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UBC Theses and Dissertations

Attention demands of movements of varying complexity Tennant, James Mark 1973

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THE ATTENTION DEMANDS OF MOVEMENTS OF VARYING COMPLEXITY BY JAMES MARK TENNANT B.P.E., U n i v e r s i t y of Manitoba, 1969 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF PHYSICAL EDUCATION i n the School of P h y s i c a l Education and R e c r e a t i o n We accept t h i s t h e s i s as conforming t o the re q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA J u l y , 1973 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f t h e r e q u i r e m e n t s f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h C olumbia, I agree t h a t the L i b r a r y s h a l l make I t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f The U n i v e r s i t y o f B r i t i s h Columbia Vancouver 8, Canada ABSTRACT The experiment was designed t o d i v i d e the a t t e n t i o n demands of a t o t a l motor response time i n t o two components, the i n i t i a t i o n of a response and the execution of a movement. The purpose was t o determine the e f f e c t s of movement complexity on the r e l a t i v e degree of a t t e n t i o n r e q u i r e d during these component processes. S i x male r i g h t handed S's were t e s t e d i n a s i t u a t i o n i n v o l v i n g two d i s c r e t e r e a c t i o n s t o two s t i m u l i separated by a short time i n t e r v a l . j.The f i r s t stimulus was a s s o c i a t e d w i t h the performance of a primary motor t a s k t h a t was v a r i e d i n complexity and t h a t was performed w i t h the S's r i g h t hand. The second or probe stimulus was a s s o c i a t e d w i t h a simple r e a c t i o n time performed w i t h the l e f t hand. The probe stimulus was presented during the S's performance of the primary task and the r e a c t i o n to t h i s stimulus was used as an index of the a t t e n t i o n a l demands of the primaryy t a s k . The r e s u l t s of the primary task i n d i c a t e t h a t the r e a c t i o n time (RT) component of the response was not a f u n c t i o n of movement complexity, a l -though there was an apparent d i f f e r e n c e between the simplest response and responses of greater complexity. Movement complexity a f f e c t e d the movement time (MT) component of the response i n t h a t MT inc r e a s e d as complexity i n c r e a s e d . The second or probe r e a c t i o n time (PRT) was delayed when the probe occurred d u r i n g the i n i t i a t i o n of the response and during the execution of the response. When the probe was presented d u r i n g the i n i t i a t i o n of the response, the PRT was r e l a t e d d i r e c t l y t o the RT, and when presented during the execution of the response, the PRT r e l a t e d d i r e c t l y t o MT. PRT was a l s o seen t o v a r y throughout the range of movement w i t h the longest PRTs o c c u r r i n g at the beginning and end of a movement terminated at a t a r g e t . These r e s u l t s provide evidence f o r a model of human performance t h a t suggests component processes of l i m i t e d c a p a c i t y i n t h a t the a t t e n t i o n demands of i n i t i a t i n g and executing a motor task tend t o vary w i t h task com-p l e x i t y and p o s i t i o n of the responding limb i n moving t o a t a r g e t . F u r t h e r , the r e s u l t s i n d i c a t e d t h a t i n general RT and MT can be used t o assess the a t t e n t i o n demands of a p a r t i c u l a r motor response. i i TABLE OF CONTENTS CHAPTER PAGE I Statement of the problem 1 I n t r o d u c t i o n 1 Purpose of the Study 3 S i g n i f i c a n c e o f the Study . 3 Hypotheses 4 L i m i t a t i o n s 4 D e l i m i t a t i o n s 4 D e f i n i t i o n o f Terms 5 I I Review of L i t e r a t u r e 6 A Model of a Motor Response 6 Time C h a r a c t e r i s t i c s of Human . . * * - « • Performance 1 0 A t t e n t i o n C h a r a c t e r i s t i c s of Human Performance 1 1 I I I Method and Procedures 1 7 Subjects 1 7 Apparatus 1 7 Experimental C o n d i t i o n s 2 0 Experimental Design 2 3 A n a l y s i s of Data 2 4 RT t o Primary Task 2 4 MT t o Primary Task 2 4 RT t o Secondary Task (PRT) 2 5 i n IV R e s u l t s and D i s c u s s i o n 26 R e s u l t s 26 RT - C o n t r o l , Phase I , and Phase I I 26 PRT - Phase I 32 MT - C o n t r o l , Phase I and Phase I I 38 PRT - Phase I I 43 D i s c u s s i o n 49 RT - C o n t r o l , Phase I and Phase I I 49 PRT - Phase I . . . . 52 MT - C o n t r o l , Phase I and Phase I I 53 PRT - Phase I I 54 Comparison of A t t e n t i o n During Phase I and Phase I I 56 V Summary and Conclusions 58 References 6l Appendices A. P i l o t Study 65 B. I n d i v i d u a l Men Scores . . . . 67 i v LIST OF TABLES PAGE I A n a l y s i s of Variance of C o n t r o l RT . 26 I I A n a l y s i s of Variance of RT During Phase I . . . 28 I I I A n a l y s i s o f Variance of RT During Phase I I . . . 30 IV A n a l y s i s of Variance of RT During C o n t r o l , Phase I , and Phase I I 32 V A n a l y s i s of Variance o f PRT During C o n t r o l and Phase I 33 VI A n a l y s i s of Variance of P r t During Phase I . . . 35 V I I A n a l y s i s of Variance of C o n t r o l MT 38 V I I I A n a l y s i s of Variance o f Phase I I MT 40 IX A n a l y s i s o f Variance o f Phase I MT 42 X A n a l y s i s of Variance of MT During C o n t r o l , Phase I , and Phase I I 43 XI A n a l y s i s o f Variance of PRT During C o n t r o l and Phase I I 45 X I I A n a l y s i s of Variance o f Phase I I PRT 47 v LIST OF FIGURES FIGURE PAGE 1. B e h a v i o r a l model of the human nervous system (Welford, 196 5) 6 2. P o s i t i o n of subject a t apparatus 18 3. The apparatus 19 4. Mean RT during c o n t r o l , Phase I , and Phase I I as a f u n c t i o n of movement complexity 27 5. Mean phase I RT as a f u n c t i o n of I S I 29 6. Mean phase I RT f o r each c o n d i t i o n as a f u n c t i o n of I S I 31 7. Mean phase I PRT as a f u n c t i o n of movement complexity and mean c o n t r o l PRT 34 8. Mean PRT du r i n g phase I f o r a l l c o n d i t i o n s as a f u n c t i o n of I S I 36 9. Mean PRT du r i n g Phase I f o r each c o n d i t i o n as a f u n c t i o n of I S I and mean c o n t r o l PRT 37 10. Mean MT during c o n t r o l , phase I,, and phase I I as a f u n c t i o n of movement complexity 39 11. Mean phase I I MT as a f u n c t i o n of I S I 41 12. Mean phase I I PRT as a f u n c t i o n of movement complexity and mean c o n t r o l PRT 44 13. Mean phase I I PRT as a f u n c t i o n of I S I 4° 14. Mean phase I I PRT f o r each c o n d i t i o n as a f u n c t i o n of I S I and mean c o n t r o l PRT 48 v i CHAPTER I STATEMENT OF THE PROBLEM I n t r o d u c t i o n I n order t o understand motor s k i l l s , models o f human performance have been formulated t o s p e c i f y the component processes i n t e r v e n i n g between the onset of a stimulus and the t e r m i n a t i o n o f i t s response. I t has been shown ( E l l s , 1969; F i t t s and Peterson, 1964; F i t t s and Radford, 1966; Henry, 196l; Henry and Rodgers, i960) t h a t a complete motor response i s composed of at l e a s t two ind e -pendent components, the i n i t i a t i o n of the response and the execution of the movement. Each of these components has been f u r t h e r subdivided i n t o more s p e c i f i c processes. Welford (1965» 19°&) has suggested a model f o r the initiafciony6f>,a response c o n s i s t i n g of three c e n t r a l mechanisms: a p e r c e p t u a l mechanism which pe r c e i v e s and encodes s t i m u l i from the environment; a d e c i s i o n mechanism which designates the a p p r o p r i a t e response and then r e t r i e v e s the motor program t o govern the motor behavior from a motor memory; and an e f f e c t o r mechanism which c o n t r o l s the response. Keele (1968) has suggested t h a t movement i s c o n t r o l l e d by means of three processes: a motor program; k i n e s t h e t i c feedback; and, v i s u a l feedback. A c h a r a c t e r i s t i c of the human organism i s t h a t t here always i s a f i n i t e p e r i o d of time between the p r e s e n t a t i o n of a stimulus and the i n i t i a t i o n of a response. This delay, known as r e a c t i o n time (RT), i s due t o processing i n f o r -mation r e l a t e d t o the s e l e c t i o n and o r g a n i z a t i o n of the response. I n terms of RT resea r c h e r s have found t h a t a number of f a c t o r s l e a d t o a decrement i n per-formance. One such f a c t o r i s the complexity of movement patte r n s r e q u i r e d d u ring the response. A number of i n v e s t i g a t o r s have obtained e m p i r i c a l evidence (Henry, 196l; Henry and Rodgers, I960; N o r r i e , 1967; O'Brien, 1959; Sidowski, Morgan and Eckstrand, 1958) i n d i c a t i n g an i n c r e a s e i n RT t o a stimulus when the 2 . response t o t h a t stimulus i n v o l v e s a more complex movement. These r e s u l t s suggest t h a t i n c r e a s e d movement complexity r e f l e c t s i n c r e a s e d demands w i t h i n the organism i n order t o mainta i n greater c o n t r o l over limb movements. But where w i t h i n the organism these delays a c t u a l l y occur i s not known. Some recent experimental work has provided a b a s i s f o r d i s t i n g u i s h i n g whether these delays are due t o c e n t r a l processes, or are caused by p e r i p h e r a l f a c t o r s such as number o f motor u n i t s i n v o l v e d , a c t i o n of a n t a g o n i s t i c muscles, muscular weakness or, v i s c o s i t y o f the muscles. T h i s i s based on a number of stu d i e s which have shown t h a t the c e n t r a l mechanisms have a l i m i t e d p r o c e s s i n g c a p a c i t y i n t h a t two task s r e q u i r i n g the simultaneous a t t e n t i o n of the c e n t r a l mechanisms can i n t e r f e r e w i t h each other. These st u d i e s have been re p o r t e d i n r ecent reviews o f the p s y c h o l o g i c a l r e f r a c t o r y p e r i o d (PRP) theory ( B e r t e l s o n , 1966; Smith, 1967). I n her review Smith concluded t h a t the s i n g l e channel theory as suggested by Welford (1959; 1967) was the best supported e x p l a n a t i o n of PRP. T h i s theory p o s t u l a t e s t h a t i f a second stimulus a r r i v e d during the response p r o c e s s i n g a s s o c i a t e d w i t h a f i r s t s t i m u l u s , the second stimulus would have t o be "h e l d i n s t o r e " (Welford, 1959) u n t i l p r o c e s sing of the f i r s t stimulus was completed. I n recent work (Posner, 1969) i t has been suggested t h a t one way of i n v e s t i g a t i n g the a t t e n t i o n a l demands o f the f i r s t stimulus i n a PRP e x p e r i -ment i s by u s i n g the probe technique. This i n v o l v e s p r e s e n t i n g a second stimulus or probe t h a t must be processed during the RT i n t e r v a l of the f i r s t s t i m u l u s . Thus, i f c o n t r o l i s taken t o ensure t h a t the s i g n a l s do not r e q u i r e c o n f l i c t i n g sensory or e f f e c t o r processes, the delay t o the probe may be a t t r i b u t e d t o the c e n t r a l processes. I n t h i s way i t has been found t h a t i f the a t t e n t i o n a l demands of the primary task are in c r e a s e d , or i f the primary task i s made more d i f f i c u l t , the c a p a c i t y a v a i l a b l e f o r atte n d i n g t o the second stimulus w i l l 3. d e c l i n e , r e s u l t i n g i n a p r o g r e s s i v e l y longer second RT (PRT). The probe technique has a l s o been used t o measure a t t e n t i o n d u r i n g the execution of movement. Th i s i n v o l v e s the p r e s e n t a t i o n o f a second stimulus or probe t h a t must be processed during the movement time i n t e r v a l of the primary t a s k . R e s u l t s of these experiments i n d i c a t e t h a t the delay i n the probe task was r e l a t e d t o the p r e c i s i o n o f the movement as PRT's during the movement t o a sm a l l t a r g e t were greater than the PRT's when moving to a l a r g e r t a r g e t ( E l l s , 1969; Posner and Keele, 1969, 1970). A l s o , i t was found t h a t a t t e n t i o n a l demands of a movement were a s s o c i a t e d w i t h the p o s i t i o n i n the movement where the probe s i g n a l occurred ( E l l s , 1969; Posner, 1969; Posner and Keele, 1969, 1970). G e n e r a l l y i t was found t h a t a t t e n t i o n f o l l o w e d a "U" shaped t r e n d . PRT's were grea t e r a t the beginning o f movement, decreased t o a r e l a t i v e l y low value i n the middle, and showed a s l i g h t i n c r e a s e near the end. The present study was designed t o use the above p r i n c i p l e s i n de t e r -mining the e f f e c t s t h a t task complexity had on the a t t e n t i o n demands of the c e n t r a l processes d u r i n g the initiation-it'.