collision and rapid acceleration and deceleration of the lamina propria (a whipping effect) break the molecular bonds. If this is the case, then vibration dose should be calculated on the basis of peak acceleration. From Equation (1), the acceleration dose becomes tp

De =∫ ω2Adt

(4)

0

where the vibration amplitude is now raised to the first power and the frequency is raised to the second power (opposite to the case in Equation 3). For a one-to-ten-hour range of duration, a critical level of acceleration is given in the Handbook of Human Vibration2. As illustrated in Figure 1, the acceleration-

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frequency-duration relation is defined as a critical band. Mathematically, the relation is 1 hr (5) RMS acceleration = (1 m/s)Fo _____ tp where tp is the duration (phonation time). The relation is valid for Fo in the range of 10–1000 Hz, which includes all of the phonation range. Since acceleration is plotted in root-mean-squared (RMS) values and since RMS acceleration is ω2A/M2 for sinusoidal vibration, we get a critical amplitude-frequency-duration relation M2(m/s) 1hr A = ________ = (0.036m/s) _____ , 2 πω Fot p

(6)

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This is an inverse relation between amplitude and frequency typical for all physical systems, suggesting that high frequency energy must be bounded. Note that the critical vibration amplitude is only 0.36 mm at 100 Hz for one hour duration, and less at higher frequencies and longer durations. For speech, amplitudes of 1–2 mm and frequencies between 100 and 300 Hz are

Fig. 1. Standard for vibration dose, after Griffin2. Male and female data points are our calculations.

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typical. The data points in Figure 2 (open circles for females with low, medium, and high speaking pitches and filled circles for males in similar pitch categories) compare our calculations for RMS acceleration to this standard for tool use, assuming one hour of continuous phonation. Note that the safe limits are exceeded by an order of magnitude. For example, at 200 Hz and a 2 mm amplitude, the RMS acceleration is 2256 m/sec2, whereas the safe limit is about 200 m/sec2. In terms of g-units of the earth’s gravitational acceleration (1 g = 9.8 m/sec2), this vocal fold acceleration amounts to 230 g-units. Blood vessels, cells, nerve endings, and protein scaffolds in the lamina propria of the vocal fold (and to a

Fig. 2. Block diagram of intervention strategy to be used after research is completed.

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lesser extent the thyroarytenoid muscle) must withstand this continual acceleration and deceleration, at least over short time periods. Frequent recovery times are therefore needed during vocalization, but we question if listening pauses, breathing pauses and non-voiced segments in speech are always adequate recovery for those who teach in monologue fashion all day. Also, is the trade-off between amplitude and duration as simple as Equation 6 suggests when there is intermittency in phonation? These are the questions for which the answers are not yet known.

Clinical applications

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Figure 2 shows a block diagram of an eventual self-monitoring and intervention strategy to be developed as a long-range goal. The strategy is divided into two parts, field testing and laboratory testing. In field testing, it is expected that the vocal dose will be able to be self-measured by the occupational voice user and compared to a norm developed by extensive dosimetry. If the dose is low (according to the established norms), vocal fatigue per se is not indicated, but there may be general body fatigue. The person explores either non-fatigue-related vocal problems or global fatigue syndromes. If the dose is high, testing continues to assess recovery times. If recovery occurs daily, laryngeal muscle fatigue is indicated and further focused neuromuscular testing and neuromuscular therapy can be sought by the occupational voice user (e.g., laryngeal massage, or throat relaxation). If recovery does not occur daily, lamina propria fatigue is indicated, which takes the person to the clinician-administered testing phase. (The lamina propria consists of several layers of nonmuscular tissue near the vibrating surface of the vocal folds, including elastin and collagen fibers and proteoglycan fluids.) We hypothesize that vocal fold lamina propria recovery time is a function of (1) genetics, as expressed by extracellular protein deficiencies in the lamina propria, resulting in a ‘tender larynx’ syndrome, (2) tissue environment (irritation by gastroesophageal reflux, drug intake, pollutants, smoking, etc.), (3) vocal dose, and (4) vocal economy (reduction of impact or vibration stress at constant vocal output). In functional form, we can write tr = f (genetics, tissue environment, vocal dose, vocal economy),

(7)

where tr is the self-determined recovery time. In the laboratory testing stage of Figure 2, vocal economy is assessed by measurements not described here, augmented by clinical judgment of a vocologist (a licensed speech-language pathologist specializing in voice). If economy is low, economy-based therapy is recommended. If economy is normal, a further judgment about intervention is based on the habitual intensity. If speaking intensity is normal and there are no tissue environmental problems (no reflux, allergies, smoking, etc.), a ‘tender larynx’ syndrome is indicated, for which amplification may be the best treatment. But if speaking intensity is high, or if there is a poor tissue environment, the therapy will first be aimed toward reducing intensity and making better use of vocal hygiene principles.

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Summary Systematic studies are needed to relate vibration dose to vocal injury. These studies are difficult to conduct because nobody wants to induce injury. But since there are populations of workers who are likely to injure themselves daily on the job, field studies are called for. These field studies can be balanced with some laboratory studies in which the vibration dose is not excessive, but well controlled in terms of duration, frequency, and amplitude. Most importantly, workers who are at risk need to be taught how to self-monitor their exposure. This requires some training by vocologists. Research is ongoing to develop autoperceptive rating scales for vocal fatigue24. Muscle fatigue is rated well by vocal effort, but lamina propria fatigue may require clever ratings of ‘soft phonation’, thereby testing the biomechanical condition of the non-muscular portion of the vocal fold.

Acknowledgments This work was supported by grant No. R01 DC 04224-01 from the National Institute on Deafness and Other Communication Disorders.

