The 1st European Annual Conference on Human Decision Making and Manual Control: Proceedings of the European Annual Manual 1981

first european annual conference

on human decision making

and manual control

2 5 - 2 7 m a y 1 9 8 1

d e l f t u n i v e r s i t y o f t e c h n o l o g y

A . V A N L U N T E R E H D E L F T U N I V . OF T E C H N O L O G Y L A B . FOR M E A S U R E M . A N D C O N T R O L D E P T . OF M E C H . E N G R S

H E K E L H E G 2

2628 CD D E L F T

N E T H E R L A N D S

J

P r o c e e d i n g s o f the

first european annual conférence

on human décision making

and manual control

h e l d a t the DELFT UHIVERSITY OF TECHNOLOGY

May 25 - 2 7 , 1981

Conférence Chairman : Henk G. S t a s s e n O r g a n i s a t i o n : Wim L.Th. T h i j s

Man-Machine Systems Group L a b o r a t o r y f o r Measurement and. C o n t r o l Bept. o f Mech. E n g i n e e r i n g D e l f t U n i v e r s i t y o f Technology Mekelweg 2 2628 CD DELFT Nether Lands

5

-foreword

T h i s volume c o n t a i n s t h e p r o c e e d i n g s o f t h e F i r s t European Annual C o n f e r e n c e on Human Décision Making and Manual C o n t r o l , f o r s h o r t European A n n u a l Manual, held. a t t h e D e l f t U n i v e r s i t y o f T e c h n o l o g y at D e l f t , The N e t h e r l a n d s from May 2 5 - 2 7 , 1 9 8 1 . I t contains the complete m a n u s c r i p t s o f t h e papers présenter! a t t h e m e e t i n g . The p a p e r s a r e o r d e r e d as p r e s e n t e d .

The European A n n u a l Manual c a n be seen as an European v e r s i o n o f t h e A n n u a l Manual as h e l d a l r e a d y f o r 17 times i n t h e U.S.A.

I t i s c h a r a c t e r i z e d as an i n f o r m a l and f l e x a b l e c o n f e r e n c e , where a group o f p e o p l e , a l l workers i n t h e Man-Machine Systems a r e a can

d i s c u s s about t h e i r p r o b l e m s . D i f f e r e n t from t h e Annual Manual, U.S.A. where a i r c r a f t and s p a c e c r a f t c o n t r o l p l a y s such an i m p o r t a n t r o l e , t h e European A n n u a l Manual w i l l d e a l t o a l a r g e r e x t e n t w i t h t o p i c s i n t h e p r o c e s s i n d u s t r y , c a r d r i v i n g , m a n i p u l a t o r s and r e h a b i l i t a t i o n . A l s o the s u p e r v i s i o n o f complex Systems w i l l be a v e r y i m p o r t a n t t o p i c . The n e x t European A n n u a l Manual i s p l a n n e d a t FAT, n e a r Bonn, Fédéral R e p u b l i c o f Germany, i n t h e surnmer o f 1 9 Ö 2 .

Henk G. S t a s s e n Wim L.Th. T h i j s

7

-table of contents

SESSION

1 Page

P e r f o r m a n c e and W o r k l o a d

PREDICTION OF VISUAL SEARCH PERFORMANCE BASED ON VISUAL LOBE AREA 12

MEASUREMENTS

F.K. K r a i s s ,

A. Knaeuper *

VISUAL SEARCH: RELATION BETWEEN DETECTION PERFORMANCE AND VISUAL

27

FIELD S I Z E

A.F. Korn

EFFECT OF LEARNING, AGE AND TYPE OF SHIFT ON THE PERFORMANCE OF A

55

CRITICAL INSTABILITY TRACKING TASK (CIT) BY BUSDRIVERS BEFORE THEIR

WORK (A PRELIMINARY REPORT)

M.L.I. P o k o r n y ,

C.H.J.M. Oçmeev, D.H.J. Blom

A MODEL OF THE HUMAN HELICOPTER PILOT DURING I . L . S . APPROACH DESIGN

45

OF A DISPLAY FOR CONTROLS OPERATING

D. Diep

}

J . Papon, D. V i a r d

SESSION 2

D i s p l a y s

DISPLAYING PROCESS STRUCTURE

54

L. Bairibr-idge

HOW PEOPLE DISCOVER INPUT/OUTPUT RELATIONSHIPS

62

R.N. Pikaar

COPING WITH COMPLEXITY

69

J. Rasmusserij M. L i n d

THE STRUCTURING OF INFORMATION ON VISUAL DISPLAY UNITS

92

A.J.B. v a n B o x t e l ,

C. Slccppendel

SEARCH TIME AND COLOR CODE SIZE '

97

G. D e r e f e l d t ,

H. Marmolin

ERGONOMICS OF MAN-MACHINE COMMUNICATION: VISUAL PERFORMANCE

1 1 0

ASPECTS

P. Haubner

A DEVICE FOR THE MEASUREMENT OF CONTRAST RESOLUTION, SPATIAL AND 126

TEMPORAL RESOLUTION BY MEANS OF A VDU SCREEN

F.W. Umbach,

J.W.H. Kalsbeek, D. Bosman

PREDICTION AND STATE I N SIMPLE DYNAMIC SYSTEMS : WHAT ÏS LEARNED?

129

P.J. Venemans

TABLE OF CONTENTS

SESSION

3

S u p e r v i s o r y C o n t r o l , Décision M a k i n g , F a u l t Management

PROBLEM SOLVING BEHAVIOR OF PILOTS IN ABNORMAL AND EMERGENCY

142

SITUATIONS

G. Johanns en, W.B. Rouse

SIMULATION OF THE PILOT'S LONG TERM STRATEGY DÜRING IFR

151

FLIGHTS

D. Soulatges

EXPERIMENTAL AND THEORETICAL ANALYSIS OF HUMAN MONITORING AND

165

DECISION MAKING BEHAVIOR IN FAILURE DETECTION TASKS

R.C. van de Graaff, P.H. Wewerinke

A "ONITORING AND DECISION MAKING PARADIGM: EXPERIMENTS AND 180

HUMAN OPERATOR MODELING

W. Stein

FIELD STUDY OF THE ACTIVITIES OF PROCESS CONTROLLERS

195

Ï. Queinnea, G. de T e r s s a c , P. Thon

MODELING THE HUMAN OPERATOR'S SUPERVISORY BEHAVIOR

203

T.N. White

HUMAN PROBLEM SOLVING IN A PROCESS CONTROL TASK 218

W.B. Rouse, N.M. M o r r i s

SESSION h

Manual C o n t r o l S t u d i e s

CURRENT RESEARCH NEEDS IN MANUAL CONTROL 228

E. Edwaids

MOTIVATTONAL FACTORS AND PERFORMANCE IN A MANUAL TRACKING TASK

233

T. Bösser, E. M e l c h i o r , M. Schütte

ON THE STABILITY PROBLEM OF HUMAN ARM AND HAND MOVEMENTS

243

CONTROLLING EXTERNAL LOAD SYSTEMS

W. Setzer, G. V o s s i u s

EFFECTS OF VISUAL AND VESTIBULÄR MOTION PERCEPTION ON CONTROL

254

TASK PERFORMANCE

R.J.A.W. Hosman, J.C. van d e r V a a r t

MAN-MACHINE INTERACTION I N AEROSPACE CONTROL SYSTEM

275

D.R. Towill

COMPUTER ASSISTED MANUAL CONTROL OF CARGO HANDLING WITH

287

SULP CRANES

9

-TABLE OF CONTENTS

SESSION

5

Human B e h a v i o u r i n C a r D r i v i n g

SIGNIFTCANT CHANGES IN DRIVER-VEHICLE RESPONSE MEASURES

298

FOR EXTENDED DURATION SIMULATED DRIVING TASKS

W.W. Wievwille, W.H. Muto

DRIVERS' INTERNAL REPRESENTATION AND SUPERVISORY CONTROL:

515

A FIRST MODEL VERIFICATION IN RELATION TO DRIVING EXPERIENCE

TASK DEMANDS AND DETERIORATED VISION

G. J. Blaauw

PSYCHO-MATHEMATICAL MODEL OF VEHICULAR GUIDANCE BASED ON

528

FUZZY AUTOMATA THEORY

U. Kramer, G. Rohr

LEVEES OF STEERING CONTROL ; SOME NOTES ON THE TIME-TO-LINE

545

CROSSING CONCEPT AS RELATED TO DRIVING STRATEGY

H. Godthelpj H. K o n i n g s

SESSION 6

M i s c e l l a n e o u s

THE EFFECT OF ELECTROTACTILE AND VISUAL FORCE FEEDBACK ON

358

LEARNING AND PERFORMANCE IN A TELEMANIPULATION TASK

J.P. Gaillard

COMPUTER AIDED TREATMENT OF PATIENTS WITH INJURIES OF THE

576

SPINAL CORD

H.G. Stassen, A. van L u n t e r e n , R. Hoogendoorn,

G. J . v a n d e r K o l k , P. B a l k , G. M o r s i n k , J.C. Schuurman

COMPETENCY AND OPERATOR TRAINING REQUIREMENTS IN PROCESS

389

INDUSTRIES

J. Wix>stad

s

H. A n d e r s s o n

VOICE INPUT AND THE MEDICAL RECORD

403

H. C. P r i c e

session 1

performance and workload

12

-PREDICTION OF VISUAL SEARCH PERFORMANCE BASED ON VISUAL LOBE AREA MEASUREMENTS

K.F. K r a i s s , A. Knaeuper

R e s e a r c h I n s t i t u t e f o r Human E n g i n e e r i n g (FAT) D-5307 Wachtberg-Werthhoven, F.R. Germany

ABSTRACT

A f t e r a r e v i e w of t h e p e r t i n e n t l i t e r a t u r e , a n o v e l p r o c e d u r e t o p r e d i c t s e a r c h Performance i s p r e s e n t e d w h i c h i s based on v i s u a l l o b e a r e a measurements. In a d d i t i o n , t h e p r o c e d u r e d i s t i n g u i s h e s between random and s y s t e m -a t i c s e -a r c h i n g s t r -a t e g i e s .