©;, and execution o f , a motor t a s k . Purpose of the Study The purpose of t h i s i n v e s t i g a t i o n was t o analyze the e f f e c t s o f move-ment complexity on the a t t e n t i o n r e q u i r e d during the i n i t i a t i o n o f a response and the execution o f a movement. S i g n i f i c a n c e o f the Study Researchers commonly use the l e n g t h of r e a c t i o n time as an index f o r measuring p r o c e s s i n g demands on man's c e n t r a l o p e r a t i o n s . Subsequently, i n v e s t i g a t o r s t h a t have found movement complexity during a response t o cause an i n c r e a s e d delay i n r e a c t i o n time have assumed t h i s decrement i n performance 4. to be of a c e n t r a l nature. But the p o s s i b i l i t y e x i s t s t h a t t h i s decrement i n performance could a l s o be the r e s u l t of p e r i p h e r a l f a c t o r s , such as number of motor u n i t s i n v o l v e d , a c t i o n of a n t a g o n i s t i c muscles, muscular weakness, or v i s c o s i t y o f the muscles. Therefore, i t i s d e s i r a b l e t o determine at what stage w i t h i n the human organism's response t h i s time decrement occurs. Hypotheses 1. The time taken t o i n i t i a t e a primary response (RT) i s inc r e a s e d as a f u n c t i o n of the complexity o f the movement r e q u i r e d d u r ing the execution of t h a t response. 2. The time taken t o i n i t i a t e a response to a second stimulus (PRT) presented d u r i n g the i n i t i a t i o n of a primary response i s increased as a func-t i o n of the complexity of movement r e q u i r e d during the primary response. 3. The time taken t o i n i t i a t e a response t o a second stimulus (PRT) presented d u r i n g the execution ( i . e . , movement) of a primary response i s increased as a f u n c t i o n of the complexity of movement r e q u i r e d d u r ing the primary response. L i m i t a t i o n s The study w i l l be l i m i t e d by the f o l l o w i n g f a c t o r s : 1. The sample s i z e of s i x s u b j e c t s . 2. The methods and procedures used i n i n v e s t i g a t i n g the problem. D e l i m i t a t i o n s This study w i l l be r e s t r i c t e d t o : 1. The s p e c i f i c types of movements used i n the experimental t a s k s . 2. A d e s c r i p t i o n o f performance as hypothesized by Welford's model of behaviour '(1965, 1968). 5. 3. An a n a l y s i s of f u n c t i o n a l behaviour according to Posner's concept of a t t e n t i o n (Posner, 1969; Posner and Boies, 1970; Posner and Keele, 1969, 1970). D e f i n i t i o n of Terms A t t e n t i o n . The mental operations t h a t r e q u i r e access t o man's l i m i t e d c a p a c i t y c e n t r a l p r o c e ssing system i n the sense t h a t they w i l l i n t e r f e r e w i t h any other task which i s to be performed simultaneously (Posner and Keele, 1970). Movement Complexity. The r e l a t i v e degree of a t t e n t i o n necessary t o i n i t i a t e and c o n t r o l a motor response. CHAPTER I I REVIEW OF LITERATURE A Model o f a Motor Response. Performance of a r a p i d d i s c r e t e motor act c o n s i s t s of two b a s i c components, the i n i t i a t i o n of the response and the execution of the movement. Each of these components r e q u i r e s t h a t i n f o r m a t i o n be processed i n order t h a t the appropriate response i s performed s a t i s f a c t o r i l y . As an a i d i n understanding motor s k i l l s , h y p o t h e t i c a l models o f human per-formance are developed t o diagram the f l o w of such i n f o r m a t i o n between the environment and an i n d i v i d u a l ' s behaviour. These models attempt to s p e c i f y the number of f u n c t i o n a l ' components r e q u i r e d t o produce observed performance, and, to d e s c r i b e the p r o p e r t i e s o f these components, Welford (1965) has suggested such a model of the human sensory-motor system (Figure l ) . T h i s model views s k i l l s performance i n terms of a cha i n of mechanisms i n t e r v e n i n g between sensory i n p u t and motor output. s 0 e r n g s a e n s P e r c e p t u a l Mechanism PM D e c i s i o n Mechanism DM E f f e c t o r Mechanism EM M u s c 1 e s Fi g u r e 1: B e h a v i o r a l model of the human nervous system (Welford, 1965) 7. The p e r c e p t u a l mechanism (PM) r e f e r s t o those processes d e a l i n g w i t h t h e . p e r c e p t i o n of e x t e r n a l s t i m u l i from the environment and the encoding of t h i s sensory i n p u t . T h i s mechanism r e c e i v e s much more i n f o r m a t i o n than can be t r a n s m i t t e d and, t h e r e f o r e , some form of i n f o r m a t i o n compression must take p l a c e . I t has been suggested (Crossman, 1964) t h a t t h i s compression i s achieved f i r s t by p e r i p h e r a l f i l t e r s which only accept d i s c r e t e samples o f the incoming sensory i n f o r m a t i o n . I n t h i s way a l l but the dominant and important f e a t u r e s of the environment i n the incoming data are r e j e c t e d . Second, the a c t u a l sensory c a p a c i t y i s l i m i t e d by absolute sensory t h r e s h o l d s , j u s t n o t i c e a b l e d i f f e r e n c e s , and absolute judgements. Once the environmental i n f o r m a t i o n i s encoded, i t i s passed t o the d e c i s i o n mechanism (DM) as an i n f o r m a t i o n s i g n a l t o which a response i s r e q u i r e d . W i t h i n the DM t h e r e are two component processes necessary f o r the i n i t i a i o n of the r e q u i r e d response, w i t h the f i r s t being response s e l e c t i o n or the d e s i g -n a t i o n of the ap p r o p r i a t e response. Using a computer analogy Henry and Rodgers (i960) have suggested t h a t the second component would be the r e t r i e v a l of motor programs from motor memory which are used t o govern the d e s i r e d motor behaviour. I t i s p o s t u l a t e d (Henry and Rodgers, i960; Schutz; 1970) t h a t t h i s response program i s compiled of a number of subprograms, each of which governs one element o f the motor ta s k . Consequently, the greater the number of movement elements i n v o l v e d i n the response the greater w i l l be the number of subprograms i n c o r p o r a t e d i n t o the motor program. A f t e r r e t r i e v a l the motor program i s made a v a i l a b l e t o the e f f e c t o r mechanism (EM). The EM c o n t r o l s the response and i n t h i s way i s d i s t i n c t from the d e c i s i o n s t o i n i t i a t e them. Marteniuk (1970:2) has proposed a k i n e s t h e t i c model which e x p l a i n s the methods of c o n t r o l which guide the response execution 8. of d i s c r e t e motor a c t s . For t h i s model Marteniuk d e s c r i b e s k i n e s t h e s i s as "those sensations d e r i v e d from motor i n n e r v a t i o n or e f f e r e n t outflow and from r e c e p t o r s w i t h i n the j o i n t cap-sules and ligaments." From t h i s d e f i n i t i o n i t i s apparent t h a t there are two sources o f sensory-s t i m u l a t i o n , c e n t r a l and p e r i p h e r a l . This leads t o two separate models of c o n t r o l : 1. E f f e r e n c e , 2. Closed Loop. 1. E f f e r e n c e . B a s i c a l l y the i n t e r p r e t a t i o n o f t h i s theory i s t h a t a motor response can be performed s o l e l y on the b a s i s of c e n t r a l c o n t r o l . R e cently t h i s form of motor response c o n t r o l has r e c e i v e d a great d e a l of a t t e n t i o n by a number of notable researchers who have u t i l i z e d two separate approaches f o r i n v e s t i g a t i o n . One approach has been to deprive or d i s t o r t p e r i p h e r a l k i n e s t h e t i c a f f e r e n c e i n order to g a i n support t h a t p e r i p h e r a l k i n e s t h e t i c feedback i s not necessary f o r execution and c o n t r o l of a motor response. A number of e x c e l l e n t reviews o f work done i n t h i s area have been pu b l i s h e d r e c e n t l y (Greenwald, 1970; Kimble and Perlmuter, 1970; Marteniuk, 1970). The second approach has been t o compare measurements of e r r o r detec-t i o n w i t h e r r o r c o r r e c t i o n i n a d i s c r e t e motor response. I t has been found t h a t e r r o r s can be c o r r e c t e d more r a p i d l y ' t h a n sensory feedback can be detected (Higgins and Angel, 1970; R a b b i t t , 1966a, 1966b, 1967). These r e s u l t s have been i n t e r p r e t e d by these authors as evidence of a c e n t r a l mechanism which operates t o c o n t r o l the response. B a s i c a l l y , these two approaches d i f f e r as t o the source of s t i m u l a t i o n t h a t i n i t i a t e s the response execution. The view i n t h i s study i s t h a t the motor program s e l e c t e d from the memory storage i s "read out" t o the EM p r o v i d i n g the EM w i t h an image of the d e s i r e d outcomes. The r o l e of t h i s image i s two f o l d : 9. a) As soon as the motor program has been read out and the image f u l l y developed, n e u r a l i n s t r u c t i o n s i n the form of e f f e r e n t output are r e l e a s e d by the EM t o the muscles. I f i t i s assumed t h a t each response com-ponent, or subprogram, has a corresponding image, i t would f o l l o w t h a t move-ments i n v o l v i n g s e v e r a l subprograms would r e q u i r e a greater p e r i o d of time to formulate a complete image. b) The image serves as a s t o r e d r e p r e s e n t a t i o n o f what the c o r r e c t performance should be. I n t h i s way the response program i n the form of an image i s used as a source of r e f e r e n c e w i t h i n the c l o s e d l oop form of c o n t r o l . 