Postural
Stability
and Stereo-Ambiguity
Visual Environments
in Man-Designed
David J. Lasley
Russell D. Hamer
Robert Dister
Theodore E. Cohn
School of Optometry
Umversltyof California at Berkeley
Berkeley, CA94720
Reprmted from
IEE Transactaons
on Biomedical Engmeenng
1991, Vol. 38, No. 8, pp. 808-813
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IEEE TRANSACTIONS
ON BIOMEDICALENGINEERING,VOL 38, NO 8 AUGUST1991
808
Postural Stability and Stereo-Ambiguity
in
Man-DesignedVisual Environments
David J Lasley,
Russell
D Hamer, Robert Dlster,
AbstractS---Our modernrectihnear visual environment contains visual stimuli for whichevolution has not had time to optimally shape visual processing. One such stimulus, periodic
stripes, is knownto lead to visual depth ambiguity.In this paper we showthat postural instabihty, as measuredby the variance of fore and aft sway,is increased by viewingsuch stimuli.
This instabdity maybe the precursor of falls. Designers must
evaluate the visual ~mpresslonsconveyedby their systems in
order to avoid postural instability due to visual amblgmty.
and Theodore E Cohn, Semor Member, IEEE
sense of sight [2]. As with other humanskills, the standard of perfect posture is rarely, if ever, achieved The
residual minimumlevel of random activity is called postural sway [3], [4] Under some circumstances postural
sway can be increased to the point where we ’qose our
balance" and fall [5], [6~
Role of Vision m Postural Stab:ltty
I
INTRODUCTION
W~gu
laave been investigating effects of stereoambious visual stlmuh, and m particular, of the stimulus provided by an escalator tread In a prior paper [1]
we showed that such stimuli cause subjective disorientation and vve hypothesized that the cause lay m the "wallpaper illusion " Weoffered the conjecture that such disorientation is a manifestation of a chain of events that can,
albeit rarely, culminate m a fall Briefly, the stereoamblguousstimulus gives rise to false fusion, a stable
but inappropriate angle of visual convergence This leads
both to disorientation and to postural instability, the latter
possibly leading to a fall The main focus in this paper is
measurements of postural stability in the presence of a
stereoamblguous stimulus Weshow here, for the first
time, the existence of several elements of the theoretical
chain of events a) inappropriate binocular convergence
consistenl with false fusion and the wallpaper illusion, b)
heightened postural instability,
and c) correlation between subjective disorientation and postural instability
Background
Many take for granted that humans can stand upright
on two legs with "correct posture " But the orientation
of the humanbody with respect to gravity is an active skill
mvolwngyears of learning and coordination of dozens of
muscles, of our vestibular nervous system, and of our
Manuscnl~t received July 11, 1989, revised June 28, 1990 This work
was supported mpart by grants from the Institute for Transportation Studles and the Umverslty of CahformaTransportation Center, U C Berkeley,
the National Eye Institute (EY 02830, EY 07083, and EY 07606) to TEC,
and by a Core Center Grant (EY 03176) from the National Eye Institute
J M Enoch
The autho’s are w~th the School of Optometry, Umverslty of Cahforma
at Berkeley, Berkeley, CA94720
IEEE Log Number 9101192
Lee and Llshman [6] (and others [7], [8]) have demonstrated that posture can be manipulated in the laboratory by controlling the visual stimuli They created a
moveable room which could be viewed from a stationary
platform The observer was not informed that the room
was suspended from above and could be controlled to
swing or oscillate left-right with respect to his frame of
reference, with chosen amplitudes and frequencies Despite the constancy of the gravitational cues, the observer’s postural center of gravity was observed to vary with
the same frequency as the swinging room As the amplitude of the sway of the swing was increased, the amplitude of the observer’s postural sway increased to the level
that subjects occasionally lost their balance Clearly visual cues are afforded great importance in the maintenance of posture, and may even supercede the sensing of
gravity [7]
Normally, as we move about the world, we need not
worry about swinging rooms or other artificial