A t a s k network model has been worked out t h a t p e r m i t s t o d y n a m i c a l l y simu-l a t e v i s u a simu-l s e a r c h w i t h v a r i o u s p a r a m e t e r s o f f i e simu-l d s i z e , v i s u a simu-l simu-l o b e a r e a and eye movement c h a r a c t e r i s t i c s .

The v a l i d i t y o f the p r o p o s e d p r e d i c t i n g method i s d e m o n s t r a t e d by c o m p a r i s o n w i t h e x p e r i m e n t a l d a t a as w e l l as by S i m u l a t i o n runs u s i n g t h e above men-t i o n e d model.

INTRODUCTION

The prédiction of v i s u a l s e a r c h p e r f o r m a n c e i n v a r i o u s a p p l i c a t i o n s has a t -t r a c -t e d considérable a -t -t e n -t i o n d u r i n g -t h e l a s -t y e a r s (ENGEL (1976), DRURY and CLEMENT (1978), KRENDEL and WODINSKY ( 1 9 7 0 ) ) . A r e v i e w o f t h e c u r r e n t s t a t u s o f v i s u a l models i s g i v e n , e.g., by MORAWSKI, DRURY and KARWAN (1980), and BLOOMFIELD (1975).

Most of t h e s e models a r e based on eye movement considérations o n l y . I n some p a p e r s an attempt has been made t o e x p l a i n différences i n s e a r c h p e r f o r m a n c e which may be a t t r i b u t e d t o s y s t e m a t i c o r random s e a r c h s t r a t e g i e s .

On t h e o t h e r hand one can f i n d i n t h e l i t e r a t u r e a few p a p e r s d e a l i n g w i t h t h e measurement of t h e so c a l l e d v i s u a l l o b e o r c o n s p i c u i t y a r e a (ENGEL (1976), WIDDEL and KASTER ( 1 9 8 1 ) ) .

In t h i s paper i t i s s u g g e s t e d t h a t t h e extend and shape o f t h e v i s u a l l o b e a r e a i s one o f the main f a c t o r s i n f l u e n c i n g t h e o v e r a l l s e a r c h time i n a p a r t i c u l a r t a s k .

1. VISUAL LOBE AREA MEASUREMENTS

The v i s u a l l o b e a r e a i s d e f i n e d as t h e p e r i p h e r a l a r e a around t h e c e n t r a l f i x a t i o n p o i n t from which s p e c i f i c i n f o r m a t i o n c a n be e x t r a c t e d i n a s i n g l e g l a n c e . T h i s région i s a f f e c t e d by v a r i o u s p a r a m e t e r s a s , e.g., a d a p t a t i o n

-

13

l e v e l o f the e y e , t a r g e t c h a r a c t e r i s t i c s , b a c k g r o u n d , e x p é r i e n c e , and m o t i -v a t i o n . I t i s s m a l l , i f the t a r g e t i s embedded i n a complex b a c k g r o u n d o r s u r r o u n d e d by i r r e g u l a r l y p o s i t i o n e d non t a r g e t s o f h i g h s i m i l a r i t y , and l a r g e , i f s i m p l e s t i m u l i s t a n d c l e a r l y i n f r o n t o f a homogeneous b a c k g r o u n d . I n t h e l i t e r a t u r e two methods t o measure the v i s u a l l o b e a r e a a r e g i v e n . ENGEL (1976) d e s c r i b e s a t a c h i s t o s c o p i c a p p r o a c h . I n t h i s c a s e t h e s u b j e c t i s asked t o f i x a t e i n t h e m i d d l e o f t h e s c r e e n . S u b s e q u e n t l y , the t a r g e t appears f o r a s h o r t t i m e a t v a r i o u s d i s t a n c e s and d i r e c t i o n s i n the p e r i p h -e r y . A f t -e r a s -e r i -e s o f p r é s -e n t a t i o n s , th-e t a r g -e t d é t -e c t i o n p r o b a b i l i t y can be c a l c u l a t e d as a f u n c t i o n o f t h e d i s t a n c e from t h e f i x a t i o n p o i n t .

WIDDEL and KASTER (1981) s u g g e s t a more r e a l i s t i c p r o c é d u r e w h i c h makes use of eye p o i n t o f r e g a r d measurements. They make the a s s u m p t i o n t h a t a t some f i x a t i o n p o i n t d u r i n g t h e s c a n n i n g p r o c e s s t h e t a r g e t i s d e t e c t e d p e r i p h e r a l l y . S u b s e q u e n t l y , t h e n e x t saccade i s v o l u n t a r i l y d i r e c t e d o n t o the t a r g e t r e s u l t i n g i n a f i x a t i o n on the t a r g e t . T h e r e f o r e t h e f i x a t i o n p r e c e d i n g t a r g e t d é -t e c -t i o n may be used -t o c a l c ú l a -t e -t h e e x -t e n d o f -the v i s u a l l o b e a r e a . A f -t e r v a r i o u s p r é s e n t a t i o n s t h e v i s u a l l o b e a r e a may a g a i n be d e s c r i b e d as t a r g e t d é t e c t i o n p r o b a b i l i t y o v e r f i x a t i o n d i s t a n c e .

Up t o now a c o m p a r i s o n o f b o t h methods has n o t been p e r f o r m e d . T h e r e f o r e i t can n o t be s t a t e d whether b o t h y i e l d the same r e s u l t s . From t h e d a t a g i v e n by ENGEL, and WIDDEL and KASTER i t may, h o w e v e r , be c o n c l u d e d t h a t the v i s u a l

l o b e a r e a i n many c a s e s can be a p p r o x i m a t e d by a Normal D i s t r i b u t i o n as d e -s c r i b e d by the f o l l o w i n g é q u a t i o n

_ i l

p ( S , o » = p ( 0 ) • e 2 ( f • k(<f>) (1) w i t h p ( 0 ) = p r o b a b i l i t y o f t a r g e t d é t e c t i o n at a s i n g l e g l a n c e d u r i n g f o v e a l i n s p e c t i o n a = s t a n d a r d d é v i a t i o n ô = f i x a t i o n d i s t a n c e from t h e t a r g e t (j) = f i x a t i o n d i r e c t i o n w i t h r e s p e c t t o t h e t a r g e t

I n t h i s é q u a t i o n p ( 0 ) i s d e t e r m i n e d by one o f the two methods d e s c r i b e d above by a v e r a g i n g o v e r v a r i o u s s u b j e c t s and e x p e r i m e n t a l r u n s . I n some c a s e s , t h e v i s u a l l o b e a r e a appears t o have an e l l i p t i c f o r m . F o r s i m p l i c i t y , a c i r c u l a r v i s u a l l o b e a r e a , i . e . , k(<j)) = c o n s t . , i s used i n t h i s paper t o d e s c r i b e t h e p r o b a b i l i t y t o d e t e c t t a r g e t i n a d i s t a n c e 6 a t a s i n g l e g l a n c e . I t h a s , how-e v how-e r , t o bhow-e how-emphasizhow-ed t h a t o t h how-e r shaphow-es o f t h how-e v i s u a l l o b how-e a r how-e a can bhow-e ushow-ed as w e l l i f more a p p r o p r i a t e .

2 . PREDICTION OF SEARCH PERFORMANCE 2.1 P r o b a b i l i t y o f T a r g e t D é t e c t i o n

As d e s c r i b e d a b o v e , the p r o b a b i l i t y p ( ô ) to d e t e c t a t a r g e t by a s i n g l e g l a n c e f o l l o w s from é q u a t i o n ( 1 ) . I n the s p é c i a l c a s e o f f o v e a l i n s p e c t i o n we have p ( ô ) = p ( 0 ) . I f p ( 0 ) < 1, the t a r g e t r é g i o n must be scanned s e v e r a l

14

times t o guarantee détection. The c o n t r i b u t i o n s p.(<5) o f v a r i o u s o b s e r v a t i o n s may be summed up y i e l d i n g a parameter v a l u e np which i s l a t e r r e -f e r r e d t o as p„TT1,,.

