SOFTWm ERGONOMICS: EFFECTS OF COMPUTER APPLICATION ...

S O F T W m ERGONOMICS:

EFFECTS OF COMPUTER APPLICATION DESIGN

PARAMETERS ON OPERATOR TASK PERFORMANCE AND HEALTH

Jon A. Turner New York University Robert A. Karasek, Jr. Columbia University

June 1983

Center for Research on Information Systems Computer Applications and Information Systems Area Graduate School of Business Administration New York University

Working Paper Series CRIS R56 GBA #83-84(CR)

Published in ERGONOMICS, 1984 Vo1.27, No.6, pp.663-690 The order of the authors' names has been selected by chance to signify equal contribution to this paper. Addresses are: Computer Applications and Information Systems Area, NYU Graduate School of Business Administration, 90 Trinity Place, New York, NY 10006, (212)285-6086; Department of Industrial Engineering and Operations Research, Columbia University, New York, NY 10027, (212)280-2935. The authors are indebted to Dr. Judith Reitman-Olson, Professor Ben Shneiderman, Dr. Phyllis Reisner, Professor Henry C. Lucas, Jr., and Professor Walter Reitman for their comments on a previous version of this paper.

Center for Digital Economy Research Stem School of Business IVorking Paper IS-83-84

Page 2

Abstract Evidence i s reviewed t h a t the operating c h a r a c t e r i s t i c s of computer application systems, i n addition t o physical c h a r a c t e r i s t i c s of display u n i t s (CRTs), a r e t h e cause of many observed e f f e c t s on operator h e a l t h and task effectiveness. These e f f e c t s a r e hypothesized t o occur through changes i n task s t r u c t u r e , and t h e man-machine redivision of labor t h a t r e s u l t s when computer application systems a r e introduced i n t o work s e t t i n g s . F i r s t , t h e association between task dimensions and models of operator performance effectiveness and well-being a r e reviewed. Second, application system design parameters t h a t a f f e c t task s t r u c t u r e a r e i d e n t i f i e d . Then, empirical evidence supporting t h i s t h r e e p a r t causal linkage application system parameters t o t a s k c h a r a c t e r i s t i c s t o operator i s presented. effectiveness and health

-

-

The findings suggest t h a t by improving dialogue q u a l i t y , taking advantage of two way communication t o reduce uncertainty, using smaller and l e s s integrated systems and matching system performance t o operator needs a job can be created t h a t i s l i k e l y t o improve both operator well-being and effectiveness.

Keywords Information Systems, Systems Design, Software Design, Job Design, Task Environment.


Page 3

1.0

Introduction Use of cathode ray tube displays (CRT's) i n U.S.

workplaces has

increased a t such a rapid pace t h a t t h e r e has been l i t t l e time for assessment of the e f f e c t s of t h i s new man-machine i n t e r f a c e on human performance and health.

Primary emphasis of research t o d a t e appears

t o have concentrated on t h e physical c h a r a c t e r i s t i c s of CRT terminals themselves (Grandjean, 1980), including such parameters a s screen luminosity and color, f l i c k e r r a t e s , and character resolution, a s well as ergonomic considerations, f o r example, seating position and keyboard location.

Evidence of the e f f e c t s of such f a c t o r s on

s p e c i f i c i l l n e s s e s continues t o be equivocal ( f o r example, c a t a r a c t s Zaret, 1980;

-

AAO, 1982).

However, t h e r e i s very consistent evidence of more generalized psychosomatic s t r e s s problems based on s e l f - r e p o r t data i n a v a r i e t y of studies from several countries (Smith e t a l . ,

1981;

Aronsson, 1980;

The implication of

Turner, 1980;

Bradley, 1977).

Johansson and

t h i s consistent psychosomatic evidence i s t h a t t h e problem may not be solely the physical parameters of the CRT's themselves or the positioning of the display i n t h e work s e t t i n g , but a d d i t i o n a l l y , t h e s t r e s s resulting from operating c h a r a c t e r i s t i c s of t h e o v e r a l l computer application system.

By operating c h a r a c t e r i s t i c s we mean the

command sequences performed by t h e operator i n order t o control t h e system and the responses produced by t h e system.


Page 4 I n s u p p o r t o f t h i s p o s i t i o n , n o one has s u g g e s t e d t h a t c o m p l a i n t s a b o u t u s i n g computer s y s t e m s would be s u b s t a n t i a l l y d i m i n i s h e d i f p r i n t i n g t e r m i n a l s w e r e s u b s t i t u t e d f o r C R T ' s , w h i c h would change many of the d i s p l a y ' s p h y s i c a l parameters.

Thus, it i s i m p o r t a n t t o

d i s t i n g u i s h ' p h y s i c a l ' problems b a s e d on CRT h a r d w a r e and p l a c e m e n t from p r o b l e m s t h a t may a r i s e d u e t o t h e r e a l l o c a t i o n o f t a s k s between man and machine and the c o n t e n t o f t h e r e s u l t i n g human t a s k s . I n i n t e r p r e t i n g t h e i r f i n d i n g s Smith e t a l . , 1 9 8 1 o b s e r v e , "

..

there was n o t a s t r o n g r e l a t i o n s h i p between t h e amount o f t i m e s p e n t

working a t the VDT [CRT]

and r e s u l t a n t h e a l t h c o m p l a i n t s

...

T h e r e f o r e , it seems l i k e l y t h a t there must be o t h e r f a c t o r s beyond t h e p h y s i c a l p r e s e n c e o f the VDT [CRT]

t h a t c o n t r i b u t e t o the h e a l t h

c o m p l a i n t s and stress l e v e l o f t h e c l e r i c a l o p e r a t o r s " ( p .

6-7).

It

i s m a i n t a i n e d t h a t c h a n g e s i n t a s k e n v i r o n m e n t r e s u l t i n g from t h e

r e d e s i g n o f work t o make u s e o f computer s y s t e m s i s l i k e l y t o be o n e such f a c t o r . A s J o h a n s s o n and Aronsson ( 1 9 8 0 ) o b s e r v e ,

" t o the e x t e n t t h a t

d i f f e r e n c e s between computer e l e c t r o n i c s and t h e human n e r v o u s s y s t e m

-

w i t h their r e s p e c t i v e r e a c t i o n t i m e s

-

do u n d e r l i e r e p o r t s o f

t e n s i o n , f a t i g u e and s o o n , i t i s h a r d l y s u r p r i s i n g t h a t s p e c i a l VDU [CRT] s p e c t a c l e s and b e t t e r f u r n i t u r e d e s i g n h a v e n o t e l i m i n a t e d these s t r a i n s . " S u p p o r t i n g e v i d e n c e comes from t h e f a c t t h a t computer u s e r s w i t h d i f f e r e n t t a s k s t r u c t u r e s ( i . e . , same job w i t h d i f f e r e n t

d i v i s i o n s o f l a b o r between worker and c o m p u t e r ) h a v e d i f f e r e n t h e a l t h outcomes ( B r a d l e y , 1981;

T u r n e r , 1980;

Bjorn-Andersen,

1976), a

c o n c l u s i o n s u p p o r t e d i n r e c e n t NIOSH s t u d i e s ( S m i t h e t a l . , 1 9 8 1 ) .


Page 5 D e s i g n i n g e f f e c t i v e man-machine systems i n v o l v i n g h i g h o r d e r human m e n t a l f u n c t i o n s i s h a r d e r t h a n d e s i g n i n g s y s t e m s w i t h a good p h y s i c a l f i t ( i . e . , keyboard p o s i t i o n o r s e a t i n g h e i g h t )

.

The

c o g n i t i v e p r o c e s s e s i n v o l v e d i n complex c o n t r o l s i t u a t i o n s a r e p o o r l y u n d e r s t o o d whereas t h e p h y s i o l o g i c a l l i m i t a t i o n s o f humans a r e q u i t e

w e l l documented.

In addition, t h e relevant characteristics of

computer a p p l i c a t i o n systems a r e h a r d e r t o measure t h a n a r e t h e c h a r a c t e r i s t i c s o f a p i e c e o f hardware, and t h e r e s e a r c h f i n d i n g s about t h e s e systems a r e not w e l l organized f o r u s e by d e s i g n e r s . The g o a l o f t h i s p a p e r i s t o s t r u c t u r e r e l e v a n t r e s e a r c h f i n d i n g s i n t o models which a r e meaningful t o computer a p p l i c a t i o n d e s i g n e r s . I t i s h y p o t h e s i z e d (Diagram 1 ) t h a t t a s k c h a r a c t e r i s t i c s i r f t e r v e n e

between computer a p p l i c a t i o n system d e s i g n p a r a m e t e r s and worker outcomes ( T u r n e r , 1 9 8 0 ) .

When a n a p p l i c a t i o n s y s t e m is implemented,

i n t e n t i o n a l l y o r n o t , l a b o r i s r e a l l o c a t e d between man and machine r e s u l t i n g i n a new s e t of t a s k s f o r b o t h worker and machine t h e man-machine d i v i s i o n o f l a b o r i s changed.

--

i.e.,

These t a s k s a r e t h e n

r e i n t e g r a t e d i n t o a f u n c t i o n a l system by g i v i n g t h e o p e r a t o r a p p r o p r i a t e c o n t r o l sequences and system s t a t u s i n f o r m a t i o n t o complete t h e work.

[PLACE DIAGRAM 1 ABOUT HERE]

S u b s t a n t i a t i n g t h i s p o s i t i o n r e q u i r e s f o r g i n g a l i n k a g e between, 1) t a s k c h a r a c t e r i s t i c s t h a t might e f f e c t t h e w e l l b e i n g and

performance e f f e c t i v e n e s s o f w o r k e r s u s i n g computer s y s t e m s ( s e c t i o n 2 of t h e p a p e r and p a t h I i n Diagram l ) , and 2 ) computer a p p l i c a t i o n


Page 6 system design parameters, such as those used i n data-base management, process c o n t r o l , and word processing, which may e f f e c t task c h a r a c t e r i s t i c s ( s e c t i o n 3 of t h e paper and path I1 i n Diagram 1 ) . I n section 4 of t h i s paper the empirical evidence linking these s e t s of parameters i s summarized i n t a b l e s f o r use by system designers t o r e l a t e technical system parameters t o t h e i r e f f e c t s on human behavior.

2.0

Task Characteristics and Worker Outcomes

I n t h e sections below several l i t e r a t u r e s a r e reviewed f o r appropriate models i n t h e areas of human s i g n a l detection, learning effectiveness, information processing, and coordination of t a s k s .

The

implications of t h i s broad material i s summarized i n Diagram 2 .


2.1

Performance Effectiveness Welford (1976) has summarized t h e l i t e r a t u r e on performance

effectiveness of work tasks i n terms of an information processing model ( s e e a l s o Broadbent, 1 9 7 1 ) .

The model s t a t e s t h a t an individual

distinguishes relevant signals from t h e environment and, then, t r a n s f e r s associations between such s i g n a l s and appropriate responses t o long term memory f o r future use.

Two primary themes a f f e c t i n g

these mechanisms a r e , f i r s t , t h e importance of arousal l e v e l , and, second, t h e r o l e of operator p a r t i c i p a t i o n i n learning and memory retention.


Page 7 2.1.1

Signal D e t ection Efficiency. -

A v a r i e t y o f f a c t o r s a f f e c t how

q u i c k l y a n d e f f e c t i v e l y a n o p e r a t o r c a n work.

'Unpredictability' of

information s u p p l i e d t o a n o p e r a t o r b y a s y s t e m c a n d e c r e a s e

e f f i c i e n c y f o r several reasons.

Operators w i l l normally 'group' o r

' c o d e ' i n f o r m a t i o n by t i m e , l o c a t i o n , c o l o r e t c .