2. Closed Loop. The second method of c o n t r o l w i t h which the motor program i s executed conceives man as being analogous t o a computer machine i n which the operations pass s u c c e s s i v e l y from one n e u r a l i n s t r u c t i o n t o another as the machine proceeds t o execute the l i s t of i n s t r u c t i o n s t h a t comprise a motor program. I t i s t h e o r i z e d t h a t a f t e r some minimum p e r i o d of time t h i s form of c o n t r o l would augment the i n i t i a l e f f e r e n t c o n t r o l o f movement. M i l l e r , Galanter, and Pribram (i960) proposed a close d loop theory which would e x p l a i n the method of c o n t r o l w i t h which the motor program i s executed. I n t h i s model of e f f e c t o r c o n t r o l each n e u r a l i n s t r u c t i o n of the motor program i s s u c c e s s i v e l y t e s t e d against some c r i t e r i a e s t a b l i s h e d w i t h i n the image. I f the t e s t d e t e r -mines t h a t the response has not been appropriate up t o t h a t p o i n t the EM con-cerns i t s e l f w i t h e r r o r c o r r e c t i o n u n t i l the d e s i r e d outcome has beenrreached. Information t o conduct these t e s t s i n d i s c r e t e r a p i d movements i s provided t o the EM by the k i n e s t h e t i c r e c e p t o r s l o c a t e d w i t h i n the j o i n t capsules and ligaments (Smith, 1969). The purpose of t h i s model has been t o d i v i d e a d i s c r e t e motor response i n t o component p a r t s and subprocesses. On t h i s b a s i s , the demands made on these c e n t r a l processes by a response can be measured. The b a s i c assumption 1 0 . i s t h a t by ov e r l o a d i n g a subjects (S's) c a p a c i t y a decrement i n performance w i l l occur at some stage i n the sensory-motor c h a i n . I f the S's task s are designed t o impair performance i n one p a r t i c u l a r h y p o t h e t i c a l process, pro-p e r t i e s of t h a t process can be i n f e r r e d from the p a t t e r n of r e s u l t s . Time C h a r a c t e r i s t i c s of Human Performance. A f e a t u r e of the human organism i s t h a t i t always takes a f i n i t e , p e r i o d of time t o i n i t i a t e a r e q u i r e d response a f t e r the p r e s e n t a t i o n of a c e r t a i n s t i m u l u s . This delay between the p r e s e n t a t i o n of a stimulus and the i n i t i a i o n of a response i s c a l l e d r e a c t i o n time (RT). A great d e a l o f study has been done on the f a c t o r s t h a t a f f e c t RT and res e a r c h e r s now use the l e n g t h o f RT as an index f o r measuring the demand made by the response on the c e n t r a l processes. One such f a c t o r i s the complexity of the movement p a t t e r n r e q u i r e d d u r i n g the execution of the response. A number of i n v e s t i g a t i o n s (Sidowski, et a l . , 1958; Henry and Rodgers, I 9 6 0 ; N o r r i e , 1967; O'Brien, 1967) have obtained e m p i r i c a l evidence i n d i c a t i n g an in c r e a s e i n RT t o a s i g n a l when the response t o t h a t s i g n a l i n v o l v e s a more complex movement. Th i s phenomena was c o n v i n c i n g l y demonstrated i n a study by Henry and Rodgers (19&0) who r e q u i r e d S's t o r e a c t t o a stimulus and to complete a movement as q u i c k l y as p o s s i b l e . T h i s study r e v e a l e d t h a t the RT f o r a complex type of movement was s i g n i f i c a n t l y slower than the RT f o r a simple type o f movement. As w e l l , they found t h a t the g r e a t e s t i n c r e a s e i n RT as a f u n c t i o n of movement com-p l e x i t y came at low l e v e l s o f complexity and t h a t i n c r e a s i n g complexity beyond t h i s caused o n l y small increases i n RT. The r e s u l t s of these s t u d i e s suggest t h a t the i n c r e a s e i n RT a s s o c i -ated w i t h i n c r e a s e d movement complexity r e f l e c t i n c r e a s e d demands w i t h i n the organism i n order t o maintain greater c o n t r o l over limb movements. S p e c i -f i c a l l y , i t could be hypothesized t h a t the i n c r e a s e i n RT r e f l e c t s a decrement 11. i n performance w i t h i n the c e n t r a l processor. However, the p o s s i b i l i t y e x i s t s t h a t the performance decrement could a l s o be the r e s u l t of p e r i p h e r a l f a c t o r s such as number of motor u n i t s i n v o l v e d , a c t i o n of a n t a g o n i s t i c muscles, muscular weakness, o r, v i s c o s i t y of the muscles. A t t e n t i o n C h a r a c t e r i s t i c s of Human Performance. Some experimental work has provided a b a s i s f o r d i s t i n g u i s h i n g delays due t o c e n t r a l processes from those caused by p e r i p h e r a l f a c t o r s . This work i s based on the theory of the p s y c h o l o g i c a l r e f r a c t o r y p e r i o d (PRP)'which claims t h a t the c e n t r a l pro-c e s s i n g mechanisms have l i m i t e d p r o c e s s i n g c a p a c i t y . I t has been found t h a t two t a s k s r e q u i r i n g the ^ simultaneous a t t e n t i o n of the c e n t r a l processor can i n t e r f e r e w i t h each other. S e v e r a l comprehensive reviews of proposed t h e o r i e s of the PRP e f f e c t and eva l u a t i o n s o f t h e i r r e l a t i v e adequacy i n handling PRP data have been r e p o r t e d r e c e n t l y (Broadbent, 1958; Reynolds, 1964; B e r t e l s o n , 1966; Smith, 1967(b); Herman and Kantowitz, 1970). U n f o r t u n a t e l y , these reviews do not a l l reach the same c o n c l u s i o n as t o which theory best e x p l a i n s the data. I t i s the view o f t h i s paper, and as concluded by Smith (1967a, 1967b, 1969a, 1969b), t h a t the s i n g l e channel as suggested by Welford (1959; 1967) was the best supported e x p l a n a t i o n of PRP. Welford (1959) p o s t u l a t e s t h a t i f a second stimulus a r r i v e s during the response processing a s s o c i a t e d w i t h a f i r s t s t i m u l u s , the second stimulus would have t o be "held i n s t o r e " u n t i l the pro c e s s i n g of the f i r s t s timulus i s completed. T h i s theory would p r e d i c t t h a t a second stimulus t h a t must be processed during the RT i n t e r v a l of a f i r s t stimulus would be lengthened by an amount equal t o the i n t e r v a l between the a r r i v a l of the stimulus and the end of the f i r s t response. Thus, according t o the s i n g l e channel theory, i t should be p o s s i b l e to measure processing c a p a c i t y . I f con-t r o l i s taken t o ensure t h a t the s i g n a l s do not r e q u i r e c o n f l i c t i n g sensory 12. and e f f e c t o r processes, the delay may be a t t r i b u t e d t o the c e n t r a l processes (Posner, 1969). I n t h i s way i t has been found t h a t i f the a t t e n t i o n a l demands of the primary task are in c r e a s e d , the c a p a c i t y a v a i l a b l e f o r at t e n d i n g to the second task w i l l d e c l i n e , r e s u l t i n g i n a p r o g r e s s i v e l y longer second r e a c t i o n time (PRT). The knowledge t h a t mental operations can be measured i n terms of t h e i r time requirements i s not new, and the concept o f a l i m i t e d p r o c e s s i n g c a p a c i t y i s w e l l e s t a b l i s h e d (Davis, 1956; Welford, 1959, 1967). However, i t has been suggested r e c e n t l y t h a t a l l p rocessing performed on a given s i g n a l does not requ i r e , the l i m i t e d c a p a c i t y mechanism and i t i s not yet c l e a r which components of the human sensory-motor system r e q u i r e access t o t h i s system (Smith, 1967a, 1969a, 1969b; Posner, 1969; Posner and Boies, 1970; Posner and Keele, 1969, 1970). A s e r i e s o f experiments have been r e c e n t l y conducted t o i n v e s t i g a t e t h i s problem u s i n g the p r i n c i p l e s o u t l i n e d above. Posner and colleagues (Posner, 1969; Posner and Boies, 1970; Posner and Keele, 1970) have used these s i n g l e channel p r i n c i p l e s i n an attempt t o determine whether the mental operations which r e l a t e e x t e r n a l a f f e r e n t s t i m u l i to st o r e d i n f o r m a t i o n r e q u i r e c e n t r a l p rocessing c a p a c i t y . T h i s would be w i t h i n the PM i n the terms of the present paper. These i n v e s t i g a t o r s v a r i e d the a t t e n t i o n demands w i t h i n the PM by us i n g a l e t t e r matching task to measure the time f o r encoding a l e t t e r . With the use of the probe technique as described above i t was shown t h a t during the f i r s t few hundred m i l l i s e c o n d s (msecs) a f t e r p r e s e n t a t i o n of the f i r s t l e t t e r t h e r e was no s u b s t a n t i a l i n t e r f e r e n c e between the t a s k s . However, t h i s assumes t h a t encoding normally takes p l a c e d u r i n g , t h i s time p e r i o d a f t e r the f i r s t s timulus has been presented. Posner and Keele (1970) then conducted a second s e r i e s o f experiments t o i n v e s t i g a t e t h i s problem. The r e s u l t s i n d i c a t e d t h a t 13. e n c o d i n g seems t o c o n t i n u e f o r about 300-500 m s e c , and a b o u t t h e t i m e e n c o d i n g i s c o m p l e t e t h e PRT b e g i n s t o show a s u b s t a n t i a l i n c r e a s e , o r s l o w i n g down. Work i n t h i s a r e a has l e d P o s n e r t o c o n c l u d e ( P o s n e r and B o i e s , 1970; P o s n e r and K e e l e , 1970) t h a t t h o s e p r o c e s s e s i n v o l v e d d u r i n g t h e i n i t i a l s t a g e s (PM) o f a t a s k do n o t r e q u i r e p r o c e s s i n g c a p a c i t y u n l e s s t h e two p r o c e s s e s have some s p e c i f i c i n c o m p a t i a b i l i t y . T h e s e a u t h o r s s u g g e s t t h a t t h o s e p r o c e s s e s w h i c h do a p p e a r t o demand c a p a c i t y seem t o be r e l a t i v e l y l a t e i n t h e s e q u e n c e o f m e n t a l o p e r a t i o n . A c c o r d i n g t o t h e mode l o f t h e human s e n s o r y - m o t o r s y s t e m p r e s e n t e d , t h i s w o u l d i n c l u d e t h e DM and t h e E M . T h e s e c o n c l u s i o n s a r e s u p p o r t e d by a number o f r e c e n t i n v e s t i g a t i o n s ( B r o a d b e n t and G r e g o r y , 1967; S m i t h , 1967, 1969; K a r l i n and K e s t e n b a u m , 1968; E l l s , I969) w h i c h has u s e d t h e p r i n c i p l e s o f t h e s i n g l e c h a n n e l t h e o r y t o d e m o n s t r a t e t h e d e l a y s i n PRT a r e a f u n c t i o n o f d e l a y s c r e a t e d w i t h i n t h e DM. B r o a d b e n t and G r e g o r y (1967) p e r f o r m e d a n e x p e r i m e n t d e s i g n e d t o t e s t t h e h y p o t h e s i s t h a t i n a s u c c e s s i v e s t i m u l u s s i t u a t i o n , an i n c r e a s e i n RT due t o r e s p o n s e s e l e c t i o n or r e s p o n s e r e t r i e v a l w i l l a l s o i n c r e a s e P R T . I n t h i s s t u d y b o t h t h e f i r s t and s e c o n d r e s p o n s e s r e q u i r e d a c h o i c e be tween one o f two r e a c t i o n s . An i n c r e a s e i n r e s p o n s e l a t e n c y t o t h e f i r s t s i g n a l was a f f e c t e d b y v a r y i n g t h e s p a t i a l c o m p a t a b i l i t y be tween t h e s i g n a l and t h e r e s p o n s e . I n t h e c o m p a t i b l e c o n d i t i o n S ' s were t o d e p r e s s t h e k e y i m m e d i a t e l y b e n e a t h t h e v i s u a l s t i m u l u s , w h i l e t h e i n c o m p a t i b l e c o n d i t i o n r e q u i r e d d e p r e s s i n g t h e k e y o p p o s i t e t o t h e k e y i n s p a t i a l c o r r e s p o n d e n c e w i t h t h e l a m p . A t h i r d c o n d i -t i o n was i d e n t i c a l t o t h e i n c o m p a t i b l e c o n d i t i o n w i t h t h e e x c e p t i o n t h a t t h e s t i m u l i o c c u r r e d w i t h p r o b a b i l i t i e s o f 0.80 and 0.20 r a t h e r t h a n e q u a l l y p r o b a b l y . " T h e - i n c r e a s e d RT f o r t h e c o m p a t i b l e c o n d i t i o n and t o t h e s i g n a l w i t h low p r o b a b i l i t y o f o c c u r r e n c e was r e f l e c t e d b y a n i n c r e a s e i n P R T . O t h e r s t u d i e s ( S m i t h , 1967, 1969; K a r l i n and K e s t e n b a u m , 1968; E l l s , ' 1969) 14. which used the same b a s i c probe design have demonstrated t h a t delays i n PRT are a f u n c t i o n of the number of a l t e r n a t i v e s f o r the f i r s t s i g n a l . These r e s u l t s have been i n t e r p r e t e d i n t h i s review as being an i n d i c a t i o n t h a t the processes of the DM r e q u i r e access t o the l i m i t e d c a p a c i t y p r o c e s s i n g system. I t i s not q u i t e as c l e a r whether the processes w i t h i n the EM r e q u i r e p r o c e s s i n g c a p a c i t y . To demonstrate t h i s the PRT would have t o be a f u n c t i o n of the a t t e n t i o n a l demands w i t h i n the EM t o the response t a s k . E l l s (1969), u s i n g a choice r e a c t i o n time probe, found t h a t probes i n s e r t e d d u r i n g the RT to a movement were r e l a t e d t o the accuracy of the movement during the response execution. However, these r e s u l t s were dismissed because the RT's were not a f u n c t i o n of the movement c o n d i t i o n s . E l l s i n t e r p r e t a t i o n of t h i s was t h a t the demands p r i o r t o response i n i t i a t i o n were equal f o r a l l movements t e s t e d . This would be c o n s i s t e n t w i t h the expected r e s u l t s t h a t t a r g e t width and amplitude have no s i g n i f i c a n t e f f e c t on the time r e q u i r e d t o i n i t i a t e a response ( F i t t s and Peterson, 1964). On these grounds E l l s concluded