SUM

The v a l u e o f P g ^ 1 S> however, n o t équivalent t o t h e r e s u l t i n g t a r g e t d é

-t e c -t i o n p r o b a b i l i -t y P. S i n c e s i n g l e g l a n c e s a r e independen-t o f each o -t h e r the p r o b a b i l i t y P t h a t t h e t a r g e t w i l l be d e t e c t e d x times d u r i n g n sub-séquent g l a n c e s must be c a l c u l a t e d u s i n g t h e B i n o m i n a l D i s t r i b u t i o n P(x/p,n) = Pn (x) = Ô pX • ( 1 - p )n _ X (2) n,p x w i t h x = f r e q u e n c y o f t a r g e t détection i n n f i x a t i o n s p = p r o b a b i l i t y o f t a r g e t détection i n a s i n g l e g l a n c e . Hence, i t f o l l o w s t h a t t h e p r o b a b i l i t y t o see a t a r g e t w i t h n g l a n c e s a t l e a s t once may be d e r i v e d from équation (2) by s e t t i n g x = 0, i . e . , t o see the t a r g e t n o t a t a i l , and s u b t r a c t i n g t h i s from u n i t y .

n

P = Z P(x/p,n) = 1 - P(0/p,n) = 1 - ( 1 - p )n (3)

x=1

For t h e s p e c i a l case where p<<1 équation (3) c a n be s u b s t i t u t e d by ( P o i s s o n D i s t r i b u t i o n )

P = 1 - e = 1 - e (4)

A c c o r d i n g t o t h e above équation (4) , a v a l u e of Pgjjjj = 100 % t h e n w i l l y i e l d a t a r g e t détection r a t e o f P = 63.2 %. From équations (3) and (4) i t appears t h a t t h e p r o b a b i l i t y o f t a r g e t détection i n f a c t i s n o t e q u a l t o t h e p r o b a -b i l i t y PgTjj^ = n" P summed up from v a r i o u s g l a n c e s as may have been supposed

at t h e f i r s t i n s t a n c e . T h i s f a c t i s i l l u s t r a t e d by f i g u r e 1 where P i s shown t o be depending n o t o n l y on pQ T T M b u t a l s o on t h e v a l u e o f p ( 0 ) .

o U l i

The p r o b a b i l i t y Pg*™- summed up f o r v a r i o u s o b s e r v a t i o n s i s p r o p o r t i o n a l t o the s e a r c h time needed f o r a c e r t a i n détection p r o b a b i l i t y P as w i l l be shown l a t e r .

The upmost c u r v e i n f i g u r e 1 c o r r e s p o n d s t o t h e case where o n l y one g l a n c e y i e l d s 100 % t a r g e t détection p r o b a b i l i t y ( p ( 0 ) = 1 . 0 ) . As may be seen, P g ^ =

100 % c o r r e s p o n d s d i r e c t l y t o P = 100 % t a r g e t détection (see p o i n t S i n f i g u r e 1 ) .

The lowest c u r v e i n f i g u r e 1 i s d e s c r i b e d by équation (4) and c o r r e s p o n d s t o the case where v e r y l i t t l e r e c o n n a i s s a n c e i s g a i n e d from a s i n g l e g l a n c e (p<<1), and hence, many subséquent o b s e r v a t i o n s o f t h e t a r g e t a r e a a r e needed (n-*°°) . The t a r g e t détection s c o r e c o r r e s p o n d i n g t o PQ T T M = 100 % i s h e r e o n l y

15

-" ^ ^ f o r p K H - O

PSUM=2 P|

Pj=Probability of Target Détection

for one Fixation

P= Probability of Target Détection

for n Fixations

300 P

S U M F i g u r e 1 T a r g e t d é t e c t i o n p r o b a b i l i t y P r e s u l t i n g from the p r o b a b i l i t y = n « p summed up f o r n s u b s é q u e n t g l a n c e s on the t a r g e t -1 (1-e ) = 63.2 % a c c o r d i n g to é q u a t i o n ( 4 ) , r e p r e s e n t i n g a d i s t i n c t d e c r e a s e i n performance (see p o i n t R i n f i g u r e 1 ) . T r a j e c t o r i e s f o r i n t e r m e d i a t e v a l u e s of p(0) are a l s o d e p i c t e d i n f i g u r e 1. 2.2 V i s u a l Scanning B e h a v i o u r The number of f i x a t i o n s a c t u a l l y c o n t r i b u t i n g to t a r g e t d é t e c t i o n d é p e n d s on the r a t i o between i n t e r f i x a t i o n d i s t a n c e d and the s i z e of the v i s u a l lobe a r e a which i n t h i s paper i s d e s c r i b e d by the s t a n d a r d d é v i a t i o n a and the a m p l i t u d e p(0) of a Normal D i s t r i b u t i o n . I f a f i x a t i o n bappens to be too f a r away from the t a r g e t , e . g . , <S > 20 i t s c o n t r i b u t i o n i s n e g l e c t a b l e . T h i s i s i l l u s t r a t e d i n some more d é t a i l s by f i g u r e 2 where a t a r g e t i s randomly p o s i -t i o n e d i n an a e q u i d i s -t a n -t scan p a -t -t e r n . A i l f i x a -t i o n s which may c o n -t r i b u -t e to t a r g e t d é t e c t i o n , i . e . , which l i e w i t h i n 2a d i s t a n c e o f f the t a r g e t are marked. Each f i x a t i o n c o n t r i b u t e s to t a r g e t d é t e c t i o n c o r r e s p o n d i n g to i t s a c t u a l d i s t a n c e Ô£. I f n i s the number of r e l e v a n t f i x a t i o n s and p ( ô \ ) the t a r g e t d é t e c t i o n p r o b a b i l i t y from a s i n g l e g l a n c e we get

n

PSUM " .SP(ôi >

i=1

16

-F i g u r e 2 R e g u l a r q u a d r a t i c sean p a t t e r n ( i n t e r f i x a t i o n d i s t a n c e d ) . The c i r c l e comprehends 5 f i x a t i o n s w i t h i n 2a d i s t a n c e t o a randomly p o s i t i o n e d t a r g e t . Only t h e s e f i x a t i o n s c o n -t r i b u -t e -to -t a r g e -t d e -t e c -t i o n .

From f i g u r e 2 i t becomes o b v i o u s t h a t the l e v e l o f Pgy^ r e s u l t i n g f r o m a r e g u l a r sean i s d e t e r m i n e d by the s e l e c t e d i n t e r f i x a t i o n d i s t a n c e d, as w e l l as t h e s t a n d a r d d e v i a t i o n O and amplitude p(0) of the v i s u a l lobe área. These ínterrelations have been c a l c u l a t e d f o r t h e r e g u l a r sean p a t t e r n o f f i g u r e 2 u s i n g e q u a t i o n (5) f o r a l l f i x a t i o n s w i t h i n 6 < 2a. The r e s u l t s are p r e s e n t e d i n f i g u r e 3. I t may be seen t h a t a a/d r a t i o of .8 i s needed t o g e t h e r w i t h a p(0) of .28 i n o r d e r t o a c h i e v e a Pgjj^or 100 %. O t h e r sean p a t t e r n a s ,

e.g., a h e x a g o n a l arrangement o f f i x a t i o n p o i n t s have a l s o been i n v e s t i g a t e d and y i e l d o n l y s l i g h t l y d i f f e r e n t d a t a .

O b v i o u s l y , the r e g u l a r sean p a t t e r n d e p i c t e d i n f i g u r e 2 can o n l y be o b s e r v e d i n extreme c a s e s o f t r a i n e d s y s t e m a t i c s e a r c h w h i l e u s u a l l y a random p r o c e — dure must be t a k e n i n t o a c c o u n t . Düring random s e a r c h , s u c c e s s i v e f i x a t i o n s are i n d e p e n d e n t and henee, o v e r l a p each o t h e r t h a t means t h a t many subsequent o b s e r v a t i o n s o f the t a r g e t área a r e needed u n t i l d e t e c t i o n . T h i s c a s e i s r e -p r e s e n t e d by the lowest c u r v e i n f i g u r e 1 and by e q u a t i o n ( 4 ) .

3.3 E s t i m a t i o n o f S e a r c h Time

As soon as the i n t e r f i x a t i o n d i s t a n c e d t h a t c o r r e s p o n d s t o a p_T„, o f 100 %

SUM

has been d e t e r m i n e d from f i g u r e 3 (see dashed l i n e A B ) , the number of f i x a -t i o n s (N„T V.) r e q u i r e d f o r the r e g u l a r sean of the s e a r c h e d f i e l d may be c a l

17

-N =

(4

+ 1 ) * Or + 1 ) FIX d ' Vd ' w i t h a = h o r i z o n t a l s c r e e n s i z e , b = v e r t i c a l s c r e e n s i z e , d = i n t e r f i x a t i o n d i s t a n c e . F i g u r e 3 Summed up t a r g e t d e t e c t i o n p r o b a b i l i t y Pg Tj ^ as depending on i n t e r f i x a t i o n d i s t a n c e d and v i s u a l l o b e a r e a c h a r a c t e r i s t i c s 0, p(0)

Given the r e q u i r e d number of f i x a t i o n s an e s t i m a t e of the s e a r c h time (t ) can be determined u s i n g the f o l l o w i n g e q u a t i o n :

t = N * (t + t ) (7)

s FIX FIX SAC' K , J

w i t h t = mean f i x a t i o n t i m e , c IX .

t „ . „ = mean saccade t i m e . SAC

18

-A good e s t i m a t e f o r the time needed f o r a f i x a t i o n i n c l u d i n g a saccade ranges between 350 ms and 400 ms. Thèse v a l u e s are backed up by many différent ex-p e r i m e n t s .

