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Motion Sickness Incidence as a Function of the Frequency and Accelaration of Vertical Sinusoidal Motion


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Motion Sickness incidence as a

Function of the Frequency and

AcceP-ercition of Vertica Shiusoidal Motion

Deift University of Technology

Ship Hydromechanics Laboratory


Mekelweg 2, 2628 CD Deift

The Netherlands

Phone: +31 15 2786873 - Fax: +31 15 2781836

O'HNLoN. J. F,, and M. F.. McCAui.Y. Mothw 1CkLSS a. a fwwI,o f the f'qwn'y of rwferaeicm uf iertko1

siim,widdf f ion. rospce Mcd. 45(4):3-369, 1974,

Fourteen eperIrneiitaI euwlitiutic uf vertkal s*n,tsodal motio were drfind by coi binatlims of wave frequency and ucrelera-tiun level In t partial facturial desigi. The frequency ranie

to-csflgafrd was from 5 vydes per minute (CPM or .0$3 liz in 30 CPM (.500 i%z) aad the aceraie aeccicr.itims ocr each half-wave cyck ringed from about .03 tu .lO g. Independent roup of 20 or inure atalv sibjects (Ss) were cI,øs-d for 2 ln,ur ai outil they bcan to vmiil, wliithescr t-une liii,. Motion sieiitess hwidciive (MMI). 6clineil as the ¡tercentage of Ss epericiieln

wutiIiug. uasgreatect it i (reuuvu'y nf IO CPM (.U17 1l). For all wave íreqiieiiics, MSI increased c n monotonie function of the jeccicratimu kvct. A nudlieiiinticiI niudel was ilcijycil frutit

the uhaa, andtheimplications for underlying pl,vsiülogkicl utecha-.dsms cml fur lrmrLsport:uI km !ehkle design arc' dscuceiL


bly began when he first ventured upon the sea inENCJDENCE of motion sickness in man proba-ships, In the past century, The signs and symptoms of motion sickness have beco observed in other transporta-tion vehicles: automobiles, aircraft, and spacecraft. De-spite the various environments in which motion sickness may occur, a. common characteristic of all the motions which induce motion sickness seems mo be repetitive

linear or angular acceleration of the head (12).

One component nf the complex notions of ships, air-craft, and land vehides is periodic vertical motion. This component of sea motion has long been considered as a primary factor in the etiology of motkm sickness aboard conventional seacraft (I 4,15), but little is knowti ;Lhout the characteristics of periodic vertical motion which in-duce the pathogenic effects. Practically all o the avail-able data arise from a series of studies conducted under che direction of G. R. Wendt at Wesicyan University in the l940s (1.2,3.4,5). Although that research program was pioneering, it was limited in several important

re-spects which are discussed later in this report. After a

25-year hiatus, t'hai line of research was resumed in an

at-tempt to identify the coruponctits uf vertical periodic mo-flou which induce motion sickness, and to show

quantita-tively how time incidence of motion sickness varies as a

simultaneous function of those components. 3(jf Acro: ace Mcdkir Aprii. 1974


.Hwnw, Factors Rcsearch, incorporwed. Goleta, California



Subjects:'The subjects (Ss) were 306 healthy, young

(18-:34 years) male college s:lLIdefltS who volunteered for

pay ($10), There were, in addition, six volunteers who

Were rejected due to physical conditions revealed h their responses to a medical history questionnaire. In response to another questionnaire, none of the Ss indicated having

been exposed to significant seacrair or aircraft motions

withii the preceding 2-month period i.e., all were

ap-¡)fC1tiY unacclimatized to nmotion.

Apparatus: The Ss vere exposed, iii pairs, to

jre-selected inotious in the ONR/lIFR Motion

Genera-tor (LS) .

That dcvie is ca;ble of displacing a 2.44

ni-square cabin over a 6,7 in vertical range, The cal,in

is mounted upon a carriage which rides over vertical

tracks on a 9 in tower. The carriage is driven from

he-neath by a Imydrmulic piston. The piston's excursion is de-termined by a hydraulic positioning servomechanism'

un-der remote electronic cOntrOl by apparatus contained in

the adjacent e.xperimcntcr's cabin. The frequency

re-sponsc of the entire system is across ihe range O-3 Hz. The system is capable of producing maximum

accelera-tinos in the cabin of up to a1'. Wi 0.7 g.