References

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1. Hammermik R, Henderson D, Salvi R (eds): New Perspectives on Noise-Induced Hearing Loss. New York, NY: Raven Press 1982 2. Griffin MJ: Handbook of Human Vibration. New York, NY: Academic Press 1990 3. Titze IR, Lemke J, Montequin D: Populations in the US workforce who rely on voice as a primary tool of trade: a preliminary report. J Voice 11(3):254-259, 1997 4. Sapir S, Keidar A, Mathers-Schmidt B: Vocal attrition in teachers: survey findings. Eur J Commun Disord 28(2):177-185, 1993 5. Smith E, Gray SD, Dove H, Kirchner L, Heras H: Frequency and effects of teachers’ voice problems. J Voice 11(1):81-87, 1997 6. Smith E, Kirchner L, Taylor M, Hoffman H, Lemke J: Voice problems among teachers: differences by gender and teaching characteristics. J Voice 12(3):328-334, 1998 7. Smith E, Lemke J, Taylor M, Kirchner L, Hoffman H: Frequency of voice problems among teachers and other occupations. J Voice 12(4):480-488, 1998 8. Wilson DK: Voice Problems of Children, 2nd Edn. Baltimore, MD: Williams & Wilkins 1979 9. Kent RD: Anatomical and neuromuscular maturation of the speech mechanism: evidence from acoustic studies. J Speech Hear Res 19:421-447, 1976 10. Holbrook A: Instrumental analysis and control of vocal behavior. In: Cooper M, Cooper M (eds) Approaches to Vocal Rehabilitation, pp 65-75. Springfield, IL: Charles C Thomas 1977 11. Buekers R, Bierens E, Kingma H, Marres EH: Vocal load as measured by the voice accumulator. Fol Phoniatr Logoped 47:252-261, 1995 12. Garrett JD, Luschei ES: Subglottic pressure modulation during evoked phonation in the anesthetized cat. In: Baer T, Sasaki C, Harris K (eds) Laryngeal Function in Phonation and Respiration, pp 139-153. San Diego, CA: Singular Publishing Group 1991 13. Verdolini K, Titze IR: The application of laboratory formulas to clinical voice management. Am J Speech-Language Pathol 4(2):62-69, 1995 14. Verdolini K, Druker D, Palmer P, Samawi H: Laryngeal adduction in resonant voice. J Voice 12(3):315-327, 1998

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15. Kotby MN, Shiromoto O, Hirano M: The accent method of voice therapy: effect of accentuations on FO, SPL, and airflow. J Voice 7(4):319-325, 1993 16. Stemple JC, Lee L, D’Amico B, Pickup B: Efficacy of vocal function exercises as a method of improving voice. J Voice 8(3):271-278, 1994 17. Boone D: The Voice and Voice Therapy. Englewood Cliffs, NJ: Prentice-Hall 1983 18. Ramig LO, Dromey C: Aerodynamic mechanisms underlying treatment-related changes in vocal intensity in patients with Parkinson disease. J Speech Hear Res 39(4):798-807, 1996 19. Colton RH, Casper J: Understanding Voice Problems: A Physiological Perspective for Diagnosis and Treatment. Baltimore, MD: Williams and Wilkins 1996 20. Berry D, Verdolini K, Chan R, Titze IR: A quantitative output-cost ratio in voice production. J Speech Language Hear Res (in press) 21. Titze IR: Heat generation in the vocal folds and its possible effect on vocal endurance. In: Lawrence VL (ed) Transcripts of the Tenth Symposium: Care of the Professional Voice. New York, NY: The Voice Foundation 1982 22. Chan RW, Titze IR: Viscosities of implantable biomaterials in vocal fold augmentation surgery. Laryngoscope 108(5):725-731, 1998 23. Cooper DS, Titze IR: Generation and dissipation of heat in vocal fold tissue. J Speech Hear Res 28(2):207-215, 1985 24. McCabe D, Titze IR: Chant-therapy for treating vocal fatigue among public school teachers: a preliminary study. Am J Speech-Language Pathol (in press)

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GENDER DIFFERENCES IN THE PREVALENCE OF OCCUPATIONAL VOICE DISORDERS Some anatomical factors that possibly contribute Philippe H. Dejonckere The Institute of Phoniatrics, University Medical Center, Utrecht, The Netherlands

Introduction Voice disorders in general, and occupational voice disorders in particular, occur more frequently in women than in men. For example, vocal fold nodules, considered to be a tissue reaction to chronic phonotrauma, and frequently related to occupational voice use1, are rare in adult men2,3. The difference in mean speaking frequency (110–131 Hz in males and 196–233 Hz in females) 4 only provides a partial explanation. Furthermore, the female larynx, being subject to hormone-mediated effects, is possibly rendered more vulnerable, although this has still to be clarified5. Three additional anatomical/physiological gender differences are considered here: – dorsal closure of the vocal folds during phonation; – shape of the vocal fold edge at rest; – lubrication.

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Insufficient vocal fold closure during phonation In general, the glottal closure during phonation is more complete in men than in women6. Using videostroboscopic laryngoscopy, Södersten noted incomplete glottal closure in 94% of phonations in a group of normal young women, and in 76% in a group of middle-aged women7. The most common closure pattern for both age groups was a posterior glottal chink, occurring in the phonations of 82% of the young and 61% of the middle-aged women. In soft phonation, the posterior glottal chink extended into the membranous portion of the vocal folds in most female subjects. The degree of closure significantly increased with Address for correspondence: Prof. Dr. P.H. Dejonckere, The Institute of Phoniatrics, University Medical Center Utrecht, Heidelberglaan 100, F02-504, 3584 CX Utrecht, The Netherlands Occupational voice – care and cure, pp. 11–20 edited by P.H. Dejonckere © 2001 Kugler Publications, The Hague, The Netherlands Occupational Voice: Care and Cure : Care and Cure, edited by P.H. Dejonckere, Kugler Publications, 2001. ProQuest Ebook Central,

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increasing loudness. Complete glottal closure was the most common pattern in men, being observed in 63% of the phonations. These particularities, especially the location of a glottal chink, which is mostly posterior in women, were also reported by Biever and Bless8 and Sulter et al.9. An insufficient closure implicates air escape and suggests less efficiency, but it may also contribute to generate a particular vibration pattern.