I f a n e n t i r e group

o f s i g n a l s c a n be ' b a t c h e d ' t o g e t h e r b y a human b e i n g ' s s e n s o r y a p p a r a t u s , t h e y c a n be p r o c e s s e d b y a s i n g l e r e s p o n s e s e q u e n c e , i n c r e a s i n g the i n d i v i d u a l ' s processing e f f i c i e n c y (Welford, 1976). Thus, ' p a t t e r n i n g ' or r e c o g n i t i o n o f i n f o r m a t i o n s e q u e n c e s c a n improve processing e f f i c i e n c y (although n o t i f p a t t e r n i n g i n c r e a s e s t o the l e v e l o f 'monotony',

Zubek, 1 9 6 4 ) .

Another r e a s o n t h a t

u n p r e d i c t a b i l i t y d i m i n i s h e s e f f i c i e n c y , i s t h a t c o n s t a n t s e a r c h i n g and c o n c e n t r a t i o n i s r e q u i r e d t o d e t e c t i n f r e q u e n t s i g n a l s , s i n c e it i s i m p o s s i b l e t o f o r e c a s t when a n e v e n t w i l l o c c u r ( i . e . , enemy a i r c r a f t o n r a d a r s c r e e n s , Broadbent, 1958, 1 9 7 1 ) .

T h i s constant energy

e x p e n d i t u r e q u i c k l y l e a d s t o f a t i g u e and p s y c h o l o g i c a l stress ( s e e section 2.2).

I n d e e d , J o h a n s s o n and Aronsson ( 1 9 8 0 ) f i n d

u n p r e d i c t a b l e computer s y s t e m breakdowns a s the c l e a r e s t c o n t r i b u t i o n t o job stress f o r c l e r i c a l w o r k e r s u s i n g computer a p p l i c a t i o n s y s t e m s .

2.1.2

Task and Performance. - Arousal -

non-specific

A r o u s a l l e v e l refers t o a

g e n e r a l a c t i v a t i o n l e v e l o f the f u l l n e r v o u s s y s t e m

(asleep-awake-alert)

r e l a t i n g t o a p e r s o n ' s r e a d i n e s s t o respond t o

environmental s t i m u l i .

A r o u s a l l e v e l a t work i s p r i m a r i l y a f u n c t i o n

o f t a s k demands ( i - e . , p r o c e s s i n g l o a d p e r u n i t t i m e ) , b u t a l s o c a n be e f f e c t e d by g e n e r a l i z e d s t i m u l a t i o n f r o m t h e e n v i r o n m e n t ,

(for

example, n o i s e ) and by t h e i n d i v i d u a l ' s e m o t i o n a l s t a t e .

There i s

a l m o s t u n i v e r s a l agreement ( s e e d i s c u s s i o n i n F r a n k e n h a e u s e r a n d


Page 8 J o h a n s s o n , 1974) t h a t performance e f f e c t i v e n e s s i s r e l a t e d t o a r o u s a l by a *U-shaped' curve: too low

-

i n e f f e c t i v e r e s p o n s e o c c u r s when a r o u s a l i s

b e c a u s e of e r r o r s o f o m i s s i o n (Welford, 1 9 7 6 ) , or b e c a u s e of

t h e f a t i g u i n g demands o f s e l f - m o t i v a t e d c o n c e n t r a t i o n . i n e f f e c t i v e r e s p o n s e o c c u r s when a r o u s a l i s too h i g h e r r o r s o f commission and f a t i g u e .

And

- because

of

The n a t u r e o f s u c c e s s f u l l y

achievable t a s k s vary w i t h a r o u s a l (and visa-versa):

a difficult task

c a n b e a c h i e v e d o n l y a t a low o v e r a l l a r o u s a l l e v e l ( a s w e l l a s w i t h i n a very r e s t r i c t e d arousal range);

a s i m p l e r task may be f a c i l i t a t e d

by h i g h a r o u s a l , and h a v e s u c c e s s less d e p e n d e n t o n a r o u s a l l e v e l .

-

O p e r at o r Autonomy and L e a r n i n g E f f e c t i v e n e ss

2.1.3

. -

A b r o a d theme i n t h e performance e f f e c t i v e n e s s l i t e r a t u r e i s t h e

s i g n i f i c a n c e of o p e r a t o r autonomy i n p e r f o r m a n c e of s k i l l e d t a s k s .

Of

c o u r s e , a n o p e r a t o r ' s own c u r r e n t s k i l l l e v e l i s a major d e t e r m i n a n t o f t a s k s which h e s h o u l d be able t o p e r f o r m , b u t a dynamic view o f complex t a s k performance emphasizes t h e i m p o r t a n c e o f l e a r n i n g new skills. Several researchers (e.g.,

Bainbridge, 1974) p o i n t o u t t h a t the

t a s k s i t u a t i o n i t s e l f contains s e v e r a l important determinants of learning f a c i l i t y .

A s Welford ( 1 9 7 6 ) , Baker and Young ( 1 9 6 0 ) , and

B e l b i n and Downs ( 1 9 6 4 ) o b s e r v e , a n o p p o r t u n i t y f o r a c t i v e r e s p o n s e t o the t a s k stimulus

1974)

-

-

and even c o n t r o l o f s u b t a s k s e q u e n c i n g (Duncan,

f a c i l i t a t e s memory r e t e n t i o n f o r complex t a s k s .

The o p e r a t o r

e x e c u t e s a s o l u t i o n s t r a t e g y a n d the machine ' f e e d s b a c k ' a performance measure c o n f i r m i n g t h e o p e r a t o r ' s m e n t a l 'model* o f complex system o p e r a t i o n .

Welford ( 1 9 7 6 ) o b s e r v e s t h a t a c t i v e


Page 9 feedback f a c i l i t a t e s learning both by allowing f i n e r response adjustments t o be made and by illuminating t h e l i m i t of an a c t i o n ' s effectiveness.

An important implication of the need f o r a c t i v e

response i s t h a t the system must be prepared t o accept a l l possible operator responses [ l ] . I n more complex work s i t u a t i o n s , involving multiple t a s k s , again,

a major parameter of effectiveness i s found t o be the o p e r a t o r ' s freedom i n selecting a response s t r a t e g y , f o r example, insuring s a f e landing p a t t e r n s f o r a i r c r a f t (Sperandio, 1971) o r supplying power t o steelmaking furnaces ( Bainbridge, 1972)

.

Indeed, Bainbridge (1974)

concludes t h a t t h e goal of an operator m u s t be formulated i n broad terms ( i . e . , landing an a i r c r a f t s a f e l y i n a i r t r a f f i c c o n t r o l ) so a s not t o inadvertently r e s t r i c t h i s solution s t r a t e g y by predetermining intermediate goals ( i.e. airport)

, a i r c r a f t being held t o

m i n i m u m time t o

.

According t o Umbers (1979), t h e primary determinant of operator effectiveness i s the broad solution s t r a t e g y adopted: 'closed loop' (feedback:

action -->

e r r o r r e p o r t -->

opposing e r r o r ) o r 'open loop' (feedforward: -->

prediction of future e r r o r -->

whether it i s correction

assessment of s i t u a t i o n

preventive c o r r e c t i o n ) .

I n the

most e f f e c t i v e control processors, t h e operator has s u f f i c i e n t knowledge of system functioning, and s u f f i c i e n t information on environmental impacts t o be able t o predict t h e f u t u r e s t a t e of the system and, thus, use open-loop s t r a t e g i e s .

He i s able t o take

advance action against problems instead of having t o wait f o r feedback

i n order t o a c t . 'touch-up'

Closed-loop feedback may be used f o r f i n a l

corrections when open-loop s t r a t e g i e s a r e used.


Page 10 Several f a c t o r s may i n h i b i t using open-loop s t r a t e g i e s , however. Umbers (1979) observes t h a t a s the work load increases operators tend t o switch from open-loop t o closed-loop s t r a t e g i e s (which usually r e s u l t i n l e s s e f f e c t i v e performance).

Bainbridge (1974) explains

t h a t operators attempt t o r e t a i n equilibrium i n arousal l e v e l :

when

the s i t u a t i o n has heavy demands (high arousal l e v e l ) , a planning s t r a t e g y i s selected implying l i t t l e additional c o r t i c a l arousal ( a closed loop system). Open loop s t r a t e g i e s a l s o require s u b s t a n t i a l experience;

i.e.,

learning about system functioning i s necessary before predictions of future s t a t e s can be made.

Work place design can i n h i b i t these

s t r a t e g i e s by inadvertently placing important l i m i t a t i o n s on 'degrees of freedom' of action available t o an operator ( ~ p e r a n d i o ,1971):

for

example, biophysiologically r e s t r i c t i v e environments (inappropriate l i g h t , h e a t , temperature) ;

administrative procedures;

and machine

interfaces t h a t l i m i t s k i l l usage (Kahn, 1981, discusses t h i s problem as q u a l i t a t i v e 'underload*). As an operator t r i e s t o vary h i s strategy i n response t o d i f f e r e n t work loads and t h e technology o r administration r e s i s t s , the technical [computer] a i d which was useful a t a c e r t a i n task load level may become a s t r e s s f a c t o r a t another level (Sperandio, 1971).

2.2

Working Life ~ u a l i t y Both the learning effectiveness and t h e process control

l i t e r a t u r e s concentrate primarily on the parameters of successful performance;

much l e s s a t t e n t i o n has been devoted t o understanding

the mechanisms of performance -- breakdown ---

-

o r operator d i s t r e s s .

An


Page 11 umbrella term for degradation of performance i n t h e information processing approach i s ' f a t i g u e ' . Although comprehensive models of why fatigue develops a r e sparse (Welford, 1976) f21, t h e r e i s a well developed l i s t of fatigue consequences formulated by Welford i n terms of t h e information processing model.

Heavy task loads lead t o decreasing accuracy of

signal discrimination, slowing of sensory responses, and i r r e g u l a r timing of responses.

Of significance f o r complex t a s k s , f a t i g u e a l s o

leads t o disorganization of the o p e r a t o r ' s s t r a t e g i e s f o r combining sub-tasks ( B a r t l e t t , 1943, Welford e t a1

., 1950), including

omission

of infrequent tasks and disruption of short-term memory, possibly due t o over use or l o s s of 'keeping t r a c k ' information.

These l a t e r two

mechanisms imply t h a t the actual work done by an operator w i l l increase under fatigue since time saving encoding processes break down, f u r t h e r accelerating fatigue.

Nevertheless, t h e above f a t i g u e

paradigm implies t h a t even i f overload induces f a t i g u e , performance effectiveness w i l l resume a f t e r a short recovery period.

2.2.1

S t r e s s Consequences. -

S t r e s s research goes beyond t h e i s s u e of

simple performance degradation t o focus on global disruption of an operator's a b i l i t y t o function and h i s physical and mental h e a l t h . Frustration of goals and delay of a c t i o n a r e common themes. In t h e s t r e s s model, performance d i s r u p t i o n may extend f a r beyond the original task boundary and, through generalized 'tension'

or

' a n x i e t y ' , e f f e c t the i n d i v i d u a l ' s e n t i r e psychological o r i e n t a t i o n . The r e s u l t may be l o s s of s e l f esteem, s o c i a l aggression, o r s l e e p disruption (Langner and Michaels, 1961;

Lazarus, 1966;

Karasek,


Page 1 2 1979;

Dohrenwend and Dohrenwend, 1 9 7 4 ) .

P h y s i c a l i l l n e s s may a l s o

r e s u l t , s u c h a s muscular aches (Karasek e t a l .

1982b);

g a s t r o i n t e s t i n a l problems (House e t a 1 . , 1 9 7 9 ) ;

and c a r d i o v a s c u l a r

d i s e a s e ( ~ a r a s e ke t a l . , 1981; 1979;

Kasl,

Friedman e t a l .

1958;

House e t a l . ,

1980).

Such b r o a d r a n g i n g c o n s e q u e n c e s r e q u i r e a n ' a c t i v e ' system d i s r u p t i o n , not j u s t t h e ' p a s s i v e ' p r o c e s s i n g model.

force for

fatigue of t h e information

Under what c i r c u m s t a n c e s d o e s a n i n d i v i d u a l ' s

a r o u s e d e n e r g y s w i t c h from c o n s t r u c t i v e p e r f o r m a n c e t o i n t e r n a l l y destructive strain?