The cabin's internal space was bisected into separate

oon.mpartmei.ts by a floor-to--ceiling insulated partition.

Access to each compartment was gained through a sepa-rate door and no communication was permitted between

compartn.mcnis. An aircraft-type seat with a lap belt and headrest was mounteti in each compartment. Voice corn-mnurIIcaIi(m was achieved between the experimenter and


S via

separate earphone/microphone systems

mnnunted in headsets. Two closed-circuit TV systems

al-lowed the experimenter to visually monitor the Ss. The

compartments were maintained at a dry-bulb temperature

of 2L2°C mo 22.2CC by independent aìr conditioning


Procedure: Originally, 280 Ss were randomly assigned

in groups of 20 io purticipatc in each of 14 experimental conditions. In three conditions, additional Ss were ran-domly assigned in order w achieve greater statistical re-liability of the ensuing data. Each condition was defined by a particular comhinatinn of wave frequency (f) and acceleration level. The measure of acceleration was the


MOTION SICKNESSO'HANLON & McCAULEY time iritcgral of the aboizte value cf acceleration (ä)

rnparted ja each hall-wave cycle.*

The 14 cxperimental conditions, defined by

combina-tiçrns of f and ä are given in Table i. along willi the

corresponding displacement values and the number of Ss in each condition. For conditions employing a given / level, wave amplitude (i.e., t/2 total dispbcement)

was adjusted to yield the desired a levels in different

conditions. A.s may b inferred From the table, more than 1 4 combinations 01 the given f and a levels would have been required io achieve a co.mpletcty balanced !actorial experimenta1 design. I4owever, those additional treatment conditions were both impossible to achieve with the pres-eat apparatus aiid were highly unrealiMie with respect to vertical periodic motion encountered in conventional

sea-craft. As it was, the conditions that were used included

vertical displacements between .30 ni and 5.66 ni,

there-fore bracketing the range of ocean wave heights ¡n Sea

States l6(6).

Subjects vere instructed thaL their exposure would last

for 2 hours, but that they would be removed sooner in case of emesis (vomiting). After instruction, the two Ss were seated within their respective compartments and their tteads positioned against the headrests. No earth-fixed visual reference was available, and thc interior cabin lights remained on. The Ss were not prohibited from closing their eyes, bui sleeping was not permitted; the Ss were required to press one of five buttons every

minute, upon presentation of a tone, o describe their

approximate state of symptom development. The results o! these data are not included in the present repart.

The experimenter aurally and visually monitored the Ss. using the apparatus described, to ensure their safety

and to stop the motion generator if either S vomited.

Upon emesis, the affected S was removed from his corn-pariment and, after a delay of 30-60 s, the exposure was resumed for the other S.

The motion sickness incidence (MSI) in each

condi-tion was measured by the percentage of Ss who experi-enced enìesis at any time during the period of exposure. RESULTS

Table li lists the MSI values recorded in each

experi-mental condition. One aspect of those results was a

monotonie increase of MSI, with , at every level of f. Attempts were made to fit a general equation to the data

for describing MSI as a function of ô or a logical

transform of a. lt was determirtcd that the equation for the integral of the normal distribution function (i.e., the normal ogive) accurately described the relationship

be-tween MSI and log d. The generai expression was:

'lt hs Iiecn a frequent pra1icc 1A sihiulate ccelcratiun &luring inusuidat motion in terms of the absolute value of peilz aecc1 craton (a,1,); or alternatively, as the root-nsean-square uf

ac-celcrition in each half-wave cycle (Cri,), Howc'cr, a seems to represent the pbydologicasliy effective stimulus hcfler, hnd for that reissen it Was used here. The transformation of 4 into the other measures of acceleration is simple for sinusoidal mot.ioii (Le., 4 - .637 -" .901 a,,).