that' a t t e n t i o n d uring the RT i n t e r v a l could not be a f u n c t i o n of the c h a r a c t e r i s t i c s of the movement f o l l o w i n g . The probe technique has a l s o been used to measure a t t e n t i o n during the execution of the response. T h i s i n v o l v e s the p r e s e n t a t i o n of a second stimulus or probe t h a t must be processed during the movement time i n t e r v a l of the primary t a s k . I t i s i n t e r p r e t e d t h a t the PRT w i l l r e f l e c t the a t t e n t i o n needed d u r i n g the response t o c o n t r o l the movement. Posner (1969), Posner and Keele (1969),- and E l l s (l9°9) have shown th a t w h i l e feedback i s being processed there i s a d e l a y i n the p r o c e s s i n g of a probe s i g n a l . I n the study by Posner and Keele (l9°9) the t a s k s i n v o l v e d two l e v e l s of movement d i f f i c u l t y , w r i s t r o t a t i o n of 120° t o e i t h e r a narrow t a r g e t (2°) or a wide t a r g e t (30°). The r e s u l t s showed t h a t the delay i n 15. PRT was r e l a t e d t o the r e q u i r e d accuracy of the movement as the PRT's du r i n g the movement t o a sm a l l t a r g e t were greater than the PRT's when moving t o a l a r g e r t a r g e t . A l s o , the a t t e n t i o n a l demands of the movement were found t o be a s s o c i a t e d w i t h the p o s i t i o n i n the movement where the probe s i g n a l occurred. E l l s (1969) a l s o found t h a t probes i n s e r t e d during the movement were a f u n c t i o n of movement accuracy. However, the r e s u l t s were not completely i d e n t i c a l f o r both experiments. I n the study by Posner and Keele the a t t e n t i o n demands fo l l o w e d a U shaped probe f u n c t i o n w i t h PRT's greater at the beginning of movement, decreasing t o a r e l a t i v e l y low l e v e l i n the middle, and a s l i g h t i n c r e a s e near the end. E l l s r e p o r t e d t h a t the PRT was a c o n s t a n t l y decreasing f u n c t i o n of the probe p o s i t i o n , the c l o s e r t o the t a r g e t the f a s t e r the PRT. A p o s s i b l e e x p l a n a t i o n f o r t h i s phenomena i s t h a t i n the Posner and Keele study no r e s t r i c t i o n was placed on overshooting the t a r g e t w h i l e E l l s d i d not a l l o w overshoots. Therefore, i t i s conceivable t h a t the in c r e a s e d PRT at the end of movement cou l d be a f u n c t i o n of the c o r r e c t i o n of overshoots. An a l t e r n a t e e x p l a n a t i o n a t t r i b u t e s the i n c r e a s e i n PRT t o temporal u n c e r t a i n t y . This theory, commonly r e f e r r e d t o as expectancy theory, hypothesizes t h a t the S l e a r n s the r e l a t i v e values of the I S I and formulates a mean which represents the value of peak expectancy. I t i s p r e d i c t e d t h a t PRT's at the mean"I'SI are responded t o r e l a t i v e l y f a s t e r , and s i g n a l s o c c u r r i n g before or a f t e r t h i s mean are r e a c t e d t o r e l a t i v e l y more sl o w l y . T h i s could e x p l a i n the "U" shaped r e s u l t s of Posner and Keele, and the l a c k of such a t r e n d i n the r e s u l t s r e p o r t e d by E l l s . I n the work by E l l s the expectancy theory would riot apply because t h i s study used a choice response f o r the probe t a s k . Posner and Keele (1969) conducted another i n v e s t i g a t i o n t o compare the a t t e n t i o n demands of d i f f e r e n t systems of movement c o n t r o l . To separate the sources o f feedback i n f o r m a t i o n four c o n d i t i o n s were used: a) S unable 16. t o see movement t o a stop, b) S unable t o see movement t o a t a r g e t which S had p r e v i o u s l y l e a r n e d and was t h e r e f o r e h o l d i n g i n memory, c) S able t o see movement t o a t a r g e t , d) S able t o see movement t o a p o s i t i o n where there had been a t a r g e t . PRT was greater than simple RT f o r a l l movement c o n d i t i o n s except f o r the b l i n d movement t o a stop. I t was assumed t h a t under t h i s con-d i t i o n the S was not r e q u i r e d to make c o r r e c t i o n s and, t h e r e f o r e , no processing c a p a c i t y f o r feedback was necessary. The longer PRT's f o r the other c o n d i t i o n s i n d i c a t e d t h a t the processing of both k i n e s t h e t i c and v i s u a l feedback i n t e r f e r e d w i t h the response t o the probe. LThe PRT's were longest when the movement t o a t a r g e t was c o n t r o l l e d k i n e s t h e t i c a l l y . CHAPTER I I I METHODS AND PROCEDURES Subjects S i x male r i g h t handed u n i v e r s i t y students who were unacquainted t o both the task and apparatus p a r t i c i p a t e d i n the experiment. Apparatus The subject (S) sat at a twenty-eight i n c h h i g h t a b l e d i r e c t l y i n f r o n t of the experimental apparatus (Figure 2 ) , The l a t e r a l p o s i t i o n of the c h a i r was permanently f i x e d such t h a t when seated the S's r i g h t shoulder was a l i g n e d w i t h the approximate center l i n e ^ o f the experimental apparatus. The p o s i t i o n of the c h a i r from the t a b l e was a d j u s t a b l e so t h a t the d i s t a n c e between the S and the t a b l e was t o the S's l i k i n g . The experimental apparatus which was placed on the t a b l e was perpen d i c u l a r t o the t a b l e top f o r four inches and was then i n c l i n e d at an angle of 55° from the v e r t i c a l away from the S. The 20 i n c h by 20 i n c h console (Figure 3) f a c i n g the S c o n s i s t e d o f a panel which contained a recessed RT key, a v i s u a l stimulus d i s p l a y , a response t a r g e t , and g r i p type PRT button. When depressed the RT key was sunk 0.31 inches below the surface of the console i n a w e l l 0.81 inches i n diameter. T h i s was t o ensure t h a t the i n i t i a l response f o r a l l t r i a l s and a l l S's was the same; i . e . a l i f t i n g out of the w e l l . T h i s RT key was c e n t r a l l y l o c a t e d on the v e r t i c a l m i d l i n e of the console and 6 inches away from the near edge. The v i s u a l stimulus d i s p l a y was at eye l e v e l and c o n s i s t e d o f a r e d stimulus l i g h t and an orange warning l i g h t each 0.5 inches i n diameter. The midpoint o f the r e d stimulus l i g h t was a l s o l o c a t e d on the v e r t i c a l m i d l i n e of the console 10.5 inches Figure 2 : P o s i t i o n of subject at apparatus F i g u r e 3: The apparatus 20. d i r e c t l y above the RT key. The midpoint of the orange warning l i g h t was 0.625 inches above and 0.31 inches t o the l e f t of the center of the r e d l i g h t . IThe response t a r g e t was a c i r c u l a r metal d i s c 2.44 inches i n diameter counter sunk i n t o a hole w i t h i n the console 2.56 inches i n diameter which allowed f o r clearance between the t a r g e t and console when the t a r g e t was depressed. LThe top of the t a r g e t was f l u s h w i t h the console surface. Because the center of t h i s t a r g e t was only 2 inches d i r e c t l y below the r e d stimulus l i g h t , the S was able t o watch both a t the same time. The d i s t a n c e from the center o f the RT key t o the near edge of the t a r g e t was 7.25 inches. The g r i p type PRT button was a button 0.31 inches i n diameter" c e n t r a l l y l o c a t e d on the top of a padded c y l i n d r i c a l hand g r i p . T h i s p i e c e of the apparatus was connected t o the bottom l e f t hand corner of the apparatus by a four f o o t w i r e which enabled the S t o h o l d i t wherever he f e l t comfortable. The S wore earphones through which a u d i t o r y s t i m u l i i n the form of tape recorded tones were presented. During the experiment t h i s . t a p e was c o n t i n u a l l y played, but the sound was o n l y heard by the S when the c i r c u i t to the earphones was c l o s e d at the appropriate times. The time i n t e r v a l s between the orange warning l i g h t and r e d stimulus l i g h t , and between the r e d stimulus l i g h t and the a u d i t o r y stimulus were c o n t r o l l e d by a t i m i n g module. T h i s module was manufactured by C H . S t o e l t i n g Company, Chicago, I l l i n o i s . The time delays i n responding and moving are measured i n m i l l i s e c o n d s on three Model 120 A Klockcounter e l e c t r o n i c m i l l i s e c o n d c l o c k s produced by Hunter Manufacturing Company, Incorporated. Experimental C o n d i t i o n s To r e a l i z e the purpose of t h i s experiment i t was necessary t o f i n d 21. a p a t t e r n of movement which could be v a r i e d t o produce three l e v e l s of movement complexity. C h a r a c t e r i s t i c s of these experimental c o n d i t i o n s were t h a t the movements be n a t u r a l t o the S so t h a t a l a r g e number of p r a c t i c e t r i a l s were not r e q u i r e d , and t h a t the s t a r t i n g p o s i t i o n and i n i t i a l movement be the same f o r each response. "'The appropriate movement pa t t e r n s were determined from a p i l o t study (Appendix A). Throughout the experiment the S grasped a round peg 3 inches l o n g and 0.40 inches wide i n h i s r i g h t hand u s i n g h i s thumb and four f i n g e r s such t h a t approximately 0.20 inches of t h i s peg extended beyond h i s f o r e -f i n g e r and 1 t o 1.5 inches extended beyond h i s l i t t l e f i n g e r . At the s t a r t of each t r i a l the S r o t a t e d (pronated) h i s r i g h t arm and hand enabling him to depress the recessed RT key w i t h the peg such t h a t h i s f o r e f i n g e r r e s t e d on the surface of the r e a c t i o n console. I n response t o the p r e s e n t a t i o n of stimulus one, at some random i n t e r v a l (2, 3, or 4 seconds) a f t e r the warning l i g h t , the S r e l e a s e d the RT key by l i f t i n g the peg. Movement patter n s r e q u i r e d during the response v a r i e d from simple ( C l ) t o complex (C3). Experimental c o n d i t i o n C l represented the simplest response. T h i s movement r e q u i r e d the S t o r e l e a s e the RT key by withdrawal of the peg. Experimental c o n d i t i o n C2 was a movement t h a t terminated at a t a r g e t . This was considered to be a movement of r e l a t i v e i n termediate complexity. During t h i s c o n d i t i o n the S was r e q u i r e d t o withdraw the peg from the RT key, reach forward and s t r i k e the t a r g e t w i t h the same end of the peg t h a t had depressed the RT key. The movement f o r experimental c o n d i t i o n C3 was o p e r a t i o n a l l y d e f i n e d as being of greater complexity than C l or C2. The S was r e q u i r e d t o withdraw the peg from the RT key, reach forward r o t a t i n g ( s u p i n a t i o n ) h i s arm and hand, and s t r i k e the t a r g e t w i t h the opposite end of the peg t h a t had depressed the RT key. 22. Under each of the three c o n d i t i o n s of movement complexity the S was r e q u i r e d t o perform a secondary t a s k , a response t o stimulus two ( a u d i t o r y ) . At the s t a r t of each t r i a l the PRT button was depressed w i t h the thumb of the l e f t hand. Upon occurrence of stimulus two, or probe, the S responded by r e l e a s i n g the PRT button. The time i n t e r v a l between the p r e s e n t a t i o n of stimulus one ( v i s u a l ) and stimulus two ( a u d i t o r y ) was r e f e r r e d t o as the probe i n t e r v a l . Presenta-t i o n of the probe or a u d i t o r y stimulus could be governed i n twoaseparate ways. During the f i r s t phase of t h i s experiment the probe was delayed t o f o l l o w stimulus one by some predetermined time ( m i l l i s e c o n d s ) . This method was used when the probe was t o be i n s e r t e d during the i n i t i a t i o n of the primary response or the RT p e r i o d . As recommended by Welford (1967) a minimum probe i n t e r v a l of 90 m i l l i s e c o n d s (msecs.) was chosen t o c o n t r o l against the S grouping these responses. F u r t h e r , a number of i n v e s t i g a t i o n s (Welford, 1967) have found t h a t when probes are i n s e r t e d s h o r t l y before or a f t e r the end of RT, the PRT r e s u l t s are i n e x p l i c a b l y i n c o n s i s t e n t . For t h i s reason the longest probe i n t e r v a l s f o r each c o n d i t i o n were at l e a s t 20 msec, l e s s than the mean RT f o r t h a t c o n d i t i o n . T h i s s e l e c t i o n of the probe i n t e r v a l s was based on the RT r e s u l t s of the p i l o t study. During the second phase of t h i s experiment the probe was delayed t o f o l l o w the i n i t i a t i o n of the movement by some predetermined time. This method was t o be used when the probe was to be i n s e r t e d during the execution of the primary response, or movement time (MT) i n t e r v a l . T his was achieved by having the probe i n t e r v a l s t a r t e d when the S r e l e a s e d the RT button. The s e l e c t i o n of i n t e r v a l s was based on the MT r e s u l t s of the p i l o t study. 