Configuration of the vocal fold edge

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Vocal fold nodules are generally considered to occur as a result of vocal trauma2,10, and more specifically as a tissue reaction to repeated localized mechanical stress or an insult to vocal tissues at approximately the center of the membranous part11,12. The typical stroboscopic vibration pattern is hourglass-shaped, with insufficient dorsal as well as ventral glottic closure and localized contact of the vocal fold margins3. The insufficient ventral closure, thus anterior to the point of development of the nodules, is an important condition for eliciting the localized mechanical stress, which may consist of alternating (a) collision traumata11-13, and (b) tearing forces on the mucosa3,14. The latter would seem to be due partially to the cohesion force of mucus molecules and partially to the centrifugal force where the amplitude of oscillation is maximal (lifting of the cover). The dorsal glottic gap would seem to be due to insufficient adduction force or muscle imbalance, while the explanation for the ventral gap is less obvious. The male/female ratio for vocal fold nodules in adults appears to be very unbalanced15: a ten-year review of 220 adult patients with vocal nodules included 209 females (95%) and 11 males (5%). The higher speaking and singing pitch in females, which enhances the rate of mechanical stress, can only account for a male/female ratio of 1:2. The aim of this study was to investigate whether gender differences exist in the curving of the vocal fold margin, as measured on histological specimens, and where appropriate, whether these differences explain why females seem to be more prone to the hourglass-shaped oscillation pattern16. Material and methods The material consisted of 19 adult Japanese larynges (nine male, ten female) from autopsy cases without known laryngeal pathology (Collection of Professor Hirano, Kurume). Age did not differ significantly between the groups, and the age range (18–45 years) is compatible with what is known about the occurrence of vocal fold nodules3,15. Measurements were performed on histological specimens of transverse sections at precisely the glottic level. A 20x magnification was used in order to obtain a precision of 0.1 mm (vernier). Before the measurements were made, each specimen was carefully oriented with respect to a midline, from the anterior commissure to the mid-distance between the glottic narrowing

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at the level of the processus vocales. At standard lengths of 1, 2, 3 mm, etc., from the ventral commissure, the distances from the midline to the vocal fold margin and those from the midline to the cartilaginous lamina were measured. All measurements were performed on both the right and left sides, thus in total, per mm from the ventral commissure, and for each distance, 18 values for male subjects and 20 values for female subjects were obtained. Results Figures 1 and 2 show the average distances, including standard error and standard deviation, from the midline to the vocal fold margin, at 1, 2, 3 mm, etc., from the ventral commissure in men and women, respectively. Figure 3 shows these same averaged distances from the midline to the margin of the vocal fold for males and females, respectively, at 1-7 mm from the ventral commissure. A significant difference was found between the sexes for the 1-mm distance (F>M: p < 0.01), and the 4, 5, 6 and 7 mm distances (M>F: p < 0.05) from the anterior commissure (Wald-Wolfowitz runs test). No significant difference was found for the 2 and 3 mm distances (2-mm distance: p = 0.08). At its most ventral part, the membranous glottis is wider in females, while at its more dorsal part, the ratio is reversed. There was no significant difference in averaged values for the right and left sides. Discussion

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Besides anatomical factors, two different types of dysfunction could account for the insufficient dorsal closure of the glottis during phonation: 1. hypotonia in the adductor muscles, e.g., in vocal fatigue due to over-use, such as fre-

Fig. 1. Average distances, with standard error and standard deviation, from the midline to the vocal fold margin, at 1, 2, 3 mm, etc. from the ventral commissure, in men.

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Fig. 2. Average distances, with standard error and standard deviation, from the midline to the vocal fold margin, at 1, 2, 3 mm, etc. from the ventral commissure, in women.

Fig. 3. Average distances from the midline to the margin of the vocal fold for males and females, respectively, at 1–7 mm from the anterior commissure.

quently occurs in professionals; 2. imbalance between the tonus of the adductor and abductor muscles, i.e., insufficient relaxation of the posterior cricoarytenoid muscles, e.g., in muscular tension dysphonia due to stress, which is also common in voice professionals17. These findings show that the insufficient ventral closure seems to be made easier in women due to the gender differences in the configuration of the shape of the vocal fold margin. This particularly concerns the first mm distance from the commissure. The average length of the ventral macula flava is about 1.5 mm. Histologically, at the level of the macula flava, the tissue appears to be

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Fig. 4. Simplified mechanical model (sinusoidal oscillation) showing the combined effect on the vibratory pattern of an insufficient vocal fold adduction in the dorsal part, and of a bowed shape of the vocal fold edge, leading to a limited contact zone of the both folds during vibration, with localized and alternating percussion forces, and also tearing forces of the mucus. This critical contact zone is located at about one-third of the vocal fold length from the ventral commissure. A straight line joining the ends of the vibrating edge has also been drawn. From left to right: increasing oscillation amplitudes.

