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The joint effects of task complexity and response probability on response latency : a test of the existence… Leech, Maureen I. 1977

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THE JOINT EFFECTS OF TASK COMPLEXITY AND RESPONSE PROBABILITY ON RESPONSE LATENCY: A TEST OF THE EXISTENCE OF A DEFENSIVE STRATEGY IN A TWO-CHOICE REACTION TIME TASK by MAUREEN I. LEECH B.P.E., University of B r i t i s h Columbia, 1971 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF PHYSICAL EDUCATION i n THE FACULTY OF GRADUATE STUDIES School of Physical Education and Recreation We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA December, 1977 ( 6 ) Maureen I. Leech, 1977 In p r e s e n t i n g t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h Co lumb ia , I a g ree that 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 tudy . 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 purposes 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 . It i s u n d e r s t o o d tha 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 not be a l l o w e d w i thout my w r i t t e n p e r m i s s i o n . Depa rtment The U n i v e r s i t y o f B r i t i s h Co lumbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date / i ABSTRACT The main purpose of this study was to determine i f subjects would employ a defensive type strategy in a two-choice reaction time task using tasks of unequal response complexity. The methodology used to investigate this problem involved examining the joint effects of two levels of task complexity and eight levels of response probability on response latency in one simple and seven choice experimental conditions. The hypothesized effects of response probability on response latency for tasks of unequal complexity are summarized as follows: (1) below a probability level of .50, response latency was expected to decrease as response probability decreased, and (2) above a .50 probability level no significant increase or decrease in response latency relative to the equal probability level was expected. The experimental task was a discrete, two-choice reaction time task, in which subjects were required to depress several response keys in a predetermined order following the onset of one of two possible stimulus lights. Two tasks of varying complexity were used: (1) a simple task involving two response keys only, and" (2) a complex task requiring the depression of five response keys in a specific order. Probability levels of 1.0, .90, .75, .60, .50, .40, .25, .10 provided eight experimental conditions under which the two tasks were performed. Sixteen male students from the University of British Columbia served as subjects. The empir ica l r e s u l t s d id not provide support for the pred ic ted hypotheses. It was found that for tasks of unequal complexity, subjects d i d not adopt a defensive s trategy by preparing for the more d i f f i c u l t or less probable response. Results for both tasks i l l u s t r a t e d a c l a s s i c a l p r o b a b i l i t y e f f e c t , i . e . , an increase i n p r o b a b i l i t y r e s u l t s i n a decrease i n response la tency , contrary to the pred ic ted r e s u l t s for tasks of unequal complexity. A l s o , the extreme p r o b a b i l i t y l eve l s of .90 and .10 had a marked e f fect on the response latency for both tasks with the simple task showing greater v a r i a b i l i t y than the complex task due to these p r o b a b i l i t y l e v e l s . Data from t h i s experiment tended to support the premise that response p r o b a b i l i t y i s a decreasing funct ion of task complexity, i . e . , the more complex the task the less e f fec t response p r o b a b i l i t y has on the r e s u l t i n g response la tency. i i i ACKNOWLEDGEMENTS To the members of my committee, Dr. K. D. Coutts, Dr. R. W. Schutz, Dr. G. D. Sinclair and Dr. J. C. Yuille, I would like to express my appreciation for their assistance throughout the preparation of this thesis. To my chairman, Dr. Schutz, I wish to express a special appreciation for his continued encouragement and guidance throughout my academic career. i v TABLE OF CONTENTS s Page LIST OF TABLES v i i LIST OF FIGURES , v i i i Chapter 1. INTRODUCTION 1 STATEMENT OF THE PROBLEM 5 DEFINITION OF TERMS 5 DELIMITATIONS 7 ASSUMPTIONS AND LIMITATIONS 7 HYPOTHESES 8 2. REVIEW OF SELECTED LITERATURE . 12 MODELS OF CHOICE REACTION TIME 13 Falmagne's Model 14 Falmagne and Theios' Model 16 Schutz's Model 17 Lupker and Theios' Model 21 TASK COMPLEXITY 24 STIMULUS-RESPONSE PROBABILITY 27 TASK COMPLEXITY BY RESPONSE PROBABILITY 31 Task Complexity 31 Response P r o b a b i l i t y 32 Task Complexity by Response P r o b a b i l i t y Interaction . . 33 N. V TABLE OF CONTENTS Chapter Page 3. METHODS AND PROCEDURES 35 Subjects 35 Apparatus 35 Procedures 38 Experimental Conditions 39 Experimental Design 44 Analysis of Data 44 4. RESULTS AND DISCUSSION 48 Data Reduction . 48 Task Complexity Effects , 52 Experimental Condition Effects 52 Order Effects . . . ) 53 RESULTS AND DISCUSSION OF PREPLANNED COMPARISONS FOR HYPOTHESES 1 TO 4 . . . 55 Hypothesis 1 58 Hypothesis 2 61 Hypothesis 3 64 Hypothesis 4 67 Summary of Hypotheses 70 5. SUMMARY AND CONCLUSIONS - 73 Summary 73 Conclusions 73 SUGGESTIONS FOR FURTHER RESEARCH 74 v i TABLE OF CONTENTS Page BIBLIOGRAPHY 75 APPENDICES 80 A. Procedures 81 B. Results 87 v i i LIST OF TABLES Table Page 1. Mean RLs for TCI and TC2 in the SRT and CRT Conditions in Experiments by Ryan and Schutz 32 2. Response Probability and Number of Trials for each Experimental Condition for TCI and TC2 40 3. Specific Weighting Coefficients of the Preplanned Comparisons For Hypotheses 1 to 4 Inclusive 47 4. Mean Response Latencies (msec.) and Standard Deviations for TCI and TC2 Under Eight Experimental Conditions . . . 