18th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Amsterdam 1996
6.3.1: Physiological Modelling - Visual System

PARAMETRIC ANALYSIS OF SACCADIC EYE MOVEMENT
DEPENDING ON VIGILANCE STATES
Akinori Uenot

Yoshihisa Otat

Moriichiro TakasettHaruyuki Minaniit anit

iInstitute of Biomedical Engineering, Faculty of Science and 'Technology, Keio University,Hiyoshi 3-14-1, Kohoku-ku, Yokohama, Kanagawa 223, Japan'+School of Medicine, Keio University Shinanorriachi 35, Shinjuku-ku, Tokyo 160, Japane-mail address : ueno@bmel.elec.keio.ac.jp
Abstract The piirpose of this study was t,o investigate
tlie relationship between characteristics of saccadic eye
oiovement and Vigilance st,ates. We surveyed this by com-paring the wave-form parameter of saccadic velocity toEEG parameter obhined from spectral power of a and/j wave bands or to subjective vigilance states and sleepiness. Our resiilt,s showed that the shapes of saccadic velocit,y changed into blunt. according to a decline in thevigilance statm and also to a increase in sleepiness. This
indicates the possibility for estiniatiori of vigilance statesby using charact,erist,icsof saccadic eye movement.

Fig. 1 P r o t o c o l of s h o r t - t e r m experiment

0:Oo 005

I. INTRODUCTION

0:15020

0 30

Fig. 2 Protocol of long-term experiment

For assessing vigilance states it is common to use bioelectrical signal such as EEG or some kind of subjective
rating scales. Howevcr. most of these methods have shown
disadvantage so far as requiring attachment of electrodeson the body surface for signal detecting or interruption oft>heoperation to est,irnate self-perccivcd fceling states. So
it is iiuportant, t,o propose a new effective method for estiniat,ion of vigilance states without any attachment andany interruption of operation. Therefore we studied on relat,ionship between vigilance states and characteristics ofsaccadic eye movement (saccade) to examine a possibility
for estiriiat,ion of vigilance states by using characteristics
of saccade.

Fig.1. All sessions were conducted for 31nin. and movements of the dominant. eye and EEG (Fz) were detected in
JTS and NTS. In JTS, one visual target, appeared a t oneof six possible locations of 2.5, 5.0. or 7.5deg on the rightor left side from the center, then jumped horizoritally to
one of three possible locations in the other side a t 2sec
interval. The target jumped repeatedly until the end of
the session and the subject,s followed this continuously. InNTS, the subject.s moved their dominant eye repeatedly
to locations where they memorized just before the beginning of each measurenient referring to two visual targets
presented in a display symmetrically from the center.
In long- term experiment, a series of nieasiirement performed every 2 hours from 11:00 in the morning t,o 9 0 0
11. METHODS
in the next morning. So a experiment consisted of 12Ezp F: rim,eri tal p r o cF:dwrc
series of measurement, and one series consisted of 6 sesIn order to investigate the relationships between char- sions, that is Rest I, Calibrat,ion, JTSI Rest 11, Self-rating,shown inactcristics of saccade and vigilance states changing in short- and KSS )Kwansei Gakuin Sleepiness Scaic)
Fig.2. JTS is all tlie same LS in short-term experiment exterm and long-term period respectively, we conducted twocept, for measuring time and additional det,ection of EEG
different experiments, t,hat is short-term experiment andlong-term experiment. In short-tcrm experiment, seven a t Cn and Pz. In Self-rating session, subjects scored selfperceived vigilance state between 0 and 10. 10 represents
riide subject,s (mean agc22.7) participated and five of theseven subject,s (mean age22.9) participated in long-term highest vigilance level. In KSS session, subjective sleepiness was assessed by using KSS, which is Japanese trarislaexperiment..
tion from Stanford Sleepiness Scale[']. KSS ratings ranges
Short-term experiment consisted of Rest, Jump-Targetsession (.TTS), and Non-Target session (NTS) as shown in from 0 to 7 and 7 represents sleepiest.