The s e a r c h time t d e r i v e d above i s équivalent t o the time c o n s t a n t d u r i n g random s e a r c h (compare équation ( 4 ) ) and g i v e s t h e r e f o r e an e s t i m a t e of the time needed t o f i n d 63.2 % of the t a r g e t s . The improvement t h a t c o u l d p o s s i b l y be r e a c h e d by a t r a i n e d s y s t e m a t i c s e a r c h s t r a t e g y i s e n t i r e l y d e p e n d i n g on the v i s u a l l o b e a r e a c h a r a c t e r i s t i c p(0) and may be l o o k e d up from f i g u r e 1.

3. SIMULATION OF SEARCH BEHAVIOUR

I n s e c t i o n 1 and 2 a t h e o r e t i c a l approach f o r the prédiction o f v i s u a l s e a r c h performance was p r e s e n t e d . S u b s e q u e n t l y , a computer s i m u l a t i o n model i s de-v e l o p e d t h a t i s used t o c o n f i r m the prédiction procédure d e s c r i b e d abode-ve.

F o r the model f o r m u l a t i o n a network approach seemed t o be most a p p r o p r i a t e . As a t o o l f o r network s y n t h e s i s the s i m u l a t i o n language SAINT (Systems A n a l y s i s o f I n t e g r a t e d Networks o f T a s k s ) was used. F o r détails c o n c e r n i n g the symbology and network s y n t h e s i s the r e a d e r i s r e f e r r e d t o CHUBB (1981).

3.1 Network Model f o r Random S e a r c h

T h i s network ( f i g u r e 4) c o n s i s t s of e l e v e n t a s k s w i t h t h e f o l l o w i n g l a b e l s

START, STOP, STRTCOOR, SACDIREC, SACAMPLI, FIXC00RD, SACDURAT, FIXDURAT, TRGTDIST, DETECTPR, PRESSBUT

Main f u n c t i o n s o f each o f thèse t a s k s are d e s c r i b e d below.

START : TASK 1 s t a r t s the s i m u l a t i o n r u n f o r a p r e d e t e r m i n e d t i m e , e.g., 100 s, and i f r e q u i r e d i t c o l l e c t s d a t a f o r p l o t t i n g eye move-ments.

STOP : TASK 2 s t o p s the s i m u l a t i o n r u n a f t e r c o m p l e t i o n i f the s i m u l a -t i o n i s n o -t s-topped by TASK 1 which s i g n a i s -the dé-tec-tion o f t a r g e t .

STRTCOOR : T a r g e t and s t a r t c o o r d i n a t e s are drawn from a u n i f o r m d i s t r i b u -t i o n w i -t h i n -the l i m i -t s o f -the s e a r c h e d f i e l d . The -time o f -t h i s f i r s t f i x a t i o n ( i n s) i s drawn from a B e t a P e r t D i s t r i b u t i o n

(B(m,a,b)), approximated t o e x p e r i m e n t a l l y d e t e r m i n e d d a t a from WIDDEL and KASTER (1981). The p a r a m e t e r s o f t h i s d i s t r i b u t i o n a r e :

m = .2 (most l i k e l y v a l u e ) ,

a = .02 ( o p t i m i s t i c ( s m a l l e s t ) v a l u e ) ,

b = 1 . 0 ( p e s s i m i s t i c ( l a r g e s t ) v a l u e ) . ^ A f t e r c o m p l e t i o n t h e r e i s ' a d e t e r m i n i s t i c b r a n c h t o TASK 4.

19

-—A/\A*

y .

L A B L START

y .

TIME .02 i , STAT N U M . C O M V ATAS R E L : IA.1*UF,1 JTGV1O0 L A B L S T O P TIME .0 STAT N U M . C O M

—W-L A B —W-L S T R T C O O R TIME DS.12 STAT N U M . C O M M A R K REL ATAS REL-.IA.3SUF.3 SA.1=DS.1 SA.2=DS,2 SA.3=DS,1 SA.4-DS.2 L A B L SACDIREC TIME .0 STAT N U M . C O M ATAS REL:IA,4=UF,4 S A . S s D S , 5 SA.WzDS.IO L A B L S A C A M P L I TIME .0 STAT N U M . C O M ATAS REL:IA.5=UF,5 SA,6=DS.6 L A B L FIXCOORD TIME .0 STAT N U M . C O M ATAS REL:IA,6=UF,6 L A B L S A C D U R A T T l M É <SA-1.)*0.04 STAT N U M . C O M M O D F 1

) 0

L A B L FIXDURAT

) 0

TIME DS.12 STAT N U M . C O M L A B L TRGTDIST

"\ /7

L A B L D E T E C T P R TIME .0 TIME .0 STAT N U M . C O M

J

\L

STAT, N U M . C O M

ATAS REL.IA,9=UF,9

J

\L

A T A S REL:IA,10=UF,10

SA,11=DS.H

L A B L P R E S S B U T

TIME .3

STAT INT,REL

A T A S R E L : IA.11=UF"

F i g u r e 4 Task network model f o r random v i s u a l s e a r c h

SACDIREC : A random d i r e c t i o n f o r t h e n e x t saccade i s s e l e c t e d i n TASK 4. Task d u r a t i o n i s 0 s e c o n d s . A f t e r c o m p l e t i o n a d e t e r m i n i s t i c b r a n c h t o TASK 5 i s made.

SACAMPLI : The saccade a m p l i t u d e ( i n deg) i s a l s o drawn from a B e t a P e r t D i s t r i b u t i o n w h i c h i s a p p r o x i m a t e d t o expérimental d a t a from WIDDEL and KASTER (1981) as above. The p a r a m e t e r s a r e :

m 1.5, à = 1.5, b = 23.0.

T h i s a l s o t a k e s no time and a d e t e r m i n i s t i c b r a n c h i n g i s per-formed t o TASK 6.

FIXCOORD : A new f i x a t i o n p o i n t i s computed u s i n g t h e l a s t f i x a t i o n c o -o r d i n a t e s , t h e saccade d i r e c t i -o n d e t e r m i n e d i n TASK 4 and t h e saccade a m p l i t u d e d e t e r m i n e d i n TASK 5. I t îs checked whether the new p o i n t i s w i t h i n t h e s c r e e n . I f n o t t a s k s 4./.6 a r e r e -p e a t e d i n o r d e r t o détermine a new f i x a t i o n -p o i n t . S u b s e q u e n t l y , a b r a n c h t o TASK 7 i s p e r f o r m e d .

SACDURAT : TASK 7 y i e l d s t h e saccade d u r a t i o n u s i n g t h e r e l a t i o n t gAC =

20

-FIXDURAT

i n accordance w i t h e x p e r i m e n t a l l y determined d a t a (WIDDEL and KASTER ( 1 9 8 1 ) ) , but which i s o n l y v a l i d f o r s m a l l s a c c a d e s . For l a r g e saccades (> 6 degrees) a maximum d u r a t i o n of .2 s i s assumed f o l l o w e d by a d e t e r m i n i s t i c b r a n c h to TASK 8.

TASK 8 y i e l d s the f i x a t i o n d u r a t i o n which i s drawn from the same d i s t r i b u t i o n as i n STRTC00R.

TRGTDIST : The d i s t a n c e between the l a s t f i x a t i o n p o i n t and the t a r g e t (determined i n STRTCOOR) i s computed. A f t e r t a s k c o m p l e t i o n a d e t e r m i n i s t i c b r a n c h i n g to TASK 10 i s p e r f o r m e d .

DETECTPR : TASK 10 s i m u l â t e s the v i s u a l lobe a r e a as d e s c r i b e d i n s e c t i o n 1. I f the t a r g e t i s d e t e c t e d b r a n c h i n g i s performed to TASK 11,

o t h e r w i s e to TASK 4 where a new f i x a t i o n p o i n t i s computed.

PRESSBUT : TASK 11 s i m u l â t e s t a r g e t r é c o g n i t i o n ( s i g n a l e d by p r e s s i n g a button) and stops the s i m u l a t i o n r u n . S i m u l t a n e o u s l y , the s e a r c h time i s r e g i s t e r e d .

3.2 Network Model f o r S y s t e m a t i c Search

T h i s network, as d e p i c t e d i n f i g u r e 5 c o n s i s t s of e i g h t t a s k s w i t h the f o l l o w i n g l a b e l s

START, STOP, STRTCOOR, FIXATION, SACCADE, TRGTDIST, DETECTPR, PRESSBUT START STOP same f u n c t i o n as above same f u n c t i o n as above

V

L A B L START

V

TIME .02

V

STAT N U M . C O M

V

ATAS REL: |A.1=UF.1

TGV, 100 L A B L STOP TIME .0 STAT N U M . C O M

-w*

L A B L MARK AIASL STRTCOOR DS.12 N U M . C O M R E L REL:IA,3=UF.3 SA,1=DS.1 SA,2=DS,2 L A B L FIXATION \ Y1 TIME DS.12 / r—A i ATAS REL:IA,4=UF.4 STAT N U M . C O M

L A B L S A C C A D E \ li ' TIME ( S A - D X 0 . 0 4 / V i STAT N U M . C O M

V

MODF 1 ¡ L A B L T R G T D I S T

^ V

L A B L D E T E C T P R TIME .0

^ V

TIME .0 STAT N U M , C O M

J

V : STAT N U M . C O M

A T A S REL: 1A,6 = UF,6

J

V : ATAS REL:IA,7=UF, 7 SA,11=DS,11

L A B L PRESSBUT TIME .3 STAT INT. REL ATAS R E L : I A , 8 - U F . 8

21

-STRTCOOR : T a r g e t c o o r d i n a t e s a r e drawn from a u n i f o r m d i s t r i b u t i o n as above. The s t a r t c o o r d i n a t e s are s e l e c t e d by the modeler

( e . g . , the s e a r c h b e g i n s a t upper l e f t c o r n e r o f the s c r e e n ) .