49 5. Mean Response Latencies (msec.) for TCI and TC2 Under Eight Probability Conditions 49 6. Analysis of Variance for the Effects of Order of Presentation, Experimental Conditions and Task Complexity on Response Latency 51 7. Hypotheses 1 to 4: Hypothesized Results and Calculated F Ratios of the Preplanned Contrasts 56 8. Response Probability Means and Their Differences Utilized in the Preplanned Contrasts of Hypotheses 1 to 4 57 9. Comparison Values for the Test of Hypothesis 1, Including and Excluding Subject 11's Results in the SRT Condition . . 59 10. Mean RLs and Differences for EC1 and EC5 Utilized in the Sta t i s t i c a l Test of Hypothesis 2 62 v i i i LIST OF FIGURES Figure Page 1. The hypothesized results for TCI and TC2 over Response Probability levels . 11 2. Response latency distributions based on the two-state CRT model proposed by Falmagne (1965) 15 3. Schutz's proposed model of Information Processing and Response Retrieval Mechanisms in a CRT task 19 4. Pictorial description of the Subject's console apparatus . 36 5. The hypothesized results for TCI and TC2 over Experimental Conditions . . . . 43 6a. The empirical results for TCI and TC2 over Experimental Conditions 50 6b. The empirical results for TCI and TC2 over Response Probability levels 50a Chapter 1 INTRODUCTION In the learning and performance of any skilled act, neural coding of the component parts and the spatial and temporal sequencing of each motor s k i l l is stored and retrieved from memory. Response latency (RL) has frequently been employed as an indicator of the information processing involved during memory retrieval in simple reaction time (SRT) and choice reaction time (CRT) studies (Burrows and Okada, 1976; Lupker and Theios, 1975; Sternberg, 1969; Theios, Smith, Haviland, Traupmann, and Moy, 1975). Many factors have been shown to affect the RL of SRT and CRT tasks, and by controlling these factors in experimental conditions, researchers have attempted to further understand the functional processes involved in retrieving information from memory. The problem to which this study is directed involves two such factors, namely, task complexity (TC) and response probability (RP). Research on the separate effects of TC and RP on RL have provided empirical evidence which lends general support to the following: 1. An increase in TC results in an increase in RL for SRT tasks and for CRT tasks of equal probability (Glencross, 1973; Henry and Rogers, 1960; Sidowski, Morgan, and Eckstrand, 1958). 2. An increase in stimulus-response probability results in a decrease in RL (Bertelson and Tisseyre, 1966; Blackman, 1972; Hinrichs and Krainz, 1970; Hyman, 1953). 1 2 The joint effects of TC and RP on RL have, to date, been neglected by most researchers in this area. Two studies, Ryan (1972) and Schutz (1972) have attempted to interpret the interaction of TC and RP on RL as related to motor memory retrieval. From these results, i t appears that in a CRT situation involving tasks of unequal complexity, an increase in RP does not result in a decrease in CRT. In the condition of equal RP, i t was found that the more complex task had a faster RL than the simple task. The empirical results of these two studies are highly contradictory to prevelant research examining the separate effects of TC and RP on RL. In order to provide a tenable explanation of the results obtained from experiments examining the joint effects of these two variables, i t is useful to employ a model of memory storage and retrieval. A vast majority of literature dealing with memory has proposed various models of memory storage to explain verbal learning, however, few models have been postu-lated which deal specifically with motor memory retrieval. One such model proposed by Schutz (1972), divides memory storage into three independent areas: 1. Selective Attention (SA) - storage capacity of one response programme (engram) only; very high accessibility. 2. Primary Memory (PM) - limited storage capacity; high accessibility. 3. Secondary Memory (SM) - unlimited storage capacity; less accessibility than PM. / During stimulus presentation i t is assumed that the template corresponding to the required response can be in one of these three storage areas. An independent search of each of the storage areas is initiated once the 3 name of the required response has been determined. The search process involves examination of SA f i r s t ; i f the correct response is not found, PM and f i n a l l y SM are searched. If the programme is in SA prior to the onset of the stimulus, i t would follow that the time required to search the various memory storage areas would be greatly reduced, resulting in a decrease in RL. In a recent experiment examining two, three, and four state models of CRT, Lupker and Theios (1975) provided strong evidence in support of a two-state CRT model. This present study, however, is not directly concerned with providing evidence to support two, three, or four state models of CRT. What is of concern, is the ab i l i t y of a subject to voluntarily prepare for the occurrence of a particular stimulus by 'readying' himself to ini t i a t e the appropriate response programme. Falmagne and Theios (1969) and Schutz (1972) identify this preparatory state as the ab i l i t y to place the correct response engram into selective attention, whereas Theios (1973) explains this readiness state with a push down stack type model in which a short term memory buffer is searched seria l l y . The response with the highest probability of occurrence is placed at the top of the memory stack while the less probable response w i l l be placed in the stack according to their individual probabilities. Although researchers disagree on the theoretical composition of memory storage areas, there tends to be supportive evidence for the following: 1. A subject can voluntarily prepare for a particular response. 