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firm, stiffer and less flexible18. Hirano et al. also reported that, in excised larynges, the anterior commissure angle, i.e., the angled straight lines from the anterior commissure to both vocal processes, was larger in females than in males19. The mean values were 16 (SD 5) for males (n = 10) and 25 (SD 6) for females (n = 10). This difference was interpreted as a consequence of the fact that the length of the membranous vocal fold was greater in males than in females (ratio 1.6:1), while the glottic width at the vocal process did not differ significantly between the sexes (males: mean 4.3 mm, SD 1.0; females: mean 4.2 mm, SD 0.8). Moreover, the angle of the laminae of the thyroid cartilage is also larger in females (120°) than in males (average 90°)20. However, contrary to the laryngoscopic aspect in a normal subject, the margin of the vocal fold appears to be distinctly bowed in histological specimens of horizontal sections at the glottic level, as it is in cases of denervation, even before muscular atrophy has occurred. This mainly seems to be due to the loss of muscular tonus in the vocal muscle: the shape of the vocal fold margin then becomes mainly determined by fibroelastic structures of the vocal ligament and the maculae flavae. To lesser extent, functional paresis related to vocal fatigue or hypotonia could cause a similar effect. A combination of insufficient vocal fold adduction in the dorsal part and the bowed shape of the vocal fold edge, especially in the ventral part, leads to a limited contact zone of the both folds during vibration, with localized and alternating percussion forces, and also tearing forces of the mucus3. This critical

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contact zone is located at about one-third of the vocal fold length from the ventral commissure (Fig. 4). Higher subglottal pressure (in this case, possibly compensatory behavior) is positively correlated with peak impact stress during phonation21. The clinical diagnosis of vocal fold nodules has been associated with high subglottic pressure values22. Conclusion The constitutional configuration of the most ventral part of the membranous vocal fold in adult women could facilitate the eliciting of the hourglass-shaped vibration pattern. This vibration pattern is associated with the pathogenesis of vocal fold nodules, since it implicates localized mechanical stress on the vocal fold margin.

Histomorphological structure of the vestibular fold, focused on lubrication

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Lubrication is an essential element in vocal fold physiology. The mucus-producing system of the human laryngeal mucosa consists of unicellular and multicellular glands. In both types, the structural unit is the goblet cell23. The goblet cell represents the morphologically simple unicellular mucous gland of the surface epithelium. The multicellular glands are appreciably more complex. There are two main types in normal laryngeal mucosa: subepithelial and intraepithelial multicellular glands24. The vestibular fold is covered by a pseudostratified ciliated epithelium (respiratory epithelium). Mucus-secreting goblet cells are found within this respiratory epithelium and are prominent within the mucosa of the ventricular folds and within the loose fibers of the quadrangular membrane24. Beneath the respiratory epithelium, numerous seromucinous tubulo-alveolar glands are present, especially near to the laryngeal saccule. There are various amounts of seromucous glands and muscular tissue in the adipose stroma of the vestibular fold. The laryngeal mucous glands are of the exocrine compound tubulo-alveolar type25. The alveolus or acinus is the cluster of cells that makes up a single secretory unit. These glands and goblet cells help to lubricate the surface of the larynx. Such secretions are essential for normal laryngeal function, and particularly vocal fold vibration. In addition, lysozyme and other antibacterial proteins and glycoproteins in the secretions of these glands and goblet cells protect the larynx against bacterial infections. Gender differences in the histological structure of the vestibular fold, especially in the amount of glandular tissue, could account for more or less resistance to voice load.

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Material and methods The material consisted of 49 adult Japanese larynges (29 male, 20 female) from autopsy cases without known laryngeal pathology (Collection of Professor Hirano, Kurume). Age did not significantly differ between the groups, ranging from 17–72 years. Several types of stains were used: hematoxylin-eosin, elastica Van Gieson, and alcian blue. The parameters investigated were: gender, age, topographic level (1 to 5 from ventral to dorsal), number of glands (count), relative amount (in percent) of glandular tissue, fibro-elastic tissue, muscular tissue and fat tissue (average value of subjective evaluation by two experienced laryngologists, rating separately on visual analogue scales). There was no statistically significant difference between males and females with regard to age. Results Reproducibility and validity The average correlation coefficient between the ratings of the two laryngologists was 0.89, indicating good agreement. The correlation between the result of the gland counting and the rating of the relative amount of glandular tissue in the vestibular fold was also high: on average 0.87. Analysis of variance showed the following results: Grouping variable: age categories No significant difference was observed for number of glands, or percentage of glandular, fibro-elastic, muscular or fat tissue.

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Grouping variable: gender Number of glands: the average number (for all levels) was significantly higher ( p = 0.003) in males than in females (Fig. 5). Relative amount (in percent) of glandular tissue: the average percentage (for all levels) was significantly higher ( p = 0.003) in males than in females. As expected, this finding is redundant with the comparison of the number of glands. Relative amount (in percent) of fibro-elastic tissue: the average percentage (for all levels) was significantly lower ( p = 0.003) in males than in females (Fig. 6). Grouping variable: topographic level Number of glands: the various levels differed significantly ( p = 0.04). Relative amount of glandular tissue: the various levels differed significantly ( p = 0.03): glands are mainly located ventrally and dorsally. Relative amount of fibroelastic tissue: the various levels differed significantly ( p = 0.00004): fibroelastic tissue is mainly located ventrally. Relative amount of muscular tissue: the various levels differed significantly ( p < 0.00001): muscle is mainly located dorsally.

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Fig. 5. Number of glands in the plica vestibularis: the average number (for all levels) is significantly higher ( p = 0.003) in males than in females.

Fig. 6. Relative amount (in percent) of fibro-elastic tissue in the plica vestibularis: The average percentage (for all levels) is significantly lower ( p = 0.003) in males than in females.

Conclusions As a general rule, large interindividual differences are observed in the histological structure of the plica vestibularis. Males show slightly more glands in the plica vestibularis than females, and slightly less fibro-elastic tissue. The histological structure of the plica vestibularis differs from the ventral to the dorsal levels.