mamputatlons of the visual environment However, as visual patterns in our environment have become increasingly rectilinear (lines and edges), we have been confronted with
visual stlmuh that increase the demandsupon our capacity
for interpretation The central question asked here is can
an interaction of the visual system with certain visual patterns modify our postural stabihty9
Visual Patterns and Stereo-Ambzgutty
Visual space can be thought to have three dimensions
up-down, left-right, and fore-aft It is in the latter dimension, mediated in part by the perception of depth
(stereopsis),
where ambiguities can potentially cause
changes in postural stability
In some cases, stereo-amblgulty arises with w~ual
st~muh occurring in commoneveryday situations
One
example of this is the "wallpaper" illusion The "wallpaper" dluslon was first described by Meyer [9] about a
I,.hsLEYet al
MAN-DESIGNEDVISUAL ENVIRONMENTS
809
b
d
L F-LdLj b,, j i
Fig 1 Schematic representanon of eye mlsahgnment while viewing a periodic target If the observer fixates point b with both eyes, the angle between them ~s appropriate to the distance of the object from the observer
If the observer fuses adjacent similar features, such as the cleat comers
shownat b and b’, the eyes adopt the wrong angle of convergence for the
distance of the object This state ~s termed "false fusion "’ In this case,
dlsparmesof points on the object lead to a sensation that it Is closer Inset
binocular eyemovementsof an observer wewmg
a striped pattern The difference of the two eye posmonsignal,, estimates the binocular convergence
of the subject The right-most deflection (b) shows a 4 s period during
which the observer fixates a small fixation target at 2 m Prmr and followmgdeflections (a) occurred whenthe fixation was removedto 1 m m front
of the target plane and then entirely withdrawnThe subject could only see
a large striped pattern during this tm~eHis subjective report was of a wallpaper-hke illusion The stable difference signal indicates in mapprppnate
angIe of convergence for the distance of the target
century and a half ago It occurs whena person with normalbinocular vision viewsa pattern that is periodic in the
horizontal mendianof the wsual field. Whenviewing such
a pattern, the two eyes mayadopt an angle of convergence
that is Inappropriateto the actual distance of the object,
but which, becauseof the penodm~ty
of the object, allows
fusion to take place If this occurs, the object mayappear
to be substantially closer to (or farther from) the viewer
than It really is, binocular and monoculardepth cues are
not m accord, and disorientation is commonly
reported
This IS illustrated by the diagramin Fig 1 If the two
eyes fixate a commonpoint b, then the images to both
eyes will be fused in the brain into single unitary perceptual ’hmage" Under these conditions a normal percept
should result becausethe angle of convergenceof the two
eyes IS appropriateto the distance of the object. If, on the
other hand, the left eye fixates b and the right eye fixates
b’, there Is fusmnwith an inappropriate angle of convergence This is termed "false fusion" [10] The falsely
fused object appears to he in a plane passingthroughpoint
[I0] which is closer to the eyes m this exampleThis
latter perception competesw~th and sometimesdominates
other visual cues to the actual distance of the object
Whenthere is a conflict in sensory reformation available from the different sensory modalmes,disorientation
can result It seemedto us likely that such disonentatlon
maybe related to postural instabd~ty[1], [2], but so far a
direct link has not beenestablished
Escalator as an AmbtguousStereo Sttmulus
False fusion engenderedby wallpaper is not likely to
be hazardous to the viewer However, escalator tread
plates also havethe repeating periodic pattern intnnsIc to
the "wallpaper" Illusion Theescalator IS of considerable
importancein this context since, unlike wallpaper, near
which fails are relatively uncommon,
It IS an altitudetranslating device encounteredby most urban pedestrians,
whichis the site of thousandsof debilitating falls annually
[1]
Thevisual stimuli available to an escaIator rider consist
centrally of the movingsurface, called the treads These
are flanked by featureless, reflective, buff-polishedstainless steel skirts Thetread surface consists of alternating
