Salt-Lichtenhan How Does Wind Turbine Noise Affect People

7232019 Salt-Lichtenhan How Does Wind Turbine Noise Affect People

httpslidepdfcomreaderfullsalt-lichtenhan-how-does-wind-turbine-noise-affect-people 19

20 | Acousti cs Today | Winter 2014

Introduction

Recent articles in Acoustics Today have reviewed a number of difficult issues concern-ing wind turbine noise and how it can a ff ect people living nearby (Leventhall 2013Schomer 2013 Timmerman 2013) Here we present potential mechanisms by whicheff ects could occur

Te essence of the current debate is that on one hand you have the well-funded wind

industry 1 advocating that infrasound be ignored because the measured levels arebelow the threshold of human hearing allowing noise levels to be adequately docu-mented through A-weighted sound measurements 2 dismissing the possibility thatany variants of wind turbine syndrome exist (Pierpont 2009) even when physicians(eg Steven D Rauch MD at Harvard Medical School) cannot otherwise explainsome patientsrsquo symptoms and 3 arguing that it is unnecessary to separate wind tur-bines and homes based on prevailing sound levels

On the other hand you have many people who claim to be so distressed by the eff ectsof wind-turbine noise that they cannot tolerate living in their homes Some moveaway either at 1047297nancial loss or bought-out by the turbine operators Others live withthe discomfort often requiring medical therapies to deal with their symptoms Some

even members of the same family may be una ff ected Below is a description of thedisturbance experienced by a woman in Europe we received a few weeks ago as part ofan unsolicited e-mail

ldquoFrom the moment that the turbines began working I experienced vertigo-like symp-toms on an ongoing basis In many respects what I am experiencing now is actuallyworse than the lsquodizzinessrsquo I have previously experienced as the associated nausea ismuch more intense For me the pulsating humming noise that the turbines emit is the predominant sound that I hear and that really seems to aect me

While the Chief Scientist [the person who came to take sound measurements in herhouse] undertaking the measurement informed me that he was aware of the low

frequency hum the turbines produced (he lives close to a wind farm himself and hadrecorded the humming noise levels indoors in his own home) he advised that I couldtune this noise out and that any adverse symptoms I was experiencing were simply psychosomaticrdquo

Alec N Salt and

Jeff ery T Lichtenhan

Department of Otolaryngology

Washington University

School of Medicine

St Louis MO 63110

How Does Wind Turbine Noise A ff ect People

T e many ways by which unheard infrasound and low-frequency sound fromwind turbines could distress people living nearby are described

copy C

a n S t o c k P h o t o I n c

a r c h i d e a p h o t o


Redistribution subject to ASA license or copyright see httpacousticalsocietyorgcontentterms Download to IP 7120520197 On Mon 31 Mar 2014 21



| 21

We asked how she felt when she was away from the windturbines to which she replied

ldquoI did manage to take a vacation towards the end of Augustand for the two weeks we were away I was perfectly 1047297 nerdquo

Te goal of our work in this 1047297eld is to understand whetherthe physiology of the ear can or cannot explain the symp-

toms people attribute to wind turbine noise As it is generallythe case when debate in1047298uences a speci1047297c industryrsquos 1047297nancialinterests and legal well-being the scienti1047297c objectivity ofthose associated with the industry can be questioned Liabil-ity damage claims and large amounts of money can hang inthe balance of results from empirical studies Whether it isa chemical industry blamed for contaminating groundwaterwith cancer-causing dioxin the tobacco industry accused ofcontributing to lung cancer or athletes of the National Foot-ball League (NFL) putatively being susceptible to brain dam-age it can be extremely difficult to establish the truth whensome have an agenda to protect the status quo It is only whensufficient scienti1047297c evidence is compiled by those not workingfor the industry that the issue is considered seriously

Origins of Our Involvement

in Infrasound from Wind Turbines

What is the evidence leading us to conclude that unheardinfrasounds are part of the wind turbine problem and howdid we become involved in this debate We are small groupof basic and applied scientists which means that our workaddresses fundamental questions on how the ear works in

normal and diseased states While developing paradigmsfor our studies we had been using a classic technique calledldquolow-frequency biasingrdquo ndash measurement of auditory responsesto a test sound within the range of audibility while simulta-neously presenting a low-frequency tone (eg 48 to 50 Hz)to displace the sensory organ of the inner ear Some auditoryresponses saturate when displaced by the bias tone which canbe used to establish whether the sensory organ is vibratingsymmetrically or whether a 1047298uid disturbance has displacedit to one side A condition called ldquoendolymphatic hydropsrdquo