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Conclusions To summarize, besides the well-known differences in the size and framework of the larynx, and in habitual pitch, there are also more subtle gender differences in the anatomical and physiological characteristics of the vocal folds and surrounding tissues. Further research is needed to clarify to what extent insufficient vocal fold closure, ventral bowing of the vocal fold edge, and reduced amount of glands in the plica vestibularis may interfere with resistance to voice loading.

References

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1. Sataloff RT: Professional Voice: The Science and Art of Clinical Care. New York, NY: Raven Press 1991 2. Hirano M, Kurita S, Matsuo K, Nagata K: Laryngeal tissue reaction to stress. In: Lawrence V (ed) Transcripts of the Ninth Symposium on Care of the Professional Voice, Part 2, pp 10-20. New York, NY: The Voice Foundation 1980 3. Dejonckere P, Lebacq J, Laloyaux P, Plaghki L: Etiopathogénie des nodules vocaux. Rev Laryngol (Bordeaux) 1994 4. Hirano M: Clinical Examination of Voice. Vienna/New York: Springer Verlag 1981 5. Chagnon F, Stone RE Jr: Nodules and polyps. In: Brown WS, Vinson BP, Crary MA (eds) Organic Voice Disorders, pp 219-244. San Diego/London: Singular Publishing Group 1996 6. Södersten M, Lindestadt PA: Glottal closure and perceived breathiness during phonation en normally speaking subjects. J Speech Hear Res 33:601-611, 1990 7. Södersten M: Vocal Fold Closure During Phonation. PhD. Thesis, Studies in Logopedics and Phoniatrics No 3. Huddinge University Hospital, Stockholm 1994 8. Biever DM, Bless DM: Vibratory characteristics of the vocal folds in young, adult and geriatric women. J Voice 3:120-131, 1989 9. Sulter AM, Schutte HK, Miller DG: Standardized laryngeal videostroboscopic rating: differences between untrained and trained male and female subjects, and effects of varying sound intensity, fundamental frequency and age. J Voice 10:175-189, 1996 10. Stringer SP, Schaefer SD: Disorders of laryngeal function. In: Paparella MM et al (eds) Otolaryngology, pp 2225-2272. Philadelphia, PA: WB Saunders 1991 11. Titze IR: Mechanical stress in phonation. J Voice 8:99-105, 1994 12. Titze IR: Principles of Voice production. Englewood Cliffs, NJ: Prentice Hall 1994 13. Gray SD, Titze IR, Lusk RP: Electron microscopy of hyperphonated vocal cords. J Voice 1:109-115, 1987 14. Dikkers FG, Nikkels PGJ: Benign lesions of the vocal folds: histopathology and phonotrauma. Ann Otol Rhinol Laryngol 104:698-703, 1995 15. Nagata K, Kurita S, Yasumoto S, Maeda T, Kawasaki H, Hirano M: Vocal fold polyps and nodules: a 10-year review of 1156 patients. Auris Nasus Larynx (Tokyo) 10 (Suppl):S27S35, 1983 16. Dejonckere PH: In: Ribari O, Hirschberg A (eds) Proceedings of the Third European Congress of the European Federation of Oto-Rhino-Laryngological Societies (EUFOS), pp 417420. Bologna: Monduzzi 1996 17. Morrison MD, Nichol H, Rammage LA: Diagnostic criteria in functional dysphonia. Laryngoscope 94:1-8, 1986 18. Hirano M, Matsuo K, Kakita Y, Kawasaki H, Kurita S: Vibratory behavior versus the structure of the vocal fold. In: Titze IR, Scherer RC (eds) Vocal Fold Physiology: Biome-

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19.

20. 21. 22. 23. 24.

chanics, Acoustics and Phonatory Control, pp 26-40. Denver, CO: The Denver Center of the Performing Arts 1983 Hirano M, Kiyokawa K, Kurita S: Laryngeal muscles and glottic shaping. In: Fujimura O (ed) Vocal Physiology: Voice Production, Mechanisms and Functions, pp 49-65. New York, NY: Raven Press Ltd 1988 Fried MP, Meller SM: Adult laryngeal anatomy. In: Fried MP (ed) The Larynx, 2nd Edn. St Louis, MO: CV Mosby 1995 Jiang JJ, Titze IR: Measurement of vocal fold intraglottal pressure and impact stress. J Voice 8:132-144, 1994 Schutte HK: Aerodynamics of phonation. Acta Oto-Rhino-Laryngol Belg 40:344-357, 1986 Michaels L: Ear, Nose and Throat Histopathology. London: Springer Verlag 1987 Bak-Pedersen K, Nielsen KO: Subepithelial mucous glands in the adult human larynx. Acta Otolaryngol (Stockh) 102:341-352, 1986 Nassar VH, Bridger P: Topography of the laryngeal mucous glands. Arch Otolaryngol 94:490498, 1971

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25.

P.H. Dejonckere

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VOICE DOSIMETRY Romain Buekers Department of Otorhinolaryngology, University Hospital, Maastricht, The Netherlands

Introduction

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Analogue-to-noise dosimetry in industry is the title that is preferred for measuring or monitoring vocal output. In trade and industry and in the world of sport, ergometric studies are performed in order to determine the physical suitability of a certain task and to measure the physical strain involved in a certain type of work. However, speaking and talking are not usually considered to be physical exertion. Colton and Casper1, Pausewang Gelfer et al.2, Rantala et al.3, Smets et al.4, Smith et al.5 and Vilkman et al.6 mention that the use of the voice is a heavier exertion than normally realized. Anyone who speaks at full volume for some time finds out what an effort this really is. In a phoniatric clinic, the number of voice disorders related to vocal load is substantial. It is generally assumed that persons who have to speak loudly are at greater risk for throat and voice problems5,7. All patients with voice complaints report a heavy vocal load; however, many people with such a load (e.g., actors and singers) do not suffer from voice complaints, which would suggest that there is no perfect correlation between vocal load and vocal complaints. Quantitative data dealing with vocal load and vocal use are scarce. Studies of vocal use in natural conditions are difficult to obtain. Devices to record speaking time, fundamental frequency, sound level, etc., have been developed for such documentation. There are now portable speech and voice accumulators that register vocal use on the job during an entire day. Objective measurement of vocal use and vocal load is very important, not only for the prevention of disorders and for decisions regarding vocal ability, but also for curative vocal rehabilitation and the counseling of patients in restarting their job. Voice dosimetry is carried out with different instruments and for different reasons.