23. Experimental Design A repeated measures design was used where a l l S's performed a l l c o n d i t i o n s . To c o n t r o l f o r an order e f f e c t each S was assigned t o one of s i x p o s s i b l e p r e s e n t a t i o n orderings of the three experimental c o n d i t i o n s . Each S attended t h r e e , two 9 and one h a l f - h o u r (approximate) sessions at the same d a i l y time on consecutive days. The S performed 450 t r i a l s f o r each of the experimental c o n d i t i o n s . Under each c o n d i t i o n the S was given 5 p r a c t i c e t r i a l s of the experimental c o n d i t i o n alone ( i . e . without the presence of the secondary task) which were f o l l o w e d by the measurement of t e n t r i a l s f o r a c o n t r o l v a l u e . The S was then g i v e n 5 p r a c t i c e t r i a l s responding to the probe stimulus alone. These were then f o l l o w e d by the measurement of f i v e t r i a l s of the PRT alone f o r c o n t r o l data. Next the successive RT phases of the experiment were conducted which meant t h a t the a u d i t o r y probe stimulus was presented at some randomly v a r i e d i n t e r v a l a f t e r stimulus one. During the f i r s t phase the probe i n t e r v a l s f o r each experimental c o n d i t i o n f o l l o w e d stimulus one by some predetermined time: C l - 90, 110, 130 and 150 m s e c ; C2 - 90, 110, 130, 150 and 170 msec; C3 - 90, HO, 130, 150, 170, 190 msec The S was given 10 p r a c t i c e t r i a l s of the complete experimental t a s k . This was f o l l o w e d by the measurement of 240 successive RT's f o r each experimental c o n d i t i o n . For C l 60 t r i a l s at each of the 4 probe i n t e r v a l s were t e s t e d , f o r C2 i t was 48 t r i a l s per probe i n t e r v a l , and f o r C3 i t was 40 t r i a l s per probe i n t e r v a l . The order of the 4 probe i n t e r v a l s f o r C l was randomly v a r i e d w i t h i n 24 t r i a l b l o c k s so t h a t a f t e r 24 t r i a l s each probe had occurred s i x times. The order of the 5 probe i n t e r v a l s f o r C2 was randomly v a r i e d so t h a t a f t e r 25 t r i a l s each probe had 2k. occurred f i v e times. The order of the 6 probe i n t e r v a l s f o r C3 was randomly-v a r i e d w i t h i n blocks so t h a t a f t e r 24 t r i a l s each probe occurred 4 times. For the second phase of the experiment the probe i n t e r v a l s were made t o f o l l o w the i n i t i a t i o n of movement by some predetermined time. For C l , C2 and C3 the probe i n t e r v a l s were 20, 80, 140 and 200 msec, a f t e r the beginning o f the movement. LThe order of probe i n t e r v a l s f o r each experimental c o n d i t i o n were randomly v a r i e d so t h a t w i t h i n each block of 24 t r i a l s each probe i n t e r v a l occurred s i x times. Under each c o n d i t i o n the s e s s i o n was completed by o b t a i n i n g more c o n t r o l measures, t e n t r i a l s of the experimental c o n d i t i o n alone and f i v e t r i a l s of the probe response alone. A n a l y s i s of Data Data a n a l y s i s was performed on the mean RT's, MT's, and PRT's f o r a l l t r i a l s w i t h i n each c o n d i t i o n . RT t o Primary Task. The e f f e c t s of movement complexity on the i n i t i a t i o n of a response was determined by a simple a n a l y s i s of vari a n c e comparing the mean RT's of the c o n t r o l data f o r each experimental c o n d i t i o n . These means represented 120 t r i a l s , 60 t r i a l s from pre t e s t c o n t r o l s and 60 t r i a l s of the post t e s t c o n t r o l . To determine whether the probe i n t e r f e r e d w i t h the i n i t i a t i o n of the primary t a s k , t h e mean RT f o r each experimental c o n d i t i o n from the successive RT data were compared w i t h the corresponding c o n t r o l data f o r each experimental c o n d i t i o n . Again an a n a l y s i s o f va r i a n c e was used. MT t o the Primary Task. From the c o n t r o l data the mean MT f o r the two experimental c o n d i t i o n s r e q u i r i n g movement t o the t a r g e t were analyzed by a simple a n a l y s i s of vari a n c e t o determine the e f f e c t s of movement 25. complexity on the execution of the movement. Each mean represented 120 t r i a l s , 60 from the pre t e s t measurements and 60 from the post t e s t measurements. The mean MT's from the successive response data were ; s i m i l a r l y compared w i t h . the corresponding c o n t r o l data i n order t o determine whether the probe i n t e r -f e r e d w i t h the MT during the primary task. RT t o the Secondary Task (PRT). The PRT's were analyzed f o r both phases of the experiment, when the probe was presented during the i n i t i a t i o n of the response, and when the probe was presented during the execution of the movement. A three way a n a l y s i s of variance was performed on the mean PRTs of the common probe i n t e r v a l s f o r each c o n d i t i o n t o determine whether the a t t e n t i o n needed f o r processes during the i n i t i a t i o n of a response and the execution of a movement inc r e a s e d w i t h a movement complexity. .The three v a r i a b l e s t h a t c o n s t i t u t e d t h i s a n a l y s i s were S's, c o n d i t i o n s and probe i n t e r v a l s . For the above analyses, where the o v e r a l l F i n d i c a t e d s i g n i f i c a n c e , the Scheffe method (Scheffe, I964) was used t o determine where .the s i g n i f i c a n t d i f f e r e n c e s occurred. CHAPTER IV RESULTS AND DISCUSSION RESULTS RT - C o n t r o l , Phase I and Phase I I I t was hypothesized t h a t the time taken t o i n i t i a t e a primary response would i n c r e a s e as a f u n c t i o n of the complexity of movement r e q u i r e d during the execution of t h a t response. The r e s u l t s t e s t i n g t h i s hypothesis are shown i n F i g u r e 4 which presents the mean c o n t r o l RT f o r each of the three c o n d i t i o n s of movement complexity, p l u s the phase I RT's (probe pre-sented during RT i n t e r v a l ) and phase I I RT's (probe presented during MT i n t e r v a l ) . An a n a l y s i s of v a r i a n c e f o r the c o n t r o l data r e v e a l e d t h a t the c o n d i t i o n e f f e c t was not s i g n i f i c a n t . A summary of t h i s a n a l y s i s appears i n Table 1. TABLE 1 ANALYSIS OF VARIANCE OF CONTROL RT Source of Variance df MS F p Ss 5 2739 Cond. 2 574 1.05 > .05 E r r o r 10 548 T o t a l 17 F i g u r e 4: Mean RT during c o n t r o l , Phase I , and Phase I I as a f u n c t i o n of movement complexity 28. I t was a n t i c i p a t e d t h a t t h i s hypothesis would a l s o apply t o the successive response phases of the experiment. The mean RTs f o r each of the three c o n d i t i o n s of movement complexity during phase I of the successive response task are a l s o presented i n Fi g u r e 4. The tr e n d of these data are a c t u a l l y opposite t o what was expected, however, an a n a l y s i s of vari a n c e r e v e a l e d t h a t the c o n d i t i o n main e f f e c t was not s i g n i f i c a n t (Table I I ) . TABLE I I ANALYSIS OF VARIANCE OF RT DURING PHASE I Source o f Variance df MS F P Ss 5 4225 Cond. 2 464 0.35 I S I 3 1366 3L77 < .00: L i n e a r 1 4033 94.41 Quadratic 1 33 S x Cond 10 1337 S x I S I 15 43 Cond. x I S I 6 72 3.60 < .01 S x Cond. x I S I 30 20 T o t a l 71 < .001 Further r e s u l t s from the phase I a n a l y s i s r e v e a l e d t h a t the l e n g t h of the I S I had a s i g n i f i c a n t e f f e c t on RT (Table I I ) . The mean RT's over a l l c o n d i t i o n s f o r phase I are summarized i n Fi g u r e 5 as a f u n c t i o n o f the I S I . 29. F i g u r e 5: Mean phase I RT as a f u n c t i o n of I S I 30. The Scheffe procedure was used to test the main effect of ISI on RT and this test showed significant differences among a l l ISI except between the 130 and 150 msec, interval. Figure 6 shows the interaction between conditions and ISIs for phase I which produced a significant F (Table I I ) . Further analysis using the Scheffe test on the table of effects from this interaction disclosed that the RT for C2 at ISI 90 caused an interaction. The mean RT for each of the three conditions of movement complexity during phase II were presented i n Figure L\. An analysis of variance revealed that the condition main effect was not significant and that the ISI main effect was significant (Table I I I ) . TABLE I I I ANALYSIS OF VARIANCE OF RT DURING PHASE II Source of Variation df MS Ss • 5 Cond. 2 ISI 3 S x Cond. 1 0 S x ISI 1 5 Cond. x ISI 6 S x Cond. x ISI 3 0 Total 7 1 1 3 6 1 4 2 1 6 4 1 4 0 2818 2 5 1 2 3 2 3 0 . 7 7 5 . 6 0 5 . 3 5 < . 0 1 < . 0 5 31. F i g u r e 6: Mean phase I RT f o r each c o n d i t i o n as a f u n c t i o n of ISI 32. Table IV reports an analysis which was conducted to determine whether the time required to i n i t i a t e a response was changed when a second stimulus was presented. The condition main effect was not s i g n i f i c a n t , although the contrast between control, phase I , and phase I I produced a si g n i f i c a n t F. Further analysis using the Scheffe test disclosed that the mean for a l l RT measurements i n phase I I was greater than the mean for a l l control and phase I RT measurements. TABLE TV ANALYSIS OF VARIANCE OF RT DURING CONTROL, PHASE I , AND PHASE I I Source of Variance df MS F p Ss 5 666o Phase 2 7928 29.25 <.001 Cond. 2 152 O.H S x Phase 10 271 S x Cond. 10 1325 Phase x Cond. 4 533 4.40 <.025 S x Phase x Cond. 20 121 Total 53 PRT - Phase I Hypothesis two predicted that the time taken to i n i t i a t e a response v t o a .second stimulus presented during the i n i t i a t i o n of a primary response 33. would vary as a function of the complexity of movement required during the primary response. Figure 7 presents the mean PRTs for control and each experimental condition of movement complexity. An analysis of variance that included the control as w e l l as experimental conditions revealed that the condition main effect was s i g n i f i c a n t (Table V). The Scheffe procedure was used to test for the differences between these means and i t was found that the PRT means for both C2 and C3 were s i g n i f i c a n t l y d i f f e r e n t from the controls PRT. The Scheffe procedure was also used to compare the probe presented during the RT to the task with the probe when i t occurred by i t s e l f . I t was found that the grand mean for a l l conditions during phase I (250 msec.) was s i g n i f i c a n t l y greater thahnthe mean for a l l conditions during control (183 msec). In addition, the trend analysis indicated a li n e a r r e lationship between the four conditions. TABLE V ANALYSIS OF VARIANCE OF PRT DURING CONTROL AND PHASE I Source of Variance df MS F p Ss 5 7502 Cond. 3 10643 5.05 <.025 Linear 1 26344 12.51 <.005 Quadratic 1 2646 1.26 > .05 Error 15 2106 Total 23 F i g u r e 7: Mean phase I PRT as a f u n c t i o n of movement complexity and mean c o n t r o l PRT 35. The r e s u l t s r e l a t i n g e f f e c t of the l e n g t h of the I S I on the mean PRT f o r a l l c o n d i t i o n s are presented i n Figure 8. An a n a l y s i s of va r i a n c e i n c l u d i n g o nly the three movement c o n d i t i o n s showed th a t the I S I main e f f e c t was s i g n i f i c a n t (Table V I ) . The Scheffe procedure was used on these data and showed s i g n i f i c a n t d i f f e r e n c e s among a l l I S I . I n a d d i t i o n , the t r e n d a n a l y s i s showed a s i g n i f i c a n t l i n e a r t r e n d . TABLE V I ANALYSIS OF VARIANCE OF PRT DURING PHASE I Source of Variance df MS F P • Ss 5 41121 Cond. 2 24030 I S I 3 1645 31.69 <.oo: L i n e a r 1 4920 94.6 Quadratic 1 5 0.1 S x Cond. 10 6961 S x I S I ; 15 52 Cond. x I S I 6 142 I.69 > .05 S x Cond. x I S I 30 84 T o t a l . 