which is found in humans with Meacuteniegraverersquos disease can displacethe sensory organ as the space containing the 1047298uid calledendolymph swells In our animal experiments we initiallyused 20 to 50 Hz bias tones but for many reasons and inlarge part based on a study in which we found that the earresponded down to 1 Hz (Salt and DeMott 1999) we startedusing the lowest frequency our hardware could generate 48Hz a frequency considered to be infrasound Over the courseof hundreds of experiments we have found numerous biasingeff ects with 48 Hz tones at levels of 80 to 90 dB SPL (ie-13 to -3 dBA) We also found that the ear became about20 dB more sensitive to infrasonic bias tones when the 1047298uidspaces in the cochlear apex were partially occluded as occurswith endolymphatic hydrops

In late 2009 the 1047297rst author received a report of a womanwith Meacuteniegraverersquos disease whose symptoms ndash primarily dizzinessand nausea ndash were severely exacerbated when she was in the

vicinity of wind turbines From our animal data we knewthis woman was likely hypersensitive to very low-frequencysounds Our subsequent review of the literature on wind-tur-bine noise revealed two aspects that were absolutely astound-ing

1 Almost all measurements of wind turbine noise are A-weighted making the unjusti1047297ed assumption that hearingis the only way by which infrasound generates physiologiceff ects Te few studies that reported un-weighted measure-ments of wind-turbine noise or recalculated spectra by re-moving the A-weighting from published A-weighted spectraclearly demonstrated increasing energy towards low frequen-cies with highest energy levels in the infrasound region Wewere surprised that objective full-frequency measurementsshowed that wind turbines generate infrasound at levelscapable of stimulating the ear in various ways Under suchcircumstances A-weighting measurements of turbine noisewould be highly misleading

ldquo Almost all measurements of wind

turbine noise are A-weighted making

the unjusti ed assumption that hearing

is the only way by which infrasound

generates physiologic eff ectsrdquo





2 Literature and websites from the wind industry oftencontained strong statements that wind turbine infrasound wasof no signi1047297cance Tis view was largely based on publicationsby Leventhall (2006 2007) Wind turbine noise was de-scribed as comparable to rustling leaves 1047298owing streams air-conditioned offices or refrigerators heard from the next roomIf wind turbine noise really was comparable to such sourcesthen complaints would not be expected But the turbinessounds are only comparable to these sources if the ultra-lowfrequencies emitted by the turbines are ignored through A-weighting Stations that monitor infrasound or low frequencyseismic (vibrational) noise for other purposes (for the detec-tion of explosions meteors volcanic activity atmosphericactivity etc) are well-aware that low frequency sounds ema-nating from distant wind farms or coupling to the groundas vibrations can in1047298uence their measurements Te UKMinistry of Defense has opposed wind turbines cited within50 km of the Eskdalemuir Seismic Array We have seen noreports of the Ministry opposing the presence of refrigeratorsin the region suggesting they appreciate that sounds emittedfrom wind turbines and refrigerators are quite diff erent It wasthus quite astounding to see the vast majority of wind tur-bine noise measurements excluding the low frequency noisecontent Given the knowledge that the ear responds to lowfrequency sounds and infrasound we knew that comparisonswith benign sources were invalid and the logic to A-weightsound measurements was deeply 1047298awed scienti1047297cally

The Earrsquos Response to Infrasound

Experimental measurements show robust electrical responsesfrom the cochlea in response to infrasound (Salt and DeMott1999 Salt and Lichtenhan 2013) Tis 1047297nding was initiallydifficult to reconcile with measures showing that hearingwas notably insensitive to such sounds but the explanationbecame clear from now-classic physiological studies of the earshowing that the two types of sensory cell in the cochlea hadvery diff erent mechanical properties (Cheatham and Dallos2001)