Address for correspondence: Romain Buekers, PhD, Department of Otorhinolaryngology, University Hospital, Postbus 5800, 6202 AZ, Maastricht, The Netherlands Occupational voice – care and cure, pp. 21–27 edited by P.H. Dejonckere © 2001 Kugler Publications, The Hague, The Netherlands

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Instruments for monitoring vocal behavior

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Holinger et al.8 developed a vocal intensity controller for the treatment of vocal abuse. This device is online sound level measurement: intensities below 75 dB reward the speaker with a green light, intensities above 75 dB are warnings and are shown by a red light. Ryu et al.9 devised a speech accumulator which records the vibration time of the vocal cords via a small contact microphone attached to the neck. They were interested in the length of time patients spoke and the relationship between speaking times and a particular voice disorder. The speech accumulator was clinically used in patients with vocal polyps and vocal nodules, and the longest speaking time in one day was 182 minutes in the case of a bus guide. On analysis, not only total speaking time per day or per hour, but also sound level, environmental noise level, and how a patient speaks (continuous or interrupted, vocal misuse, fundamental frequency) have to be considered. Watanabe et al.10 devised a speaking timer for measuring the actual speaking time per hour in a patient with spastic dysphonia. The variances in speaking time are correlated with healthy adults and with the degree of vocal spasticity or progressing therapy. Ohlsson et al.11 described the operation of a voice accumulator that allows registration of fundamental frequency and phonation time during a 12-hour period. The voice signal is picked up by a contact microphone – covering the time during which the vocal folds are vibrating – and the voice fundamental frequency within 60-600 Hz is accumulated in a microprocessor device. The accumulator was used to analyze vocal behavior over two working days in a group of nurses and a group of speech pathologists. The subjects in both groups overestimated (60-70%) their amount of voice use during a working day: phonation time appears to make up less than 20% of a working day, and the average voice fundamental frequency of the speech pathologists was significantly lower than that of the nurses. Rantala et al.12 recorded speech samples on a portable DAT recorder in order to study the vocal habits and speaking style of professional voice users in their natural working environment. They obtained results for Fo, sound pressure level (SPL), speech time, phonation time, and the mean duration of utterances and pauses in a teacher’s morning and afternoon lessons. As expected, speech samples from the laboratory were not necessarily comparable with spontaneous speech in a natural working environment.

Instruments for speech acoustics Speech is the most important mode of communication. The acoustics of the workplace (classrooms, auditoria, meeting rooms, sport halls, reception desks, calling centers, etc.) should therefore be based on the highest possible condi-

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tions, not only for a high degree of speech recognition and intelligibility, but also – and this is frequently disregarded – for the lowest possible vocal effort and vocal strain of the speaker. With the help of modern electronics and voice amplifiers, many of these problems can be minimized or solved, but the acoustic design and environmental noise determine whether the conditions of speaking require excessive vocal effort, which may result in vocal fatigue or in vocal symptoms or even voice disorders. Institutes of occupational health study provide standards for acoustics, such as, background noise levels, reverberation times, sound levels, and rapid speech transmission indices (RASTI) in classrooms during instruction. Pekkarinen and Viljanen13 state that the acoustic conditions of a classroom are good if speaking is possible without excessive vocal effort and if speech is perceived correctly without any strain to listen. They selected 31 typical Finnish school classrooms and found that there were high equivalent continuous sound levels, that most classrooms reverberated too much, and that speech intelligibility was not up to standard in such rooms. They advise that RASTI values should be 0.75 or better. Acoustic consultants today confirm that there is a lack of instructions for the acoustic design of classrooms and insufficient isolation from external noise levels. Adverse acoustic circumstances aggravate the exertion of the vocal organs. Furthermore, factors other than acoustic ambient ones play a role: temperature, dryness and humidity, and the presence of any irritating dust substances. It is possible to measure these factors, and this is done by occupational health or health risk analysis or toxicology. Interaction with the vocal organs and speech production, fundamental frequency, or sound pressure level, has only been investigated in a laboratory setting14.

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Instruments for vocal load The quantification of vocal load supposes the control of all speech-straining factors. Table 1 contains a summary of these factors. Measuring speech output provides an indication of vocal load. A device to Table 1. Summary of speech-straining factors 1. 2. 3. 4. 5. 6. 7. 8. 9.

speaking extra loudly (more than 70 dB) speaking for a long time speaking at a pitch outside the normal range speaking with strong intonations (more than six semitones) speaking with an abnormal resonance speaking while affected by strong emotions poor surrounding acoustics an environment affected by dust, gases, vapors, dryness, etc. smoking and alcohol

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record speaking time and the intensity of vocal use, will registrate the most important parameters of voice straining. To measure vocal load while working, we developed a portable device that registers phonation loudness and time over at least several hours 15. This voice accumulator had to fulfil the following conditions: 1. Registration of phonation duration and intensity during an advisable time period of about 12 hours. Intensity of phonation was preferred to frequency because of the closer relationship between intensity and vocal load16,17, and because people only use a small part of their pitch capacity while they are speaking17 (Fig. 1). 2. Ambulant registration (radio and battery supplied): many subjects have to be mobile at their place of work (Fig. 2). From a technical point of view, the following criteria were applied: a. linearity of the microphone in the total intensity and frequency span; and b. insensitivity of the microphone to other voices and environment noises. The voice accumulator and its functions are shown in Figures 2, 3 and 4.