cleats and grooves about 1 5 and 5 mmwide, respectively The cleats are usually highly polished while the
grooves are painted black, giving the tread a luminance
profile that IS periodic [12] For an observer of average
height viewingthe tread, this repeating pattern has a spatlal frequencyof about 6 cycles per degree of visual angle This spatial frequencyis very close to the peakspatial
frequency of the contrast sensmvlty functmn of the humanvisual system[11], [12] Thecontrast of the tread is
measured[12] to be about 0 995, whichis higher than that
of most other visual patterns in the visual environment,
which typically measure far less than 0 90 Hence, the
tread presents a highly visible visual pattern to the viewer
810
IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL 38,
The purpose of the present study is to estabhsh some
additional links amongthe various sensory and motorsystem behaviors discussed above First It was necessary to
estabhshthat the stereo-ambiguityof repeating v~sualpatterns eau,~es obser~ableinappropriate convergence,as described above, for thls has not heretofore been shown
Second, we sought to establish whether the postural system is affected by visual stimuli that cause both mappropnate cortvergenceand the associated "false fusion" both
In the laboratory and mthe field Finally, welooked for
evidencelinking postural effects to the &sonentatlonpreVlOuslyshownto occur with false fusion [1]
II METHODS
A Eye Position Measurements of an Observer Vlewmg
Stimuh wtth Stereo-Ambtgutty
Wefirst sought to estabhsh objective evidence of mappropriate convergence during periods of erroneous
depth perception, for without such evidence the theory
linking stereoambaguousstamuh to fails would have no
basis. Binocular eye movementsof an observer vlewlng a
vertically striped pattern were measuredwith a Stanford
Research Instltute (Model IV) Eyetracker The Eyetracker monitors the position of reflected (Purkmje) images frora the optical surfaces of the eye (cornea and the
lens, froat and back surfaces) formed from an infrared
hght source [13] The image positions, which are converted into voltage signals, indicate the rotational angle
of the two eyes The difference of these Is formedto give
a signal proportional to the angle of binocular convergence of the subject The voltage signals were sampledat
a rate of 500 Hz(12 bit precision) and displayed on
chart recorder
The subject was posltaoned m the Eyetracker by clampmgthe rrtouth arounda bite bar fitted with dental impres°sion compound.The target was a vertically striped 50
wide by 30° high black-on-white pattern, and was viewed
at 2 m &stance Each period of the striped pattern subtended 0 25° The luminance of the background was 10
cd/m2 and the contrast of the striped pattern was about
9O%.
The observer was instructed to fixate the end of a
pointer, held alternately m the plane of the target or up to
1 m m front of it In this waythe subject was encouraged
to alternately fixate the target plane or m front of at. He
was asked to indicate whenhe experienced false fusion
Exampleeye movementrecordings are shownm the inset
of Fig 1, whichshowsa voltage amplituderecording corresponding to difference of the two eyes’ positions as
function of time The epochs labeled a occur when the
subject was asked to fixate the pointer held briefly 1 m m
front of the target plane after whichthe target was m~mediately removedDunngb the two eyes accurately fixate the target Theentire samplelasts about eight seconds.
Calibration of the voltage signal confirmedthat the subject wastixatlng almost 1 m m front of the true objective
plane tha~ containedthe striped pattern In addition, verbal report m&catedthat false fusion, and the wallpaper
dluslon, occurred dunngthat period Fromth~s it maybe
NO 8,
AUGUST 199I
referred that inappropriate convergenceof the eyes can be
elicited from such repeating patterns, and the resulting
sensory fusion Is supportable by such repeating patterns
B Posturographlc Measurements
1) SubJects Nine subjects were selected from the
University student population and ranged m age 20-30
years for the laboratory test Three ad&tionalstudent subjects were utilized m the field test All subjects had normal visual acuity and stereoaculty
2) Visual Stzmuh for the Laboratory Study The visual