Te auditory portion of the inner ear the cochlea has twotypes of sensory cell Te inner hair cells (IHC shown greenin Figure 1) are innervated by type I a ff erent nerve 1047297bers thatmediate hearing Te stereocilia (sensory hairs) of the IHCsare free-1047298oating and do not contact the overlying gelatinoustectorial membrane (shown gray) Tey are mechanically dis-placed by 1047298uid movements in the space below the membrane As their input is 1047298uid-coupled to the vibrations of the sensoryorgan they exhibit ldquovelocity sensitiverdquo responses As the veloc-ity of motions decreases for lower-frequency sounds their1047298uid-coupled input renders the IHC insensitive to very low-frequency sounds Te other type of sensory cell the outerhair cells (OHC shown red in Figure 1) are innervated bytype II a ff erent nerve 1047297bers that are not as well understood astype I 1047297bers and probably do not mediate conscious hearingper se In contrast to the IHC the stereocilia of the OHCsare inserted into the tectorial membrane Tis direct mechani-cal coupling gives them ldquodisplacement sensitiverdquo propertiesmeaning they respond well to lowndashfrequency sounds andinfrasound Te electrical responses of the ear we had beenrecording and studying originate from the sensitive OHCsFrom this understanding we conclude that very low frequencysounds and infrasound at levels well below those that areheard readily stimulate the cochlea Low frequency sounds

and infrasound from wind turbines can therefore stimulatethe ear at levels well below those that are heard

Te million-dollar question is whether the eff ects of windturbine infrasound stimulation stay con1047297ned to the ear andhave no other in1047298uence on the person or animal At presentthe stance of wind industry and its acoustician advisors is thatthere are no consequences to long-term low-frequency and in-frasonic stimulation Tis is not based on studies showing thatlong-term stimulation to low-level infrasound has no in1047298u-

Figure 1 e sensory organ of the cochlea showing inner and outerhair cell and neural anatomy




| 23

ence on humans or animals No such studies have ever beenperformed Teir narrow perspective shows a remarkable lackof understanding of the sophistication of biological systemsand is almost certainly incorrect As we consider below thereare many physiologic mechanisms by which long-term infra-sound stimulation of the cochlea could have eff ects

One important aspect of wind turbine noise that is relevant toits physiological consequences is that the duration of exposurecan be extremely long 24 hours a day and lasting for days orlonger depending on prevailing wind conditions Tis is con-siderably diff erent from most industrial noise where 8 hourexposures are typically considered interspersed by prolongedperiods of quiet (ie quiet for 16 hours per day plus allweekends) Tere are numerous studies of exposures to higherlevel infrasound for periods of a few hours but to date therehave been no systematic studies of exposure to infrasoundfor a prolonged period Te degree of low-frequency cochlear

stimulation generated by wind turbine noise is remarkablydifficult to assess due to the almost exclusive reporting of A-weighted sound level measurements It certainly cannot beassumed that cochlear stimulation is negligible because A-weighted level measurements are low For example with 5 Hzstimulation cochlear responses are generated at -30 dBA andstimulation is sufficient to cause responses to saturate (indi-cating the transducer is being driven to its limit) at approxi-mately 20 dBA (Salt and Lichtenhan 2012 Salt et al 2013) We have also shown that 125 Hz low-pass 1047297ltered noise at just45 dBA produces larger responses than wide band noise with

the same low-frequency content presented at 90 dBA (Saltand Lichtenhan 2012) We conclude that low frequency re-gions of the ear will be moderately to strongly stimulated forprolonged periods by wind turbine noise Tere are a numberof plausible mechanisms by which the stimulation could haveeff ects

1 Amplitude Modulation Low-Frequency Biasing of

Audible Sounds

Modulation of the biological mechano-electric transducerof the inner ear by infrasound is completely diff erent fromthe amplitude modulation of audible sounds that can bemeasured with a sound level meter near wind turbines undersome conditions Tis can be demonstrated in low-frequencybiasing paradigms in which a low-frequency tone and higher-frequency audible tone are presented simultaneously to asubject

OHCs respond to both low- and high-frequency componentsand modulate the high-frequency components by eithersaturation of the mechano-electric transducer or by cyclicallychanging the mechanical ampli1047297cation of high frequenciesIHCs being insensitive to the low-frequency tone see ahigh pass-1047297ltered representation of the OHC response ndash anamplitude modulated version of the audible probe tone asshown in Figure 2 As hearing is mediated through the IHCs

that receive approximately 90-95 of a ff erent innervationof the auditory nerve the subject hears the higher-frequencyprobe tone varying in amplitude or loudness A similar bias-ing in1047298uence on cochlear responses evoked by low-level tonepips was explained by the low-frequency bias tone changingOHC-based cochlear ampli1047297er gain (Lichtenhan 2012) Tissame study also showed that the low frequency apical regionsof the ear were most sensitive to low-frequency biasing Stud-ies like this raise the possibility that the amplitude modula-tion of sounds which people living near wind turbines report