Copyright © 2001. Kugler Publications. All rights reserved.

After the measurements had been made, the voice accumulator was connected to a personal computer for analysis of the data; analysis of a six-hour registration took approximately ten minutes. The subjects wore the voice accumulator during work. It was initialized and calibrated with a laptop computer, using a Brüel & Kjaer sound level meter (type 2231) placed 30 cm from the mouth. The microphone (Sennheiser MKE 48 PU) was adjusted and attached in such a way that the loudness on the sound level meter was equal to or within 1 dB(A) of that of the voice accumulator. The voice accumulator noted the loudness once a second during registration.

Fig. 1. Phonetogram with speaking field in total voice range. Occupational Voice: Care and Cure : Care and Cure, edited by P.H. Dejonckere, Kugler Publications, 2001. ProQuest Ebook Central,

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4

Copyright © 2001. Kugler Publications. All rights reserved.

Fig. 2. The voice accumulator in operation with head microphone and accumulator (amplifier, ADC memory, and battery pack) in the bag (total weight: 600 g). Fig. 3. a. The azM voice accumulator measuring 15x9x4 cm; b. the battery pack; c. the microphone. Fig. 4. Diagram of the voice accumulator and microphone.

Fig. 5. Primary school teachers.

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Copyright © 2001. Kugler Publications. All rights reserved.

Fig. 6. Telephone operators.

Fig. 7. Sports instructors.

The dB(A) scale was divided into 2 dB(A) intervals, starting at 60 and ending at 112 dB(A). For reproduction of the data, we registered three clusters: 60-72 dB(A): silence-quiet speech; 72-90 dB(A): loud speech instructions; 90-112 dB(A): screaming-yelling. The results of measurements in three occupations are illustrated in Figures 5, 6 and 7. This ‘on the job’ measurement of the duration and intensity of vocal output reveals accurate quantification of individual or occupational vocal demands. These data on vocal load may be helpful in rehabilitating patients with voice disorders and in the ergometric aspects of an occupation. The condition for passing judgment on someone’s (in)capability to fulfil a certain profession

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is the precise determination of the vocal needs for that profession. The usefulness of this quantification is shown in the fact that the subjective estimation differs considerably from the objective measurements.

References

Copyright © 2001. Kugler Publications. All rights reserved.

1. Colton RH, Casper JK: Understanding Voice Problems. Baltimore, MD: Williams and Wilkins 1990 2. Pausewang Gelfer M, Andrews ML, Schmidt CP: Effects of prolonged loud reading on selected measures of vocal function in trained and untrained singers. J Voice 5:158-167, 1991 3. Rantala L, Haataja K, Vilkman E, Körkkö P: Practical arrangements and methods in the field examination and speaking style analysis of professional voice users. Scand J Logoped Phoniatr 19:43-54, 1994 4. Smets EMA, Garsen B, Bonke B, De Haes JCJM: The multidimensional fatigue inventory (MFI). J Psychosomat Res 39:315-325, 1995 5. Smith E, Gray SD, Dove H, Kichner L, Heras H: Frequency and effects of teachers’ voice problems. J Voice 11:81-87, 1997 6. Vilkman E, Lauri ER, Alku P, Sala E, Sihvo M: Loading changes in time based parameters of glottal flow waveforms in different ergonomic conditions. Fol Phoniatr Logopaed 49:247263, 1997 7. Fritzell B: Voice problems and professions. In: Sodersten M (ed) Vocal Fold Closure During Phonation: Studies in Logopedics and Phoniatrics 3. Stockholm: Huddinge 1994 8. Holinger A, Rolnik MI, Bailey CW: Treatment of vocal abuse disorders using a vocal intensity controller. J Speech Hear Disord 39:298-303, 1974 9. Ryu S, Komiyama S, Kannae S, Watanabe H: A newly devised speech accumulator. ORL 45:108-114, 1983 10. Watanabe H, Shin T, Oda M, Fukaura J, Komiyama S: Measurement of total actual speaking time in a patient with spastic dysphonia. Fol Phoniatr 39:65-70, 1987 11. Ohlsson A-C, Brink O, Löfqvist A: A voice accumulator – validation and application. J Speech Hear Res 32:451-457, 1989 12. Rantala L, Paavola L, Körkkö P, Vilkman E: Working-day effects on the spectral characteristics of teaching voice. Fol Phoniatr Logopaed 50:205-211, 1998 13. Pekkarinen E, Viljanen V: Acoustic conditions for speech communication in classrooms. Scand Audiol 20:257-263, 1991 14. Vilkman E, Lauri ER, Alku P, Sala E, Sihvo M: Ergonomic conditions and voice. Logoped Phoniatr Vocol 23:11-19, 1998 15. Buekers R, Bierens E, Kingma H, Marres EHMA: Vocal load as measured by the voice accumulator. Fol Phoniatr Logopaed 47:252-261, 1995 16. Holbrook A: Instrumental analysis and control of vocal behaviour. In: Cooper M (ed) Approaches to Vocal Rehabilitation. Springfield, IL: Thomas 1977 17. Maulet M: Une expérience d’utilisaton de Speech Viewer aupres de patients atteints de déficience auditive. In: Maglieri DI (ed) Proceedings European Voice Technology Seminar London. London: Prentice Hall Inc 1990 18. Buekers R: Voice Performances in Relation to Demands and Capacity: Development of a Quantitative Phonometric Study of the Speaking Voice. Doctoral Thesis, Maastricht University, 1998

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Room acoustics

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ROOM ACOUSTICS How they affect vocal production and perception David M. Howard and James A.S. Angus Department of Electronics, University of York, Heslington, York, UK

Introduction

Copyright © 2001. Kugler Publications. All rights reserved.