2. If correct, i.e., the subject correctly prepared for the response programme associated with the presented stimulus, the resulting RL wil l be faster than i f the subject was unprepared. 4 As t h i s p resent study dea ls only w i t h a t w o - c h o i c e response l a t e n c y t a s k , the sub jec t w i l l e i t h e r be prepared or unprepared f o r the presented s t i m u l u s . For the purpose o f t h i s exper iment , the prepared s t a t e , analogous to s e l e c t i v e a t t e n t i o n , but not n e c e s s a r i l y o c c u r r i n g as an independent s torage area w i l l be r e f e r r e d to as response read iness (RR). The type of response s t r a t e g y employed by s u b j e c t s i n CRT e x p e r i -ments i n v o l v i n g e i t h e r TC or RP determines which response programme i s v o l u n t a r i l y prepared f o r i n RR p r i o r to s t i m u l u s p r e s e n t a t i o n . In a CRT s i t u a t i o n i n v o l v i n g RP o n l y , the s u b j e c t w i l l prepare f o r the response w i t h the h i g h e s t s u b j e c t i v e p r o b a b i l i t y of occurrence f o r the next t r i a l . In CRT experiments examining TC, which i n v o l v e a s imple and a complex t a s k , i t i s thought that the s u b j e c t w i l l prepare f o r the more d i f f i c u l t task w i th g r e a t e r f requency than the s imple t a s k . I t i s s p e c u l a t e d that the sub jec t compensates f o r the longer r e l e a s e t ime a s s o c i a t e d w i t h the more complex task by a t tempt ing to reduce search t ime ( i . e . , prepare f o r the complex task i n RR). The response s t r a t e g y employed by s u b j e c t s i n CRT experiments i n v o l v i n g the j o i n t e f f e c t s of TC and RP has not yet been f u l l y e x p l a i n e d or suppor ted . On the b a s i s of the proposed model , the f o l l o w i n g genera l hypotheses are presented to p rov ide a p o s s i b l e e x p l a n a t i o n f o r the i n t e r -a c t i o n of TC and RP on RL. \ 5 STATEMENT OF THE PROBLEM The purpose of this study is to investigate the joint effects of task complexity and response probability on response latency in simple and choice reaction time tasks in an attempt to identify the type of response strategy employed by the motor memory retrieval process. DEFINITION OF TERMS1 Primary Memory (PM). A memory storage area for items recently perceived. It has a limited capacity as to the number of items i t can contain and a limited time period of retention of these items. Primary memory is analogous to "short-term memory (STM)", or "immediate memory (IM)". Response Latency (RL). The amount of time elapsing between the presentation of a stimulus and the f i r s t measurable overt response to that stimulus. Response latency is defined to be an indicator of the amount of information processing conducted during a stimulus-response (S-R) task. Response latency is synonymous to the term "reaction time". Simple Reaction Time (SRT). SRT refers to the time elapsing between the occurrence of a single fixed stimulus and the i n i t i a t i o n of it s assigned response (Fitts and Posner, 1967). Choice Reaction Time (CRT). The RL in a task involving a choice of one response from a set of two or more possible responses. The following definitions, unless otherwise specified, are as defined by Schutz (1972). 6 Response Probability (RP) . The preset objective probability of the occurrence of a specific stimulus-response pair. Response Programme. An unobservable compilation of neural messages governing a motor task. It is assumed to be analogous to a computer programme and composed of a number of independent subprogrammes or response units. Response Readiness.(RR). A state of readiness in which the subject is capable of preparing for one response engram at a time. Decay occurs very rapidly in the absence of reinforcement. For the purposes of this study, response readiness is analogous to the term "selective attention" as functionally defined by Schutz (1972), but not necessarily occurring as an independent storage area. Secondary Memory (SM). A memory store containing items which have been perceived and reinforced, and then absent from consciousness for a period of time. This storage system has an unlimited capacity as to the number of items i t can contain. Secondary memory is analogous to "long-term memory (LTM)". Task Complexity (TC). A subjective measure of the number of sub-programmes or response units retrieved, and the organization of these units into an appropriate temporal sequence (Glencross, 1973). It is assumed that the greater the number of subprogrammes involved in a particular response programme, the more complex the response task. Task complexity is synonymous to the term "response complexity". The two levels of task complexity used in this study are: Task Complexity One (TCI). A simple task involving the depression of two response keys only. 7 Task Complexity Two (TC2). A complex task (relative to TCI) involving the depression of five response keys in a predetermined order. DELIMITATIONS 1. The study is delimited to a two-choice reaction time task. 2. The study is delimited to two levels of task complexity (TCI, TC2). 3. The study i s delimited to eight response probabilities (1.0, .90, .75, .60, .50, .40, .25, .10). 4. The study is delimited to a discrete reaction time task, as a serial self-paced task may e l i c i t a different response strategy. ASSUMPTIONS AND LIMITATIONS The following assumptions are made: 1. A response programme can voluntarily be prepared for prior to stimulus presentation, this state being referred to as response readiness. 