The feasibility of pupillometry as an indicator for assessing operator workload during manual tracking was studied. The mean and maximum pupillary responses of 12 subjects performing tracking tasks with three levels of difficulty (bandwidth of the forcing function were 0.15, 0.30 and 0.50 Hz respectively) were analysed. The results showed that pupillary dilation increased significantly as a function of the tracking difficulty which was reflected by the significant increase of tracking error (RMS). The present study supplies additional evidence that pupillary response is a sensitive and reliable index which may serve as an indicator for assessing operator workload in man-machine systems

Beatty, J.

Jiang, Q.

Parasuraman, R.

English

NASA Technical Reports Server

Physiological Assessment of Operator l_brkloadDuring t'anual"tracking:
(I) Pupillary Pesponscs
c_liyanJiang, Raja Parasuraman and Jackson Bentty
x
Uni._rsity of California, Los Angeles
The feasibility of pupillcmetry as an indicator for assessing op-
erator workload during J:nnual tracking was studied. The mean and mnx-
irnrn pupillary responses of 12 subjects performing tracking tasks with
three levels of difficulty (bandwidth of the forcing function were
0.15, 0.30 and 0.50 Hz respectively) were analysed. The results
showed that pupillary dilation increased significantly as a function
of the trackint' difficulty v.hich was reflected by the siffnifica.,t in-
crease of tracking error (li'S). The present study s,pplies additional
evidence that pupillary response is a sensitive and reliab'e index
which may serve as an indicator for assessing operator v._-kload in
man-r_mh ine systems.
INTf_ IISTIC_
The assessment of operator workload in complex rran-rmchine sys=
tc..-_has becnrnerx)reimportant for evaluating and enhancing the over-
all system [_erforrnnnceas systefr_sbecome more advanced and. sophisti-
cate¢1. The traditionalmethods for evahmtinff the workload are sub-
jective evaluation (Cooper, 19_9), rhea.curesof primary and secondary
task performance, and systems or engineering analysis. Results have
shown that neither any single approach nor con_binationof methods can
assess or predicate the v_)rkloadadequately.
Physiological par_neters, however, have manifested themselves as
potential indicators in workload assessment (l_'iem_,ilIeand l_'illip'es,
1'.)78).These indicatorsmay reflect the dynamic chanL,e of the func-
tional status of the operator induced by the task before or ,vithout
performance decrcr_nt (Strasser, I.¢_77).Of the physiological measures
indicating momentary coTnitive workload, pupillometric response ap-
pears to be most sensitive and reliable (gahnernnn, Tursky, Shapiro,
and (;rider,1969). For cognitive processing, _lltiplc neurophysioloff-
ical assesse_nt has been etrphasizedrecently since the hypotheses of
multinle and hierachical resources were pointed out (Wiekens,1980, Bo-
atty, 19R0). K_, seems to he a potential indicator both for general
and specific brain activation if _Itiple channels of _ could be an-
alysed (Rarth and [leatty, 19RI, unpublished report). FTiq studies dur-
i inff mnnual tracking sheerthat the theta v,_avesincrease as a function 0
of trackin_ difficulties (Jianff, Long, lie and Zhao, 1977, unpdblished
report), lastin_ oeriod and performance detract (Rornfeld and r¢ent-
1.-
• " X
1982005792-053
https://ntrs.nasa.gov/search.jsp?R=19820005797 2020-03-21T15:56:22+00:00Z
ty, 1.077). It seems plausible to interpret this phenomenon as due to
either an increase of tracking difficulty or as a result of trying,
best to attain the desired performance as the experiment demands. The
study of psychophysiologiealmechanisn_ of theta waves indieates that
they are related to information processin_ and mental effort
4 (Schaefer, 1977).
\ Task-evoked pupillnry responses have been studied extensively in
coffnitivetasks and practical irrl_lieationsfor operator workload meas-
urement has heen suggested (Bratty, 198_). As a part of the study of
multiple assessment of operator workload, the effect of trackinv,dif-
ficulty on pupillary responses was studied in the present experiment
and the feasibility of pupillometry for assessinR',operator workload
, was discussed.
"l_ve]veuniversity sti_dentsparticipated this experiment as sub-
jects. _e mRnual tracking system consisted of an auditory display, a
fin_er joystick and a controlled element (K/S, simulated by ana'o_
conln,,te r).
Tl_edifficulty of rileta3_ was determined by the bandwidth of the