Communication using speech is unique to human beings and our speaking and hearing faculties are highly developed. In order to communicate using speech, the acoustic pressure wave produced by the speaker has to reach the ears of the listener(s) without being significantly altered during transmission. Unfortunately, this is not the case in many environments where humans communicate with each other. For those who use their voices professionally, such as teachers, lawyers, actors, singers, market traders, politicians, stock market traders, doctors, nurses, this can mean that they are effectively competing acoustically with the local environment in order to communicate their messages, usually by increasing their vocal effort to raise the acoustic output. This is likely to promote vocal impairment for the speaker, as well as requiring more conscious effort on the parts of both speaker and listener(s) to maintain a useable communication channel. Not only is this fatiguing for all concerned, but it also affects adversely the mental state of readiness in all concerned to process the ideas contained in the message itself. The effect that the local environment can have on the transmission of the acoustic pressure wave from speaker to listener arises from the dimensions of its enclosing surfaces, how the surfaces lie relative to each other, and the materials from which they are composed. The production and the perception of speech can both be affected by room acoustics, either detrimentally or advantageously. The purpose of this chapter is to summarize the important relevant aspects of the acoustics of speech production as well as speech perception, to discuss the effects that room acoustics can have on the transmission of speech from speaker to listener, to describe the potential effects of interfering sounds, and to provide some suggestions that might be applied in practical situations

Address for correspondence: David M. Howard, Department of Electronics, University of York, Heslington, York, YO10 5DD, UK

Occupational voice – care and cure, pp. 29–46 edited by P.H. Dejonckere © 2001 Kugler Publications, The Hague, The Netherlands Occupational Voice: Care and Cure : Care and Cure, edited by P.H. Dejonckere, Kugler Publications, 2001. ProQuest Ebook Central,

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that could reduce the reduce the speaker’s vocal effort and hence the chances of vocal impairment. Figure 1 shows the three key elements of the process that are important when considering how room acoustics affect vocal production and perception: – sound sources – room acoustics – peripheral hearing These three headings provide the basic structure to this chapter. The nature of all sources of sound present in a space is important when considering how speech production and perception might be affected, and these are discussed under sound sources. All speech is essentially produced in some form of enclosed environment for acoustic purposes, even when it is produced outside, and the nature of the acoustic effect of the space on speech will be considered under the heading room acoustics. The nature of the effect that room acoustics might have on the perception of speech is related to how the acoustic signal arriving at each ear is analyzed by the peripheral hearing system.

Sound sources

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The sound source that is wanted in the context of listening to a speaker is the acoustic output from that speaker. In order to communicate useful information using speech or any other means, the signal itself must vary in some manner. The important variations that must be preserved in the acoustic speech signal are its frequency and time content, or its timbre and rhythm.

Fig. 1. Key elements of the process that are important when considering how room acoustics affect vocal production and perception.

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Copyright © 2001. Kugler Publications. All rights reserved.

The most commonly used acoustic model of speech production that describes the frequency content of speech is the ‘source-filter’ model detailed by Fant1, and a summary description is given below. Detailed descriptions of the acoustic of speech production in terms of the source-filter model are given elsewhere (e.g., Denes and Pinson2; Fry3; Borden and Harris4; Kent and Read5; Howard6). The source-filter model describes the acoustic output during speech as resulting from a ‘raw’ sound being generated somewhere between the larynx and the lips (spaces that are collectively known as the vocal tract), which is modified by the shape of the cavity that it passes through before emanating from the lips and/or nostrils. The key features of the source-filter model are illustrated in Figure 2. This ‘raw’ sound is either voiced (as in the vowel in bee) when the vocal folds of the larynx are vibrating, or voiceless (as in the consonant in see) when air is forced past a constriction in the vocal tract, or a mixture of both (as in the consonant in zoo) when the vocal folds vibrate and air is forced past a constriction somewhere in the vocal tract. The average spectral slope associated with these two ‘raw’ sounds are –12 dB per octave for voiced and 0 dB per octave for voiceless, as indicated in Figure 2. As the sound is transmitted via the vocal tract to the lips (and nostrils if the soft palate is lowered), the acoustic resonant characteristics of the vocal tract cavity due to its particular shape modifies the spectrum of the ‘raw’ sound, with an average spectral response slope that is flat or 0 dB per octave, as indicated in Figure 2. The resonant characteristics, usually referred to as formants, are particularly prominent during voiced speech, as indicated. As the sound is radiated from the lips, it is subject to a +6 dB per octave spectral rise known as lip radiation. Overall therefore, the output spectra of voiced and voiceless speech have an average slope of –6 dB and +6 dB per octave, respectively. If an average spectral measurement is made for speech over some tens of seconds, the resulting long-term average spectrum would in fact exhibit a –6 dB per octave slope. This is because the voiced sounds in speech occur more frequently, and they are typically higher in amplitude than voiceless sounds. There are acoustic events that occur rapidly during speech that should be preserved if the listener is to perceive an intelligible message. As different sounds are produced by varying the shape of the vocal tract as the articulators (tongue, jaw, lips, etc.) are moved, the vocal tract response shape (see Fig. 2) varies. The filter of the source-filter model is therefore time-varying during speech production. This has the effect of changing the frequencies of the formants, and these variations, or formant transitions, can vary for different speech sounds between approximately 10 msec for plosives (/b/ /p/ /d/ /t/ /g/ /k/ in English) and 250 msec for diphthongs (e.g., eye, ear, you). The average syllable length in speech is approximately 250 msec. The most rapid acoustic events during speech are the short (