FIXATION : The séquence o f f i x a t i o n s i s c o n t r o l l e d i n such a way t h a t a r e g u l a r s c a n p a t t e r n w i t h i n t e r f i x a t i o n d i s t a n c e d c o v e r i n g the whole s e a r c h e d f i e l d i s g e n e r a t e d (as d e p i c t e d i n f i g . 3 ) . The time f o r TASK 4 (one f i x a t i o n ) i s d e r i v e d from the expérim e n t a l d i s t r i b u t i o n o f f i x a t i o n d u r a t i o n (as a b o v e ) . A d e t e r -m i n i s t i c b r a n c h i n g t o TASK 5 i s p e r f o r -m e d .

SACCADE : TASK 5 y i e l d s the s a c c a d e d u r a t i o n c o r r e s p o n d i n g t o the i n t e r -f i x a t i o n d i s t a n c e d -f o l l o w e d by a d e t e r m i n i s t i c b r a n c h t o TASK 6.

TRGTDIST : same f u n c t i o n as above

DETECTPR : same f u n c t i o n as above

PRESSBUT : same f u n c t i o n as above.

3.3 S i m u l a t i o n R e s u l t s

U s i n g the networks d e s c r i b e d above, the e f f e c t o f v a r i o u s v i s u a l l o b e a r e a s on s e a r c h p e r f o r m a n c e can be t e s t e d a n a l y t i c a l l y . I n o r d e r t o do s o , two shapes have been s e l e c t e d f o r the viéual l o b e a r e a as d e p i c t e d i n f i g u r e 6. I n a d d i -t i o n , an ex-tend o f 30* 25 d e g r e e s was assumed f o r -t h e s e a r c h e d f i e l d .

As a f i r s t s t e p an e s t i m a t e i s made about the time c o n s t a n t f o r random s e a r c h u s i n g v i s u a l l o b e a r e a No. 1. As e x p l a i n e d e a r l i e r a v a l u e o f a t l e a s t 63.2 % t a r g e t détection (time c o n s t a n t f o r random s e a r c h ) i s a c h i e v e d as soon as the summed up détection p r o b a b i l i t y from a i l f i x a t i o n s i s P g ^ =

100 % a i l over t h e s e a r c h e d f i e l d . T h i s i s t h e case f o r a o/â r a t i o of

.8 and an i n t e r f i x a t i o n d i s t a n c e d = 4.4 deg as d e r i v e d from f i g u r e 3 (marked p o i n t B ) . U s i n g équations (6) and (7) t h i s c o r r e s p o n d s t o a number of N „T T, = 56 f i x a t i o n s and a s e a r c h time o f t = 22 s.

FIX s When p e r f o r m i n g the same c a l c u l a t i o n s f o r v i s u a l l o b e a r e a No. 2, the i n t e r

-f i x a t i o n d i s t a n c e i s d = a/.45 = 4.4 deg ( -f i g u r e 3, p o i n t A ) , i . e . , t h e same as above, y i e l d i n g an i d e n t i c a l r e s u i t f o r random s e a r c h . Hence, the différent shape of the v i s u a l l o b e a r e a shôuld not i n f l u e n c e random s e a r c h p e r -formance a t a i l . As i n d i c a t e d i n f i g u r e 7 t h i s can be j u s t i f i e d by network s i m u l a t i o n runs where about i d e n t i c a l c u r v e s f o r random s e a r c h (RANDOM 1,2) can be seen f o r b o t h v i s u a l l o b e a r e a s .

As t h e o r e t i c a l l y p r e d i c t e d a s y s t e m a t i c s e a r c h s t r a t e g y d o e s n ' t improve p e r -formance f o r v i s u a l l o b e a r e a No. 1 where p ( 0 ) r e a c h e s o n l y a v a l u e o f .275 as compared to random s e a r c h (compare a l s o f i g u r e 1 ) .

I n c o n t r a s t t o t h i s f i n d i n g the r e s u l t s f o r s y s t e m a t i c s e a r c h show marked différences f o r the second v i s u a l l o b e a r e a c h a r a c t e r i s t i c s . F o r the p2(0)=

1.0 c a s e a t a r g e t détection r a t e of 86 % a t p o i n t PQTJJ^ = 100 % can be obs e r v e d from t h e obs i m u l a t i o n r u n . T h i obs i obs l e obs obs than t n e t h e o r e t i c a l l y e x p e c t -ed 100 % (see p o i n t S i n f i g u r e 7 ) . The différence may be e x p l a i n e d by l e s s than p e r f e c t c o v e r a g e o f the s e a r c h e d a r e a d u r i n g t h e s i m u l a t i o n s .

22

-F i g u r e 7 S i m u l a t e d s e a r c h performance f o r random and system-a t i c s e system-a r c h s t r system-a t e g i e s system-and the v i s u system-a l lobe system-aresystem-as of f i g u r e 6

23

-The déviation may a l s o be due t o the f i n i t e n e s s of the random t e s t and t h e u n s y s t e m a t i c c o v e r a g e a t t h e edges o f the s e a r c h e d f i e l d . I n p r i n c i p l e how-e v how-e r , thhow-e a n a l y t i c a l r how-e s u l t s s t r o n g l y s u p p o r t t h how-e t h how-e o r how-e t i c a l f i n d i n g s .

In a d d i t i o n t o the example p r e s e n t e d above, s i m u l a t i o n s w i t h o t h e r v i s u a l l o b e a r e a s and i n t e r f i x a t i o n d i s t a n c e s d were made. A i l o f thèse e x p e r i m e n t s c o n f i r m e d our t h e o r e t i c a l l y e x p e c t e d d a t a . The d e s c r i b e d network models may t h e r e f o r e be c o n s i d e r e d as a v a l i d représentation o f v i s u a l s e a r c h straté-g i e s .

4. COMPARISON WITH EXPERIMENTAL DATA

In o r d e r t o p e r f o r m a f u r t h e r v a l i d a t i o n t h e o r e t i c a l s e a r c h p e r f o r m a n c e prédictions a r e s u b s e q u e n t l y compared w i t h expérimental d a t a as p r e s e n t e d by WEDDEL and KASTER (1981), and ENGEL (1976).

In the expérimental s e t - u p used by WIDDEL and KASTER the s u b j e c t s had t o scan a s c r e e n w i t h an extend o f 30 x 25 deg on w h i c h the v i s u a l s e a r c h mate-r i a l was p mate-r e s e n t e d c o n s i s t i n g o f a numbemate-r o f u n i f o mate-r m mate-randomly s p mate-r e a d symbols. These symbols were i d e n t i c a l w i t h the e x c e p t i o n o f one, t h e t a r g e t w h i c h had to be d e t e c t e d by t h e s u b j e c t s . The t a r g e t was p o s i t i o n e d randomly w i t h i n the s t i m u l u s f i e l d d u r i n g e a c h présentation. A s y s t e m a t i c v a r i a t i o n o f the d i f f i c u l t y o f v i s u a l p e r c e p t i o n was o b t a i n e d by i n c r e a s i n g t h e number o f b a c k -ground symbols. The s u b j e c t s Were randomly a s s i g n e d t o two expérimental groups who had t o t a k e p a r t i n e i g h t s e s s i o n s w i t h f i f t e e n présentations. One group was t r a i n e d w i t h a s c a n l i n e w h i c h was moving o v e r t h e s c r e e n i n o r d e r t o s t i m u l a t e s y s t e m a t i c s e a r c h w h i l e t h e o t h e r group c o u l d a p p l y a f r e e i n d i v i d u a l s c a n .

The a u t h o r s présent expérimental d a t a f o r t h e v i s u a l l o b e a r e a i n t h r e e c o n -d i t i o n s . These -d a t a were i n e a c h case a p p r o x i m a t e -d by a Normal D i s t r i b u t i o n r e s u l t i n g i n t h e p ( 0 ) , O parameters g i v e n i n t a b l e 1 .

T a b l e 1 Comparison o f t h e o r e t i c a l and expérimental r e s u l t s of WIDDEL AND KASTER (1981)

Table 1 Comparison of theoretical data and expérimental results of WIDDEL, KASTER (1981)

Field Number Visual Interfix- Number Fixation Time to Détection Rate in t Si.se of Lobe Area ation of F i x a - Duration Search

Items Parameters Distance tions for ( i n c l . F i e l d Theoretical Expérimental

PS U M= 1- ° Saccades) once

DUJM _Random

System-a t i c (deg) p(0)/a d(deg)

NF I X

(ms) ts( s )

30 352 .275/3.5 4.4 56 393 22.0 63.2(39-83)* 68.9 57-72 X 467 .224/3.5 3.8 63 397 25.0 63.2(39-83)* 67.9 50-51

25 576 .184/3.5 3.3 80 363 29.0 63.2(39-83)* 66.9 51-65

24

-U s i n g t h e f i e l d s i z e and the v i s u a l l o b e áreas parameters the number o f f i x a t i o n s needed f o r pm„ , = 100 % c a n be c a l c u l a t e d u s i n g f i g u r e 3 and

rSUM

équation ( 6 ) . The time t needed t o s e a r c h t h e f i e l d once r e s u l t s from a m u l t i p l i c a t i o n w i t h average f i x a t i o n t i m e s . S u b s e q u e n t l y , from f i g u r e 1 prédictions f o r t h e t a r g e t détection r a t e may be d e r i v e d assuming random or s y s t e m a t i c s e a r c h s t r a t e g y .