Frequency (CPM) (iÍz) s tO .167 20 .333 30 .00


Accekrtitkin a (g) .025 .05 .10 .21) o a io 5 30 60 15 52 Sl 0 15 25

Aerospace Medicine Apr11. 1974 367

Frernicucy Açcder*tion 4 Igl (CPM) (Hz) .025 .05 .10 .21) .30 .40 .053 2.80 5.60


20 lO 1.67 .70 1.40 2.50 5.60 20 20 20 20 20 .333 .35 .70 1.40 2.10 20 26 27 33 30 .500 .30 .61 .91 1.22 22 21) 20 20 log i MSI



-.1 irij2ir dx

where i .iiid e are defined as usuaI x is a variable of

integration in units of log a. and ts and z are

param-cleat with values determined empirically.

Parameter estirnatiomi was aeconiplished by fitting the

general equation to Ute MS! values measured at every log ô level, for each level of f separately, according to the method of least squares. The results obtained for

the three higher levels of! are shown in Fig. i .

The parameter, t, corresponds to the log a value

as-sociated with a 50% MSI value for a particular f level. Values of . obtained at dificrent f levels also indice the relative effectiveness of log a as a stimulus for

mo-tion sickness at those wave frequencies: lower Lvalues

indkate that less acceleration is required to produce the same MSI.

11u data indicated that ,u increased with


be-tween .167 and .500 Hz. Yet z cannot 'be a monotonie

function of f. Logically, must also increase as f

de-clines freni .167 H to zero. 'Ihe true relationship

he-tween and I Illay he complex, hut an initial

approxi-'Onty two levels of acceleration were tend in conjunction with the lowest f lcvei (.053 Hz). These yielded only two data points, tOo few mor use in paranseter estimation. It was assumed thai arty general rclatitaohip Iwteen MSI and log 4 delermined

from the el [ser dala would [told for the lowest f level as welL


MOTION SICKN ESSOHANLON & McCAULEY ro u*, o. e t t' 't i,tci dence 1

Fig. 1. Motion Sickness Incidence (within 2 1iour) as a function of log average acceIeraiou () for each wave f reqoency (f).

mation of that relationship was made by fitting the

quadratic equation to he data according to the method of

least squares, so that:

u. .654 + 3.697 log! + 2.320 (1ogI)

where jis in Hz and , is a log a scale with a ¡ri units of g.

By substituting i,hc observed value of .40 tog a for o,

and by substituting the above expression for

itt the iit

equation, a model was derived for expressing MSI as a

function of a and f. A graphic representation of that

model is shown in Fig. 2, along with the actual data used

in the derivation. The 14 data points arc the sanie as

previously presented in Table Ii. The deviation of each of the actual data points from the corresponding points on the derived surface is shown in Fig. 2 by the dashed interconnecting hues. Etch dash and each space

repre-sents a I % differetice between the actual and derived

'' A'

't,.' /''t',


, (ep,,.

Fig. 2. Empirically derived reliuiotishiri of MSI (pez'cent cinesis within 2 hours) tu wave frequency and average acceleraLkm im-arted during each half-wave cycPe fui' vertical sinusoidal motion. 368 Aefoipace Mdicnr 4 prit, 1974

1 L t t -. ; .te;









points. As shown, the curved surface fits the actual data in a satisfactory manner. The MSI ohservcd in only one

group (10 g â and .333 Hz f) deviated from the corre-sponding point on the derived surface by more than

6%. Moreover, the root.-mean-square of deviations of the actual data points from the respective derived points was only 3.96%, indicating again that the model closely

fits the data. DISCUSSION

In its present rudimentary stage, the model has limited practical utility. lt ignores the obviously important fac-tors of exposure period and acclimatization to motion.

Our guess is that progressive acclimatization would

syste-nalicatty reduce the overall height of the MSI. surface without changing its basic shape in either the f or ü


In spite of its limitations, the existing model may have

potetitial application for the design of desirable ride

char-acteristics ici future land, sea, and air craft. Our data in-dicate that even moderate accelerations at frequencies near .2 Hz should he avoided as these produce the high-est incidence of motion sickness. Humans can

apparent-ly tolerate higher accelerations at higher frequencies

(e.g., .5-I .0 Hz) Without experiencing the same lendcncy

toward motion sickness. An engineering strategy to

"snIoott! out" a ride should be considered cautiously if high-frequency motion (over .5 Hz) is to he reduced at

the expense of increasing the energy in the lower

frc-qLIcncy hands associated with motion sickness. One

should avoid applying such a strategy when there is a

danger of producing a ride which leads to an

nuiticces-saril\? high MSJ.t*

in historical perspective, the work begun by Wendt

and hi associates was extended in this study. The earlier work has been criticized for providing results of limited generality due to procedural inadeqtuacies ( I 0) , ( I 3).