Figure 2 Demonstration of biologically-generated amplitudemodulation to a non-modulated stimulus consisting of an audibletone at 500 Hz tone summed with an infrasonic tone at 48 Hz ecochlear microphonic response which is generated by the OHC in-cludes low and high frequency components e IHC detect only thehigh frequency component which is amplitude modulated at twice

the infrasound frequency for the stimuli in this example





as being so highly annoying may not be easily explained bymeasurements with an A-weighted sound level meter Ratherthe low-frequency and infrasound levels need to be consideredas contributing to the perceived phenomenon Subjectivelythe perceived 1047298uctuation from an amplitude modulatedsound and from a low-frequency biased sound are identicaleven though their mechanisms of generation are completelydiff erent For the subject the summed eff ects of both types ofamplitude modulation will contribute to their perception ofmodulation Acousticians therefore need to be aware that thedegree of modulation perceived by humans and animals livingnear wind turbines may exceed that detected by a sound levelmeter

2 Endolymphatic Hydrops Induced by

Low Frequency Tones

As mentioned above endolymphatic hydrops is a swellingof the innermost membrane bound 1047298uid compartment ofthe inner ear Low-frequency tones presented at moderate tomoderately-intense levels for just 15 to 3 minutes can inducehydrops (Figure 3) tinnitus (ringing in the ears) and changesin auditory potentials and acoustic emissions that are physi-ological hallmarks of endolymphatic hydrops (Salt 2004Drexl et al 2013)

Unlike the hearing loss caused by loud sounds the symptomsresulting from endolymphatic hydrops are not permanent andcan disappear or at least 1047298uctuate as the degree of hydropschanges Return to quiet (as in Figure 3) or relocation away

from the low-frequency noise environment allow the hydropsand the symptoms of hydrops to resolve Tis which wouldbe consistent with the womanrsquos description of her symptomsgiven earlier As hydrops is a mechanical swelling of themembrane-bound endolymphatic space it a ff ects the mostdistensible regions 1047297rst ndash known to be the cochlear apex andvestibular sacculus Patients with saccular disturbances typi-cally experience a sensation of subjective vertigo whichwould be accompanied by unsteadiness and nausea As wementioned above an ear that has developed endolymphatic

2009) Te possibility of a positive feedback ndash low-frequency

hydrops becomes gt20 dB more sensitive to infrasound be-cause the helicotrema becomes partially obstructed (Salt et al

induced hydrops that causes the ear to be more sensitive to

low frequencies ndash has to be considered To date all studiesof low-frequency tone-induced hydrops have used very shortduration (1-2 min) exposures In humans this is partly due toethical concerns about the potential long-term consequencesof more prolonged exposures (Drexel et al 2013) Endolym-phatic hydrops induced by prolonged exposures to moderatelevels of low-frequency sound therefore remains a real pos-sibility

3 Excitation of Outer Hair Cell A ff erent Nerve Pathways

Approximately 5-10 of the a ff erent nerve 1047297bers (whichsend signals from the cochlea to the brain - the type II 1047297bersmentioned above) synapse on OHCs Tese 1047297bers do notrespond well to sounds in the normal acoustic range and theyare not considered to be associated with conscious hearingExcitation of the 1047297bers may generate other percepts such as

feelings of aural fullness or tinnitus Moreover it appears thatinfrasound is the ideal stimulus to excite OHC a ff erent 1047297bersgiven what has been learned about these neurons from in vitrorecordings (Weisz et al 2012 Lichtenhan and Salt 2013) Invivo excitation of OHC a ff erents has yet to be attempted withinfrasound but comparable 1047297bers in birds have been shownto be highly sensitive to infrasound (Schermuly and Klinke1990) OHC a ff erents innervate cells of the cochlear nucleusthat have a role in selective attention and alerting whichmay explain the sleep disturbances that some people living

Figure 3 Brief exposures to low-frequency tones cause endolymphatic hydrops in animals (Salt 2004) and tinnitus and acousticemission changes consistent with endolymphatic hydrops in humans(Drexel et al 2013) e anatomic pictures at the right show thedierence between the normal (upper) and hydropic (lower) cochleae e endolymphatic space (shown blue) is enlarged in the hydropiccochlea generated surgically in this case




| 25

near wind turbines report (Nissenbaum et al 2012) Telikelihood that OHC a ff erents are involved in the eff ects oflow-frequency noise is further supported by observations thattype II innervation is greatest in the low-frequency cochlearregions that are excited most by infrasound (Liberman et al1990 Salt et al 2009)