F o r comparison t h e l a s t column f o r t a b l e 1 g i v e s a range o f e x p e r i m e n t a l d a t a as determined i n v a r i o u s e x p e r i m e n t a l c o n d i t i o n s . S i n c e t h e s e d a t a a r e i n each case based on o n l y 20 s i n g l e measurements t h e y s h o u l d be com-pared w i t h t h e c o r r e s p o n d i n g c o n f i d e n c e i n t e r v a i s which a r e a l s o g i v e n i n t a b l e 1.

From t h e d a t a p r e s e n t e d i n t a b l e 1 i t appears t h e s e a r c h p e r f o r m a n c e p r é -d i c t i o n s a r e i n l i n e w i t h t h e e x p e r i m e n t a l l y -d e t e r m i n e -d t i m e s . I n -d -d -d i t i o n , i t i s a g a i n shown t h a t n o t much improvement c a n be e x p e c t e d from a system-a t i c s e system-a r c h s t r system-a t e g y system-as l o n g system-as t h e p(0) v system-a l u e o f t h e v i s u system-a l l o b e system-a r e system-a i s c o n s i d e r a b l e lower t h a n u n i t y .

In the paradigm used by" ENGEL (1976) t h e s u b j e c t s had t o s e a r c h a s c r e e n o f 22.3 deg • 16.8 deg o f v i s u a l a n g l e . The s c r e e n c o n t a i n e d a random d o t p a t t e r n of 220 s i m i l a r d i s k s w i t h a d i a m e t e r o f .55 deg and one d i s s i m i l a r t e s t ob-j e c t , t h e t a r g e t which d i f f e r s from t h e background d i s k s i n d i a m e t e r . The minimum c e n t r e t o c e n t r e d i s t a n c e was 1.5 times t h e d i a m e t e r o f t h e b a c k -ground d i s k s i n o r d e r t o p r e v e n t o v e r l a p p i n g i n t h e s t i m u l u s p a t t e r n . The s t i m u l u s f i e l d was p r e s e n t e d 4 s i n each s e a r c h experiment and t h e o b s e r v e r had t o i n d i c a t e t h e d i s c o v e r y o f t h e t e s t o b j e c t by means o f a l i g h t s i g n a l .

T a b l e 2 g i v e s a comparison o f t h e o r e t i c a l l y p r e d i c t e d and e x p e r i m e n t a l l y d e t e r m i n e d d a t a i n much t h e same way as was d e m o n s t r a t e d f o r t a b l e 1.

T a b l e 2 Comparison o f t h e o r e t i c a l and e x p e r i m e n t a l r e s u l t s (averages o f e x p e r i m e n t a l d a t a from ENGEL (1976))

Table 2 Comparison of theoretical and experimental results (averages of experimental data from ENGEL (1976))

E x p e r i -m e n t a l C o n d i -t i o n ! D - D o I V i s u a l L o b e A r e a P a r a m e t e r s p(0)/a I n t e r f i -x a t i o n D i s t a n c e d(deg) N u m b e r o f F i x a -t i o n s f o r W 1 - 0 N F I X Fixation Duration ( i n c l . Saccades) (ms) T i m e t o S e a r c h F i e l d o n c e ts( s ) D é t e c t i o n Rate in t T h e o r e t i c a l Random S y s t e -m a t i c E x p e r i m e n t a l .08 .10 .13 .21 1.0/2.0 1.0/2.6 1.0/4.8 1.0/6.5 4.4 6.3 11.7 15.8 30 20 9 6 330 340 330 310 9.9 6.8 2.98 1.86 63.2(48-78)* 63.2(48-78)* 63.2(48-78)* 63.2(48-78)* 100.0 100.0 100.0 100.0

* confidence interval for N=48 D : diameter of background disks ** extrapolated values Do : diameter of test disk

-

25

-I t may be seen t h a t the a c t u a l s e a r c h p e r f o r m a n c e ranges f o r a i l o f the f o u r i n d i c a t e d expérimental s i t u a t i o n s between the v a l u e s p r e d i c t e d f o r random and s y s t e m a t i c s t r a t e g y . Extreme v a l u e s f o r s y s t e m a t i c s e a r c h , i . e . ,

100 % do not o c c u r . However, the i n c r e a s e i n p e r f o r m a n c e as compared w i t h the random a p p r o a c h i s f o r some c a s e s considérable r e a c h i n g up t o 83 % due to the h i g h v a l u e of p ( 0 ) = 100 %. Thus, a l s o f o r t h i s example v i s u a l p e r -formance i s c o r r e c t l y p r e d i c t e d when the p r o p o s e d procédure i s a p p l i e d .

5. CONCLUSION

In t h i s p a p e r a method has been d e s c r i b e d t o p r e d i c t v i s u a l s e a r c h p e r f o r m -ance u s i n g d a t a on the v i s u a l l o b e a r e a and on eye movement t i m e s . These d a t a must be made a v a i l a b l e by s e a r c h i n g t h e l i t e r a t u r e f o r a p p r o p r i a t e d a t a o r by s p e c i a l expérimentation.

As soon as thèse p a r a m e t e r s are known a r e l i a b l e prédiction of s e a r c h p e r -formance can be p e r f o r m e d i n a s i m p l e s t r a i g h t f o r w a r d way. The d e s c r i b e d method i s s u p e r i o r t o o t h e r models p u b l i s h e d i n the l i t e r a t u r e i n t h a t i t

discriminâtes v a r i o u s stratégies o f v i s u a l s e a r c h , i . e . , random and system-a t i c . I t i s shown t h system-a t the s y s t e m system-a t i c procédure does n o t i n system-any csystem-ase l e system-a d to an improvement i n p e r f o r m a n c e but o n l y i n c a s e s where détection p r o b a -b i l i t y p(0) i s h i g h f o r s i n g l e g l a n c e s .

W h i l e i n t h i s paper o n l y s i m p l e s e a r c h s i t u a t i o n s have been c o n s i d e r e d i t i s e x p e c t e d t h a t t h i s method can a l s o be a p p l i e d i n more complex a p p l i c a t i o n s where the v i s u a l l o b e a r e a changes w i t h i n one s e a r c h f i e l d o r where v a r i o u s t a r g e t s a p p e a r .

To s u p p o r t t h e t h e o r e t i c a l f i n d i n g s a t a s k network model has been worked out t h a t p e r m i t s t o d y n a m i c a l l y s i m u l a t e v i s u a l s e a r c h w i t h v a r i o u s p a r a m e t e r s of f i e l d s i z e , v i s u a l l o b e a r e a and eye movement c h a r a c t e r i s t i c s . T h i s model w i l l be used f o r the f u r t h e r a n a l y s i s o f s e a r c h b e h a v i o u r .

6. REFERENCES

/1/ ENGEL, F.L.: " V i s u a l c o n s p i c u i t y as an e x t e r n a l déterminant o f eye movements and sélective a t t e n t i o n " . PHD. T h e s i s , T.H. E i n d h o v e n ,

1976.

III DRURY, C.G., CLEMENT, M.R.: "The e f f e c t of a r e a , d e n s i t y and number

of background c h a r a c t e r s on v i s u a l s e a r c h " . Human F a c t o r s , 2 0 ( 5 ) , 1978, p. 597-602.

/3/ KRENDEL, E.S., WODINSKY, J . : " V i s u a l s e a r c h i n u n s t r u c t u r e d f i e l d s " . I n : MORRIS, A., HORNE, E . P . ( E d s . ) , V i s u a l S e a r c h T e c h n i q u e s , N a t i o n a l R e s e a r c h C o u n c i l , Washington D.C., 1960, p. 151-169.

Ikl MORAWSKI, T., DRURY, C G . , KARWAN, M.H. : " P r e d i c t i n g s e a r c h p e r f o r m

-ance f o r m u l t i p l e t a r g e t s " . Human F a c t o r s 3, 2 2 ( 6 ) , 1980, p. 707-718.

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-/5/ BLOOMFIELD, J.R.: " T h e o r e t i c a l approaches t o v i s u a l s e a r c h " .

I n : DRURY, C G . , FOX, J.A. ( E d s . ) , Human R e l i a b i l i t y i n Q u a l i t y C o n t r o l . London, T a y l o r & F r a n c i s , 1975, p. 19-28.

/6/ WIDDEL, H., KASTER, J . : "Eye movement measurements i n the assessment and t r a i n i n g o f v i s u a l P e r f o r m a n c e " . I n : MORAAL, J . , KRAISS, K.F.

( E d s . ) , Manned Systems D e s i g n , Methods, Equipment and A p p l i c a t i o n s . Plenum P r e s s , New Y o r k and London, 1981, p . 251-270.