M c G r a t h b s ( 1 9 7 6 ) s i m p l e ' o v e r l o a d ' model o f

stress ( o v e r l o a d o c c u r s when e n v i r o n m e n t a l demands e x c e e d a n i n d i v i d u a l ' s a b i l i t y t o c o p e ) s u g g e s t s t h a t t h e c i r c u m s t a n c e s may be s a i d t o depend on t h e i n d i v i d u a l : 'personality'

(Welford, 1 9 7 6 ) .

h i s s k i l l , e x p e r i e n c e and

I n K a r a s e k ' s (1976, 1 9 7 9 ) ' r e s i d u a l

s t r a i n ' model, t a s k p a r a m e t e r s a l s o d e f i n e a s t r e s s f u l c i r c u m s t a n c e : n o t o n l y t h e magnitude o f t h e l o a d , b u t t h e i n d i v i d u a l ' s d e g r e e o f freedom o f a c t i o n i n t h e f a c e o f a demanding t a s k [ 3 ] ,

and t h e

a v a i l a b i l i t y o f s o c i a l s u p p o r t and a s s i s t a n c e . L i m i t a t i o n s o n t h e o p e r a t o r ' s r e s p o n s e s t r a t e g y c o u l d be a d i r e c t r e s u l t o f t h e man-machine d i v i s i o n o f l a b o r where t h e c o n t r o l l i n g f a c t o r i s a computer a p p l i c a t i o n s y s t e m ' s o p e r a t i n g p a r a m e t e r s .

This

may l e a d t o a l a c k o f t a s k v a r i e t y a n d r i g i d t a s k p r e s c r i p t i o n s w h i c h h a v e b e e n a s s o c i a t e d w i t h p s y c h o l o g i c a l stress a n d j o b d i s s a t i s f a c t i o n (Hackman and Lawler, 1971; Karasek, 1 9 7 9 ) .

C a p l a n e t a l . , 1975;

G a r d e l l , 1971;

A r i g i d , machine p a c e d t a s k d o e s n o t a l l o w a d j u s t m e n t

t o d a i l y v a r i a t i o n s i n human c a p a b i l i t y , l e a d i n g sometimes t o e x c e s s s t r a i n and a t o t h e r t i m e s t o u n d e r u t i l i z e d c a p a c i t y , a l t h o u g h


Page 13 empirical evidence on the e f f e c t s of machine-paced t a s k s remains somewhat equivocal [4]. According t o Karasek's model (1976, 1979), when an individual receives an appropriate signal ( s t r e s s o r ) from t h e environment he prepares psychological and physiological mechanisms f o r a resolving ' a c t i o n ' placing t h e organism i n a s t a t e of ' p o t e n t i a l energy' (stress). arousal

-

However, i f appropriate action cannot be taken a f t e r t h i s because the appropriate actions a r e r e s t r i c t e d by low job

autonomy o r are not known ( i n s u f f i c i e n t knowledge) energy m u s t be dissipated (Ziegarnik, 1 9 2 7 ;

-

t h e aroused

Henry and Cassel, 1969)

and i n t h e process may lead t o deleterious physiological and psychological consequences ( e . g . , s t r a i n , i l l n e s s ) .

The s t r e s s

model's focus on physically traumatic consequences of high l e v e l s of arousal and constant need f o r complex adaptation has been well documented using animal subjects by Selye (1973) and colleagues i n several decades of research. The e f f e c t of work load on s t r a i n and f a t i g u e may, however, not always be l i n e a r

-

a t very low t a s k load l e v e l s added t a s k s may

diminish boredom and s t r a i n (Siegal and Wolf, 1969).

Frankenhaeuser

and Johansson (1981) find t h a t adrenaline, a measure of psychological s t r a i n , i s elevated a t both very low and very high work loads [5].

2.2.2

Operator -Independence. --

Another aspect of t h e man-machine

division of labor created (unintentional or n o t ) by computer application systems a r e s o c i a l l y interdependent t a s k s t r u c t u r e s .

New

dependencies form between application system operators and system support s t a f f s , data entry groups, and computer operators a s well a s


Page 1 4 with supervisors and co-workers.

Turner (1980) suggests t h a t an

o p e r a t o r ' s natural recourse i n times of system breakdown or malfunction i s t o seek interpersonal assistance: obtainable, s t r e s s r e s u l t s .

i f it i s not

However, r e l a t e d findings from l i t e r a t u r e

on ' s o c i a l support' conclude t h a t freely-chosen assistance and emotional support from co-workers and supervisors can d i m i n i s h the adverse e f f e c t s of s t r e s s on the individual (Larocco e t a l . Karasek e t a l .

1982a).

1980;

These l a t t e r research findings implicate

close emotional integration between individuals a s an ameliorating ( ' s t r e s s b u f f e r i n g ' ) mechanism.

However, such p o s i t i v e interpersonal

r e l a t i o n s can be negatively affected by changes i n work process t h a t accompany 'labor restructuring' technologies ( T r i s t and Bamforth, 1951).

These associations highlight the importance of the o f t e n

overlooked interpersonal aspects of task s t r u c t u r e change.

2.3

Summary of Task Characteristics That Influence Operator Well-Being and Performance The search f o r models of human behavior i n performing sensory and

control functions a t a complex man-machine i n t e r f a c e can be summarized with the following themes ( r e f e r t o Diagram 2 and Table 1 ) :

[PLACE TABLE 1 ABOUT HERE]

2.3.1

Dynamic Variation i n Human Arousal Level and Work ------ Load which

Affects- --Both Effectiveness and Psychological S t r a i n . -------

The nervous

system arousal l e v e l which i s required t o enable an operator t o


Page 15 accomplish s p e c i f i c tasks varies i n a complex non-linear manner according t o the overall work load t h e operator faces and other sources of s t r e s s .

Neither too l i t t l e arousal, nor too much

(corresponding, f o r example, t o very heavy t a s k loads) a r e optimal f o r e f f e c t i v e performance. physiological changes

Extremes of arousal can a l s o lead t o adverse

-

of prolonged overload.

w i t h severe i l l n e s s possible under conditions

This suggests t h a t t h e o p e r a t o r ' s work load

should be adjusted according t o burdens imposed by r e l a t e d tasks and other operator s t r e s s sources, i n order t o keep arousal l e v e l w i t h i n an acceptable range [6].

Achieving an arousal balance i s a l s o an

important condition f o r learning e f f e c t i v e n e s s ,

2.3.2

Operator Autonomy -i n Selection of-a Control Strategy. -

It i s

found t h a t operators neither learn individual t a s k s e f f e c t i v e l y , nor a r e able t o build a c l e a r model of o v e r a l l system functioning without autonomy t o a l t e r control s t r a t e g i e s .

Without a c l e a r conceptual

model of a system an operator i s unable t o employ feed forward predictive s t r a t e g i e s associated w i t h e f f e c t i v e performance.

I n the

s t r e s s l i t e r a t u r e , lack of control when facing heavy t a s k demands i s associated w i t h both psychological s t r a i n and physical i l l n e s s :

the

operator i s unable t o most e f f e c t i v e l y a l l o c a t e h i s personal resources, and may a l s o face residual s t r a i n from t a s k s which require arousal, but f r u s t r a t e required a c t i o n .

2.3.3

Uncertainty i n -Machine Function at t h e Man-Machine Interface. ---.--

Uncertainty i n expectations of sensory loads and unanticipated system responses prevent an operator from e f f e c t i v e l y formulating input information and from being able t o take optimum c o r r e c t i v e action.


Page 16 Unexpected system breakdowns w i t h unpredictable durations have been shown t o be one of the g r e a t e s t sources of operator psychological stress.

2.3.4

Unanticipated Task Interdependencies and Exception Conditions

Resulting from Computer Application Systems.

The interdependence of

individuals and work groups are usually a l t e r e d by t h e redivision of labor i m p l i c i t i n a new system design:

an operator may become

dependent on new work methods and consequently l o s e sources of assistance i n task performance t h a t were previously enjoyed.

Another

r a r e l y examined consequence of computer application systems i s t h a t they may e s t a b l i s h r i g i d procedures f o r accomplishing a t a s k whose i r r e g u l a r i t i e s previously had been d e a l t with by a wide v a r i e t y of non-computerized personal problem solving s t r a t e g i e s .

Irregularities

not anticipated by system designers a r e converted i n t o exception conditions

3.0

-

which can dramatically increase operator work load.

Application System Design Parameters and Task C h a r a c t e r i s t i c s The f i r s t p a r t of t h i s paper i d e n t i f i e d themes r e l a t i n g t a s k

requirements t o operator performance and well-being. the task environment a r e p a r t i c u l a r l y important:

Four aspects of

operator autonomy

over control s t r a t e g y s e l e c t i o n , operator uncertainty about system operation, a l t e r e d task interdependencies, and o v e r a l l work load r e l a t i v e t o arousal l e v e l .

I n t h i s s e c t i o n corresponding computer

application system parameters a r e considered.


Page 1 7 Too o f t e n w r i t e r s r e f e r t o l o o s e l y d e f i n e d n o t i o n s , s u c h a s ' u s e r p e r c e i v e d s y s t e m q u a l i t y ' or ' u s e r f r i e n d l y ' w i t h o u t e x p l a i n i n g t h e c o n s t i t u e n t s o f these n o t i o n s o r t h e mechanisms b y which t h e y i n f l u e n c e human b e h a v i o r .

While few would d i s a g r e e t h a t ' e a s e - o f - u s e '

o r ' f a u l t t o l e r a n t ' a r e d e s i r a b l e system f e a t u r e s , t h e y are c o n c e p t s which are t o o g e n e r a l t o p r o v i d e much g u i d a n c e t o a p p l i c a t i o n

designers.

No one p u r p o s e l y makes a s y s t e m ' h a r d ' t o u s e , b u t it i s

n o t c l e a r , f r e q u e n t l y , j u s t w h a t aspects o f a s y s t e m make it e a s y t o u s e i n a p a r t i c u l a r work s e t t i n g o r w h a t t r a d e - o f f s w i t h o t h e r f e a t u r e s are i n v o l v e d i n a c h e i v i n g t h i s o b j e c t i v e . A t t h e o t h e r e x t r e m e o f d e t a i l , numerous p r e s c r i p t i o n s f o r

d e s i g n i n g s p e c i f i c s y s t e m components e x i s t , f o r example, s c r e e n layouts o r dialogues (Martin, 1973).

While t h e s e c h e c k l i s t s may

c o n t a i n some u s e f u l i n f o r m a t i o n f o r i n e x p e r i e n c e d d e s i g n e r s , a s Shneiderman ( 1980a) o b s e r v e s , t h e y o f t e n c o n t a i n c o n f l i c t i n g recommendations.

Focusing o n a p a r t o f a s y s t e m , w i t h o u t a s e t o f

g e n e r a l p r i n c i p l e s , c a n e n c o u r a g e o v e r l o o k i n g b r o a d e r i s s u e s , s u c h as j o b d e s i g n , t h a t may h a v e f a r r e a c h i n g c o n s e q u e n c e s . R e s e a r c h e r s c o n c e r n e d w i t h t h e 'human f a c t o r s ' o f computer s y s t e m s , h a v e t e n d e d t o be q u i t e e x p l i c i t i n t h e i r meaning o f ease-of-use,

d e f i n i n g it i n t e r m s t h a t permit q u a n t i t a t i v e measurement

( f o r example, l e a r n i n g b a s i c programming l a n g u a g e f u n c t i o n s and combining t h e m i n t o more complex q u e r i e s ) and p e r f o r m i n g e x p e r i m e n t s i n v o l v i n g p e o p l e u s i n g s y s t e m s t o do d i f f e r e n t k i n d s o f t a s k s (Reisner, 1981).