2. Only one response programme or engram can be in the readiness state prior to stimulus presentation. 3. In a two-choice reaction time task the memory search and retrieval process examines the engram prepared for in response readiness f i r s t . If the associated response is not found, the search process w i l l examine PM for the correct response. A correct response programme in the response readiness state w i l l have a faster RL relative to a response programme not prepared for prior to stimulus presentation. 8 The investigation is limited by: 1. The accuracy of the timing equipment. 2. The functioning of the CRT apparatus. 3. The sample size of sixteen subjects. HYPOTHESES The hypotheses are: 1. Simple reaction time i s longer for TC2 than TCI when TC2 i s of greater complexity than TCI. Since task complexity is a subjective measure of the number of subprogrammes comprising a response programme, i t follows that a more d i f f i c u l t task wi l l contain a greater number of subprogrammes relative to a simple task. In the response search and release stage of the motor memory retrieval process, as outlined by Schutz (1972), each subprogramme is thought to require some f i n i t e amount of time to be read out or released to the response action stage. These subprogrammes are read out serially , and therefore, the greater the number of subprogrammes the longer the release time, resulting in an increase in RL for the more complex task. 2. In a choice reaction time situation with equal response probabilities, the difference between TC2 and TCI is less than in the simple reaction time condition. It is assumed that in a CRT situation the subject w i l l adopt a defensive strategy to minimize errors in his performance. In a condition of equal response probability, i t is proposed that the complex task w i l l 9 be in a state of RR more often than the simple task, independent of response probability, to compensate for the increased task complexity factor. The shorter search time for TC2 w i l l offset the longer release time for the more complex task as discussed in Hypothesis 1, resulting in the difference between TC2 and TCI being less than in the SRT condition. For the specific tasks TCI and TC2, as outlined in this present experiment, i t is further proposed that RL for TC2 w i l l be less than for TCI in the equal probability condition. In the SRT condition the mean difference between TC2 and TCI is expected to approximate 20 milliseconds. As discussed above, TC2 w i l l be prepared for more often than TCI, and as a result the decrease in response search time wi l l be in excess of the 20 millisecond difference, resulting in a faster RL for the more complex task. 3. Response latency is directly related to response probability for probabilities less than p.50. It is proposed than in a CRT situation with tasks of unequal complexity, subjects w i l l adopt a defensive strategy for tasks with a probability value less than p.50 regardless of the task complexity level. The effects of TC and RP are not additive, but substitutive (Schutz, 1972), and in the case of low probability for TCI and high probability for TC2 the factor having the greatest effect on RR is a low RP (below p.50), not TC. In the above example, the subject w i l l prepare for the response programme which has the least possible chance of occurring (TCI). In this type of response strategy the subject i s , in effect, exchanging a fast RL for the more probable task in favour of response readiness and consequently 10 a fast RL for the less probable task. Below a RP level of p.50, RL is directly related to RP independent of the effects of TC (see Figure 1). 4. Response latency is independent of response probability for probabilities greater than p.50. It is proposed that for both TCI and TC2 any increase in RP above a p.50'level w i l l not yield a faster RL relative to the p.50 level. As the probability for TC2 increases above the equal probability level, conversely, the probability for TCI w i l l decrease. As discussed in Hypothesis 3, a decrease in RP below a p.50 level results in preparing for that task more often because of the defensive strategy employed by the subject. If TCI, because of a low probability, is in a state of RR with greater frequency than TC2, there can be no decrease in RL for TC2 even though i t is the more probable task. It appears that for tasks of unequal complexity, the percentage of time a particular response programme wil l be prepared for may reach a maximum at the p.50 level. A further increase in RP above p.50 w i l l not result in preparing for that task with any more frequency than at the equal probability level (see Figure 1). 11 1.0 .90 .75 .60 .50 .40 .25 .10 Response P r o b a b i l i t y F igu re 1. The hypothes i zed r e s u l t s f o r TCI and TC2 over Response P r o b a b i l i t y l e v e l s . Chapter 2 REVIEW OF SELECTED LITERATURE Studies concerning memory storage and retrieval have provided a vast amount of theoretical data in an attempt to explain how information from the environment is processed. A major experimental tool used extensively in the study of memory storage and retrieval is the choice reaction time experiment. A choice reaction time experiment is character-ized by the following properties: a set of possible stimuli, a set of possible responses, and a mapping of the stimuli into the response that is specified by the instructions (Smith, 1968). During each t r i a l , the subject is presented with a stimulus (e.g., an illuminated light on a panel situated in front of the subject) and must make a response (e.g., pressing a key located at the subject's