forcing f,mction. The cutoff freq,lencies_.._reI(_,(0.15 llz),medium (
0.30 l_) and hiffh(0.50 117..)corrcspo_dinrf,to easy, rnediLwn:and hard
trackinp: respectively. The period el *irneof tracking for eauh trial
_ms I0 seconds startin_ with a wnrnin_ signal, the word "ready". One
second after this si_mal, th_ trackin_ forc':n_function (converted to
a single tone) appeared in either of the tvx)earphones. The Ditch of
thc tone was proportional to the voltage of the forcin_ fur.ctionor
the trackin_ error. _le subjcct was asked to control the stick la_cr-
ally al_y from the car in _nich the tone was heard. _lis in turn re-
duced the rnn,olnitudeof the trackin_ error and the perceived pitch of
the tone. Zero error corresponded to 500 117..of the tone. The posi-
tive error _s displayed in the left earphone and the negative in the
right. For each level of difficulty of trackinK, there were 20 trials
of practice in order to attain n steady level of gx:rfo_nce. After
practice the data of pupillary response and trackin_ error (_S) _re
acquired and stored in the computer. Rccause of a proffr_'_nin_mnl-
flmction, th_ I_S trackin_ error data w_s obtained for only 9 of the
I? suhjccts. There were 2n trig.Isof trnckin_ for each level of dif-
ficulty. "_e order of these levels for the subjects to track _s
_ountcrb.nlanced.
Ver'ticalpupillary di_-neter,ms measured by a TV {_pillometcr
Bystern for 10 seconds follm_,in_ the warninF,signal. Z_hetrackin_
error '_re recorded for 9 seconds durin_ traekinF,, l_pillary res-
. ponses were analysed usin_ the prof_,r_rnof this laboratory_ and the
mean and rnnxirmwnamplitude of dilation durinF,traekinF,relative to the
I see. baseline were computed.
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1982005792-054
I_SUL'IS and DISOJF;$ICff
Trael{inff t_rformanee: Traekinff error (I¢_;) inerease(, si_zifi-
eantly with the bandwidth of the forcing fu,lction (F(2,8):17._5,
P¢.005). This result is consistent with other studies inHicatin_ that
the band_vidth of foreinF function ean be used as a faetor to modify
" the trackina', difficulty.
Pupillary responses: As shown in Fig. 1, the mean and maxicn_
amplitude of the pupillarv responses durinff trackinff increased with
trackinff difficulty. These increases _re sig'nifieant (F(2,11)=6.44
P_0.025, for mean dilation; F(2,11)= 6.13, P¢0.025, for r_ximum dila-
tion). The n_an pupillary diTations _ere 0.274 am, 0.33, ° m% and
0.377 rml, and the maximm dilations 0.377 rrm, 0.440 am, and (_.4,q2 rm
for the three levels of difficulty respectively. The peak dilatiot_s
were approximately ccxr_arable to those evoked by short term ._arnory
tasks with 5) 6, and 7 items (PCatt_, 1980), and the pupil dilation
during easiest tracKinff even reached the magnitude evoked by a choice
reaction tir,_ test with 8 alternatives (Bratty and l':affoner, 1980).
The foundation of inter-task comparisons is based on the findinffs that
1' : n)i_.nitude of pupillary responses during corgi!ire processing is
dependent of baseline pupillary diameter over a physiologically rea-
sc_nable ranffe of values (I_radshmv, 1969).
The _rand averaffes nf pupillary responses duing traekin7 over 12
: subjects are plotted in l'iff. 2, whieh shc_s the time. history of the
pupillary responses. It displays a sta_.e of preparation for activa-
tion delete trackinF.; a sta_e of fast dilation of pupil irvraediately
follc_in_ traekinff; a sta_e of maintaining, dilation; and a sta_e of
a little constriction before stopping', tracking. It is obvious that
the effect eft' trackin_ effort on the pupillary response is deminantly
reflected in the r_ximrn difference but also in other stares. For in-
stant,: the eonstrictinff sta_e lasted lonRer in the easy tracking', just
before rest and the incertitude of constriction was greatest in the
hardest traekin_ ease. l',_ether the latter phenoraenon is due to the
individ, ml differences or due to overload of the task for some suh-
-_ jeets as pointed out by Peavler (1974) should be tested by further
s t udy.
'l]_e available reports _uhlished so far on the physiological as-
sessment of _rklo.qd during truckin_ show that even though sor_ physi-
olozicnl indicators are sensitive to si_nificant differences between
rest and tracking, they are unable to discriminate the different lev-
els of tracking difficulty, for instance the heart rate variability
(llyn_f_n and C,reFory, 1975) and event related potentials (Isreal,
II._esney, Wickens, and Don.:hin, 1980). The present resu'.t supplies ad-