However, t h i s research i s m o s t l y c o n c e r n e d w i t h

d i f f e r e n c e s i n programming l a n g u a g e f e a t u r e s ( f o r example, s y n t a c t i c form o r d e g r e e o f p r o c e d u r a l i t y ) or programming t e c h n i q u e s ( S h e i l ,


Page 18 1981) and i s of more benefit i n t h e design of programming languages o r i n programming than i n application system design. An objective of t h i s paper i s t o i d e n t i f y those general

application system parameters t h a t influence t h e t a s k dimensions i d e n t i f i e d above and are a l s o meaningful t o system designers;

that

i s , reference factors designers consider d u r i n g t h e design process. By linking system parameters t o operator performance and well-being,

through task dimensions, t h e consequences of s p e c i f i c design trade-offs should be more evident. As Rouse (1981) observes, task-allocation decisions on t h e p a r t of a system designer a r e tantamount t o defining t h e human's job. These decisions should not be made i n a piecemeal fashion, but r a t h e r on t h e b a s i s of established p r i n c i p l e s . stated:

The design problem can be

given a p a r t i c u l a r s e t of tasks t o be performed, which tasks

w i l l be performed manually, which tasks w i l l be performed

automatically, and which w i l l be performed using some form of human-computer i n t e r a c t i o n .

The c e n t r a l issue i s t h e b a s i s upon which

these allocation decision w i l l be made.

3.1

S t r a t e g i e s for Task Allocation One approach t o a l l o c a t i n g tasks between humans and computers i s

t o p a r t i t i o n a s e t of tasks i n t o (what i s hoped w i l l be) coherent subsets (Rouse, 1981).

One subset i s allocated t o a human and t h e

other t o a computer on the b a s i s of t h e match between the information processing demands ( k i n d s of processing, amount of processing) of the task and the c h a r a c t e r i s t i c s of t h e processor (Reitman, 1982).

For


Page 1 9 example, i t i s generally acknowledged t h a t humans are good a t cognitive t a s k s , such as formulating generalizations, unstructured problem solving, and evaluation while computers a r e e f f i c i e n t a t c a l c u l a t i o n , such as data transformation, model simulation and display tasks. A r e l a t e d approach i s t o use an operator a s a supervisory

c o n t r o l l e r (Greenstein e t a l . , 1981).

The human becomes responsible

f o r 1) monitoring, involving the detecting of events t h a t require human action and the execution of appropriate a c t i o n , 2 ) intervening, or resorting t o manual control i n response t o unanticipated events o r during maintenance, 3 ) planning/managing of t h e system i t s e l f , including reprogramming, and 4 ) operator t r a i n i n g .

The machine then

performs a l l other functions. An a l t e r n a t i v e s t r a t e g y i s t o a l l o c a t e a l l t a s k s t h a t can be

performed by a computer t o a computer.

Depending on t h e o v e r a l l job,

t h e human may experience wide fluctuations i n load with periods of low activity.

A v a r i a t i o n of t h i s theme i s t o a l l o c a t e human tasks on t h e

b a s i s of e f f i c i e n t computer processing.

The human performs those

tasks t h a t r e s u l t i n maximizing machine performance based on some objective system parameter. Several considerations influence the choice of a t a s k a l l o c a t i o n strategy.

The time i n t e r v a l over which a t a s k i s performed frequently

defines acceptable processing modes.

A s Rouse (1981) notes,

it i s

q u i t e possible f o r a human t o perform a job acceptably f o r a few minutes o r hours while it would not be possible f o r him t o endure t h e same task for a period of weeks, months, o r a whole c a r e e r .

This i s


Page 20 p a r t i c u l a r l y t r u e f o r mental work load (Moray, 1979), where l e v e l s of s t r e s s t h a t are t o l e r a b l e over a short period cannot be endured over a longer period and may lead t o increased human e r r o r o r disease (Karasek e t a l . , 1982b). A second major f a c t o r t o be considered i n t h e choice of a t a s k

a l l o c a t i o n s t r a t e g y i s the question of who controls a system human or a computer.

--

the

There are any number of a l t e r n a t i v e s ranging

from complete human control t o t h e reverse.

As Rouse (1981) points

out unless control i s e x p l i c i t it i s possible f o r t h e human t o become confused about who i s supposed t o perform a p a r t i c u l a r task leading t o decreased task performance effectiveness. The basic philosophical and economic j u s t i f i c a t i o n f o r new technologies, such as computers, i s t h a t they a r e ' t o o l s ' t o extend human beings c r e a t i v e and productive c a p a b i l i t i e s . requires the operator t o be 'incharge'.

Such a perspective

I n r e a l i t y , computer

application systems a r e often designed f i r s t and operators a r e then expected t o adapt t o them. Another issue influencing t h e choice of a t a s k a l l o c a t i o n strategy i s the extent t o which human operators w i l l accept computer-aided decision making.

A fourth f a c t o r i s t h e degree of

i n t e r a c t i o n among concurrent t a s k s , t h e problem being t h a t t a s k performance effectiveness may decrease when t h e same processing resource i s required t o process multiple, concurrent tasks (due t o overhead and program complexity i n a computer and limited s h o r t term memory i n humans)

.


Page 2 1 The above allocation approaches a l l share one aspect i n common

--

they a r e s t a t i c and do not take i n t o account changes i n processor load a s a function of time.

They a l s o f a i l t o recognize t h a t some tasks

could be performed acceptably by e i t h e r humans o r computers (Rouse, 1981).

These deficiencies suggest the notion of dynamic t a s k

allocation. Chu and Rouse (1979) conclude t h a t dynamic t a s k a l l o c a t i o n has

numerous advantages including b e t t e r use of system resources, l e s s v a r i a b i l i t y i n t h e human's work load, and improved opportunity f o r learning.

The basic idea behind dynamic t a s k a l l o c a t i o n i s t h a t t a s k s

a r e assigned t o t h e processor (human or machine) with t h e g r e a t e s t instantaneous capacity f o r performing t h e t a s k .

This approach has t h e

advantage of permitting adapting t o performance l e v e l differences among operators a s well a s t o one operator over time.

For example, a

system able t o sense an o p e r a t o r ' s arousal l e v e l could dynamically r e a l l o c a t e tasks so a s not t o overload t h e human operator, while s t i l l maintaining o v e r a l l system performance ( s e e section 5.1.3) o r an operator could s e l e c t a task a l l o c a t i o n plan a t t h e beginning of each work session. I n Diagram 3 those aspects of computer application systems t h a t

influence the task environment of operators i n a man-machine system (are identified).

The information processing model of operator

performance effectiveness (Welford, 1976) suggests t h a t humans form conceptual models of the process under c o n t r o l permitting t h e selection of d i f f e r e n t control s t r a t e g i e s (Bainbridge, 1974).

These

models are used by an operator t o i n t e r p r e t information about system operation i n order t o s e l e c t a proper c o n t r o l sequence (Bainbridge,


Page 2 2 Umber, 1979;

1974;

dialogue -between models.

Miller, 1981).

I t follows, then, t h a t t h e

human and machine i s key t o the construction of these

Indeed, a s Greenstein e t a l . , (1981) observe, t h e primary

method of resolving coordination c o n f l i c t s between an operator and a computer i s t o maximize the information supplied t o each processor about present and planned actions of t h e other.

Man-machine dialogue

becomes t h e b a s i s f o r a l l overt information t r a n s f e r between operator and system and it provides the cues needed by an operator t o invoke appropriate models of system operation.


3.2

Dialogue Q u a l i t y A t a general l e v e l , dialogue m u s t not be i n c o n f l i c t with an

operator's conceptual model of the process being controlled (Gaines and Facey, 1975) or h i s task based expectations.

More s p e c i f i c a l l y ,

the dialogue must provide 1) s u f f i c i e n t information about t h e c u r r e n t system s t a t e , 2 ) information about l i k e l y f u t u r e s t a t e s ( t r a n s i t i o n s ) , and 3 ) information i n a framework t h a t i s meaningful t o t h e operator. Information about current and f u t u r e s t a t e s i s necessary f o r an operator t o be able t o apply e i t h e r feedforward o r feedback c o n t r o l techniques corresponding t o open o r closed loop control s t r a t e g i e s .

A

meaningful framework implies t h a t e n t i t i e s r e f e r r e d t o i n dialogue and the concepts related t o those e n t i t i e s should be ones with which t h e operator i s f a m i l i a r and comfortable.

That i s , t h e e n t i t i e s and

concepts should match the o p e r a t o r ' s t a s k vocabulary.

Furthermore,

the system must be able t o d e t e c t dialogue ambiguity and resolve it


Page 23 e i t h e r l o g i c a l l y o r by c l a r i f i c a t i o n from t h e o p e r a t o r .

From t h e d e s i g n e r s p e r s p e c t i v e s e v e r a l f a c t o r s , r e p r e s e n t i n g trade-offs

t h a t e f f e c t a n o p e r a t o r ' s t a s k environment, i n f l u e n c e

dialogue structure.

3.2.1

E f f i c i e n c y i s a measure o f t h e amount o f communication (number

o f t o k e n s ) r e q u i r e d t o e x p r e s s a command o r message.

This e f f e c t s a n

o p e r a t o r ' s work l o a d i n g e n e r a t i n g commands and i n i n t e r p r e t i n g messages.

For many c l a s s e s o f commands, f o r m a l l a n g u a g e s a r e l i k e l y

t o be m o r e e f f i c i e n t t h a n n a t u r a l l a n g u a g e s ( t h a t i s , n a t i v e t o n g u e ) . However, t h e e x t e n t t o which a f o r m a l l a n g u a g e c a n be u s e d d e p e n d s o n a n o p e r a t o r ' s l e v e l o f s p e c i a l i z e d knowledge.

3.2.2

N a t u r a l n e s s i s t h e d e g r e e t o w h i c h t h e d i a l o g u e form i s

similar t o a n o p e r a t o r ' s n a t i v e t o n g u e .

Formal l a n g u a g e s c o n s t r a i n s

a n o p e r a t o r t o a r i g i d format (syntax) i n o r d e r t o g a i n b e n e f i t s o f p r e c i s i o n and e f f i c i e n c y .

Departure f r o m t h i s format causes a n e r r o r ,

b u t s i n c e formal (computer) language syntax f o l l o w s p r e s c r i b e d r u l e s , these e r r o r s c a n be d e t e c t e d b y computer p r o c e s s i n g .

Formal l a n g u a g e

r e q u i r e s l e a r n i n g which may be a barrier f o r i n e x p e r i e n c e d o r infrequent operators.

However, a s Shneiderman (1980b) n o t e s , c u r r e n t

n a t u r a l ( c o m p u t e r ) l a n g u a g e s h a v e grammar and domain r e s t r i c t i o n s t h a t r e s u l t i n confusion w i t h r e g u l a r language (pro-active i n t e r f e r e n c e ) . The t r a d e - o f f between message n a t u r a l n e s s and e f f i c i e n c y c o u l d be r e s o l v e d by dynamic a d j u s t m e n t .

3.2.3

S t y l e i s t h e c o v e r t c o n t e x t o f m e s s a g e s o r commands.

It can


Page 24 range from cryptic 'lAD367E2

-

D S OVERFLOW'

t o f r i e n d l y ' T H I S SAVE

CANNOT BE MADE BECAUSE YOUR DIRECTORY IS FULL.

FROM THE FOLLOWING ERROR L I S T '

.

PLEASE SELECT O P T I O N

Shneiderman (1980b) observes t h a t

knowledgeable users a r e put off by anthropomorphized systems with advice directed t o beginners, probably because t h e dialogue s t y l e i s i n c o n s i s t e n t w i t h the expert o p e r a t o r ' s model of t h e system.

This

suggests using impersonal, formal dialogues f o r experienced operators.

3.2.4

D i r e c t i v i t y i s the extent t o which a system permits two way

communication between operator and computer.

Systems t h a t permit two

way communication ( f o r example, c e r t a i n c l a s s e s of i n t e r a c t i v e systems) have the p o t e n t i a l f o r resolving ambiguity i n messages o r commands.