4 Exacerbation of Noise Induced Hearing Loss

Some years ago we performed experiments to test a hypothesisthat infrasound was protective against noise damage (Hardinget al 2007) We reasoned that low-frequency biasing wouldperiodically close the mechano-electric transducer channelsof the sensory organ (reducing electrical responses as shownin the biasing studies above) and consequently reduce theamount of time that hair cells were exposed to the damagingoverstimulation associated with noise exposure Te experi-mental study found that just the opposite was true We foundthat simultaneous presentation of infrasound and loud noiseactually exacerbated noise-induced lesions as compared towhen loud noise was presented without infrasound Ourinterpretation was that low-frequency sound produced anintermixing of 1047298uids (endolymph and perilymph) at the sitesof hair cell loss resulting in lesions that were larger A possibil-ity to be considered is therefore that long-term exposure toinfrasound from wind turbines could exacerbate presbycusisand noise-induced hearing loss Because these forms of hear-ing loss develop and progress slowly over decades this couldbe a lurking consequence to human exposures to infrasound

that will take years to become apparent

5 Infrasound Stimulation of the Vestibular Sense Organs Recent exchanges in this journal between Drs Leventhalland Schomer concerning the direct stimulation of vestibularreceptors by sound at low and infrasonic frequencies deservecomment Dr Leventhall asserts that both Drs Schomer andPierpont are incorrect in suggesting that wind turbine infra-sound could stimulate vestibular receptors citing work byTodd in which the earrsquos sensitivity was measured in responseto mechanical low-frequency stimulation applied by bone

conduction Leventhall fails to make clear that there are nostudies reporting either vestibular responses or the absenceof vestibular responses to acoustically-delivered infrasoundTis means that for all his strong assertions Leventhall cannorefer to any study conclusively demonstrating that vestibularreceptors of the ear do not respond to infrasound Numerousstudies have reported measurements of saccular and utricularresponses to audible sound Indeed such measurements arethe basis of clinical tests of saccular and utricular functionthrough the VEMP (vestibular-evoked myogenic potentials)Some of these studies have shown that sensitivity to acousticstimulation initially declines as frequency is lowered On theother hand in vitro experiments demonstrate that vestibularhair cells are maximally sensitive to infrasonic frequencies(~1 ndash 10 Hz) Tus sensitivity to acoustic stimulation mayincrease as stimulus frequency is lowered into the infrasonicrange Direct in vivo vestibular excitation therefore remains apossibility until it has been shown that the saccule and othervestibular receptors speci1047297cally do not respond to this stimu-lation

Low-frequency tone-induced endolymph hydrops as dis-cussed above could increase the amount of saccular stimula-tion by acoustic input Hydrops causes the compliant saccularmembrane to expand in many cases to the point where itdirectly contacts the stapes footplate Tis was the basis ofthe now superseded ldquotackrdquo procedure for Meacuteniegraverersquos disease inwhich a sharp prosthesis was implanted in the stapes footplateto perforate the enlarging saccule (Schuknecht et al 1970)

When the saccule is enlarged vibrations will be applied to en-dolymph not perilymph potentially making acoustic stimu-lation of the receptor more eff ective Tere may also be certainclinical groups whose vestibular systems are hypersensitive tovery low-frequency sound and infrasound stimulation Forexample it is known that patients with superior canal dehis-cence syndrome are made dizzy by acoustic stimulation Sub-clinical groups with mild or incomplete dehiscence could existin which vestibular organs are more sensitive to low frequencysounds than the general population

ldquoThe million-dollar question is whether

the eff ects of wind turbine infrasound

stimulation stay con ned to the

ear and have no other in uence on the

person or animalrdquo





6 Potential Protective Terapy Against Infrasound

A commonly-used clinical treatment could potentially solvethe problem of clinical sensitivity to infrasound Tympanosto-my tubes are small rubber ldquogrommetsrdquo placed in a myringot-omy (small incision) in the tympanic membrane (eardrum) tokeep the perforation open Tey are routinely used in childrento treat middle ear disease and have been used successfully

to treat cases of Meacuteniegraverersquos disease Placement of tympanos-tomy tubes is a straightforward office procedure Althoughtympanostomy tubes have negligible in1047298uence on hearing inspeech frequencies they drastically attenuate sensitivity tolow frequency sounds (Voss et al 2001) by allowing pressureto equilibrate between the ear canal and the middle earTeeff ective level of infrasound reaching the inner ear could bereduced by 40 dB or more by this treatment Tympanostomytubes are not permanent but typically extrude themselves aftera period of months or can be removed by the physician Noone has ever evaluated whether tympanostomy tubes alleviatethe symptoms of those living near wind turbines From thepatientrsquos perspective this may be preferable to moving out oftheir homes or using medical treatments for vertigo nau-sea andor sleep disturbance Te results of such treatmentwhether positive negative would likely have considerablescienti1047297c in1047298uence on the wind turbine noise debate