stlmuhwere back-projectedupona translucent glass plate
that subtended 40° × 60° using a KodakCarousel projector Lenses (subject’s correction plus 2 5D) and pnsms
were placed before the eyes in a trial frame so that the
subjects’ eyes were at physiological rest (unconverged~nd
unaccommodated,
the visual state whenviewing a target
at optical mfimty)The experimental pattern consisted of
a high contrast set of vertical stripes of 1 23 cycles per
deg, a pattern knownto ehclt the wallpaper lllus~on because of its peno&cnature Thecontrol pattern wasldentlcal to the experimentalpattern, except for the ad&tlon
of five superimposedblack letter patterns whosepresence
was intended to prevent false fusion. In viewingthe control pattern, mlsahgnmentof the superimposedletters in
the two eyes would have given rise to &plopia [14], or
double images, whlch would be rea&ly perceivable by
normal subjects Each letter was approximately 170
square The stimuli were viewedin a darkened room, and
viewing &stance was 40 cm
3) Vtsual Sttmuh for the Field Test. Weused two otherwise Identical escalators ownedand maintained by the
Bay Area Rapid Transit District (BART).The treads
one of these had beenpainted as follows"first, white paint
was used to lower the cleat-groove contrast Next, a black
pattern consisting of nonpeno&celements including the
BART
logo at the center, was applied. Dunngour tests,
both escalators were unoccupiedand stationary, and were
viewed whale standing on the sway transducer posmoned
on the bottom platform
4) Postural Sway Measurement"The postural sway of
each subject was transduced as follows a 40 x 40 cm
steel platform was supported by two orthogonal cantilevered steel torsion bars. Strain gaugesmountedon these
measuredthe deformationsof the torsion bars as the subjects’ center of gravity changed position Signals were
amplified and displayed on a Tektronix 564BoscdIoscope
equippedwith a bridge amphfier, and then were digitized
(12 bit precision) and staustlcal calculations were performed The samphngrate was 50 Hz
5) Procedures. Subjects were posmoned upon the
swayplatform and were instructed to stand upright and to
attempt to remainmotionless. Subjects were instructed to
look at the center of the stimuluspattern, In order to minimize edge cues Nine 1 mmtrials were run on each sub"
ject with striped and control patterns alternated.
Weanalyzed the spectra of measuredsignals with botla
test and control patterns in two of the subjects Fig 2
showsexamplesof such spectra obtained using chart sam"
~sLEY
et
al
MAN-DESIGNED
VISUAL
811
ENVIRONMENTS
OF FORE-AFT
SPECTRA
SUBJECT:
;
l
1
AH
r I i I I~
--
SWAY
I
i
;
p , , , t[
UNPAINTED
PAINTED
MASK
£e8o
18
i
i
i
i
i
i i
8 8~
~[
I1,£
FREQUENCY
ii
i ~ i ! i
i i
1
[Hz’t
Fig2 Spectra
of foreandaft swaySpectra
wereestlmated
fromsamples
obtained
dt,nngthefield
testThese
samples
gathered
at I s intervals
Or=
dmate is the amplitudecoefficient Abscissa is the frequency specified hertz
There Is a great deal of vanabdity from sample to sample These examples
are typical of several other samples examined Generally, the spectrum
peaks at lowest frequencies and stimulus effects are to increase power This
provides a rationale for using postural variance to quantify stimulus effects
pies entered into a stat~stlcal data analysis package (Statgraphics Ver 2 6, Statistical Graphlcs Co ) The postural
~Ignal exhtblts most power at frequencies below 0 1 Hz
Th~s Is consistent with eaflter results of Scott and Dzendolet [15] The only conslstent difference between signals
measured durmg the two v~ewmgconditions is that power
increases m the test condmon(unpainted escalator)
Hence, following Dornan et al [7], we chose to est,mate the mean squared dewat~on from the mean posmon
of the center of gravity as the dependent measurementof
postural sway Th~s statistic is ch~-square dmtnbuted, but
was appro~amatedby the Gausslan distribution, for statistical testing, since the numberof samples was large
C Measuzement ofSubjecttve
Dtsonentanon
This study was conducted m the field ~Subjects were 21
normally s~ghted students Test and control escalators (see
Section II-B 2) above) were each observed for a 30 s period with order randomized After viewing was complete
subjects were asked to retrospectlvelj~ Identify which of
the two escalators was "more d~sorientmg" and whether