A r i c h e r dialogue leading t o more complete resolution of

operator uncertainty, and consequently improved performance and well being, i s possible when system designers permit operator i n i t i a t e d c l a r i f i c a t i o n dialogues. -Which of these dialogue f a c t o r s predominate depends l a r g e l y on t h e t a r g e t operator population and t h e t a s k c h a r a c t e r i s t i c s (Shneiderman, 1980b).

For instance, inexperienced, infrequent users

a r e affected by naturalness and message s t y l e while experienced, frequent users are l i k e l y t o be concerned with dialogue e f f i c i e n c y [7].

Application domains t h a t involve extensive system i n t e r a c t i o n

could have efficiency and d i r e c t i v i t y a s important parameters (because operators w i l l be prepared t o l e a r n a formal language i n order t o reduce the amount of e f f o r t they m u s t expend i n generating commands), while domains with l i t t l e i n t e r a c t i o n may have naturalness and d i r e c t i v i t y a s important c r i t e r i a .

Individual differences among


Page 25 operators ( f o r example, experience, education, personality type or decision s t y l e ) as well a s differences i n task d i f f i c u l t y may a l s o account f o r variations i n the importance of various dialogue q u a l i t y parameters.

3.3

Work Flow Another important f a c t o r t h a t influences t h e a l l o c a t i o n of tasks

work flow o r organization of the between operator and machine i s the -processing system.

A t one extreme, systems may be organized on a work

'process' basis ( i . e . , a s a 'continuous' process) where a l l of the processing of a p a r t i c u l a r type i s performed before t h e next processing s t e p i s i n i t i a t e d .

Process based systems a r e r e l a t i v e l y

easy t o design because t h e r e i s l i t t l e i n t e r a c t i o n between sub-tasks and e f f i c i e n t , because processing overhead can be kept t o a m i n i m u m . However, there i s a tendency f o r these design p r i n c i p l e s ( f o r example, task s p e c i a l i z a t i o n ) t o impinge upon an o p e r a t o r ' s t a s k s t r u c t u r e r e s u l t i n g i n small pieces of disconnected and r e p e t i t i v e work under machine control. A t the other extreme, systems may be organized on a 'work u n i t '

basis ( i . e . , a s a ' d i s c r e t e ' process) where a l l processing takes place on a p a r t i c u l a r item o r transaction before t h e next i t e m i s handled. Work u n i t based systems a r e r e l a t i v e l y d i f f i c u l t t o design because of communication, control, and coordination requirements between concurrent sub-tasks and c o n f l i c t s over shared resources.

However,

these d i s c r e t e work modules lend themselves t o decentralized processing s t r u c t u r e s i n which human intervention can be more e a s i l y accomodated.

I n computer application systems, process based systems


Page 26 tend t o be implemented by 'batch* processing organizations, work u n i t based systems a r e usually designed a s 'on-line* o r i n t e r a c t i v e systems

.

From t h e standpoint of the system designer, work flow i s a fundamental decision from which most other design issues follow. Hardware configurations and operating systems a r e d i f f e r e n t f o r on-line systems than they a r e for batch systems.

For example, a

communications c o n t r o l l e r i s needed f o r on-line systems and the operating system has t o provide terminal support a s well a s a method f o r allocating resources among a c t i v e users.

The control s t r u c t u r e

f o r invoking application system modules i s d i f f e r e n t f o r on-line systems than f o r batch systems and the module s t r u c t u r e s a r e different. Work flow a l s o defines the basic s t r u c t u r e of an application system which, i n t u r n , determines fundamental aspects of t h e new division of labor: operator.

t h e sequence and content of t a s k s performed by an

I n batch systems operators tend t o be viewed a s machines;

they perform r e p e t i t i v e , short processing cycle a c t i v i t i e s such a s data input, t e x t entry, o r data correction.

The continuous nature of

t h e processing flow encourages job s p e c i a l i z a t i o n since i n t e r a c t i o n w i t h the system i s severely limited (e.g.,

i n t e r n a l f i l e s not being

continuously available o r only one way communication permitted).

The

system i s perceived a s remote from an operator and l i t t l e attempt i s made t o provide a coherent model of i t s operation; an i n f l e x i b l e and d i s t a n t task master.

it i s , i n s h o r t ,

For instance, detection of

input data e r r o r s takes longer since they a r e not recognized u n t i l a f t e r the data a r e processed, frequently i n an over night e d i t r u n .


Page 2 7 Sometimes e r r o r s a r e corrected by a person other than t h e one who submitted t h e o r i g i n a l input increasing operator overhead.

The r e s u l t

of a d i v i s i o n of labor based on t h e continuous process model i s a job with markedly d i f f e r e n t content than one based on the d i s c r e t e process model

--

a job w i t h d i f f e r e n t work load, control over work processes,

and interdependence with other workers.

3.4

System Complexity System complexity d i r e c t l y e f f e c t s t h e man-machine d i v i s i o n of

labor though t h e number of additional e n t i t i e s ( e . g . , other users, system operating procedures) an operator must work with i n accomplishing h i s task.

Given t h a t an operator needs t o e f f e c t i v e l y

use a 'mental model' i n order t o resolve problems a r i s i n g i n system usage, then the complexity of the system w i l l be a f a c t o r i n t h e ease with which t h i s model may be developed and u t i l i z e d .

W i t h simple

systems, i t i s r e l a t i v e l y easy t o determine t h e system s t a t e since there a r e few possible conditions.

Complex systems have many s t a t e s

and i t i s d i f f i c u l t t o t e l l the i n t e r n a l s t a t e of the system from t h e content of operator messages.

System complexity may be thought of a s

having t h r e e components.

3.4.1

Functional -Complexity r e f e r s t o t h e number and importance of

functional a c t i v i t i e s included i n an a p p l i c a t i o n system.

Software

systems with a r i c h s e t of functional a c t i v i t i e s provide more complete operator support, but a t the expense of system s i z e , perfoAance, and cost, since each new function requires a processing routine. Furthermore, systems may require subroutines from other applications,

Center for Digital Economy Research Stem School of Business \Vorking Paper IS-83-84

Page 2 8 data f i l e s from another system, o r hardware manipulations beyond t h e domain of the immediate system the operator understands (such as tape or d i s k pack mounts).

I n t e r na l Complexity i s a measure of application system s i z e

3.4.2

and t h e i n t r i c a c y of the technology used t o build a system.

Large

systems place demands on operators t o understand and hence t o l e a r n , t o determine s t a t u s , and t o control.

A s systems grow, f o r instance,

i n message a c t i v i t y o r data base s i z e , i n t e r n a l timing becomes more c r i t i c a l and the operation of t h e system i s more d i f f i c u l t t o p r e d i c t and t o understand.

External --Complexity i s a description of a system's community

3.4.3

of users.

Systems t h a t serve many heterogeneous user groups a t

d i f f e r e n t geographic locations make agreeing on system requirements d i f f i c u l t (Turner, 1981a).

No one user i s able t o influence a system

without negotiations with the o t h e r s , f o r example, i n changing t h e format of output r e p o r t s .

T h i s interdependence among operators i s a

major determinant of the man-machine d i v i s i o n of labor with t h e r e s u l t t h a t the task environment of any one operator i s o f t e n sub-optimal. System designers frequently s t r i v e f o r complexity because it permits them t o work with the l a t e s t equipment o r because it i s promoted by t h e i r ' t e c h n i c a l ' ethos r a t h e r than it being a r a t i o n a l solution f o r increasing man-machine system performance or operator well-being.

Sometimes complexity i s encouraged by an organizational

s e t t i n g , often a t the expense of t h e people who w i l l operate t h e system.


Page 29 3.5

System Performance The f i f t h aspect of system design t h a t p a r t i c u l a r l y a f f e c t s

operators i s the way a system performs.

Systems t h a t f a i l t o meet

performance requirements both decrease the effectiveness of a man-machine system a s well a s increase operator s t r a i n .

Frustration

occurs when the operator i s i n a s t a t e of readiness t o accomplish a task (high a r o u s a l ) , but t h e system blocks e f f e c t i v e action, f o r example, by long response time d u r i n g t e x t data entry. composed of two components:

3.5.1

Performance i s

dynamic performance and r e s i l i e n c e .

Dynamic performance r e f e r s t o those performance metrics t h a t

a r e important measures of system 'throughput' f o r a p a r t i c u l a r application.

For instance, on-line systems usually need response

times of several seconds o r s h o r t e r above which operator performance degrades.

Overall response time may depend on data s e t locations on

physical devices, operating o r monitor system s t r u c t u r e , hardware a r c h i t e c t u r e and speed, and system loading.

Each s i t u a t i o n w i l l have

i t s own s e t of c r i t i c a l performance f a c t o r s .

Complicating matters,

these f a c t o r s w i l l have variable rather than constant values, s o it i s t h e d i s t r i b u t i o n of these performance f a c t o r values over time and t h e i r interaction t h a t determines performance. An important performance f a c t o r o f t e n overlooked i s t h e

' frequency' w i t h which an application system f a i l s and t h e ' d u r a t i o n ' of i t s unavailability.

From t h e o p e r a t o r ' s perspective, t h i s may be

the most important of a l l performance measures since u n a v a i l a b i l i t y of a system frequently prevents useful work from being accomplished. Even though a system f a i l s , work deadlines a r e seldom relaxed.

The


Page 30 operator i s then placed i n the awkward position of wanting t o work, but being prevented by t h e system from doing so.

Sometime i n the

f u t u r e , when the system becomes available, t h e operator w i l l have t o work doubly hard t o meet the deadline.

The f r u s t r a t i o n , uncertainty,

and work s t r e s s i n t h i s s i t u a t i o n can cause serious psychological and physiological damage (Johansson and Aronsson, 1980). System designers have several ways t o achieve robustness and thereby reduce the impact of system f a i l u r e on operators.

The

r e l i a b i l i t y of hardware, t h e degree of parallelism i n hardware design, and t h e q u a l i t y of an operating system influence t h e frequency w i t h which a system f a i l s .

The amount of system s t a t u s information

available t o an operator when an e r r o r occurs, t h e likelihood of data l o s s o r data base damage d u r i n g t h e f a i l u r e , and amount of knowledge and e f f o r t required f o r recovery, determines how much work w i l l be required for recovery and how uncertain w i l l be t h e process.

3.5.2

Resilience - r e f e r s t o t h e way a system responds when an e r r o r

i s encountered.

Operator e r r o r s can be of form, such a s misspellings,

which lend themselves t o program detection and correction.

O r they

can be e r r o r s of meaning, where the form of the command i s c o r r e c t , but it i s used i n an improper context.

To be able t o recognize and

correct e r r o r s of form requires a system t o have e i t h e r a simple command s e t or f a i r l y complicated e r r o r recovery r o u t i n e s because of t h e large number of possible e r r o r conditions.


Page 3 1 Handling e r r o r s of meaning requires some form of limited i n t e l l i g e n c e i n a system.

Systems can contain a representation of

domain s p e c i f i c knowledge than can be used f o r deductive reasoning about the f a i l u r e .

( c - f . , Davis, 1977, f o r a description of MYCIN, a

knowledge based decision aiding system f o r i n f e c t i o n diagnosis and therapy s e l e c t i o n ) .

Command sequences can be analyzed t o deduce

i n t e n t and deviations from prescribed p a t t e r n s recognized.

Systems

with these c a p a b i l i t i e s a r e mostly experimental and t h e techniques on which they a r e based, such as methods of knowledge representation, a r e not i n the usual r e p e r t o i r e of application designers.

3.6

Summary of Application System Design Parameters That Influence Operator Task Environments. In summary, it has been argued t h a t t h e s t r a t e g y selected f o r

allocating tasks between man and machine determines the content of an operator's job.

These s t r a t e g i e s can range from a matching of the

information processing requirements of a t a s k with t h e c a p a b i l i t i e s of a processor, t o a l l o c a t i n g a l l tasks t h a t can be done by computer t o a computer.

