Motion Sickness incidence as a
Function of the Frequency and
AcceP-ercition of Vertica Shiusoidal Motion
Deift University of Technology
Ship Hydromechanics Laboratory
Library
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
THE
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 repetitivelinear 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
JMEs F. O'HANt.ON and MICIIAEI. E. MCCAULEY
.Hwnw, Factors Rcsearch, incorporwed. Goleta, California
93017
MATERIAlS AND METhODS
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
ead
S via
separate earphone/microphone systemsmnnunted 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
systems.
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,,).
TAI3LIt L EXI'LRIMENTAL DESiGN WITH FUll-WAVE
DISPLACEMENT IN ME t-.RS (li)?) AN!) NUMBER 0F
SUTUECTS (ItOrroM) FOR EACH CONDITION.
Frequency (CPM) (iÍz) s tO .167 20 .333 30 .00
TAULE IL MSI VAUJES (PERCENT EMESIS) RECORDED tN EACH MOTION CONDITION.
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
N20
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 MSIr
loo -.1 irij2ir dxwhere 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
f
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','j,,
, (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;
/
/
,'t
/
/
/
/
X
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
di-niensions.
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 motionsick-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.
MOTION SJCKNESS-.cYHANLON & MCCAULEY
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
repons
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
in-tensity.
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,
g EIERENCTS
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