71 Figure 9 presents the i n t e r a c t i o n of I S I w i t h the three c o n d i t i o n s i n terms of PRT. An a n a l y s i s of va r i a n c e , Table V I , r e v e a l e d t h a t the con-d i t i o n by I S I i n t e r a c t i o n was not s i g n i f i c a n t . 36. F i g u r e 8: Mean PRT during-phase I f o r a l l c o n d i t i o n s as a f u n c t i o n of I S I 37 Fi g u r e 9: Mean PRT during Phase I f o r each c o n d i t i o n as a f u n c t i o n of I S I and mean c o n t r o l PRT 38. MT - C o n t r o l , Phase I , and Phase I I I t was expected t h a t the e f f e c t of movement complexity on MT would be t o i n c r e a s e MT. Mean c o n t r o l , phase I , and phase I I MT's f o r each of the two c o n d i t i o n s i n which the movement was terminated at a t a r g e t are shown i n F i g u r e 10. An a n a l y s i s of va r i a n c e f o r the c o n t r o l data y i e l d e d an F r a t i o of 16.13 r e v e a l i n g t h a t the c o n d i t i o n e f f e c t was s i g n i f i c a n t (Table V I I ) . TABLE V I I ANALYSIS OF VARIANCE OF CONTROL MT Source of V a r i a t i o n df MS F P Ss. 5 243 Cond. 1 3675 16.13 €.025 E r r o r 5 228 T o t a l 11 During phase I I of the successive response t a s k s , when the probe was presented during the MT, i t was found t h a t the movement complexity e f f e c t was no longer s i g n i f i c a n t . An a n a l y s i s of v a r i a n c e , summarized i n Table V I I I , f o r these data y i e l d e d an F r a t i o of 4*63 r e v e a l i n g t h a t the c o n d i t i o n main e f f e c t was not s i g n i f i c a n t . P r e s e n t a t i o n of the probe during the RT component of the response d i d not have the same e f f e c t . An a n a l y s i s of vari a n c e f o r these data d i s -c l o s e d t h a t the c o n d i t i o n main e f f e c t was s i g n i f i c a n t . An o u t l i n e of t h i s 39. F i g u r e 10: Mean MT during c o n t r o l , phase I , and phase I I as a f u n c t i o n of movement complexity 40. a n a l y s i s appears i n Table IX. I t was a l s o o f i n t e r e s t at t h i s time t o determine whether the l e n g t h of the I S I , or the r e l a t i v e p o s i t i o n of the probe w i t h i n the movement, i n f l u e n c e d MT. F i g u r e l l i l l u s t r a t e s the mean phase I I MT's as a f u n c t i o n of I S I . An a n a l y s i s of v a r i a n c e f o r these data showed th a t the I S I main e f f e c t was s i g n i f i c a n t (Table V I I I ) . The Scheffe procedure was used t o t e s t the main e f f e c t o f I S I on MT and t h i s t e s t showed the I S I of 20 t o be d i f f e r e n t from a l l o t h e r M S I . TABLE V I I I ANALYSIS OF VARIANCE OF PHASE I I MT Source of V a r i a t i o n df MS F P Ss 5 3635 Cond. 1 6888 4.63 > .05 I S I 3 77 15.02 < .001 -S x Cond. 5 1488 S x I S I 15 :5 Cond. x I S I 3 7 0.71 S x Cond. x I S I 15 10 T o t a l 47 From F i g u r e 10 i t can be seen t h a t the phase I I MT data show a d i f f e r e n t f u n c t i o n than the c o n t r o l MT data. To pursue t h i s an a n a l y s i s of va r i a n c e was conducted t o determine i f the p r e s e n t a t i o n o f the probe had an F i g u r e 11: Mean phase I I MT as a f u n c t i o n of I S I 42. e f f e c t on MT (Table X ) . The c o n t r a s t between c o n t r o l , phase I and phase I I produced a s i g n i f i c a n t F. Further a n a l y s i s u s i n g the Scheffe procedure re v e a l e d t h a t the mean f o r a l l MT measurements i n phase I I d i f f e r e d from the phase I mean. TABLE IXs ANALYSIS OF VARIANCE FOR PHASE I MT Source of V a r i a t i o n d f MS F P Ss 5 1786 Cond. 1 9352 14.1 < .025 I S I 3 9 1.2 > .05 S x Cond. 5 665 S x I S I 15 8 Cond. x I S I 3 3=3 0.3 S x Cond. x I S I 15 10 T o t a l 47 43. TABLE X ANALYSIS OF VARIANCE OF"MT DURING CONTROL PHASE I , AND PHASE I I Source of V a r i a t i o n df MS F p Ss 5 1380 Phase 2 501 Cond. 1 7540 S x Phase 10 101 S x Cond. 5 635 Phase x Cond. 2 98 S x Phase x Cond. 10 64 T o t a l 35 PRT - Phase I I I t was hypothesized t h a t the time needed t o i n i t i a t e a secondary response t o a stimulus presented during the execution of a primary response i s i n c r e a s e d as a f u n c t i o n of the complexity of movement r e q u i r e d during the execution of the primary response. The r e s u l t s which r e l a t e s p e c i f i c a l l y t o t h i s hypothesis are presented i n F i g u r e 12. An a n a l y s i s of v a r i a n c e , Table X I , over a l l c o n d i t i o n s i n c l u d i n g c o n t r o l showed the c o n d i t i o n s main e f f e c t t o be s i g n i f i c a n t . The Scheffe procedure was used t o t e s t d i f f e r e n c e s among c o n d i t i o n s . I t was found t h a t t h ere was a d i f f e r e n c e between a l l c o n d i t i o n s except C2 and C3. 44. F i g u r e 12: Mean phase I I PRT as a f u n c t i o n of movement complexity and mean c o n t r o l PRT 45. TABLE XI ANALYSIS OF VARIANCE OF PRT DURING CONTROL AND PHASE I I Source of V a r i a t i o n df MS F p Ss 5 1861 Cond. 3 6614 13.25 ' <.001 E r r o r 15 499 As expected, the l e n g t h of the I S I s i g n i f i c a n t l y a f f e c t e d the PRT. Fig u r e 13 presents the mean PRT over a l l c o n d i t i o n s as a f u n c t i o n of I S I and t h i s d e p i c t s a s i g n i f i c a n t e f f e c t (Table X I I ) . The Scheffe procedure was used t o t e s t d i f f e r e n c e s among the I S I . I t was found t h a t each I S I was d i f f e r e n t except f o r I 4 0 msec, and 2 0 0 msec. I S I ' s , and the 80 msec, and 200 msec. I S I ' s . I n a d d i t i o n , the t r e n d a n a l y s i s showed.both a s i g n i f i c a n t , l i n e a r and quadratic t r e n d . 4 6 . F i g u r e 13: Mean phase I I PRT as a f u n c t i o n of I S I 47. TABLE X I I ANALYSIS OF VARIANCE OF PHASE I I PRT Source of V a r i a t i o n df MS Ss 5 Cond. 2 I S I 3 Linear Quadratic S x Cond. 10 S x I S I 15 Cond. x I S I 6 S x Cond. x I S I 30 T o t a l 71 1 1 10465 13827 3541 6525 4034 1283 182 138 176 10.77 19.48 0.78 34.0 22.1 <.005 <.001 <.001 <.00l Figure 14 i l l u s t r a t e s the mean c o n t r o l PRT, and mean phase I I PRT f o r each c o n d i t i o n as a f u n c t i o n of I S I . An a n a l y s i s of va r i a n c e i n c l u d i n g the three movement complexity c o n d i t i o n s i n d i c a t e d t h a t the c o n d i t i o n by I S I i n t e r a c t i o n was not s i g n i f i c a n t . A summary of t h i s a n a l y s i s appears i n Table X I I . F i n a l l y , a " t " t e s t was conducted on the mean PRT's of phase I and phase I I . No s i g n i f i c a n t d i f f e r e n c e was found. J i i i _ _ r 20 80 140 200 ISI F i g u r e 14: Mean phase I I PRT f o r each c o n d i t i o n as a f u n c t i o n of I S I and mean c o n t r o l PRT 49. DISCUSSION RT - C o n t r o l , Phase I , and Phase I I Since the mean c o n t r o l RT's, present i n Fi g u r e 4, were not s t a t i s t i -c a l l y d i f f e r e n t from each other i t cannot be concluded t h a t movement com-p l e x i t y a f f e c t e d RT. Th i s i n d i c a t e s t h a t the time r e q u i r e d t o i n i t i a t e a response was un a f f e c t e d by the complexity of movement r e q u i r e d during the execution of the response. On the b a s i s of previous emperical i n v e s t i g a t i o n s d e a l i n g s p e c i f i c a l l y w i t h t h i s experimental v a r i a b l e (Henry, 196l; Henry and Rodgers, i960; N o r r i e , 1967; O'Brien, 1959; Sidowski et a l , 1958) i t was expected t h a t the RT r e s u l t s would i n c r e a s e w i t h movement complexity. D e t a i l e d assessment of the a n a l y s i s of v a r i a n c e i n Table I r e v e a l s t h a t no s i g n i f i -cance was found because o f an u n u s u a l l y l a r g e e r r o r term and i n s p e c t i o n o f the raw data d i s c l o s e d a l a r g e l e a r n i n g e f f e c t . I t was found t h a t f o r each S, r e g a r d l e s s of the order i n which the c o n d i t i o n s were presented, the RT's on day one were always the slowest. A l s o , these RT's became p r o g r e s s i v e l y f a s t e r on day two, and by day three the f a s t e s t RT's were being recorded. A second f a c t o r which c o n t r i b u t e d t o the l a r g e e r r o r term was the i n c o n s i s t e n t performance of one S whose c o n t r o l RT appeared to be much slower than h i s RT during the successive task aspect of the experiment. Even though there was no s i g n i f i c a n t d i f f e r e n c e between c o n d i t i o n s i n F i g u r e 4 i t appears t h a t there was an apparent d i f f e r e n c e as the c o n t r o l RT f o r C2 and C3 seem t o be gr e a t e r than the c o n t r o l RT f o r C l . C o n s i d e r i n g the reasons f o r the l a c k of s i g n i f i c a n c e to be v i a b l e , i t i s p o s s i b l e t o consider the decrement i n RT performance t o be a r e f l e c t i o n o f movement com-p l e x i t y . I n t h i s l i g h t i t c o u l d be i n t e r p r e t e d t h a t C2 and C3 i n v o l v e move-ments of gr e a t e r complexity than C l . 50. I t i s p o s s i b l e t h a t the RT component during the successive t a s k aspect of the experiment was a l s o b i a s e d . From F i g u r e 4 i t i s p o s s i b l e t o observe the e f f e c t of the phase I successive response t a s k on the RT com-ponent of the primary response. Although no s i g n i f i c a n t d i f f e r e n c e s were found between the mean RT f o r the c o n t r o l c o n d i t i o n and the corresponding mean f o r phase I (Table TV), the graph shows t h a t f o r phase I the means are approximately equal whereas the three mean c o n t r o l RT's tend, t o be unequal. I t seems p o s s i b l e t o conceive t h a t d u r i n g the double s t i m u l a t i o n task the S adopted a s t r a t e g y which designated the probe task t o be the primary t a s k d e s p i t e the i n s t r u c t i o n s t o the S on the importance of the f i r s t t a s k . I t i s i n t e r p r e t e d t h a t t h i s s t r a t e g y would tend t o e l i m i n a t e the i n f l u e n c e of movement complexity on RT. I n a d d i t i o n , the f i n d i n g t h a t RT d i f f e r e d over I S I i n d i c a t e s t h a t RT was a f f e c t e d by the p o s i t i o n of the probe during the RT i n t e r v a l . On the b a s i s of recent l i t e r a t u r e (Herman and McCauley, 1969) i t was expected t h a t no I S I e f f e c t on RT should be observed f o r I S I greater than 50 t o 100 msec, or at the most, i f t h e r e was an I S I e f f e c t , i t was f e l t t h a t the longer the I S I , or the l a t e r the occurrence of the probe d u r i n g the RT i n t e r v a l , the l e s s would be the e f f e c t on the RT i t s e l f . However, t h i s was o b v i o u s l y not the case because the r e s u l t s showed a t r e n d i n the d i r e c t i o n opposite t o t h a t p r e d i c t e d , i n t h a t the longer the I S I the slower the RT became. Two i n t e r p r e t a t i o n s of these r e s u l t s seem p o s s i b l e . According t o the model employed i n the present study, the experimental c o n d i t i o n s were designed t o overload the l a t e r stages of the c e n t r a l processor. I n t h i s r e g a r d , when the probe occurred d u r i n g these stages i t i s p o s s i b l e t h a t 51. perhaps t h e r e would be a greater performance decrement due merely t o the i n t e r u p