HS CHUBB, G.P.: "SAINT: A d i g i t a l S i m u l a t i o n language f o r the study o f manned S y s t e m s " . I n : MORAAL, J . , KRAISS, K.F. ( E d s . ) , Manned

Systems D e s i g n , Methods, Equipment and A p p l i c a t i o n s . Plenum P r e s s , New Y o r k and London, 1981, p. 153-179.

lol KREYSZIG, E.: " S t a t i s t i s c h e Methoden und i h r e Anwendungen". Vandenhoeck & R u p r e c h t , Göttingen, 1968, p. 107-117, 390.

/9/ SNYDER, H.L., TAYLOR, D.F.: "Computerized a n a l y s i s o f eye movements d u r i n g s t a t i c d i s p l a y v i s u a l s e a r c h " . A e r o s p a c e M e d i c a l R e s e a r c h L a b o r a t o r y , R e p o r t AMRL-TR-75-91, 1975.

/10/ ENOCH, J.M.: " E f f e c t o f the s i z e o f a complex d i s p l a y upon v i s u a l s e a r c h " . J o u r n a l o f O p t i c a l S o c i e t y o f A m e r i c a , 49, 1959, p. 280-286.

/11/ WILLIAMS, L.G.: " T a r g e t c o n s p i c u i t y and v i s u a l s e a r c h " . Human F a c t o r s 8, 1966, p. 80-92.

/12/ MEGAW, E.D., RICHARDSON, J . : " T a r g e t u n c e r t a i n t y and v i s u a l s c a n n i n g s t r a t e g i e s " . Human F a c t o r s 21, 1979, p. 303-315.

27

-VISUAL SEARCH : RELATION BETWEEN DETECTION

PERFORMANCE AND VISUAL FIELD SIZE

A.F. Korn

F r a u n h o f e r - I n s t i t u t für I n f o r m a t i o n s - und D a t e n v e r a r b e i t u n g D-7500 K a r l s r u h e 1, FRG

A b s t r a c t

We are c o n s i d e r i n g t h e f o l l o w i n g s i t u a t i o n : a r e m o t e l y c o n t r o l l e d v i e w i n g d e v i c e produces a v i s u a l présentation o f a remote scène. T h i s d i s p l a y p r o v i d e s the same d e g r e e o f v i s u a l présence to a remote o b s e r v e r as i f he were v i e w i n g the scène d i r e c t l y . I n o r d e r to m i n i m i z e r e q u i r e d o p e r a t o r

command and d a t a l i n k bandwidth, the f i e l d o f v i e w s h o u l d be an optimum. The f o l l o w i n g e x p e r i m e n t s were p e r f o r m e d t o i n v e s t i g a t e t h i s problem.

In a v i s u a l s e a r c h experiment a s i n g l e v e h i c l e was t o be found among c o n f u s -i n g o b j e c t s c o n s -i s t -i n g o f v a r -i o u s components o f a e r -i a l p -i c t u r e s . Here t y p i c a l s c e n e r i e s have been s i m u l a t e d : a f o r e s t , a meadow, a v i l l a g e , and an open f i e l d .

The v i s u a l s e a r c h t i m e was measured as a f u n c t i o n o f the v i s u a l f i e l d s i z e t h a t was v a r i e d s y s t e m a t i c a l l y . The f i e l d c o u l d be s h i f t e d a c r o s s the TV d i s p l a y by eye and headmovements o r by hand ( j o y s t i c k ) . I n the f i r s t case t h e c o o r d i n a t e s o f t h e c o r n e a l r e f l e x were used t o a d j u s t the p o s i t i o n o f t h e v i s u a l f i e l d c o n c e n t r i c a l l y around the f i x a t i o n p o i n t .

D e c r e a s i n g the v i s u a l f i e l d s i z e from 2 4 ° , w h i c h i s the s i z e o f t h e TV d i s p l a y , t o 3° v i e w i n g a n g l e , w h i c h i s t h e t h r e e f o l d s i z e o f t h e v e h i c l e , r e s u l t s i n an i n c r e a s e o f p r o c e s s i n g time by a f a c t o r 10. T h e r e a r e no s i g n i f i c a n t différences between s h i f t i n g the p i c t u r e - w i n d o w by eye, head, o r hand movements.

The r e s u l t s can be i n t e r p r e t e d i n terms o f one o f the m a j o r f u n c t i o n s performed by p e r i p h e r a l v i s i o n , namely t h e g u i d a n c e o f eye movements and o r i e n t a t i o n i n s p a c e .

A n a l y s i s o f the d i f f e r e n t s c a n p a t h s g i v e s some h i n t s at the s i z e o f c o n s p i c u i t y a r e a s .

I n t r o d u c t i o n

I n RPV ( r e m o t e l y p i l o t e d v e h i c l e ) r e c o n n a i s s a n c e m i s s i o n s TV o p e r a t o r s have t o i n t e r p r e t the t r a n s m i t t e d d a t a o n - l i n e . V i e w i n g time i s p h y s i c a l l y d e t e r m i n e d by t h e f l i g h t p a r a m e t e r s and the o p t i c a l p a r a m e t e r s o f the s e n s o r . The human f a c t o r s a s p e c t s o f the e l e c t r o - o p t i c a l system d e s i g n a r e c o n c e r n e d p r i m a r i l y w i t h the i n t e r a c t i o n between t h e d i s p l a y e d m a t e r i a l and t h e o b s e r v e r ' s v i s u a l and v i s u a l p e r c e p t i o n S y s t e m s .

The détection performance dépends upon ( R e f . 1 ) :

• System parameters such as r e s o l u t i o n and the s i z e o f the a r e a t o be c o v e r e d .

• Scène p a r a m e t e r s w h i c h c o n s t i t u t e t h e v i s u a l c o n s p i c u i t y o f t a r g e t s i n a n a t u r a l scène such as s i z e , shape, and c o n t r a s t o f a t a r g e t o r g l o b a l

28

-and l o c a l c o n t e x t , i . e . the immediate -and t o t a l s u r r o u n d i n g s .

• O b s e r v e r - r e l a t e d f a c t o r s such as m o d u l a t i o n t r a n s f e r f u n c t i o n of the v i s u a l system, luminance a d a p t i o n , o c u l o m o t o r r e s p o n s e (eye movements,

s c a n n i n g b e h a v i o u r ) , r e a c t i o n t i m e , the amount o f i n f o r m a t i o n w h i c h can be a c c e p t e d from i n d i v i d u a l f i x a t i o n s ( g l i m p s e s ) , s t r e s s p l a c e d on t h e o b s e r v e r by the p h y s i c a l environment o r n a t u r e o f the t a s k , and the o b s e r v e r ' s t r a i n i n g and s k i l l .

I n o r d e r t o maximize t h e t a r g e t a c q u i s i t i o n p r o c e s s a v e r y l a r g e number o f p i c t u r e p o i n t s s h o u l d be t r a n s m i t t e d to the ground s t a t i o n t o o b t a i n a l l the i n f o r m a t i o n w h i c h i s needed by the o b s e r v e r d u r i n g t h e s e a r c h p r o c e s s . I n g e n e r a l , the l i t e r a t u r e i n d i c a t e s t h a t d i s p l a y f i e l d o f v i e w s i z e s

g r e a t e r than 30 degrees but l e s s t h a n 60 d e g r e e s are d e s i r a b l e ( R e f . 2 ) . A 40 degree f i e l d o f view w i t h a s p a t i a l r e s o l u t i o n o f 60 l i n e s p e r d e g r e e , a 8 ' b i t grey l e v e l r e s o l u t i o n , and a frame r a t e o f 25 p i c t u r e s per second r e q u i r e a d a t a t r a n s m i s s i o n r a t e o f 1 150 M b i t p e r second. Because o f

t e c h n i c a l d i f f i c u l t i e s and jamming s e n s i t i v i t y the r e q u i r e d h i g h t r a n s m i s s i o n r a t e i s not d e s i r a b l e .

C o n s i d e r i n g the l i m i t e d c a p a b i l i t i e s of the human v i s u a l system one r e c o g n i -zes t h a t o n l y a s m a l l f r a c t i o n o f t h i s i n f o r m a t i o n can be a c c e p t e d from the s e a r c h scene at any i n d i v i d u a l g l i m p s e . T h e r e f o r e a s a t i s f a c t o r y s o l u t i o n of the problem of bandwidth r e d u c t i o n w i t h o u t l o s s o f r e l e v a n t i n f o r m a t i o n can be a c h i e v e d by t r a n s m i t t i n g o n l y a s m a l l p i c t u r e a r e a around the o b s e r v e r ' s f i x a t i o n p o i n t . A f u r t h e r r e d u c t i o n o f bandwidth i s p o s s i b l e by the v a r i a t i o n o f the s p a t i a l r e s o l u t i o n i n t h a t a r e a a c c o r d i n g to the p r o p e r t i e s of the human r e t i n a ( R e f . 3 , 4 ) . The r e t i n a i s c h a r a c t e r i z e d by a c e n t r a l r e g i o n o f h i g h r e s o l u t i o n ( f o v e a ) w i t h g r a d u a l l y r e d u c e d

r e s o l u t i o n as d i s t a n c e from the f o v e a i n c r e a s e s .