finger tips) as soon as possible after the stimulus appears. Each stimulus is associated with a definite response (S-R matching) which has been predetermined and learned through practise prior to testing. Choice reaction time involves a decision, that i s , although the subject knows approximately when the next stimulus w i l l occur, he does not know which stimulus-response pair w i l l be required. Once the stimulus has been presented, the subject must then decide which response to i n i t i a t e . The c r i t i c a l time period elapsing between stimulus onset to the in i t i a t i o n of the response is response latency. This dependent variable is an 12 1 13 indicant of the temporal demands placed upon the response retrieval mechanisms in a choice reaction time task. To further understand the functional processes involved in CRT, researchers have manipulated several experimental variables to determine how response latency is affected. For example, such variables as S-R compatibility, task complexity, i n t e r - t r i a l interval, number of S-R pairs, sequential dependencies in serial and discrete tasks, level of motiva-tion, instructional emphasis, length of foreperiod, and stimulus-response probability have been researched extensively in the last 25 years. A comprehensive review of a l l factors affecting response latency is far beyond the scope of this investigation. Consequently, only those studies dealing with the two c r i t i c a l experimental variables, task complexity and stimulus-response probability w i l l be reviewed. In addition, a survey of the major theoretical models of memory storage and retrieval pertinent to this investigation w i l l be discussed. MODELS OF CHOICE REACTION TIME Models of CRT can i n i t i a l l y be divided according to which process, stimulus identification or information retrieval, i s accepted as the primary determinant of RT (Keele, 1973). Within each of these two major classifications, there exists many differing theoretical explanations to account for the data obtained from CRT experiments. In a comprehensive overview of the CRT models preoccupied with stimulus categorization, Smith (1968) discussed several of these conflicting theories, e.g., template matching versus feature testing, serial exhaustive search pattern versus self-terminating search, and serial classification models versus 14 s t a t i s t i c a l decision models. This present study, however, is response retrieval oriented, and the stimulus categorization process has been deemphasized. Consequently, the theoretical models to be discussed are those relevant to the basic assumption of a response readiness state, a concept c r i t i c a l to this investigation. Falmagne's Model One of the f i r s t probabilistic models of CRT was proposed by Falmagne (1965). Falmagne based this model on the subject's 'preparedness' to a given stimulus. Specifically, for any given stimulus, the subject could either be prepared or unprepared for i t s presentation. For each of these two states of preparation, Falmagne assumed a theoretical d i s t r i -bution underlying the empirical RLs. If the subject was prepared for the stimulus, the RL would be faster in comparisons to the RL of an unprepared stimulus. Consequently, when comparing the two distributions, the prepared distribution had a smaller mean RL relative to the unprepared distribution. It was possible for the subject to be prepared for more than one stimulus at a time, or unprepared for any one stimulus in a particular t r i a l . The scanning process accounted for the difference in the two distribution means. Falmagne assumed that subjects would f i r s t scan those representa-tions of the stimulus for which he was prepared. If the correct response was not found, the unprepared stimulus representations were then scanned. The search process was terminated after the f i r s t scan i f the subject was prepared for the stimulus and continued to scan the unprepared stimulus representation i f a match was not found. According to Lupker and Theios (1975) Falmagne's two-state model was able to give good predictions of mean RLs, variances, and repetition effects using a 1:1 S-R mapping in a 15 s i x - c h o i c e RT task w i t h p r e s e n t a t i o n p r o b a b i l i t i e s of . 5 6 , . 2 4 , . 1 0 , . 0 6 , . 0 3 , . 0 1 . However, i n a l a t e r study as r e p o r t e d by Lupker and Theios (1975)', Falmagne demonstrated a p r o p e r t y of t w o - s t a t e models t h a t the data from h i s s i x - c h o i c e experiment f a i l e d to s a t i s f y . Accord ing to Lupker, and T h e i o s , i n any t w o - s t a t e model there e x i s t s a p o i n t , t ( o ) , where the p r o b a b i l i t y d e n s i t i e s o f the two t h e o r e t i c a l d i s t r i b u t i o n s over lap (see F igure 2 be low) . F igure 2. Response l a t e n c y d i s t r i b u t i o n s based on the t w o - s t a t e CRT model proposed by Falmagne (1965). At t ( o ) , the d e n s i t y f o r the RL d i s t r i b u t i o n s f o r a l l s t i m u l i have the same v a l u e . Lupker and Theios s t a t e : " I n t u i t i v e l y , t h i s means that i f the t w o - s t a t e model i s c o r r e c t , there should e x i s t a s m a l l i n t e r v a l of RT where, a l l e m p i r i c a l d i s t r i b u t i o n s , the h ( t ) s , have the same p r o p o r t i o n of c a s e s , independent o f the s t i m u l u s or o ther v a r i a b l e s such as p r e s e n -t a t i o n p r o b a b i l i t y . " Falmagne found t h a t the data from h i s s i x - c h o i c e RT experiment d i d not s a t i s f y t h i s f i x e d p o i n t p r o p e r t y . These r e s u l t s l ed Falmagne and Theios (1969) to i n t r o d u c e a f i v e - s t a g e model o f CRT to e x p l a i n the d a t a . 