Conclusions and Concerns

We have described multiple ways in which infrasound andlow-frequency sounds could a ff ect the ear and give rise to thesymptoms that some people living near wind turbines reportIf in time the symptoms of those living near the turbinesare demonstrated to have a physiological basis it will becomeapparent that the years of assertions from the wind industryrsquosacousticians that ldquowhat you canrsquot hear canrsquot a ff ect yourdquo or thatsymptoms are psychosomatic or a nocebo eff ect was a greatinjustice Te current highly-polarized situation has arisen

because our understanding of the consequences of long-terminfrasound stimulation remains at a very primitive level Basedon well-established principles of the physiology of the ear andhow it responds to very low-frequency sounds there is ample justi1047297cation to take this problem more seriously than it hasbeen to date Tere are many important scienti1047297c issues thatcan only be resolved through careful and objective research

Although infrasound generation in the laboratory is techni-cally difficult some research groups are already in the processof designing the required equipment to perform controlledexperiments in humans

One area of concern is the role that some acousticians andsocieties of acousticians have played Te primary role ofacousticians should be to protect and serve society from nega-tive in1047298uences of noise exposure In the case of wind turbinenoise it appears that many have been failing in that role Foryears they have sheltered behind the mantra now shown to

be false that has been presented repeatedly in many formssuch as ldquoWhat you canrsquot hear canrsquot a ff ect yourdquo ldquoIf you cannothear a sound you cannot perceive it in other ways and it doesnot a ff ect yourdquo ldquoInfrasound from wind turbines is below theaudible threshold and of no consequencerdquo ldquoInfrasound isnegligible from this type of turbinerdquo ldquoI can state categoricallythat there is no signi1047297cant infrasound from current designs ofwind turbinesrdquo All of these statements assume that hearingderived from low-frequency-insensitive IHC responses is theonly mechanism by which low frequency sound can a ff ect thebody We know this assumption is false and blame its origin

on a lack of detailed understanding of the physiology of theear

Another concern that must be dealt with is the develop-ment of wind turbine noise measurements that have clinicalrelevance Te use of A-weighting must be reassessed as it isbased on insensitive IHC-mediated hearing and grossly mis-represents inner ear stimulation generated by the noise In thescienti1047297c domain A-weighting sound measurements would be

ldquoFor years they have sheltered behind the

mantra now shown to be false that has been

presented repeatedly in many forms such as

lsquoWhat you canrsquot hear canrsquot aff ect yoursquo rdquo




| 27

unacceptable when many elements of the ear exhibit a highersensitivity than hearing Te wind industry should be held tothe same high standards Full-spectrum monitoring whichhas been adopted in some reports is essential

In the coming years as we experiment to better understandthe eff ects of prolonged low-frequency sound on humans it

will be possible to reassess the roles played by acousticiansand professional groups who partner with the wind industryGiven the present evidence it seems risky at best to continuethe current gamble that infrasound stimulation of the earstays con1047297ned to the ear and has no other eff ects on the bodyFor this to be true all the mechanisms we have outlined (low-frequency-induced amplitude modulation low frequencysound-induced endolymph volume changes infrasoundstimulation of type II a ff erent nerves infrasound exacerbationof noise-induced damage and direct infrasound stimulationof vestibular organs) would have to be insigni1047297cant We know

this is highly unlikely and we anticipate novel 1047297ndings in thecoming years that will in1047298uence the debate

From our perspective based on our knowledge of the physiol-ogy of the ear we agree with the insight of Nancy Timmer-man that the time has come to ldquoacknowledge the problem andwork to eliminate itrdquo

Biosketches

Alec N Salt is Professor of Otolaryn-gology at Washington University Heis a long-term member of the Acousti-cal Society of America the Associa-

tion for Research in Otolaryngologyand the American Otological SocietyHis research covers broad aspects ofsystem-level cochlear physiology witha major focus on the inner ear 1047298uids

drug delivery to the inner ear and low-frequency sound ef-fects on the ear

Je ff ery T Lichtenhan is AssistantProfessor of Otolaryngology at Washington University in St Louis