Tasks may a l s o be s t a t i c a l l y o r dynamically allocated with

evidence t h a t dynamic allocation provides t h e h i g h e s t o v e r a l l system performance. I t i s maintained t h a t a t l e a s t four o t h e r f a c t o r s c o n t r i b u t e t o

performance and t h e q u a l i t y of an o p e r a t o r ' s job.

Dialogue content

and form provide the fundamental means of communication between man and machine.

Work flow determines the way t h a t a system i s organized.

Complexity influences t h e ease with which a system can be understood and changed.

Finally, performance, and p a r t i c u l a r l y t h e way a system


Page 3 2 responds t o e r r o r s , influences an o p e r a t o r ' s a b i l i t y t o acquire s k i l l

i n using t h e system. Hypothesized associations between task c h a r a c t e r i s t i c s and these computer system parameters a r e shown i n Table 2 (and Diagram 3 ) . These hypotheses may be represented a t the g r o s s e s t l e v e l i n terms of two p a t t e r n s :

one involving the organization of work and t h e other

r e l a t e d t o system parameters.

The task c h a r a c t e r i s t i c s of workload,

uncertainty and interdependence a l l decrease as work flow becomes more d i s c r e t e ( i . e . , i n t e r a c t i v e ) largely because an operator has more l a t i t u d e i n s e l e c t i n g work s t r a t e g i e s and, t h u s , i s b e t t e r a b l e t o adapt t o changing work demands.

[PLACE TABLE 2 ABOUT HERE]

The second general p a t t e r n i s t h e improvement i n t a s k c h a r a c t e r i s t i c s associated with improvements i n system design parameters, t h a t i s , a s dialogue q u a l i t y and performance improve and system complexity decreases.

With undifferentiated systems ( t h a t i s ,

systems where parameters a r e not recorded), increasing amounts of usage lead t o increased work load, uncertainty and interdependence. The actual evidence f o r these hypotheses i s presented i n t h e following section.

4.0

Research Support f o r Relationships Among Computer System Design Parameters, Operator Task C h a r a c t e r i s t i c s and Outcomes.


Page 3 3 One of the goals of t h i s paper i s t o demonstrate confirming evidence f o r the complete causal chain from computer system parameters t o e f f e c t s on operator behavior (Diagram 1 ) . Evidence for the d i r e c t causal pathway (path 111) i s scarce, although what evidence i s a v a i l a b l e i s discussed i n section 4.2.

More voluminous i s the

evidence f o r the i n d i r e c t pathway composed of the two sub-models, paths I and I1 i n Diagram 1.

The association between operator task

c h a r a c t e r i s t i c s , performance, and well-being i s summarized i n Table 1 without d e t a i l e d discussion since the l i t e r a t u r e i s more widely known. The empirical evidence for associations between computer system design parameters and task c h a r a c t e r i s t i c s i s summarized i n Table 2 and discussed below.

4.1

Empirical Evidence L i n k i n g Computer Application System Parameters w i t h Task C h a r a c t e r i s t i c s .

4.1.1

Evidence f o r Work Load Effects. ------

Almost a l l researchers have

found a p o s i t i v e relationship between operator work load and i n t e n s i t y of computer use.

Turner (1980), i n a study of mortgage loan servicing

workers concluded t h a t work load increased with t h e amount of work done on a computer ( t a b l e 3 ) .

In a study of four newspapers and one

insurance company, Smith e t a l . ,

(1981) found a s i g n i f i c a n t d i f f e r e n c e

i n work pressure and i n q u a n t i t a t i v e work load between c l e r k s t h a t

used computer systems and a control group t h a t d i d not ( t a b l e 4 ) . K l i n g (1978), studying o f f i c e workers i n 42 c i t i e s , reported increases

i n job pressure a t t r i b u t a b l e t o using computer systems.

[PLACE TABLE 3 AND TABLE 4 ABOUT HERE]


Page 3 4 Turner (1980) found a relationship between perceived operator work load and t h e type of application system used.

Operators

(performing the same job) using batch processing systems reported g r e a t e r work load than operators using systems t h a t were more interactive.

This i s consistent with t h e notion t h a t batch systems

a r e continuous process systems t h a t r e s u l t i n machine paced operator jobs performed t o t i g h t deadlines. A r e l a t i o n s h i p has been shown between operator work load and

complexity of the system used (Turner, 1980).

Complexity was

associated w i t h increased work load f o r on-line systems and decreased work loan f o r batch processing systems.

Turner reasoned t h a t

complexity decreased system performance and made the o p e r a t o r ' s model of system operation more complicated i n the on-line case r e s u l t i n g i n r e l a t i v e l y g r e a t e r workload.

For batch systems, complexity i s r e l a t e d

t o g r e a t e r f u n c t i o n a l i t y , thus reducing workload. The a f f e c t s of various system performance f a c t o r s on work load i s well documented i n t h e l i t e r a t u r e , t h e general r e l a t i o n s h i p being 'U' shaped:

f o r example, too f a s t o r too slow a response time i s

associated w i t h increased work load ( ~ a r b a r ,1979).

4.1.2

Evidence f or Operator Autonomy Effects. -

The evidence f o r t h e

e f f e c t s of application system parameters on operator autonomy a r e equivocal.

S m i t h e t al.,

(1981) found t h a t c l e r k s using computers

reported s i g n i f i c a n t l y l e s s autonomy and g r e a t e r supervisory c o n t r o l than control groups not using computer systems ( t a b l e 4 ) .

Similar

findings were reported by Bradley (1977) and Mann and W i l l i a m s (1960), the explanation being t h a t many application systems a r e r i g i d l y


Page 35 programmed and d o n o t p e r m i t d e v i a t i o n from a p r e s c r i b e d a c t i v i t y sequence.

However, T u r n e r ( 1 9 8 0 ) , K l i n g ( 1 9 7 8 ) , a n d Sheppard ( 1 9 7 1 )

a l l f o u n d no e v i d e n c e o f d i f f e r e n c e s i n autonomy b e t w e e n w o r k e r s u s i n g

computer s y s t e m s and t h o s e t h a t d i d n o t .

T u r n e r ( 1 9 8 0 ) o b s e r v e d , when

c o n t r o l l i n g f o r j o b l e v e l , t h a t autonomy w a s r e l a t i v e l y i n d e p e n d e n t o f t h e d e g r e e o f computer u s e and showed more v a r i a t i o n among f i r m s t h a n

w i t h i n work g r o u p s .

4.1.3

f o r Interdependence Effec t s . T u r n e r ( 1 9 8 0 ) found a E v i d e n ce -

p o s i t i v e a s s o c i a t i o n between i n t e r d e p e n d e n c e and p e r c e i v e d work l o a d w h i c h he r e a s o n e d r e s u l t e d from computer u s e ( t a b l e 3 ) .

He speculated

t h a t t h i s i n t e r d e p e n d e n c e r e s u l t e d from t h e need t o r e s o l v e e x c e p t i o n

c o n d i t i o n s t h a t a r i s e when working w i t h computer a p p l i c a t i o n s y s t e m s . K l i n g ( 1 9 7 8 ) a l s o found w o r k e r s r e p o r t e d a n i n c r e a s e i n d e a l i n g w i t h o t h e r s a s a r e s u l t o f u s i n g c o m p u t e r s , as d i d Mann and W i l l i a m s (1960).

B r a d l e y ( 1 9 7 7 ) , however, found less i n t e r d e p e n d e n c e as a

r e s u l t o f computer u s e .

I t i s i n t e r e s t i n g t o n o t e t h a t , computer

d e t e r m i n e d i n t e r d e p e n d e n c e a p p e a r s t o h a v e d i f f e r e n t c a u s e s and consequences t h a n i n d i v i d u a l l y p r e s c r i b e d i n t e r d e p e n d e n c e .

It

r e q u i r e s a n o p e r a t o r t o i n t e r r u p t h i s job t o assist a f e l l o w worker o r t o seek a s s i s t a n c e h i m s e l f .

A s J o h a n s s o n and Aronsson ( 1 9 8 0 ) o b s e r v e ,

i n working w i t h c o m p u t e r s , i n d e p e n d e n c e ( r a t h e r t h a n i n t e r d e p e n d e n c e ) i s a s o u r c e o f j o b s a t i s f a c t i o n , a l t h o u g h s o c i a l i n t e r a c t i o n among

coworkers and s u p e r v i s o r s , i n o t h e r work c o n t e x t s , has a s t r o n g p o s i t i v e c o r r e l a t i o n w i t h job s a t i s f a c t i o n ( K a r a s e k e t a l .

1982a).


Page 3 6 4.2

Empirical Evidence Linking Computer Application System Parameters Directly with Operator Outcomes As previously mentioned, t h e evidence f o r a d i r e c t causal path

from application system parameters t o operator e f f e c t i v e n e s s (Diagram 1, path 111) i s sparse, and what evidence e x i s t s i s equivocal.

4.2.1

Evidence f o r Well-Being ---Effects.

Inconsistent r e s u l t s have

been found r e l a t i n g the amount of computer system use and indicators of operator well-being.

Turner(l980) i n studying t h e same c l e r i c a l

job found no s i g n i f i c a n t d i r e c t association between t h e degree of computer use reported and measures of psychological s t r a i n o r job s a t i s f a c t i o n ( t a b l e 3 ) , although t h e i n d i r e c t path through task content was confirmed.

Neither d i d he find d i f f e r e n c e s i n mean values

of reported psychological s t r a i n or job s a t i s f a c t i o n between work groups (performing t h e same job) t h a t were heavy o r l i g h t users of computer systems.

Similar findings have been reported by Kling

(1978), Kraemer e t a l .

(1981), and Smith e t a l .

(1981).

However,

Mann and Williams (1960) observed t h a t workers reported g r e a t e r job s a t i s f a c t i o n a f t e r the move of an accounting system t o a computer, while Bradley ( 1 9 7 7 ) has reported decreased job s a t i s f a c t i o n i n more intensely computerized jobs. There i s l i t t l e research r e l a t i n g computer a p p l i c a t i o n system parameters, such a s dialogue q u a l i t y , complexity, performance or work flow t o operator well being.

Turner (1980) found no d i r e c t

association between complexity o r work-flow and well being. Bjorn-Andersen (1976) has reported t h a t a move from manual t o batch processing resulted i n an increase i n job s a t i s f a c t i o n f o r c l e r k s most


Page 3 7 d i r e c t l y u s i n g a system, w h i l e a move from b a t c h t o o n - l i n e p r o c e s s i n g produced a d e c r e a s e i n s a t i s f a c t i o n .

Shneiderman (1982) r e p o r t s

h i g h e r s u b j e c t i v e e v a l u a t i o n s o f a t e x t e d i t o r o n t h e basis o f improved d i a l o g u e q u a l i t y . Kennedy and Edmonds (1974) o b s e r v e d t h a t v a r i a b l e ( i . e . , u n p r e d i c t a b l e ) d e l a y s are s o u r c e s o f o p e r a t o r stress.

J o h a n s s o n and

Aronsson ( 1 9 8 0 ) found t h a t i n t e r r u p t i o n s i n computer s e r v i c e [8] were a s s o c i a t e d w i t h i n c r e a s e d a d r e n a l i n e , b l o o d p r e s s u r e , and h e a r t r a t e o n t h e p a r t of o p e r a t o r s w a i t i n g f o r s y s t e m t o become a v a i l a b l e .

The

o p e r a t o r s a l s o f e l t more i r r i t a t e d and r u s h e d a s w e l l a s less r e l a x e d t h a n u n d e r o r d i n a r y working c o n d i t i o n s .

4.2.2

Evidence f o r Performance E f f e c t i v e n s s E f f ects.

There a r e

r e l a t i v e l y few s t u d i e s o f t h e a f f e c t s of computer u s e on p r o d u c t i v i t y o r performance a l t h o u g h t h e r e i s c o n s i d e r a b l e c i r c u m s t a n t i a l e v i d e n c e t h a t , f o r c l e r i c a l work, computers c a n p r o d u c e p r o d u c t i v i t y g a i n s o v e r manual methods (McKinsey, 1 9 6 3 ) .