16 Falmagne and Theios' Model Based on the assumption of stimulus preparation, Falmagne and Theios (1969) proposed a five-stage additive model of CRT. For each stimulus, a template or internal representation (IR) was stored in one of three memory states; selective attention (SA), immediate memory (IM), or long-term memory (LTM). On any t r i a l , the SA state was searched f i r s t , and i f no template matching was found, IM and f i n a l l y LTM were examined. Differences in RL occurred because of the search process, which terminated when the stimulus representation was found. The stimulus which subjects projected as having the highest probability of occurrence for the next t r i a l , was placed into SA. If the presented stimulus corresponded to the IR in SA, then the response was i l l i c i t e d and the total response time involved three stages only. Stage 1 was perceptual, in that the IR of the presented stimulus was created. Next, the subject checked whether the IR created matched the template in SA. If there was a match, i.e., the IR was in SA, then Stage 5 involving the coordination and i n i t i a t i n g of the response occurred. For the above example, total response time (t) would encompass these three stages only, represented by: t = t l + t2 + t5 If the correct template was not in SA, the subject then compared the IR of the stimulus to those templates in IM. Consequently an additional stage, Stage 3 requiring a time t3, was added to the total response time. t = t l + t2 + t3 '+ t5 A search into LTM resulted only after no match was found in IM, thus the total response time increased with the addition of time for Stage 4 (t4). t = t l + t2 + t3 + t4 + t5 17 For each of the three memory states, Falmagne and Theios hypothesized a separated theoretical distribution of RLs. They proposed that the prob-abil i t y of a template being in any one of these states was dependent upon the immediately preceding stimulus presented. As discussed later in this review, studies by Geller and Pitz (1970), Geller and Whitman (1972), and Geller, Whitman, Wrenn, and Shipley (1971) substantiated the dependence of RL on preceding t r i a l s in their related work on prediction outcome and CRT. Falmagne and Theios found their five-stage model was able to provide adequate theoretical predictions which f i t data from a previous experiment. Schutz's Model A response oriented CRT model was proposed by Schutz (1972) in an attempt to explain the organization and retrieval of motor information from memory. As Schutz explains, his model is a culmination of many existing theories and relevant ideas, however, the work of Falmagne and Theios (1969) as previously outlined appears to have had a significant influence on his proposed theory. Schutz's model assumes the existence of a number of independent stages involved in information processing and response organization in a CRT task. Each stage is thought to act inde-pendently with the total CRT representing the summation of time for each separate stage. The conceptual framework for this model can most effectively be discussed in terms of the basic processes involved; memory storage, memory search and response retrieval. Memory storage areas. According to Schutz, up to three storage areas similar to those outlined by Falmagne and Theios (1969) can be 18 examined during the response search process. The f i r s t area, selective attention (SA) has the capacity of one response engram only, either an event very recently experienced, or a response which has a high probability of being the required response to the next stimulus. Schutz's original hypothesis implied that for every t r i a l a response programme i s placed into SA. However, as discussed in Revision One of his theory, he acknow-ledges that SA need not be occupied on every t r i a l , but may be left empty. The second storage area, termed primary memory (PM) is thought to have a limited storage capacity of between five to ten programmes, the exact number being a function of the length of the programmes (task complexity). The third, and fin a l memory storage area secondary memory (SM), is viewed as a relatively permanent system with an unlimited storage capacity containing highly practised response programmes. Although Schutz defines his concept of SM, this storage area was not experimentally tested. Memory search processes. The type of memory search process used to examine the contents of PM was assumed to be a serial exhaustive search (as proposed by Sternberg, 1966). The type of search process was not experimentally tested, and no theoretical rationale was given to explain why this assumption was made. The search process for SM was thought to encompass a selective exhaustive search pattern, possibly serial classi-fication or parallel scanning (see Burrows and Okada, 1974; Burrows and Okada, 1976 for experimental data supporting parallel scanning). Again the type of search process involved in SM was not empirically discussed or tested. 