He recently completed his postdoc-toral fellowship in the Eaton-PeabodyLaboratory of Auditory Physiology atHarvard Medical School His researchaddresses questions on the mechanicsof hearing to low-frequency acousticsound and the auditory eff erent system Ultimately his workaims to improve the diff erential diagnostics of sensorineuralhearing loss

Cheatham MA Dallos P (2001) ldquoInner hair cell responsepatterns implications for low-frequency hearingrdquo Journal of

the Acoustical Society of America 110 2034-2044

Drexl M Uumlberfuhr M Weddell TD Lukashkin AN Wiegrebe L Krause E Guumlrkov R (2013) ldquoMultipleIndices of the lsquoBouncersquo Phenomenon Obtained from theSame Human Earsrdquo Journal of the Association for Research in

Otolaryngology (e-pub before print copy) 101007s10162-013-0424-x

Harding GW Bohne BA Lee SC Salt AN (2007)ldquoEff ect of infrasound on cochlear damage from exposure to a4 kHz octave band of noiserdquo Hearing Research 225128-138

Leventhall G (2006) ldquoInfrasound From Wind Turbines ndashFact Fiction Or Deceptionrdquo Canadian Acoustics 3429-36

Leventhall G (2007) ldquoWhat is infrasoundrdquo Progress in

Biophysics and Molecular Biology 93 130ndash137

References





Leventhall G (2013) ldquoConcerns About Infrasound from Wind Turbinesrdquo Acoustics Today 93 30-38

Liberman MC Dodds LW Pierce S (1990) ldquoA ff erentand eff erent innervation of the cat cochlea quantitative analy-sis with light and electron microscopyrdquo Journal of Compara-

tive Neurology 301443-460

Lichtenhan JT (2012) ldquoEff ects of low-frequency biasing onotoacoustic and neural measures suggest that stimulus-fre-quency otoacoustic emissions originate near the peak regionof the traveling waverdquo Journal of the Association for Research in

Otolaryngology 1317-28

Lichtenhan JT Salt AN (2013) ldquoAmplitude modulationof audible sounds by non-audible sounds Understanding theeff ects of wind turbine noiserdquo Proceedings of Meetings on Acoustics Vol 19 Journal of the Acoustical Society of America133(5) 3419

Nissenbaum MA Aramini JJ Hanning CD (2012)Eff ects of industrial wind turbine noise on sleep and healthNoise Health Sep-Oct14(60)237-43

Pierpont N (2009) ldquoWind Turbine Syndromerdquo K-SelectedBooks

Salt AN DeMott JE (1999) ldquoLongitudinal endolymphmovements and endocochlear potential changes induced bystimulation at infrasonic frequenciesrdquo Journal of the Acoustical

Society of America 106 847-856

Salt AN (2004) ldquoAcute endolymphatic hydrops generated

by exposure of the ear to nontraumatic low frequency tonerdquo Journal of the Association for Research in Otolaryngology 5203-214

Salt AN Brown DJ Hartsock JJ Plontke SK (2009)ldquoDisplacements of the organ of Corti by gel injections intothe cochlear apexrdquo Hearing Research 25063-75

Salt AN Lichtenhan JT (2102) ldquoPerception-based protec-tion from low-frequency sounds may not be enoughrdquo Pro-ceedings of the InterNoise Symposium New York

Salt AN Lichtenhan JT Gill RM Hartsock JJ(2013) ldquoLarge endolymphatic potentials from low-frequencyand infrasonic tones in the guinea pigrdquo Journal of the Acousti-

cal Society of America 133 1561-1571Schermuly L Klinke R (1990) ldquoOrigin of infrasound sensi-tive neurones in the papilla basilaris of the pigeon an HRPstudyrdquo Hearing Research 48 69-77

Schomer P (2013) ldquoComments On Recently Published Article ldquoConcerns About Infrasound From Wind Turbinesrdquo Acoustics Today 94 7-9

Schuknecht HF (1977) ldquoPathology of Meacuteniegraverersquos disease asit relates to the sac and tack proceduresrdquo Annals of Otology

Rhinology and Laryngology 86677-82

Timmerman NS (2013) ldquoWind Turbine Noiserdquo AcousticsToday 9322-29

Voss SE Rosowski JJ Merchant SN Peake WT(2001) ldquoMiddle-ear function with tympanic-membrane per-forations I Measurements and mechanismsrdquo Journal of the