Cited in Particular were the uc of very short (i.e., 20-nun) exposure periods and artificial wave-foms (i.e.,

the mnoliorus pro\ì(lcd alternating periods of constant ve-hocity----constajit acceici'ation). Nonetheless, with

im-proved ptoccdurcs, we found essentially the same curvi-linear relationship between wave frequency and MSI as

did the early workcr. Dut, by testing to'er frequencies

while holdin,g acceleration constant, our data show the peak of the curve (i.e.. the most pathogenic frequency) to be about 1(1 CPM as opposed to their estimate of 22

CIÌ1 (3). It seems safe to Conclude thai.

wave fcc-quency is a critical factor for determining the response of the physiological mechanism responsible for motion

sick-ness in vertical periodic motion, and that its rnaimum

*Kenned e: uL( Il) have previously offered essentially the same advice. They postulated the existence of i relatively benign frequency range between frequencie.s which produce motion sieL-ness (i.e., < 0.5 Hz) and those which approximate the resonance frequency of the human body (i.e., 4.C)-S.O Hz). In their view, a goat of desiu cngincers should he lo ensure that as much as possible o the total energy imparted to the occupants of vehicles h wihn tite benign frequency range r:ther than within the im-mediately higher or lower bands.



responsivity eern to be in the frequency region around .2 Hz.

The Weslcyan group never tcrnaIicaÌ1y tidicd the

effects of wave acceleration and thus had no opportunity

to observe the striking relationship between average wave accereration and MSI. Regardless of wave

fre-quency, MSI increased with

o. Whcr The MSI was

p1ottd as a functkuj of Jog a for each f level separately, aa appareiuly generat re1ationshp emerged. That

rea-tionship bears an intriguing reseniblance to the

psycho-p.Tiysivat relationship between a bhaviorai


indi-cating the sensation of a ncar-threshold stimulus and the

physical inte]1ity of that stinuus. The psychophysical

rei3tionship is described by the c1asîc phi-)og gamma

function, which lias 1,een frequently obervJ whfle piot-ting the cuniuhitive probahì1iy of correct ds.criminaions

(phi) against the log stimulus izitensty (gamina) (9).

The phã-Iog gamma function is a noriial ogVe which is thought to arise heçmuse the undcr1yng probability

dis-tribution of sensory fliresho1ds is normals both within and

between indivkiva]s, when a mean 01 p and a standard

deviation of o-again, on a log scale of stimulus


By way of analogy, emesis may bc considered as a

be-havioral response indicating that a motion sickness

threshold has been exceeded within an individual. The demonstrated ogival relationship between MSI and log a

could then he viewed as a phi-log gamma function,

imply-ing an underlyimply-ing normal distribution of emesis thresh-ords in the subject population for a given wave frequency and exposure period. The model further implies that the

mean of that distribution is frequency dependent, and that the variance of population. thresholds is constant

with respect to frequency- on a log a scale.

There are several theoretical implications o this reas-oning (or motion sickness in vertical periodic motion. it

implies that the operating characteristics of the

physi-ological mechanism responsible for emesis are similar to those of better-understood sensory processes. Further-more, it implies that the cmcsis threshold in every normal

individual will eventually be exceeded, as log a

in-creases, for any frequency within the motion sickness

region (unless, of course, other pahnlogie effects of high

aceeleratiotis intervene).

in conclusion, a preliminary model has been provided which simultaneously relates MSI to the frequency and

acceleration parameters of vertical periodic motions.

Though limited, the model can be used immediately for evaluating the relative pathogenicity of commonly en-:ountercd combinations of wave frequency and accelera-tion. ¡t may also provide new insight regarding the op-erating characteristics of basic physiological mechanisms

underlying motion sickness. ACKNOWLEDGMENTS

This recrtrch was 5upportctl under Contract No.