T h i s paper i s concerned almost e x c l u s i v e l y w i t h the e x p e r i m e n t a l q u e s t i o n how much o f the f i e l d of v i e w i s needed at each f i x a t i o n pause i n o r d e r t o get a s i m i l a r d e t e c t i o n p e r f o r m a n c e as i n the case o f n o n - r e s t r i c t e d v i s u a l f i e l d . The average l e n g t h o f f i x a t i o n pauses a r e about 1/3 second e a c h , the eyes b e i n g f i x e d about 90 % o f the time where i n v o l u n t a r y eye movements w i t h s m a l l a m p l i t u d e s (< 1 d e g r e e ) a r e not c o n s i d e r e d h e r e .

T h e r e have been s e v e r a l works on the d e t e r m i n a t i o n o f the s i z e o f t h i s f i e l d o f view f o r a s i n g l e f i x a t i o n (e.g. R e f . 5 - 7 ) . T h i s a r e a around the f i x a t i o n p o i n t from w h i c h u s a b l e i n f o r m a t i o n can be e x t r a c t e d depends upon t h e t a s k , the k i n d o f t a r g e t and background o b j e c t s , and the p i c t u r e q u a l i t y . I t i s o f t e n c a l l e d c o n s p i c u i t y a r e a w h i c h i s d e s c r i b e d as " t h e r e t i n a l f i e l d i n w h i c h the r e l e v a n t o b j e c t can be d i s c o v e r e d (without p r i o r knowledge o f

l o c a t i o n ) i n i t s background, d u r i n g a b r i e f p r e s e n t a t i o n o f the s t i m u l u s p a t t e r n " ( R e f . 5 ) . I n Ref.7 one can f i n d the term " u s e f u l v i s u a l f i e l d o f v i e w " w i t h a s i m i l a r meaning.

The aim of the p r e s e n t experiment i s to d e t e r m i n e the s i z e o f c o n s p i c u i t y a r e a s when s u b j e c t s a r e s e a r c h i n g f o r a v e h i c l e i n a n a t u r a l s c e n e . A s p e c i a l a p p a r a t u s by which a v i s u a l f i e l d w i t h a d j u s t a b l e s i z e c o u l d be s h i f t e d by e y e , head, or hand movements was employed. W i t h such a d e v i c e the h y p o t h e s i s can be t e s t e d t h a t the d e t e c t i o n time i n complex scenes such as a e r i a l p i c t u r e s , d i s p l a y e d on a TV s c r e e n , i s e s s e n t i a l l y d e t e r m i n e d by p r o p e r t i e s of the v i s u a l and c o g n i t i v e system and not so much by the k i n d of muscles i n v o l v e d i n s h i f t i n g the v i s u a l f i e l d on the d i s p l a y .

-

29

-GENERAL METHOD

S t i m u l i

S t a t i c scènes were t a k e n as s l i d e s from a 1:87 t e r r a i n model w i t h f o u r summer-sceneries: f o r e s t , meadow, f i e l d , v i l l a g e (see F i g . 4 ) . A scène c o n s i s t e d o f one o f t h e s e s c e n e r i e s and c o v e r e d a ground a r e a o f 130x130 m e t e r s2 a t a s i m u l a t e d a l t i t u d e o f 300 m e t e r s w i t h v e r t i c a l a s p e c t a n g l e .

The s l i d e s were t a k e n from d i f f u s e l y i l l u m i n a t e d scènes. The t a r g e t s were m i l i t a r y v e h i c l e s o f 4 t y p e s : 2 d i f f e r e n t t y p e s o f tanks and 2 d i f f e r e n t

t y p e s of t r u c k s . E a c h scène c o n t a i n e d o n l y one m i l i t a r y v e h i c l e as a t a r g e t w h i c h must be d e t e c t e d .

A p p a r a t u s

The s l i d e s were e i t h e r scènes o r a n e u t r a l pause p i c t u r e . They were scanned by a TV camera and p r e s e n t e d on a s t a n d a r d 6 2 5 - l i n e TV m o n i t o r w i t h 30 cm s c r e e n s i z e . The s u b j e c t s used a b i t e b o a r d t o i m m o b i l i z e t h e i r head . The h o r i z o n t a l v i e w i n g a n g l e was 24 d e g r e e s . The scheine o f t h e expérimental arrangement i s shown i n F i g . 1. The p i c t u r e on the TV m o n i t o r appeared t o t h e s u b j e c t o n l y p a r t l y w i t h i n a s m a l l s q u a r e whose p o s i t i o n c o i n c i d e d e x a c t l y w i t h h i s v i s u a l a x i s when eye movements a r e u s e d t o change t h e p o s i t i o n o f the window as i n d i c a t e d i n F i g . 1.

TV-CAMERA 0SC1LLOGRAPH MONITOR PLOTTER COMPUTER

F i g . 1 : S c h e m a t i c v i e w o f the

a p p a r a t u s t o r e s t r i c t v i s u a l f i e l d s i z e and t o change the p o s i t i o n by eye movements .

F i g . 2 : D e v i c e f o r a n a l y z i n g a v i d e o s i g n a l and t h e génération o f d i f f e r e n t p a t t e r n s .

The t w o d i m e n s i o n a l eye movements o f the s u b j e c t ' s l e f t o r r i g h t eye were d e t e c t e d by t h e c o r n e a l r e f l e c t i o n method u s i n g a S i l i c o n TV camera f o r r e g i s t r a t i o n o f the I R - l i g h t w h i c h i s r e f l e c t e d from the s u b j e c t ' s eye and an I R - m i r r o r ( R e f . 8 ) . The s u b j e c t c o u l d a d j u s t the o c u l o m e t e r by h i m s e l f because he o b s e r v e s h i s own c o r n e a l r e f l e x on the TV m o n i t o r . L o o k i n g a t t h e c e n t e r of the d i s p l a y he changes the p o s i t i o n o f the b i t e b o a r d u n t i l the p o s i t i o n o f the r e f l e x and t h e c e n t e r o f t h e d i s p l a y c o i n c i d e . The o u t p u t o f t h e TV camera i s f e d t o an e l e c t r o n i c d e v i c e where the x, y -c o o r d i n a t e s o f t h e -c o r n e a l r e f l e x a r e e x t r a -c t e d out o f t h e v i d e o s i g n a l . T h i s d e v i c e a l s o c o n t a i n s a f u n c t i o n g e n e r a t o r w h i c h générâtes a s q u a r e o f a d j u s t a b l e s i z e the c o r n e a l r e f l e x b e e i n g the c e n t e r o f the s q u a r e . The scheme o f t h i s e l e c t r o n i c d e v i c e , w h i c h i s c a l l e d V i d e o - A n a l y z e r and

- G e n e r a t o r , i s shown i n F i g . 2 . I n p u t s from a TV camera, a v i d e o r e c o r d e r , a l i g h t p e n , a j o y s t i c k , a n d from a computer a r e e s t a b l i s h e d . The Outputs can be f e d t o an o s c i l l o s c o p e , a m o n i t o r , a p l o t t e r , o r a computer. We d i d use

30

-the x-, y - a n a l o g O u t p u t s i g n a i s f o r changing the p o s i t i o n o f the square on the m o n i t o r .

I n a d d i t i o n to the d e v i c e d e p i c t e d i n

Fig.

2

an e l e c t r o n i c c i r c u i t was used to p e r f o r m the t r a n s f o r m a t i o n

x' = (x-x_>-A

of the measured eye p o s i t i o n x,y t o the d e s i r e d p o s i t i o n x',y', which i s the f i x a t i o n p o i n t i n an e q u a l l y spaced g r i d . The c o o r d i n a t e s x^, y ^ g i v e the measured eye p o s i t i o n when t h e eye f i x e s the c e n t e r o f the m o n i t o r and the d i s p l a y e d c o r n e a l r e f l e x c o i n c i d e s w i t h the c e n t e r p o i n t . A and B a r e c o n s t a n t s f o r the a d j u s t m e n t .

As mentioned e a r l i e r , t h e p o s i t i o n o f the v i s u a l f i e l d c o u l d a l s o be changed by head movements. The a p p r o p r i a t e scheme of the expérimental arrangement i s shown i n

Fig.

3.

A l i g h t s o u r c e which emits a p a r a l l e l l i g h t beam i s c l o s e l y c o n n e c t e d w i t h a f l e x i b l e r i n g around t h e s u b j e c t ' s head. The beam i s p r o j e c t e d on a d i f f u s i n g s c r e e n . The p o s i t i o n o f the c o r r e s p o n d i n g l i g h t s p o t i s measured by an e l e c t r o - o p t i c a l d e v i c e w h i c h i s n e a r l y i d e n t i c a l t o t h a t shown i n

Figs

.1

and

2.

The a m p l i t u d e s o f t h e x-, y - s i g n a l s , i . e . the Output o f the v i d e o a n a l y z e r , a r e p r o p o r t i o n a l to the r o t a t i o n a n g l e s of thè head around a v e r t i c a l and a h o r i z o n t a l a x i s f o r the s m a l l v i s u a l a n g l e s under considération.

F i n a l l y a change o f the p o s i t i o n o f the v i s u a l f i e l d was a c h i e v e d by manual c o n t r o l w i t h a j o y s t i c k . The d i r e c t i o n o f the hand movements c o r r e s p o n d s e x a c t l y to the m o t i o n d i r e c t i o n of the d i s p l a y e d v i s u a l f i e l d .

F i g .4 : Open f i e l d w i t h eye movement t r a c e s