T u r n e r (1982, 1 9 8 0 ) found a

s i g n i f i c a n t improvement i n p r o d u c t i v i t y b e t w e e n work g r o u p s ( p e r f o r m i n g t h e same c l e r i c a l j o b ) t h a t w e r e h i g h and l o w u s e r s o f computer s y s t e m s , e v e n when c o n t r o l l i n g f o r o r g a n i z a t i o n s i z e .

This

f i n d i n g i s c o n s i s t e n t w i t h t h e p r o d u c t i v i t y l i t e r a t u r e which g e n e r a l l y a s s o c i a t e s p r o d u c t i v i t y g a i n s w i t h t h e a p p l i c a t i o n of technology (Katzell, et a l . ,

1977).

However, Kraemer e t a l .

( 1 9 8 1 ) found

p r o d u c t i v i t y g a i n s a s a r e s u l t o f u s i n g computer s y s t e m s i n o n l y o n e o u t o f f i v e f u n c t i o n a l areas o f l o c a l government, and t h a t o n e performed t h e most r o u t i n e f u n c t i o n .


Page 38 There i s considerably more evidence r e l a t i n g computer application system parameters t o operator performance.

Shneiderman (1982) reports

a reduction i n work e r r o r s f o r subjects using a t e x t e d i t o r with improved dialogue q u a l i t y .

Turner (1980) found a s i g n i f i c a n t

improvement i n productivity between work groups (performing t h e same job) using batch and on-line systems. Turner e t a l -

In a laboratory experiment,

(1982), found no difference i n performance between

subjects u s i n g a r e s t r i c t e d natural language t o query an application data base and those u s i n g a formal, more structured language.

In

f i e l d experiments the structured language performed b e t t e r than the natural language. In summary, although there i s some evidence supporting t h e d i r e c t path between operator well-being o r performance and computer application system parameters, t h e o v e r a l l impression, based on t h e propronderence of r e s u l t s , i s t h a t these e f f e c t s a r e moderated by t h e o p e r a t o r ' s task c h a r a c t e r i s t i c s .

That i s , t h e decision t o use a

computer application system i n a job r e s u l t s i n a new man-machines division of labor t h a t produces a d i f f e r e n t m i x of tasks f o r t h e human t o perform, which then e f f e c t s t h e human's well-being and t h e system's overall performance.


Page 39 5.0

Improving Computer Application Systems

-

Implications f o r

Research and Practice T h i s paper has argued t h a t t h e consistent s e l f - r e p o r t s of

psychosomatic s t r e s s i n jobs using CRTs may be due t o t h e operating c h a r a c t e r i s t i c s of t h e o v e r a l l system r a t h e r than j u s t the physical parameters of the CRTs themselves.

A model t h a t r e l a t e s operator

well-being and performance effetiveness t o task environment c h a r a c t e r i s t i c s which are influenced by computer application system parameters has been presented along w i t h empirical evidence supporting t h e model. While much more work must be done i n investigating t h e r e l a t i o n s h i p between task environment changes and application system parameters, t h e studies performed t o date do present a r a t h e r compelling p i c t u r e .

For c l e r i c a l jobs, where workers have l i t t l e

choice but t o use a computer application system a f t e r a job has been redesigned t o incorporate one, t h e q u a l i t y of the job appears t o be poorer.

I n general work load and interdependence tend t o increase

with evidence of greater mental s t r a i n ( t h i s p a t t e r n i s p a r t i c u l a r l y evident i n t a b l e 3 and t o a c e r t a i n e x t e n t , i n t a b l e 4 ) .

Not only a r e

these outcomes related t o the amount of work done using a computer system, but a l s o t o the system's c h a r a c t e r i s t i c s . Bjorn-Anderson and Hedberg ( 1 9 7 7 ) observe t h a t system designers do not purposely make jobs poorer, they simply overlook job design issues.

Designers couple a lack of knowledge about work load and t a s k

interdependencies imposed by a system with untested assumptions about an operator's potential t o acquire s k i l l s and t o make task r e l a t e d


Page 40 decisions.

D e s i g n e r s ' d e c i s i o n s a r e f r e q u e n t l y g u i d e d by n e v e r s t a t e d

( i n d e e d , o f t e n u n c o n s c i o u s ) a s s u m p t i o n s t h a t o p e r a t o r s a r e unmotivated and u n i n t e l l i g e n t , c a n n o t and d o n o t want t o u n d e r s t a n d b a s i c a s p e c t s of o v e r a l l system o p e r a t i o n , e x i s t o n l y a s a c o o r d i n a t e d p a i r of e y e s

and h a n d s ( D a v i s and T a y l o r , 1 9 7 4 ) , o r t h a t management c a n be s a t i s f i e d w i t h more performance from a system ( e . g . , more t r a n s a c t i o n s p r o c e s s e d p e r h o u r ) r e g a r d l e s s o f t h e b r o a d e r consequences t o t h e f i r m , i n c l u d i n g t h o s e t o i t s human r e s o u r c e s . The r e s e a r c h f i n d i n g s a l s o s u g g e s t t h a t computer a p p l i c a t i o n need n o t h a v e a n a d v e r s e e f f e c t on working l i f e q u a l i t y s y s t e m s --

-

e f f e c t i v e n e s s p e n a l t i e s which o f f s e t t e c h n o l o g i c a l a d v a n t a g e s .

The

nor

i m p l i c a t i o n of t h e computer s y s t e m - t a s k d i m e n s i o n a s s o c i a t i o n s shown i n t a b l e 3 i s t h a t b y improving d i a l o g u e q u a l i t y , t a k i n g a d v a n t a g e o f two way communication t o r e d u c e u n c e r t a i n t y , s i m p l i f y i n g a p p l i c a t i o n d e s i g n w i t h s m a l l e r and l e s s i n t e g r a t e d s y s t e m s , a n d matching s y s t e m performance t o o p e r a t o r n e e d s , a j o b c a n b e c r e a t e d t h a t may r e s u l t i n improving o p e r a t o r w e l l - b e i n g and e f f e c t i v e n e s s .

5.1

Design Recommendations While a f u l l d i s c u s s i o n o f a p p l i c a t i o n s y s t e m d e s i g n a l t e r n a t i v e s

i s beyond t h e s c o p e o f t h i s p a p e r , s e v e r a l recommendations emerge from

t h e s e s t u d i e s which d o a p p e a r t o h a v e b r o a d a p p l i c a b i l i t y .

5.1.1

Dialogue Q u a l i t y .

Improving d i a l o g u e q u a l i t y c a n i n c r e a s e a n

o p e r a t o r ' s a b i l i t y t o g r o u p i n f o r m a t i o n r e c e i v e d more e f f e c t i v e l y . Varying d i a l o g u e n a t u r a l n e s s w i t h a n o p e r a t o r ' s s k i l l l e v e l c a n contribute t o learning effectiveness.

Together w i t h information on


Page 4 1 o v e r a l l system s t a t u s , h i g h q u a l i t y dialogue can enable a n o p e r a t o r t o c o n s t r u c t a p r e d i c t i v e model o f s y s t e m o p e r a t i o n t h a t b o t h a n t i c i p a t e s f u t u r e p r o b l e m s and and c a n d i m i n i s h the r i s k o f p s y c h o l o g i c a l s t r a i n .

5.1.2

O p e r a-tor S-k i l l Acquisition.

Systems s h o u l d be d e s i g n e d w i t h

a n u n d e r s t a n d i n g o f t h e i n t e r p l a y between t h e s k i l l r e p e r t o i r e needed t o perform complicated t a s k s , system complexity, and o p e r a t o r I n e x p e r i e n c e d u s e r s may become e x p e r i e n c e d i n a short

learning.

p e r i o d of t i m e i f a system supports s e l f documentation, l o c a l l y d e f i n e d command s e q u e n c e s , a b b r e v i a t i o n s and synonyms, e x p l a n a t i o n s o f d e c i s i o n s o r recommendations made by t h e s y s t e m , a n d other s k i l l acquisition features. Many o b s e r v e r s recommend g i v i n g o p e r a t o r s more d e c i s i o n l a t i t u d e as a way o f i n c r e a s i n g c o n t r o l o v e r t h e i r work, p e r m i t t i n g t h e m g r e a t e r s e l f r e a l i z a t i o n , a s s i s t i n g i n a c q u i r i n g new s k i l l s , a n d t h u s i n c r e a s i n g job s a t i s f a c t i o n (Mumford and W e i r , and Hedberg, 1977;

Turner, 1980).

1980;

Bjorn-Andersen

The d a t a i n table 3 s u p p o r t s the

n o t i o n t h a t i n c r e a s e d l a t i t u d e o v e r work r e l a t e d d e c i s i o n s , s u c h as t h e o r d e r i n which t a s k s a r e p e r f o r m e d , i s p o s i t i v e l y r e l a t e d t o j o b

s a t i s f a c t i o n , suggesting t h i s approach a s a u s e f u l s t r a t e g y i n job design.

This recommendation i s c o n s i s t e n t w i t h t h e job e n r i c h m e n t

literature.

5.1.3

A d a p ta bl e Systems.

Another i m p o r t a n t p o s s i b i l i t y i s t h a t

s y s t e m s be d e s i g n e d t o be d y n a m i c a l l y a d a p t a b l e t o i n d i v i d u a l operators;

f o r instance, t o s k i l l level o r state of arousal.

B r o a d l y , t h i s may be a c c o m p l i s h e d by a d j u s t i n g t h e a l l o c a t i o n o f t a s k s


Page 4 2 between system and operator, and by modifying dialogue characteristics.

Most operational level application systems provide

no f e a t u r e s f o r s t a t i c individual operator customization beyond the physical positioning of equipment, yet the techniques f o r accomplishing t h i s a r e well known. A s Bainbridge (1974) suggests, operators may adapt t h e i r

s t r a t e g i e s f o r using and controlling a system t o t h e o v e r a l l work load

i n order t o maintain a constant arousal l e v e l .

I f a system can not

adapt t o these changes i n operator s t r a t e g y , performance d e t e r i o r a t i o n and s t r e s s r e s u l t ( t h i s notion r a i s e s questions of possible confusion i n task a l l o c a t i o n s between man and machine).

Rouse (1981) suggests an approach t o system design where continuous operator monitoring, covert communication between operator and system (where the system deduces the o p e r a t o r ' s s t a t e from h i s t a s k performance), o r d i r e c t communication provide information f o r a system t o adapt t o changing operator c a p a b i l i t i e s .

Thus, t h e overall

system processing s t r a t e g y might be changed f o r an operator who was i n an exceptionally 'eager' or ' fatigued' s t a t e .

I n t h e former

s i t u a t i o n , a system might reconfigure t o s h i f t some of the processing normally done t o t h e operator, modify message handling t o a c c e l e r a t e system response and a l t e r dialogue s t y l e parameters.

I n the l a t e r

'fatigued' s i t u a t i o n , t h e system may assume more t a s k s , reduce the amount of information displayed and h i g h l i g h t important d a t a , advise the operator of the implications of c e r t a i n courses of a c t i o n , and safeguard against p o t e n t i a l l y d i s a s t r o u s operator e r r o r .

For example,

Rouse (1981) suggests increasing the proportion of menu type responses, i n t h i s s i t u a t i o n , i n order t o reduce t h e length of


Page 4 3 operator messages and the likelihood of form e r r o r s .

Computer

processing may then emphasize corrective adjustments instead of predicting future system s t a t e s . This approach suggests building dynamic systems - t h a t can adapt t o

t h e s t a t e of t h e operator rather than s t a t i c , configurable or unchangeable systems.

The overall division of labor between man and

machine can be made dependent on l i m i t a t i o n s and v a r i a b i l i t i e s of human information processing rather than being a r i g i d guideline f o r human performance and organization s t r u c t u r e . The current trend i n the used of packaged application software ( t h a t i s , a previously written application program t h a t may be s p e c i a l l y configured by the s p e c i f i c a t i o n of parameters) t o speed application development may complicate the application system designer's job.