t i o n , or even the use of some of the a t t e n t i o n c a p a c i t y t o s t o r e the probe i n f o r m a t i o n i n short term memory. Thus, si n c e the mean RT f o r a l l t r i a l s d u r i ng phase I was 245 msec, i t i s conceivable t h a t the l a t e r the p r e s e n t a t i o n of the probe, the c l o s e r would, be i t s r e l a t i v e p o s i t i o n t o those processes a s s o c i a t e d w i t h the i n i t i a t i o n of the primary response. Consequently, i f t h i s were t o be the case, we would expect the probe t o have the l e a s t e f f e c t on C l and greater e f f e c t on C2 and C3 because of t h e i r i n c r e a s e d demands. But, F i g u r e 4 shows th a t the mean RT f o r a l l I S I was gr e a t e s t f o r C l . T h i s i n d i c a t e s t h a t the e f f e c t of the probe was not due t o i t s p o s i t i o n r e l a t i v e t o those processes a s s o c i a t e d w i t h the i n i t i a t i o n of the primary response. A second i n t e r p r e t a t i o n could be t h a t the S's used a s t r a t e g y of "grouping" (Welford, 19°7), t h a t i s , the S waited f o r the p r e s e n t a t i o n o f the second stimulus before i n i t i a t i n g h i s response t o the f i r s t s t i m u l u s . The more complex the f i r s t response, the more the S would delay. I t i s suggested t h a t the S adopted t h i s s t r a t e g y during the successive response task because of the inc r e a s e d demands placed on the S's mental oper a t i o n s . So i t would f o l l o w t h a t an i n c r e a s e of these demands would r e s u l t i n a more pronounced "grouping" s t r a t e g y , o r , the more complex the f i r s t response, the more the S would delay. But t h i s was not the case as the mean RT f o r a l l I S I of the two more complex c o n d i t i o n s tended t o be f a s t e r (Figure 4). A l s o , i f the S waited f o r the second stimulus t o occur, we would expect C2 and C3 t o be longer because these two c o n d i t i o n s i n c l u d e d the longer I S I ' s of 170, and 170 and 190 r e s p e c t i v e l y . Nevertheless, there i s evidence supporting the 52. c o n t e n t i o n t h a t the S's were grouping. Probes during the MT i n t e r v a l of the primary response should not i n f l u e n c e the RT i n t e r v a l . However, RT's during phase I I o b v i o u s l y were much slower (Figure 4) than f o r c o n t r o l and phase I RT's. I f the S's were grouping, t h i s would be expected as the probe would not be o c c u r r i n g u u n t i l much l a t e r i n phase I I . PRT - Phase I A review o f previous i n v e s t i g a t i o n s of the e f f e c t s o f movement complexity r e v e a l e d t h a t the work i n t h i s area was incomplete. S e v e r a l i n v e s t i g a t o r s (Henry, 1961; Henry and Rodgers, I960; N o r r i e , I967; O'Brien, 1959; Sidowski et a l , 1958) have claimed t h a t RT was an accurate measurement of the e f f e c t s of movement complexity on the operations of .'man's c e n t r a l p rocessing system. But the p o s s i b i l i t y e x i s t e d t h a t the changes i n RT could be the r e s u l t o f p e r i p h e r a l f a c t o r s and not of the operations w i t h i n the c e n t r a l processor. The current experiment was designed t o i n v e s t i g a t e t h i s p o s s i b i l i t y . I I t was hypothesized t h a t C3 would have the great e s t e f f e c t i n d e l a y i n g RT, w i t h C2 a l s o having a l a r g e e f f e c t on RT but l e s s than C3, and C l having the s m a l l e s t e f f e c t . F i g u r e 4 shows t h a t b a s i c a l l y these r e s u l t s were obtained, mean RT's f o r C2 and C3 were slower than f o r C l , however, C2 had a grea t e r delay than C3. But, the i n t e r e s t i n g p o i n t i s th a t the mean PRT's during phase I have f o l l o w e d the exact same t r e n d , C2 and C3 are grea t e r than C l , and C2 i s grea t e r than C3:, although not s i g n i f i c a n t l y i n both i n s t a n c e s . T h i s suggests t h a t i n t h i s experiment RT i s an accurate barometer of the operations of man's c e n t r a l processing system. 53. Using c o n t r o l PRT as a standard of the minimum of a t t e n t i o n necessary t o i n i t i a t e a response, i t was found t h a t the PRT i n c r e a s e d f o r a l l c o n d i t i o n s of movement complexity ( F i g u r e 7)• T h i s i n d i c a t e d t h a t a t t e n t i o n p r i o r t o the i n i t i a t i o n o f a response increased as a f u n c t i o n of the movement complexity r e q u i r e d during the execution of the response. The i n c r e a s e i n PRT from C l t o C2 and C3 was l i n e a r (Table V ) . I t was i n t e r p r e t e d t h a t the i n c r e a s e from c o n t r o l t o C l could be att'r.'ibuted-Jt'o the e f f e c t s of movement complexity and the successive s t i m u l i e f f e c t . However, si n c e C2 and C3 were s i g n i f i c a n t l y d i f f e r e n t from C l t h i s was i n t e r p r e t e d as evidence t h a t the d i f f e r e n c e from C l t o C2, and C l t o C'3 must be due t o the complexity e f f e c t . Thus i t was concluded t h a t the r e l a t i v e degree of a t t e n t i o n necessary t o i n i t i a t e a motor response v a r i e s d i r e c t l y w i t h the complexity of movement r e q u i r e d during the execution of t h a t response. The s i g n i f i c a n c e of the I S I main e f f e c t (Table VI) i n d i c a t e d t h a t the l o c a t i o n of the probe w i t h i n the RT i n t e r v a l had a s i g n i f i c a n t i n f l u e n c e on the delay i n PRT. As expected, the l a t e r occurrences of the probe r e s u l t e d i n p r o g r e s s i v e l y f a s t e r PRT's i n a l i n e a r t r e n d . This ^supports the s i n g l e channel theory i n t h a t the probes t h a t occurred l a t e r acquired access t o the c e n t r a l processor sooner r e s u l t i n g i n a decreased PRT. The r e s u l t s of the c o n d i t i o n by I S I i n t e r a c t i o n (Table VI) were not s i g n i f i c a n t i n d i c a t i n g t h a t the I S I ' s had a s i m i l a r e f f e c t on a l l c o n d i t i o n s . F i g u r e 9 a l s o r e v e a l s t h a t C2 had the g r e a t e s t e f f e c t on PRT for, a l l I S I , which i s c o n s i s t e n t w i t h the previous apparent d i f f e r e n c e s . MT - C o n t r o l , Phase I and Phase I I I t was evident from F i g u r e 10 that the MT i n c r e a s e d w i t h the 54. complexity of movement r e q u i r e d during the response. The r e s u l t s of the s t a t i s t i c a l a n a l y s i s f o r c o n t r o l c o n d i t i o n s (Table V I I ) showed a l a r g e e f f e c t of movement complexity. I t was i n t e r e s t i n g t o note t h a t the p r e s e n t a t i o n o f the probe during the MT i n t e r v a l had a s i m i l a r e f f e c t on MT as the p r e s e n t a t i o n of the probe during the RT i n t e r v a l . That i s , during c o n t r o l and phase I the e f f e c t of complexity increased MT t o a s i g n i f i c a n t amount, however, when the probe was presented during the MT the d i f f e r e n c e between the two l e v e l s of complexity i n terms of MT was not l a r g e enough t o reach s i g n i f i c a n c e . However, i f the demands of the task were i n a c t u a l i t y i n creased during phase I I , i t would be expected t h a t the mean MT's f o r phase I I would be greater than the means f o r the c o n t r o l c o n d i t i o n s . But, t h i s was not the case. Table X r e v e a l e d t h a t there was a s i g n i f i c a n t d i f f e r e n c e due' t o the p r e s e n t a t i o n of the probe, however, the Scheffe showed th a t t h i s d i f f e r e n c e was between phase I and phase I I . There was no explanation why phase I MT was f a s t e r than c o n t r o l and thus why a d i f f e r e n c e was found between the phases. The s i g n i f i c a n c e of the I S I main e f f e c t (Table V I I I ) i n d i c a t e d t h a t the l o c a t i o n of the probe during the MT i n t e r v a l i n t e r f e r e d w i t h the MT. However, from F i g u r e 11 i t appeared t h a t these e f f e c t s were n e g l i g i b l e . PRT - Phase I I The f i n d i n g t h a t PRT inc r e a s e d as a f u n c t i o n of movement complexity i n d i c a t e s t h a t a t t e n t i o n during the execution of a response v a r i e s d i r e c t l y w i t h the r e l a t i v e degree of c o n t r o l necessary t o execute t h a t response. I t was evident from F i g u r e 12 t h a t a t t e n t i o n was r e q u i r e d during the execution of a l l responses. A l s o , i t was apparent that movements terminated a t a t a r g e t (C2 and C3) r e q u i r e d more a t t e n t i o n during the f i r s t 200 msec, of the movement 55. than d i d a non-terminal movement ( C l ) . F u r t h e r , a t t e n t i o n needed d u r i n g a r o t a t i o n a l movement t o a t a r g e t was greater than t h a t r e q u i r e d f o r movements t o a t a r g e t not i n v o l v i n g arm r o t a t i o n s as C3 was greater than C2. The s i g n i f i c a n t I S I e f f e c t (Table X I I ) suggests t h a t the amount of a t t e n t i o n r e q u i r e d by the S v a r i e d w i t h the p o s i t i o n of the probe during the MT i n t e r v a l . The g r a p h i c a l r e p r e s e n t a t i o n of the PRT data as a f u n c t i o n of I S I (Figure 13) p o i n t s out t h a t movement execution r e q u i r e s more a t t e n t i o n e a r l y i n the movement than l a t e r i n the movement, and t h a t near the end of the movement th e r e was a r e l a t i v e i n c r e a s e i n PRT suggesting t h a t a t t e n t i o n requirements were i n c r e a s i n g . These r e s u l t s are s i m i l a r t o those report e d by Posner and Keele (19°8). The I S I by c o n d i t i o n i n t e r a c t i o n was not s i g n i f i c a n t (Table X I I ) i n d i c a t i n g t h a t the I S I ' s had a s i m i l a r e f f e c t on a l l conditions*. But Fig u r e 14 r e v e a l s t h a t the i n c r e a s e i n a t t e n t i o n during the l a t e r stages of the movement as pointed out above, a p p l i e d only t o those movements terminated at the t a r g e t . The PRT at the 200 msec. I S I d i d not i n c r e a s e f o r C l suggesting t h a t the in c r e a s e d a t t e n t i o n during the l a t e r p e r i o d of MT was r e l a t e d t o the S having t o s t r i k e the t a r g e t . This supports the work o f Annett, Golby and Kay (1968) who d i d a d e t a i l e d f i l m a n a l y s i s of movement t o a t a r g e t and found t h a t although MT v a r i e d w i t h the s i z e of the t a r g e t , the i n i t i a l 15/l6 of the t o t a l d i s t a n c e was always constant. The f i n a l adjustment time during the l a s t l/l6 of the d i s t a n c e increased as the s i z e of the t a r g e t de-creased. I t was i n t e r p r e t e d i n t h i s study t h a t i t was these f i n a l adjustments as t h e t a r g e t was approached t h a t caused the i n c r e a s e a t t e n t i o n . These r e s u l t s (Figure 14) r e j e c t the "expectancy theory" which a l s o p r e d i c t e d t h a t PRT would be a "U" shaped f u n c t i o n o f I S I , w i t h the minimum 56. PRT value o c c u r r i n g at or about the mean or'expected values of I S I and t h a t as the d i s t a n c e of the probe from the mean inc r e a s e d , PRT would become p r o g r e s s i v e l y i n c r e a s e d . However, s i n c e t h i s theory i s based upon the S's l e a r n i n g the I S I d i s t r i b u t i o n and not upon the processing r e q u i r e d f o r the primary response, t h i s theory would p r e d i c t t h a t delays i n PRT would be the same f o r the three c o n d i t i o n s of movement complexity because i d e n t i c a l I S I ' s were used. However, Fi g u r e 14 c l e a r l y i n d i c a t e s t h a t there were d i f f e r e n c e s i n the or d i n a t e s of the three f u n c t i o n s . Further evidence against t h i s theory was the f i n d i n g t h a t the "U" shaped t r e n d was not c o n s i s t e n t through-out a l l c o n d i t i o n s . The inc r e a s e d a t t e n t i o n near the end of movement occurred only i n movements terminated at a t a r g e t . Comparison of A t t e n t i o n During Phase I and Phase I I The PRT r e s u l t s of phase I and phase I I i n d i c a t e t h a t the a t t e n t i o n requirements o f the two component processes of a response are independent. I t has been e s t a b l i s h e d t h a t the time r e q u i r e d f o r the i n i t i a t i o n and execution of a response are independent (Henry and Rodgers, I960; Henry, 1961; F i t t s and Peterson, 1964; F i t t s and Radford, I 9 6 6 ) . T h i s was a l s o evident i n the data of t h i s study as the apparent e f f e c t of movement complexity on RT was g r e a t e s t f o r C2, and f o l l o w e d a tren d of being somewhat l e s s f o r C3 and much l e s s f o r C l (Figu r e 4)• The a t t e n t i o n requirements during the i n i t i a t i o n o f the response c l o s e l y f o l l o w e d t h i s p a t t e r n , r e f l e c t i n g the time r e q u i r e d t o i n i t i a t e a response (Fig u r e 7). But, the e f f e c t o f movement complexity on MT was reversed as C3 had a s i g n i f i c a n t l y l a r g e r execution p e r i o d than C2 ( F i g u r e 10), and i n t e r e s t i n g l y enough, the PRT during phase I I f o l l o w e d the exact same t r e n d ( F i g u r e 12). 