such a judgment was easy or not ri
III
RESULTS
Postural Stabzhty
The results of the laboratory posturographlc measurements are summarized in Table I where they are expressed
as the variance of the voltage s~gnal Our interest was m
the effect of the v~sual stimulus on the variance of posture
towards and away from the target The table shows that
the striped pattern, without the superimposed control targets, increases the variance of the fore-aft sway, which
is predicted by our hypothes~s of stereo-amb~gmty S~x of
nine subjects showed individual effects in the predicted
d~rect~on, although the effects were generally less than a
factor of two The pooled results from all subjects show
a statmtxcally s~gmficant increase m postural instability
when wewmgthe test (stnpes only) pattern Th~s constitutes the first demonstration that a static wsual stimulus
can engender increased sway
Table II shows the results of an experiment which relates stereo-amb~gmtyto a nonlaboratory stimulus, the escalator SubJects wewedstationary escalator treads, w~th
the typical 6 cycle/deg v~ewlng surface, m the field One
812
IEEE TRANSACTIONS
ON BIOMEDICAL
ENGINEERING,
VOL38, NO
TABLE I
POSTUROGRAPHY
ME~,SUREMENTS
OF CHANGES
IN THEOBSFRVER’S
CENTER
OF GRAVITYWHILEVIEWINGE~PER|MENTAL
ANDCONTROL
PATTERN
POSTURE
VARIABILITY
EXPRESSED
AS MFAN
SQUARED
DEVIATION
FROMTHF
MEA~(VARIANCE)
Sub.lett
D F
L X
J ~
L B
D O
R K
J L
J W
A H
Pattern Experimental
(Vertical Stripes)
Control
(Vertical Stripes
with Letters)
983
1619
1403
708
1596
1439
1308
4114
1548
1455
1848
889
799
83I
1385
603
1468
973
8, AUGUST1991
parison "easy" to make, 15 judged the painted step to be
less d~sonentlngTheseare statistically significant results
(p < 0 003 and p < 0 001, respectively, binomial test)
which show that masking the ambiguousfeatures of the
tread pattern, while not materially reducing~ts v~stbfllty,
reduces the disorientation reported by subjects Subjec.
tlve dlsorientatmn and postural stablhty are thus linked,
and we suggest that the link ~s due to a common
depen.
dence uponthe existence of stereo-amblgmtym the v~sual
stimulus
IV
DIscussION
Lee and Llshman[6] have shownthat the external modification of the wsualimpressionof the worldin a left-tonght direction can cause a compensatoryleft-right sway
1413
1137
Pooled Variances
in the posture It has also been shownthat closing one’s
(1384, 1445)
(1114, 1 I63)
3 Sigma Confidence
N = 18000
N = 18000
Intervals
eyes increases the amphtudeof postural sway [6], [7]
whichattests to the importanceof y~slon in maintaining
upright stable posture Our research extends these findTABLE II
POSTUROGRAPHY
FOR THREESUBJECTSVIE~ENGTREATED
ANDUNTREATED Ings by showingthat a fore-aft modification of postural
variance can be caused by an appropriate mampulatlonof
ESCALATOR
the stereo-depth cues m visual space
Unpainted (Normal)
Painted (Treated)
Plainly, there are complexinteractions amongstthe v~sual
sensory system and two related motorsystems, those
Pooled Variance (scaled)
1 21
0 65
3 S)gma Confidence
(1 07, 1 35)
(0 59 0 71)
of binocular convergence and postural control Fig 3
Intervals
N = 1002
N = 687
summarizes
relations amongstthese entities as they relate
to the narrow problemaddressed here Visual stlmulatlon
set of treads wasstandard appearance,while the other had impinges on two eyes Responses lead to the generation
been treated with a superimposed painted pattern de- of binocular convergence control signals Mamfestatlons
sxgned to minimize the stereo-ambiguity. Examplespec- of these signals are measurableas the angle of convertra for these two viewing conditlons are shownm Fig 2 gence (A), which can be erroneous for stereoamblguous
described above The results of the field test showthat stimuli, and, if so, whichdefine the state termed "false
less swayvariance w~smeasured,by about a factor of two fusion " Whenfalse fusion occurs, the central apparatus
for the pooleddata, for the painted escalator, e g , when for computingdepth is faced with d~scordantinput, w~th
monocularcues and binocular cues at odds as to the actaal
the visual target’s tendencyto lead to the wallpaperlllustun wasminimizedTh~sresult Is also statistically slg- distance to the stimulus Theselead to two responses, both
measurable,first, subjective disorientation occurs, and
mficant.