ditional evidence that pupillary response is a sensitive and reliable
index for r_asurincr_ntal effort.
_ for the technique of the _upil raeordinF,, lhere is still a lot
to be iraproved in order to be m_ro convenient and less constraining,
for the subject, partieullary for the. "_r_.rators performin_ tasks in a
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1982005792-055
......... ¶
real _orking eondition. OwinF. to the F,reat individual differences in
the size of the eyes and the pupil, the color of the iris, and the
ability to keep the eyes relatively fixated without blinkinp:,, the stlb-
jeets should be selected appropr,ately.
" This study only _nalysed the effect of auditory traekin_ on the
pupillary responses, but the individual studies usin_ visual display
also revealed the tendency of pupillary dilation as the difficulty in-
creased and residual attention los_red (MeFeely, 1972).
One can conclude that pupillar.,, responses can diseriminate opera-
tor effort durinF, tracking and can _ cr_npared with those evoked by
other tasks. Furthermore, the innovation for the recording system is
possible, hence, pupillometry rnny serve as a promisint indicator to
assess the operator workload in mnn-mnehine systems, particularly with
additional indicators such as _ or others which can reflect the ac-
tivities of specific resources of eol_nitive prooessinp:,.
J_catty, J. A pupillornetrio index of overator _x)rkload. Technical }_e-
1,0rt No.23. UL_JL.,1980.
Boatty, J., l,_ngoner, B. L. Pupillomotrie siffns of brain activation
wry with level of eolTnitive proee_sin_. Seience, 1978, 199,
1216-1218.
l_eatty, J., and l;_,ooner, B. L. Effects of response selection and
task evoked pupillary dilations: Inplieations for a motor theory of
attention. Presented at Western Psyeholoff.ical Association, Ilm;,aii,
1980.
l_radshaw, J. l,. Raek,-round li£ht intensity and the pupillary res-
ponse in a reaction time task. Psvehonomie Science, 1969, 14,
271-277.
('ool_r, G. E. and llarpor, R. P., Jr. The use of pilot ratin_ in
the evaluation of _ireraft handlin_ totalities. Technical Report HA,CA
_-D-5153, 1969.
Isreal, J. P., Chesney, G. I,., Wiekens, C. f;., and l)onehin, E.
PJ00 and trackinp:, diffieulty,. Evidence for n_=ltiple resourees in
dual-task perfonnnnee. PsyehophysioloET, 1980, 17, 250-273,
llyndr_m, FI.W and (_reR'.ory, T. R. Speetral hnalysis of sin,;_ arrythnia
durinR', mental loadinp;. Er_onornies, 1975, 13, 255-270.
, Vnhnervn, IL, Tursky, ft., Shapiro,D and Crider, A. Pupillary, lleart
rate and skin resistance chanties dt,rinp:, a mental task. Journal of F.x-
I_rimenta_ Psye|,oloqy, 19f_9, 79, 164-167.
Kornfeld, C. an(] Beatty, J. 1,3_, st_etra durint a lonff tern ecrrpensa-
m
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1982005792-056
tory tracking, task. Bulletin of the Psyehonomic Society, 1977, 10, :
46-48.
HcFeely,T.E. r_lpil diameter and the cross-adaptive critical tracking
task; A method of workload r_asurer_nt. AD 749075, 1972.
" Peavler_ w.s. _Jpil size, information overload, and performance
difference. Fsychophysilo.,c_y, 1974, 11, 559-56G.
Schaefer, D. L. F_L" theta waves and psycholoF, ical phenomena: a re-
view and analysis. Biological Psycbolo_c_y., 1977, 5, 47-88.
Strasser, If. Physiological treasures of workload - correlations
between physiological parvr_eters and operational pcrforr_ence, In
I(.]LKlein (F_.), _thods to assess workload. M'_CD Cnferenee Print,
l',_o. 216,1977.
Ix'ickens, C. 1). The struett_re of proeessinp: resoureces. In R.
Nickcrson and R. Pew (Fx3s.). Attention and Performance VIII. New
York: Erlbaum, 198P.
Wierwille, I'l. _'.'. and Willi_es, R. C. Survey and anaTysis of opera-
tor _rkload assesment techniques. Technical :'_port S-78-101.
System.tries Inc. BlacksburF., Va. 1978.
1982005792-057
O,,.lJ 1,50
+++[ +
i °''| _"'-%:':I" '°°°
_ 0.3
,+, I,,,,.,,°,,,,+,,,.,,,+-.----+ +2
• i l I . . ,I . o
LOW MEDIUM HIGH
Fig. 1 Mean and maximum pvpillary dilations and RI_S trackir,g error (arbitrary
units) for three levels of forcing function bandwidth (low, medium and high).
High0.6
_ Medium------ Low
0.4
¢
Q 1 s s 4 5 e T 8 O
8e_ouds
Fig. 2. Grand average of pupillary responses across 12 subjects
for three levels of forcing function bandwidth (low, medium,
and high).
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1982005792-058


Physiological assessment of operator workload during manual tracking. 1: Pupillary responses

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