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1782

18th Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Amsterdam 1996
6.3.1 : Physiological Modelling - Visual System
Table 1 Correlation coefficients between PV/D and[CY20+ @] in JTS and NTS ( m e a n of every 30sec)
-0.74
-0.35
-0.75
-0.04
0.22
-0.90

dl02
U304
U5flG
n7-0.79,

17-0.28

-0.74
-0.49
0.G90

1 1 13 15 17 1921 23 1 3 5 7 9Time of day-0.86
-0.65
-0.75

Fig;. 3 Diurnal variations in [CYTable 2 Correlation coefficients between PV/D and+ p] and sleepiness(Subject #5, m e a n of every series)t,hree p a r a m e t e r s reflecting vigilance s t a t e ( m e a n10,I7

value of every session)
Siibjcct,
P2ti3U40s
16[a+ 131KSS-0.63
0.23
-0.72
-0.830.32

-0.76
-0.50
-0.74
-0.81
-0.70

Self-ratinc
0.88
0.55
0.62
0.86
0.82

1 IIIIIIIIIIIlo

1 1 1315171921 23 1 3 5 7 9Da t (1. anmlysis
Eye nioveiiieiit, data and EEG d a t a were amplified andsanipled at, 2kHx. t,ben analyzed by computer programs.
For each primary saccade t,liree paramet,ers were conipiit,etl : amplit,ude, durat,ion and peak velocity. In addit,ion, PV/D was c a l c u l a t d by dividing peak velocityb y diirat,ion, which represent,s t,he sharpness of saccadic
ve1ocit.y wave-form.
For each primary saccade, a segment of EEG (1.028s)
was selected at. t,he period just before t,he beginning of saccade, aid then analyzed by iiieans of Fast. Fourier Transform so t,hat, total power of N ( 8 ~ 1 3 H a and) p (13~100Hz)
wave bands. which i s showed as [e+ p ] , was obtained.

111. RESULTS
S1im-t-term ezperi7ne72,t
As shown in Table 1 there were negative correlations
I)cit,ween [R+ p] and PV/D in both sessions. This impliest,hat. PV/D tend to go down according to the decline int4hevigilance state regardless of sort of saccade, for J T S
and N T S induce different sort, of saccade.

Long-term. eqerim.ent
Fig.3 and Fig.4 show diurnal variations in [a+ p], KSS
rat,ings. PV/D and self-ratings for vigilance st,ate. Table 2
shows correlat,ion coefficientss of PV/D to the d h e r threers above. Thesc results show that PV/D has apositive correlation to vigilance states which are reflectedt,o EEG d a t a and subjective vigilance statme,and has anegative correliLtion to sleepiness.

Time of day

Fig. 4 Diurnal variations in subjective vigilance andPV/D (Subject fl5, mean of every series)
IV. DISCUSSION
Resultss obtained from t.wo different experiments indi.cate t,liat saccadic velocity waveform reflects both ofshort-term and long-t,erm variat,ions in vigilance states.
This suggests t,hats both of ret,icular controlling systemaind hypothalamic controlling system is concerned withcontml of saccade. The other hand, in case of subject 03and 15 results showed low positive correlations between
PV/D and [a + ,cJ]. It is possibly due to change of EEG
signal caused by sweating on the scalp, body motion, andso on. Thus it, is necessary to continue careful research on
this relationship.

V. CONCLUSION
This st,udy has shown that, the parameter of saccadic
velocity wave-form has correlation to vigilance states whichwere estimated from objective EEG d a h and subjective
vigilance and sleepiness. This indicates a possibility forassessment, of vigilance states using saccadic parametsera1783REFERENCES[I] J. Herscovitch and R.. Broughton : "Sensitivity of thestanford sleepiness scale t,o t,he effect,s of ciiniulative
partial sleep deprivation and recovery oversleeping,"
Sleep, Vo1.4, No.1, pp.83 92. 1981.