second postural instability increases Wespeculate that
increased mstablhty maybe the precursor of falls
Subjecnw, Judgements
Our assessment of subjective reports of dlsonentatlon
Anearly finding in this series of investigations showed
and ~ts relationship to stereo-ambiguityruns counter to the
that d~sonentatlon experienced by escalator riders could usual reasons advancedto explain disorientation and falls
be attributed to stereo-amblgmty [1] Wesought m this
on escalators Height has been suggested as a cause and
study to determine whether the extent of disorientation
so has escalator motmnOur subjective test prowdes¢.vlreported by observers could be related to the amountof
dencethat it is the striped pattern of the treads per so, and
stereo-amblgmty presented by escalator treads Weasked neither escalator movement
(It was stationary) nor view21 unawaresubjects to viewthe first step of two different
mgfrom a height 0t was viewed from the bottom platstationary escalators from the bottomplatform The steps
form) causes the disorientation reported by our subjects
of one escalator were painted wl~ha high contrast pattem
Theproblemof periodicity In wsual targets is not re(described above) that was intended to prevent the wallstricted to escalators Stairs, steps, carpets, and tile-floorpaper illu.,;lon Theother escalator was untreated and was
mgcan create the same type of visual amblgmtyVisually
thus typical m appearance,althoughit did exhibit the usual
ambiguouspatterns should be avoided in designs for any
scratches, mars and foreign substance spots After viewmgthe steps of the treated and untreated escalator, the walkingsurface In the case of the escalator thls is of partlcular ~mportancesince the surface ~s moving,whichmay
subjects were asked to judge whetherthe treated escalator tend to aggravatethe effects of postural lnstablhty
step was more or less "d~sonentmg"than the untreated
escalator step For this subjective judgementof treated
ACKNOWLEDGMENT
and untreated escalators, 17 out of the 21 subjects judged
the painted escalator step to be less disorienting than the
Wethank R Weule and BARTfor cooperation and for
~anpamtedstep Of the 17 subjects whoreported the corn- underwriting the escalator masking Weare indebted to
LASLI’het al
MAN [)bSIGNED VISUAL ENVIRONMENTS
813
Postura[
Irrr°r
L
rIc°n’r°____L
~-
I
v,~o!
~tlmums
Monoc~lor I
J
__
I
tra
]"~f~’J Depth -’’1 to"3
-I~..Ansducer
~ L~ .
-’’~
,~
IB,noculor
k...)’ ILeft
transducer
~ L~
~("~t-~
eye
~"
~
Motor [ [’--’ I
l
BinocularConvergence
Stgno~
(Folse Fus=bh
or Appropnote
Fusion)
Fig 3
liypotheslzed relationships between binocular convergence signal,
false fusion, &sonentat~on, and postural mstabd~ty
R Jones of Sm~th-KettlewellInstitute for Visual Sciences
for the loan of posturographlc momtormg
apparatus We
thank Hercules ComputerTechnology, Inc , 2550 Ninth ,
St Berkeley, CA94710 and Data AcqmsmonSystems,
Inc 349 Congress St, Boston, MA02210, for donanons
of eqmpment
REFERENCES
[lJ T E Cohn and D Lasley, "Wallpaper tlluslon cause of &sonentat~on and fails on escalators," Percepnon, 1991
[2] I P Howard, Human Vtsual Onentanon New York Wiley, 1982
[3] L I Wolfson, R Whipple, P Amerman, J Kaplan, and A Kleinberg, "Gait and balance in the elderly," Chn Gertat Med, vol 1,
pp 694-654, 1985
[4] F J Imms and O G Edholm, "Studies of gait of old people who
fall," Rehabtl Med, vo! 2, pp 177-180, 1980
[5] P W OverstalI,
A N Exton-Smxth, F J Imms, and A C Johnson,
"Falls in the elderIy related to postural ~mbalance," Bnt MedJ,
vol 1, pp 261-264, 1977
[61 D N Lee and J R LJshman, "Visual propnoceptlve control of
stance/’ J HumanMovement Studies, vol 1, pp 87-95, I975
[7] J Dorn~n, M B Geoff, R Ferme, and P J Halhday, "Visual input
its ~mportance m the control of postural sv, ay," Arch Phys Med
Rehabtl , vol 59, pp 586-591, 1978