Acoustical Society of America 1101432-1444

Weisz CJ Lehar M Hiel H Glowatzki E Fuchs PA(2012) ldquoSynaptic Transfer from Outer Hair Cells to Type II A ff erent Fibers in the Rat Cochleardquo Journal of Neuroscience329528-9536



| 21

We asked how she felt when she was away from the windturbines to which she replied

ldquoI did manage to take a vacation towards the end of Augustand for the two weeks we were away I was perfectly 1047297 nerdquo

Te goal of our work in this 1047297eld is to understand whetherthe physiology of the ear can or cannot explain the symp-

toms people attribute to wind turbine noise As it is generallythe case when debate in1047298uences a speci1047297c industryrsquos 1047297nancialinterests and legal well-being the scienti1047297c objectivity ofthose associated with the industry can be questioned Liabil-ity damage claims and large amounts of money can hang inthe balance of results from empirical studies Whether it isa chemical industry blamed for contaminating groundwaterwith cancer-causing dioxin the tobacco industry accused ofcontributing to lung cancer or athletes of the National Foot-ball League (NFL) putatively being susceptible to brain dam-age it can be extremely difficult to establish the truth whensome have an agenda to protect the status quo It is only whensufficient scienti1047297c evidence is compiled by those not workingfor the industry that the issue is considered seriously

Origins of Our Involvement

in Infrasound from Wind Turbines

What is the evidence leading us to conclude that unheardinfrasounds are part of the wind turbine problem and howdid we become involved in this debate We are small groupof basic and applied scientists which means that our workaddresses fundamental questions on how the ear works in

normal and diseased states While developing paradigmsfor our studies we had been using a classic technique calledldquolow-frequency biasingrdquo ndash measurement of auditory responsesto a test sound within the range of audibility while simulta-neously presenting a low-frequency tone (eg 48 to 50 Hz)to displace the sensory organ of the inner ear Some auditoryresponses saturate when displaced by the bias tone which canbe used to establish whether the sensory organ is vibratingsymmetrically or whether a 1047298uid disturbance has displacedit to one side A condition called ldquoendolymphatic hydropsrdquo

which is found in humans with Meacuteniegraverersquos disease can displacethe sensory organ as the space containing the 1047298uid calledendolymph swells In our animal experiments we initiallyused 20 to 50 Hz bias tones but for many reasons and inlarge part based on a study in which we found that the earresponded down to 1 Hz (Salt and DeMott 1999) we startedusing the lowest frequency our hardware could generate 48Hz a frequency considered to be infrasound Over the courseof hundreds of experiments we have found numerous biasingeff ects with 48 Hz tones at levels of 80 to 90 dB SPL (ie-13 to -3 dBA) We also found that the ear became about20 dB more sensitive to infrasonic bias tones when the 1047298uidspaces in the cochlear apex were partially occluded as occurswith endolymphatic hydrops

In late 2009 the 1047297rst author received a report of a womanwith Meacuteniegraverersquos disease whose symptoms ndash primarily dizzinessand nausea ndash were severely exacerbated when she was in the

vicinity of wind turbines From our animal data we knewthis woman was likely hypersensitive to very low-frequencysounds Our subsequent review of the literature on wind-tur-bine noise revealed two aspects that were absolutely astound-ing

1 Almost all measurements of wind turbine noise are A-weighted making the unjusti1047297ed assumption that hearingis the only way by which infrasound generates physiologiceff ects Te few studies that reported un-weighted measure-ments of wind-turbine noise or recalculated spectra by re-moving the A-weighting from published A-weighted spectraclearly demonstrated increasing energy towards low frequen-cies with highest energy levels in the infrasound region Wewere surprised that objective full-frequency measurementsshowed that wind turbines generate infrasound at levelscapable of stimulating the ear in various ways Under suchcircumstances A-weighting measurements of turbine noisewould be highly misleading

ldquo Almost all measurements of wind

turbine noise are A-weighted making

the unjusti ed assumption that hearing

is the only way by which infrasound

generates physiologic eff ectsrdquo















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Audible Sounds












Low Frequency Tones















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Biosketches














References









































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Low Frequency Tones















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Audible Sounds












Low Frequency Tones















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| 27






Biosketches














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Low Frequency Tones















| 25




































| 27






Biosketches














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Documents

Salt-Lichtenhan How Does Wind Turbine Noise Affect People