57. Comparison o f the r e l a t i v e degree o f a t t e n t i o n needed during each of the two component processes r e v e a l e d t h a t more a t t e n t i o n was needed during the i n i t i a t i o n of a response. The mean of a l l phase I I PRT's was 237 msec, w h i l e the mean of a l l phase I PRT's was only 250 msec. Th i s f i n d i n g i s i n agreement w i t h the work done by E l l s (1969). CHAPTER V SUMMARY AND CONCLUSIONS The purpose of t h i s study was t o determine the e f f e c t s of movement complexity on the r e l a t i v e degree o f a t t e n t i o n r e q u i r e d d u r i n g the i n i t i a t i o n of a response and the execution of a movement. Three movements of v a r y i n g complexity were s e l e c t e d on the b a s i s of RT measurements obtained from a p i l o t study. S i x male r i g h t handed u n i v e r s i t y students were p a i d t o attend t h r e e two and one h a l f hour sessions on consecutive days. A t t e n t i o n was considered t o be the delay i n r e a c t i o n time t o a second stimulus or probe t h a t was t o be processed during e i t h e r the i n i t i a t i o n of the response (phase I ) or the execution of the response (phase I I ) t o the f i r s t s t i m u l u s . T h i s probe r e a c t i o n time (PRT) was examined as a f u n c t i o n of movement complexity r e q u i r e d d u r i n g the f i r s t response. I t was found t h a t the mean c o n t r o l RT f o r each of the three t a s k s d i d not s t a t i s t i c a l l y d i f f e r although movement complexity d i d appear t o have some e f f e c t on RT as there seemed t o be an apparent d i f f e r e n c e between the mean c o n t r o l RT's of the two more complex tas k s and the mean RT of the simple s t t a s k . When the probe was presented during the RT phase of the three t a s k s i t was found t h a t the longer the i n t e r v a l between the stimulus t o the task and the stimulus t o the probe, the longer was the RT t o stimulus one. T h i s suggested t h a t the subject adopted a s t r a t e g y which had the e f f e c t of e l i m i n a t i n g the i n f l u e n c e of movement complexity. 59. C o n t r o l PRT ( i . e . r e a c t i o n t o the probe i n the absence of the primary task) was used as a standard f o r the minimum of a t t e n t i o n necessary t o i n i t i a t e a response, and i t was shown t h a t PRT during phase I in c r e a s e d f o r a l l c o n d i t i o n s of movement complexity, f o l l o w i n g the exact same t r e n d as the c o n t r o l RT means. Conclusive evidence i n support of the s i n g l e channel theory (a b a s i c assumption of t h i s experiment) was t h a t the longer the i n t e r v a l between stimulus one and stimulus two, the shorter was the r e a c t i o n time t o stimulus two (PRT). MT i n c r e a s e d w i t h t h e complexity of movement r e q u i r e d during the execution of the response. A l s o , p r e s e n t a t i o n of the probe during the MT i n t e r v a l had an e f f e c t on MT s i m i l a r t o the successive s t i m u l i on RT, the i n f l u e n c e of movement.complexity was removed. PRT i n c r e a s e d w i t h the complexity of movement r e q u i r e d during the execution of a response, f o l l o w i n g the p a t t e r n of the MT r e s u l t s . Movement terminated at a t a r g e t r e q u i r e d more a t t e n t i o n during the f i r s t 200 msec, of the movement than d i d a non-terminal movement. R o t a t i o n a l movement t o a t a r g e t r e q u i r e d g r e a t e r a t t e n t i o n than t h a t r e q u i r e d f o r movement t o a t a r g e t not i n v o l v i n g arm r o t a t i o n . Also!], the evidence suggested movement execution r e q u i r e s more a t t e n t i o n e a r l y i n the movement than l a t e r i n the movement. I n a d d i t i o n , movements terminated at a t a r g e t show an'increase i n a t t e n t i o n demands near the end of movement r e l a t i v e t o the a t t e n t i o n demands during the middle of the movement. These r e s u l t s provided a d d i t i o n a l support f o r the s i n g l e channel theory. 60. The conclusions of t h i s experiment were: 1. That f o r the purposes and c o n d i t i o n s of t h i s experiment the s i n g l e channel theory s u f f i c i e n t l y d escribes the operations of man's c e n t r a l p r o c e s sing system. 2. That the e f f e c t o r processes t h a t c o n t r o l the i n i t i a t i o n and execution of a response demand a t t e n t i o n w i t h i n the l i m i t e d c a p a c i t y c e n t r a l p r o c e s sing mechanism. 3. The a t t e n t i o n demands of a motor response tend t o vary w i t h the r e l a t i v e complexity of the response as w e l l as the p o s i t i o n of the responding limb when i t i s moving t o a t a r g e t . 4. That RT i s an accurate i n d i c a t i o n of the a t t e n t i o n demands r e q u i r e d d u ring the i n i t i a t i o n of a response. 5. That MT as s t u d i e d i n the present experiment i s an accurate i n d i c a t i o n of the o v e r a l l a t t e n t i o n demands r e q u i r e d d u r i n g the execution of a response. REFERENCES 6 2 . REFERENCES Annett, J . , Golby, C.W., and Kay, H. The measurement of elements i n an assembly task - the i n f o r m a t i o n output of the human motor system. 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Q u a r t e r l y J o u r n a l of Experimental Psychology, 19: 350-352, 1967(a). Smith, M.C. Theories of the p s y c h o l o g i c a l r e f r a c t o r y p e r i o d . P s y c h o l o g i c a l  B u l l e t i n , 67(3): 202-213, 1967(b). Welford, A.T. Evidence of a s i n g l e channel d e c i s i o n mechanism l i m i t i n g per-formance i n a s e r i a l r e a c t i o n t a s k . Q u a r t e r l y J o u r n a l of Experimental  Psychology, 11: 193-210, 1959. Welford, A.T. Performance, b i o l o g i c a l mechanisms and age: A t h e o r e t i c a l sketch. Behaviour, Aging and the Nervous System, e d i t e d by Welford, A.T. and B i r r e n , J.E. S p r i n g f i e l d , I l l i n o i s : C C . Thomas, 1965. Welford, A.T. Single-channel o p e r a t i o n i n the b r a i n . Acta P s y c h o l o g i c a , 27: 5-22, 1967. APPENDIX A PILOT STUDY 6 6 . TABLE OF RT MEANS FOR EACH CONDITION Cl C2 C3 51 197 203 226 52 176 194 209 53 177 191 202 54 162 197 209 X 178 196 211 TABLE OF MT MEANS FOR EACH CONDITION C2 C3 SI. S l 166 220 52 143 228 53 177 214 5 4 162 2 3 7 x 162 225 APPENDIX B INDIVIDUAL MEAN SCORES 6 8 . TABLE OF MEANS FOR CONTROL RT BY CONDITION Cl C 2 C3 X SI 2 7 5 3 4 7 2 6 2 2 9 5 S 2 2 L 4 2 1 7 2 3 2 2 2 1 S 3 2 1 4 2 3 5 2 5 6 2 3 5 S 4 2 0 6 2 1 6 2 1 2 2 1 1 S 5 2 2 0 2 5 6 2 5 8 2 4 5 S6 2 3 6 . 2 1 2 2 1 3 2 2 1 X 228 2 4 7 238 238 TABLE OF MEANS FOR CONTROL MT BY CONDITION C 2 C3 X SI 1 8 6 2 1 4 2 0 0 S 2 1 8 7 2 2 5 2 0 6 S 3 1 4 8 2 2 0 1 8 4 S4 2 0 0 2 3 4 2 1 7 S 5 1 9 6 2 0 2 199 S 6 1 7 9 211 1 9 5 X 183 218 2 0 0 TABLE OF MEANS FOR CONTROL PRT BY CONDITION Cl C2 C 3 X SI 1 9 3 2 1 4 1 7 4 1 9 4 S 2 189 1 7 3 1 6 4 1 7 5 S 3 1 6 8 2 1 5 1 9 3 1 9 2 S 4 181 1 7 2 1 7 6 1 7 6 S 5 1 9 2 1 9 4 1 7 7 188 S 6 183 1 7 2 1 6 2 1 7 2 X 1 5 4 1 9 0 1 7 4 183 69. TABLE OF MEANS FOR PHASE I RT BY CONDITION Cl C2 C3 X 51 284 296 261 280 52 253 217 226 232 53 226 243 270 247 54 234 220 240 231 55 245 255 234 245 56 254 225 218 232 x 250 243 241 245 TABLE OF MEANS FOR PHASE I FT BY I S I I S I 90 I S I n o I S I 130 I S I 150 X S l . 264 274 287 296 280 S2 220 230 239 240 232 S3 239 241 249 256 247 S4 224 227 238 236 231 S5 239 244 248 249 245 S6 219 230 236 245 232 X 234 241 250 254 245 TABLE OF MEANS FOR PHASE I RT FOR CONDITION BY I S I I S I 90 I S I 110 I S I 130 I S I 150 X C l 235 245 255 263 250 C2 237 239 247 248 " 243 C3 231 238 247 250 241 X 234 241 250 254 245 7 0 . TABLE OF MEANS FOR PHASE I MT BY CONDITION C 2 C 3 X SI 1 6 9 2 0 0 1 8 4 S 2 1 9 3 2 0 1 1 9 7 S 3 1 4 7 2 0 9 1 7 8 S 4 2 0 9 2 3 3 2 2 1 S 5 1 8 3 2 0 3 1 9 3 S6 178 2 0 1 1 8 9 X 180 2 0 8 1 9 4 TABLE OF MEANS FOR PHASE I MT BY ISI ISI 90 ISI 1 1 0 ISI 1 3 0 ISI 1 5 0 X SI 1 8 3 1 8 5 1 8 5 1 8 4 1 8 4 S 2 2 0 0 1 9 6 1 9 5 197 197 S 3 179 180 176 177 178 S 4 2 2 3 2 2 0 2 2 0 2 2 0 2 2 1 S 5 1 9 4 1 8 9 1 9 3 197 1 9 3 S 6 1 9 0 1 9 0 187 1 9 1 1 8 9 X 1 9 5 1 9 3 1 9 3 1 9 4 1 9 4 TABLE OF MEANS FOR PHASE I MT FOR CONDITION BY ISI ISI 90 ISI 1 1 0 ISI 1 3 0 ISI 1 5 0 X C2 181 179 179 180 180 C3 208 208 2 0 6 208 208 X 1 9 5 1 9 3 1 9 3 1 9 4 1 9 4 71. TABLE OF MEANS FOR.PHASE I PRT BY CONDITION C l C2 C3 X 51 • 188 269 182 213 52 241 344 370 318 53 183 196 225 201 5 4 180 254 207 213 •S5 253 344 395 331 S6 238 232 193 2 2 1 x 214 273 262 250 TABLE OF MEANS FOR PHASE I BY I S I I S I 90 I S I 110 I S I 130 I S I 150 X 51 222 218 210 203 213 52 332 321 316 305 319 53 208 207 200 191 201 54 226 214 212 201 213 55 3 5 1 331 326 315 331 56 229 225 213 217 221 x 261 253 246 239 250 TABLE OF MEANS FOR PHASE I PRT FOR CONDITION BY I S I I S I 90 I S I 110 I S I 130 I S I 150 X G l 220 220 208 207 214 C2 290 271 273 259 273 C3 274 267 258 250 262 x 261 253 246 239 250 72. TABLE OF MEANS FOR PHASE I I RT BY CONDITION ISI 90 ISI 110 ISI 130 ISI 150 X C l 220 220 208 207 214 C2 290 271 273 259 273 C3 274 267 258 250 262 x 261 253 246 239 250 TABLE OF MEANS FOR PHASE I I RT FOR ISI ISI 20 ISI 80 ISI 140 ISI 200 X 51 341 342 342 344 342 52 248 246 246 252 248 53 2 56 262 263 268 262 54 259 259 259 263 260 55 281 281 280 285 282 56 259 270 274 272 269 X 274 277 278 281 277 TABLE OF MEANS FOR PHASE I I RT FOR CONDITION BY ISI ISI 20 ISI 80 ISI 140 ISI 200 X C l 283 291 282 294 288 C2 270 275 277 277 275 C3 268 264 274 270 269 X 274 277 278 281 277 73. TABLE OF MEANS FOR PHASE I I MT BY CONDITION C2 C3 X S l 200 222 211 S2 211 2 1 3 212 S3 133 2 0 7 170 S4 2 3 6 2 3 5 2 3 6 S5 195 212 203 S 6 194 222 208 X 195 2 1 9 207 TABLE OF MEANS FOR PHASE I I MT BY ISI ISI 2 0 ISI 80 ISI 1 4 0 ISI 2 0 0 X S l 2 0 7 2 1 3 212 2 1 3 211 S2 2 0 9 213 2 1 3 2 1 5 212 S 3 1 6 9 1 7 2 1 6 8 1 7 2 170 S4 2 3 1 2 3 8 2 3 7 2 3 7 2 3 6 S5 201 205 204 204 203 S 6 202 211 211 208 208 X 203 208 208 208 207 TABLE OF MEANS FOR PHASE ISI 20 ISI 80 C2 191 195 C3 215 222 X 203 208 I I MT FOR CONDITION BY ISI ISI 1 4 0 ISI 200 X 196 196 195 219 220 219 208 208 2 0 7 74. TABLE OF MEANS FOR PHASE II PRT BY CONDITION Cl C2 C3 X SI ) 186 220 228 211 S2 211 243 251 235 S3 208 201 260 223 S 4 203 254 257 238 S5 242 325 314 294 S6 212 216 231 220 X 210 243 257 237 TABLE OF MEANS FOR PHASE II PRT BY ISI ISI 20 ISI 80 ISI 140 ISI 200 X SI 236 205 199 205 211 S2 263 243 212 223 235 S3 235 213 213 231 223 S 4 258 244 225 226 238 S5 310 291 276 296 294 S6 234 220 210 214 220 X 250 236 223 233 237 TABLE OF MEANS FOR PHASE II PRT FOR CONDITION BY ISI ISI 20 ISI 80 ISI 140 ISI 200 X Cl 226 210 203 203 210 C2 265 237 227 242 243 C3 277 260 238 253 257 X 256 236 223 233 237 

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