[8] D Shunmnand K D White, "’Dual roles of visual feedback on postural stabdlty," m Trends tn Ergonomtcs/HumanFactors V The
Netherlands North-Holland. 1988
[9] H Meyer, Archtvfurphyslologtsche
Hetlkunds 1841
[10] W H Ittleson,
V1sualSpace Percepnon New York Springer 1960
[II] F W Campbell and D G Green, "Optical and retinal factors affecting ~lsual resolutlon," J Phystol, vol 181, pp 576-593, I985
[12] T E Cohn, "Specifying the appearance of escalator treads Howto
mlmmlzethe &sonentatmn effect,’ m Revtew and Evaluatton of Appearance Methods and Techmques ASTMSTP 914, J J Renmlson
and W N Hale, Eds
Phlladelphm, PA Amer Soc Testing Mater, 1986, pp 69-77
eye113] H D Crane and C M SteeIe, "Accurate three-dtmensmnal
tracker," Appl Opt, vol 17, pp 691-705, 1978
I14] Bunan-VanNoorden’s Binocular Vtston and Ocular Motthty, 2nd ed
St Loul,, Mosby, 1980
[15] D E Scott and E Dzendolet, "Quantlficatmn of sway m standing
humans," Agressologte, vol 3 B, pp 35-40, 1972
David J Lasley was born m Lafayette, IN, m
1948 He graduated from the Umverslty of Cabforum from the College of Letters and Science in
1972 He recewed the Ph D m physiological opttcs from the Umverslty ofCahfornm m 1977, and
the MS degree in statlst~cs from CahfornmState
/:
Um~erslty m 1987
(~
lie became a postdoctoral fellow at the Umver¢;~
~’ ° s,t3, of Mtaml School of Me&cme
in 1978 Since
1983 he has been a Research Psychologtst at the
School of Optometry
Dr Lasley has held memberships in the Opttcal Society of America,
Sigma X1, Assocmtmn for Research m Vmlon and Ophthalmology, American Assocmt~onfor the Advancementof Science, and Ph~ Beta Kappa
Russell I-Iamer was born in NewYork C~t3,, N~, m 1946 He recewed the
bachelor’s degree m biology from the C~ty Umvers~ty of New York
(CUNY),NewYork C~ty, m 1971 and the PH D degree m sensory science
from Syracuse Umvers~ty, m 1979 H~s &ssertanon revolved a study of
v~brotactde masking between sensory channels
He was a postdoctoral researcher at the Umvers~tyof Washington from
1979 untd 1982 studying infant vtsual development He was a Postgraduate
Researcher at UCBerkeley from 1982 to 1985 and then movedto h~s present posmonof Research Assoctate at the Smith KettelweIl Eye Research
Institute where he ~s conductmgbehavioral stu&es of infant and adult v~slon
Dr Hamer is a member of the Assocmnon for Research m Vtsmn and
Ophthalmolog3, and the Opncal Society of America
Robert D~ster was born m Cleveland, OH, m
1953 He graduated in 1980 from Bdalt Law
School, Berkeley. CA. w~th a doctorate m jurisprudence He recewed a Doctor of Optometry degree in 1987 from the Untvers~ty of Cahformaat
BerkeIey
He currently ~s on the chmcal faculty of the
School of Optometry at the Umversxty of Cahforma, Berkeley, and has private practice m Alameda, CA
Dr D~ster ~s a memberof the Cahfomta State
Bar
Theodore E. Cohn (S’63-S’67-M’69-SM’80) recewed the S B degree
electrical engmeenngfrom the Massachusetts Institute of Technology.
Cambridge, m 1963, the M S and M A degrees m b~oengmeermg and
mathematics in 1965 and I966, respectwely, and the Ph D degree m
b~oengmeermgm I969, all from the Umvers~ty of M~chtgan, Ann Arbor
He was first appointed at the Umvers~tyof Cahfornm,Berkeley, in 1970
He ~s now Professor of Physmlog~cal Optics lie was a V~smngFellow at
the John Curtln School for Medical ~.esearch, Austrahan N-~nonal Umvers~ty m 1977 and Visiting Scholar at Umvers~tyof Cahfomm,San Dtego In
1989-1990 He has served as Faculty Assistant to the V~ce Chancellor for
Research at UCBerkeley H~s research interests mainly concern physmIogtcal and psychophys~calstudtes of the hm~tsof v~sual sens~twtty
Dr Cohn ~s a member of EMBS,the Assocmnonfor Research m Vtston
and Ophthalmology, AAAS,S~gma X~, and the Neurosc~ence Soetety He
~s also a memberof the Optical Soctety of America mwhich has has served
as Chair of the Techmcal Group m V~s~on