19 Response retrieval in a CRT task. The hypothesized series of stages involved in a CRT task are given in Figure 3 below: Stimulus. c + Stimulus Perception t l Stimulus Categorization t2 Response Selection t3 Response Search and Release Response Action t4 t5 Response A , CRT Figure 3. Schutz's proposed model of Information Processing and Response Retrieval Mechanisms in a CRT task. 20 As each stage r e q u i r e s some f i n i t e t i m e , the t o t a l response t ime r e q u i r e d to perform a CRT task as i l l u s t r a t e d i n F igu re 3 can be represented a s : CRT = t l + t2 + t3 + t4 + t5 The t ime taken to p e r c e i v e a s p e c i f i c s t imu lus i s cons idered to be constant f o r any g iven s u b j e c t . Once the s t imu lus i s p e r c e i v e d , the s t i m u l u s c l a s s i f i c a t i o n stage c l a s s i f i e s the coded n e u r a l impulses i n t o one of the p o s s i b l e s t i m u l i . The response s e l e c t i o n mechanism r e c e i v e s the name of the s t i m u l u s , then chooses the a p p r o p r i a t e response programme which should be r e t r i e v e d . The response search and r e l e a s e mechanism i s conducted i n an i d e n t i c a l manner to tha t proposed by Falmagne and Theios (1969). The v a r i a b i l i t y i n RL i s accounted f o r by the search p r o c e s s . The contents of SA are always examined f i r s t . I f the r e q u i r e d RP i s not found i n SA, an exhaust i ve search of PM i s conducted and, f a i l i n g t o l o c a t e the d e s i r e d RP h e r e , leads to a s e l e c t i v e search of SM. Accord ing to Schutz , a response B w i l l be i n SA w i t h p r o b a b i l i t y pB and i n PM w i t h a p r o b a b i l i t y 1-pB. Th is s i t u a t i o n i s t rue on ly when responses are r e i n f o r c e d , i . e . , c a l l e d upon f r e q u e n t l y enough to be r e t a i n e d i n PM. S p e c i f i c v a r i a b l e s are c i t e d as a f f e c t i n g the p r o b a b i l i t y of a response programme b e i n g p l a c e d i n t o SA; p r o b a b i l i t y o f the s t i m u l u s occur rence , s e q u e n t i a l e f f e c t s of s t i m u l u s p r e s e n t a t i o n , and t a s k c o m p l e x i t y . Two o f these v a r i a b l e s , p r e s e n t a t i o n p r o b a b i l i t y and task complex i t y are d i s c u s s e d l a t e r i n t h i s r e v i e w . Lupker and Theios' Model Lupker and Theios (1975) designed two experiments in order to test which of three f i n i t e state self-terminating memory scanning models of CRT was the most accurate predictor of RL. Each of the models tested assumed a state of preparation similar to response readiness which would effect RL in CRT experiments. Specifically, the three models examined were: (1) a two-state model proposed by Falmagne (1965) based on two theoretical distributions of CRT corresponding to a state of 'preparedness' and 'unpreparedness', (2) a three-state model proposed by Falmagne and Theios (1969) which assumed the memorial stimulus-response association could be found in one of three independent memory states, and (3) a four-state model based on the work of Theios (1973) and redefined by Lupker (1974). Detailed discussion of both the two and three-state models have been presented earlier in this review, therefore, only Theios and Lupker1s model w i l l be explained at length. The work of Falmagne and Theios (1969) led Theios (1973) to con-ceptualize CRT in terms of a push-down stack model which postulated a short-term memory buffer that is searched position by position in a serial self-terminating manner. Highly probable stimulus representations are placed at the top of the stack, while less likely events occupy positions further down. If on any given t r i a l , the required response is at the top of the buffer, the resulting RL wi l l be faster relative to a response association further down the stack. According to the model, mean CRT should be linear with the number of stimuli, i f a l l stimuli were given the same presentation probabilities. However, Theios found that RL was linear with the expected buffer position for approximately four memory 22 positions only (i.e., up to a four-choice situation). To account for these findings, Theios redefined his model and explained the buffer in terms of four positions only; the f i r s t three containing only one S-R association, while the fourth position (LTM) contained a l l remaining S-R associations. Lupker (1974) presented a mathematically tractable version of the push-down stack model proposed by Theios which could, for 'special cases', provide adequate predictions of CRT. Lupker and Theios (1975) explain Lupker's version of the four-state model as follows: ...that for the special case where one stimulus is presented with an arbitrary probability and the remaining n stimuli are presented with equal probabilities of (l-iT)/n, analytical solutions could be obtained for the asymptotic probability of an S-R association being in each of the four memory positions. In order to test each of the three f i n i t e state models, data from two experiments, each containing five experimental conditions, were collected and analysed in terms of mean RL, sequential RL, and distribu-tional fixed-point property. Results from the above analyses uniformly supported the two-state model as providing the best prediction of CRT (see Lupker and Theios for a detailed discussion of the experimental results). Not only was the two-state model the best predictor of CRT, i t also satisfied the fixed-point property previously discussed in Falmagne's (1965) theory of CRT. Data from Falmagne's six-choice RT task failed to comply with the fixed-point property and in a later study, Falmagne (1968) rejected the two-state model as a theoretical explanation of CRT. However, Lupker and Theios found that the two-state model was the only model which satisfied the fixed-point property from the reaction time distributions obtained from Experiments 1 and 2. In reviewing Falmagne's results, Lupker and Theios suggested that the fixed-point 23 p roper t y was not s a t i s f i e d because of the s m a l l p r e s e n t a t i o n p r o b a b i l i t i e s ( . 0 6 , . 0 3 , and .01) of three of the s i x c r i t i c a l s t i m u l i . The CRT d i s t -r i b u t i o n s of the three s t i m u l i w i t h the l a r g e s t p r e s e n t a t i o n p r o b a b i l i t i e s ( . 5 6 , . 