N00014-73-C-0040 by the Fleet and Marine Corps Medical Support Divisioi (Director, CAPT i. W. Johnson, MC, IJSN), of the Bureau of Medicine and Sargery, Department of the Navy. Technical moni-tors of tisis research were Dr. Arthur B. Callahan (Program Director), and LCDR Kenneth H. Dickerson, MSC, USN, of the Rioloiçal and Medical Sciences Divktiois of the Office of Naval Research, Department of the Navy. We deeply appreciate the cooperation and assis*ance provided to us by the above BitMed and ONR personnel.

Additionally, we eratefully acknowledge the criticad technical assistance provided by HFR saff members, including W. P, l:)eihler, C. J.). \Vlie. and V. Wrobel. n dala collection und inalbemaucal analysis,


t, Alexander, S. J... M. Coizin, C. J. Flut, Jr., E. A. Ricc'nti, aiid G. R. Wendt. 1945. Wesicyan University snidies of motion sickness: I. The effects of variations of time in-teE-vals between acccicraion.s upon sicknes.s rates. J.

I'ydroI. t9:49-62.

2. Atexnder, S. J., M. Cotuin, C, J. Hill, Jr., E. A. Ricciui, and G. R. Wemlt. I 945. Wesl.eyan University studies of motion sickness: Ii. A second approach to the pi'oblem of the effects of variation of lime. intervals between ac-ceicrations upon sickness rates. J. FschoI, i9:63-6. Alexander, S. J., M. Corzin, C. J. I-Jill, Jr., E. A. licciuti,

and G. lt. Wendt. 1945, \Vcsleyan University studies of motion sickness: Ill. The clfccts of various accelerations upon sìncss ratei. J. P.yc1io!. 20:3-8.

Alexander, S. .1., M. Cotzin, C. J. UHl, Jr.. E A. Ricciuti, and G. R. Wendt. 1945. Weslcyan University studies of motion sicLness: IV. The effects of waves conuilniog two acceleration levels iti,n sickness. J. Pryvhol. 20:9-18. 5. Alexander, S. J.. M. Cotin, J. R. Klee and G. R Vendt.

1947. Studies of motion sicL'nes: XVI. The effects upon sickness rates tsf waves of various frequencies hat identical acceiciation. J. Ext,if. P.n'clrol. 37:440-448.

6_ Bowditcit, N. I 955. A,ncrka, practical ,itn'igatw'. U. S. Navy Hydrographie. Office. Washington, D. C.: U. S. Govern-ment Printitig Office.

7. Bticincr, D. N., and C. ¡'t. t3aher. 1969. A elesciiptina of the Office of Naval Research ls4otíon Generator. Ilwruur Factors Reseorc1, lite.; Tech. Rep. 788-i.

8, Buckner, D. N .,.-md D. D. Heerwagen. 1969. A motion gen-crlor fOs eseraft. Naval Research Re'iew.c 22:1-S. 9. Ouitford, J. t. 1954. Ps)chou'1rfc methods'. New Voit:

McGraw-H ill.

IO. ItanforLi, S. W., T. IL Cone, and S. C. (lover, 1953. A ship's motion and the incidence of seasickuess. 2'/u Military Surgeon 113: l7-167.

il. Kennedy, R. S., W. F. Moroney, R.. P.1. Bale. 11. G. Gregorie. arid D. G. Smith. 1972. Comparative motion sickness symptomatol ogy and performance dccrenicrits occasioned by hurricane penetrations in C-i 21, C-130, ¿tnd P-3 Navy Aircraft. Aerpice Med. 43:1235-1239.

12. Money, K. E. 1970. Motion sickness. Phy.th,l- Rev. 50:1-39. 1). Moralc.s, M. K. 1949. Motion sickneas: Physical considera-tions regarding its etiology. fu: A Survey Repoct on Ib-man Factors in Undersea Warfare. Washin8tun, DC: Nt-tional Resesreb Council, Committee on Undersea Warfare,

pp. 399-414.

14. Siöberg, A. 1970. L.xpeiimentul studies of the eliciting isiech. anism of motion sickness. 1s A. Grayhiel (Ed.) Fourth Symposium On time Role of th Vestibular Organs in Space Esploralion, NASA Rept. No. SP-187. Washington, DC. iS. Tyler. D. 13., anl P. Bard. 1949. Motion sickness. PlvysIoI.


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