While the amount of coding i s reduced, packaged

software may be even more i n f l e x i b l e than custom designed systems, resulting i n increasing the number of exception conditions, creating t o t a l l y unexpected interdependencies, and multiplying r e s t r i c t i o n s on operator autonomy i n s t r a t e g y s e l e c t i o n .

Clearly packaged software

should be o r i g i n a l l y designed t o allow adjustment of the important man-machine i n t e g r a t i o n parameters, o r t h e o v e r a l l impact of coaputer application systems i n the future could become decidedly worse.

5.2

Limitations While t h i s a n a l y s i s suggests many p o s i t i v e d i r e c t i o n s , it a l s o

has l i m i t a t i o n s .

The design solutions a r e r e a l l y m u l t i - f a c t o r i a l and

involve interdependent trade-offs,

so it o f t e n makes so sense t o speak


Page 4 4 of improving each system parameter independently.

For instance,

dialogue q u a l i t y and performance may be compromised by t h e need t o support a multiple user community.

Also, t a b l e 3 displays simple,

l i n e a r associations, but c l e a r l y thresholds and i n t e r a c t i o n s between parameters occur which l i m i t f u l l generalization.

For example,

on-line processing could increase work load i f c a r r i e d t o extremes, o r systems could e a s i l y be designed t o allow operators so much autonomy i n s t r a t e g y and work process s e l e c t i o n t h a t decision burdens develop. The issue of system development c o s t has not been considered i n t h i s analysis.

Design techniques which i n i t i a l l y appear p r o h i b i t i v e l y

expensive frequently become accepted and packaged i n a manner t h a t does not g r e a t l y increase t o t a l system development c o s t ( e . g . , generalized data base management systems). Another l i m i t a t i o n i n t h i s conceptualizion i s t h a t many aspects of t h e new man-machine division of labor may be determined by a general philosophy of task design ( e . g . , r a t i o n a l i z a t i o n of t a s k s ) without reference t o a p a r t i c u l a r application system.

There may a l s o

be broad objectives f o r organizational change, f o r example, i s o l a t i o n

of specialized tasks o r the gathering of task performance d a t a t h a t constrain a designer.

What i s c r u c i a l here i s t o make it c l e a r t o job

designers, i n general, t h a t a computer application system, i n i t s e l f , does not automatically mean r e s t r i c t i o n i n an o p e r a t o r ' s freedom of action.

Indeed, computer systems might well be used t o enhance an

operator's job and leverage human s k i l l s .


Page 45 6.0

Conclusion The t r u e job of the 'multi-disciplinary'

computer application

system designer i s t o address t h e f u l l range of relevant i s s u e s discussed above.

His job w i l l be more complex than t h a t of present

designers

-

systems.

Operator performance and well-being a r e a function of three

factors:

The job being performed, t h e computer application system,

such i s the c o s t t o design t r u l y e f f e c t i v e and humane

and t h e operator himself. the adaptive burden.

I t i s the operator who presently bares a l l

As Bjorn-Andersen and Hedberg (1977) suggest,

the o p e r a t o r ' s p o t e n t i a l must be the s t a r t i n g point, instead of the residual a f t e r thought, f o r system design.

Only then can it be said

t h a t computer application systems have been designed a s a t o o l t o enhance human c a p a b i l i t i e s , and not t h e reverse.

Demonstrating t h i s

t o be the case i s t h e next important s t e p f o r researchers and p r a c t i t i o n e r s t o take.



Page 46 NOTES

-

It i s important t o d i s t i n g u i s h choice of s t r a t e g y t o a c h i e v e a complex g o a l , which f a c i l i t a t e s l e a r n i n g , from ' c h o i c e r e s p o n s e ' e x p e r i m e n t s i n w h i c h a l a r g e r number of c h o i c e s f o r the s u b j e c t a r e equated w i t h i n f o r m a t i o n [l]

processing load. [ 2 ] - The p h y s i o l o g i c a l model o f m u s c l e f a t i g u e d o e s n o t s e e m a p p l i c a b l e ( W e l f o r d , 1 9 7 6 ) and e x i s t i n g e x p l a n a t i o n s r e l a t a b l e t o t a s k s t r u c t u r e are o f t e n b a s e d on e x t r e m e l y g e n e r a l premises s u c h a s McGrath's ( 1 9 7 6 ) formulation: ' o v e r l o a d o c c u r s when e n v i r o n m e n t a l demands The exceed t h e i n d i v i d u a l ' s c a p a c i t y t o m e e t t h e m ' . q u e s t i o n i s , what are the p a r a m e t e r s o f demands and c a p a c i t i e s ? B a i n b r i d g e ' s ( 1 9 7 4 ) research s u g g e s t s t h e problem: t h e a c t u a l demand on a n o p e r a t o r w i l l depend upon t h e s o l u t i o n s t r a t e g y he s e l e c t s . The s o l u t i o n s t r a t e g y i n t u r n i s c o n s t r a i n e d n o t o n l y b y t h e o p e r a t o r ' s s k i l l s and a t the p r e s e n t t i m e b u t o f d e g r e e s o f freedom o f arousal a c t i o n a v a i l a b l e t o the o p e r a t o r . F u r t h e r m o r e B a i n b r i d g e h a s observed t h a t the o p e r a t o r s ' s k i l l c a p a c i t y i n the f u t u r e - i s i t s e l f a function of present t a s k conditions.

-

-

-

-

-

[31 F o r c o n f i r m i n g e v i d e n c e see, B r o a d b e n t , 1981; Benninghaus, 1981; G o i t e i n and S e a s h o r e , 1 9 8 0 ; Freeman and J u c k e r , 1980; G a r d e l l , 1979; Aronsson, 1 9 8 0 ; Karasek e t a l . , 1981b. T h i s mechanism c l o s e l y p a r a l l e l s t h e f i n d i n g s b y B a i n b r i d g e , 1974 and S p e r a n d i o , 1971 t h a t r e s t r i c t i o n i n o p e r a t o r f l e x i b i l i t y w i l l l i m i t performance e f f e c t i v e n e s s .

-

[41 S a l v e n d y , 1981 m a i n t a i n s t h a t , a f t e r c o n t r o l l i n g f o r a l l t h e o t h e r r e s t r i c t i v e f a c t o r s i n machine p a c e d jobs, machine p a c i n g i t s e l f c o n t r i b u t e d l i t t l e a d d i t i o n a l t o stress. O n t h e other h a n d , F r a n k e n h a e u s e r and G a r d e l l , 1979, and Ager e t a l . , 1975, o b s e r v e s u b s t a n t i a l h e a l t h problems f o r machine-pacing f o r s a w m i l l workers.

-

[51 S i n c e most work e n v i r o n m e n t s h a v e s i g n i f i c a n t l o a d s , e v e n a t s l a c k t i m e s , o n e would e x p e c t i n c r e a s i n g s t r a i n w i t h i n c r e a s i n g work l o a d .

-

C6l It is l i k e l y t h a t a job w i l l have q u i t e s u f f i c i e n t c h a l l e n g e s t o b r i n g a r o u s a l t o mid-range, i n which case a d d i t i o n a l work l o a d c o u l d l e a d t o a r o u s a l overload, inducing both a decrease i n performance e f f e c t i v e n e s s and a n i n c r e a s e i n p s y c h o l o g i c a l s t r a i n .

-

[7] Many s y s t e m s h a v e ' h e l p ' commands a n d ' e x p e r t ' modes t h a t p r o v i d e a n o p e r a t o r w i t h some a s s i s t a n c e . Help f u n c t i o n s r e q u i r e c o n s i d e r a b l e knowledge i n o r d e r t o be u s e d . They a l s o u s u a l l y i m p l y a h i e r a r c h i c a l s t r u c t u r e which c a n be t i m e consuming t o t r a v e r s e . An e x p e r t mode p r o v i d e s some c u s t o m i z i n g , a l t h o u g h the s e l e c t i o n o f l e v e l


Page 47 is limited.

-

[81 Although l a r g e commercial computer i n s t a l l a t i o n s r u n b e t w e e n 5 t o 2 p e r c e n t down time, t h e f r e q u e n c y o f i n t e r r u p t i o n i s much g r e a t e r t h a n these f i g u r e s would i n d i c a t e w i t h s e v e r a l c r a s h e s p e r week n o t b e i n g uncommon. Even a s o f t w a r e f a i l u r e r e q u i r e s up t o t h i r t y m i n u t e s t o r e s t a r t a p p l i c a t i o n s y s t e m s and t o resume r e m o t e s e r v i c e . C e r t a i n o p e r a t i n g s y s t e m and h a r d w a r e a r c h i t e c t u r e s a r e more r e s i l e n t t h a n o t h e r s and u n i n t e r r u p t e d s e r v i c e has become t h e o b j e c t i v e o f a f a m i l y o f s y s t e m s ( e . g . , Tandem Computers).


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Page 55


Page 56

sn Coc n a Z

E 6 $

8 ~ g 2 Center for Digital Economy Research Stem School of Business IVorking Paper IS-83-84

Page 5 7


Page 58

INTERDEPENDENCE

'a L-(

cz

UNCERTAINTY

x

a

AUTONOMY

a

PSYCHOLOGICAL WORK LOAD

I

i-

N J relationship f Effects increase as task parameter incr,-ases.

Effects decrease as task parameter increases.

0 3-shaped, curvilinear association between effects and task parameter. ** Negative association for forms of voluntary interdependence. *Evidence is presented in Section 2 and summzrized in numerous articles. This summary, while represen+.+;.= of the majority of evidence, Center for Digital Economy Research hardly be said to be unanimo Stem school of Business ail a s s o c i n t i n n c IVorking Paper IS-83-84

Page 59

T a b l e 2:

H y p o t h e s i z e d R e l a t i o n s h i p s b e t w e e n Computer S y s t e m P a r a - m e t e r s and T a s k D i m e n s i o n s Control Triad"

System Design Parameters

Dialog Quality

(pa

Wrk Flow

(interact.) System Complex. ( h i g h1

System Perf om

mmposite E d i f f . System (high usage)

Bypothesized R e l a t i o n s h i p s

-

( s c a l e d i r e c t i o n shown i n ~ a r e n t h e s e s )

Task dimension d e c r e a s e s with t h e parameter

Task dimension i n c r e a s e s with t h e parameter r

No h y p o t h e s i z e d r e l a t i o n s h i p


Table 3: Associations Between Operator Well-Being Task C h a r a c t e r i s t i c s and Computer Use I n t e n s i t y

Computer Use Intensity

SCALE

Operator Work Load

Operator Decision Making Latitude

Task Interdependence

Mental Strain Symptoms

Computer Use Intensity Operator Work Load

Operator Decision Making L a t i t u d e Task Interdependence Mental S t r a i n Symptoms

Job Satisfaction Pearson Product Moment C o r r e l a t i o n C o e f f i c i e n t s , from a study of 1001 mortgage loan s e r v i c i n g c l e r k s , showing t h e r e l a t i o n s h i p between t a s k environment, s t r a i n , s a t i s f a c t i o n , and computer u s e i n t e n s i t y s c a l e s (adapted from Turner, 1980).

*

-

S i g n i f i c a n t a t t h e 0.001 l e v e l o r b e t t e r .

Job Satisfaction

Table 4: Comparison Between Task Characteristics of Operators Using Computer Systems and a Control Group

Work ~ r esure1 s

Work Load Dissatisfaction2

Clerical Workers Using Computer Systems

Quantitative workload-Q~

Autonomy1

4.0

1.1

Clerical Control Group Scale Norms

Significant Test Level (ANOVA)

Mean scale responses for CRT operators and controls at five work groups (adapted from Smith et al., 1981)

N = About 150 CRT operators and 150 controls Source of Measures:

1 = Work Environment Scale (Insel and Moos, 1974)

- FORM - S

2 = Job Demands and Worker Health scales (Capland et al., 1975)

Control by ~u~ervisorl

SOFTWm ERGONOMICS: EFFECTS OF COMPUTER APPLICATION ...

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