2 4 , .10) d i d i n f a c t show a reasonable approx imat ion to the f i x e d -p o i n t p r o p e r t y . Lupker and Theios suggest t h a t i n Falmagne's s tudy , the s t i m u l i w i t h the th ree s m a l l e s t p r o b a b i l i t i e s occurred so i n f r e q u e n t l y that the s u b j e c t s e f f e c t i v e l y " f o r g o t " about them. When one of these i n f r e q u e n t s t i m u l i was p r e s e n t e d , the two memory s t a t e s were searched and when no c o r r e c t response was found a search of a t h i r d memory c a p a c i t y or LTM was a c t i v a t e d . The s m a l l e s t p r e s e n t a t i o n p r o b a b i l i t y i n Lupker and The ios 1 experiments was p . 1 0 ; i t would appear t h a t the problem o f f o r g e t t i n g due to a very low p r e s e n t a t i o n p r o b a b i l i t y d i d not confound t h e i r f i x e d - p o i n t p r o p e r t y r e s u l t s . A l though i t i s not the purpose o f t h i s present i n v e s t i g a t i o n to p r o v i d e data i n support of any one h e u r i s t i c model of CRT, Lupker and T h e i o s ' r e s u l t s do l end s t r o n g support f o r the acceptance o f the t w o - s t a t e model as a v i a b l e e x p l a n a t i o n of CRT. i 24 TASK COMPLEXITY The effects of varying the complexity of a particular movement on RL is an area of experimental concern dating back to the works of Merkel done in 1885. It is generally accepted that TC is directly related to RL and therefore, an increase in the level of movement complexity w i l l result in an increase in RL. This relationship has been substantiated in both SRT and CRT experiments (Glencross, 1973; Henry and Rogers, 1960; Hyman, 1953; Sidowski et a l . , 1958). Sidowski et a l . (1958) examining the effects of TC on the RL of SRT and CRT tasks, supported the positive monotonic relationship between these two variables in the SRT condition only. In this condition, the simple task (finger withdrawal from a response key) was significantly faster than the two complex tasks (one switch response.and three switch response). However, in the CRT condition (equal response probability) the simple task had a significantly slower RL than the three switch response. Sidowski explained this result as the subject directing his emphasis upon preparing for the most d i f f i c u l t response. When the simple task was required, the subject had to inhibit his preparedness for the complex task. This finding is in agreement with the results reported by Ryan (1972) and Schutz (1972) (discussed later in this review), and gives support for Hypothesis 2 as stated in Chapter 1. In addition, Sidowski showed that CRT had a slower RL than SRT, stating that CRT was more affected by TC than SRT. However, the graph reported in his findings clearly illustrated that the SRT condition was more affected by TC. 25 Henry and Rogers (1960) examined t h r e e movements of i n c r e a s i n g complex i t y and supported t h e i r main hypothes i s tha t i n a SRT c o n d i t i o n an i n c r e a s e i n movement complex i t y r e s u l t s i n an i n c r e a s e i n RL. Accord ing to Henry and Rogers , performance of s k i l l e d ac ts i n v o l v e s neuro-motor memory and a l l w e l l learned motor ac ts are s t o r e d i n the b r a i n . Us ing a computer ana logy , each motor s k i l l has a s t o r e d motor programme which , when a c t i v a t e d , d i r e c t s the a p p r o p r i a t e musculature to perform the s k i l l . As the complex i t y of the task i n c r e a s e s , more s t o r e d i n f o r m a t i o n w i l l be r e q u i r e d , and the t ime needed f o r c o o r d i n a t i n g and d i r e c t i n g the muscles i n v o l v e d , w i l l i n c r e a s e r e s u l t i n g i n a longer RL. In a subsequent s tudy , Henry (1961) found RL was not a f f e c t e d by changes i n movement complex i t y due to r e v e r s a l s of movement; s p e c i f i c a l l y , o n e - r e v e r s a l and t w o - r e v e r s a l movements. In accordance w i t h the theory proposed by Henry and Rogers (1960) , Henry p o s t u l a t e d that r e v e r s i n g move-ments would r e q u i r e a more complex temporal o r g a n i z a t i o n to stop and reve rse the movement at an a p p r o p r i a t e s p a t i a l l o c a t i o n . The r e s u l t s o b t a i n e d , however, were not s i g n i f i c a n t . S i m i l a r l y , B l a i r (1970) r e p o r t e d t h a t CRT was independent o f move-ment - complex i t y . Us ing th ree exper imenta l c o n d i t i o n s of i n c r e a s i n g complex i ty ( t u r n i n g o f f one, two, and three togg le s w i t c h e s ) , he found t h a t a l though RL d i d i n c r e a s e as complex i ty i n c r e a s e d (375 msec. - 393 msec.) the i n c r e a s e was not s i g n i f i c a n t . Accord ing to B l a i r , i t i s p o s s i b l e tha t h i s study lacked s e n s i t i v i t y , and that a Type I I e r r o r was made. As o u t l i n e d above, s e v e r a l s t u d i e s have r e p o r t e d r e s u l t s which c o n t r a d i c t the d i r e c t r e l a t i o n s h i p between TC and RL. The q u e s t i o n i s then r a i s e d ; do these r e s u l t s i n d i c a t e t h a t the TC-RL r e l a t i o n s h i p i s not v a l i d , 26 or tha t the nature of the exper imenta l v a r i a b l e s and exper imenta l p r o -cedures u s e d , account f o r the confounding r e s u l t s ? In a comprehensive s e r i e s of exper iments , G lencross (1973) i n v e s t i g a t e d t h i s problem a t t e m p t i n to determine what aspects o f complex i t y i n f l u e n c e d RL. From h i s r e s u l t s he conc luded : 1. The amount o f f o r c e r e q u i r e d had no s i g n i f i c a n t e f f e c t on RL. The three t a s k s i n v o l v e d i n a SRT c o n d i t i o n were (a) elbow f l e x i o n w i th two pound weight l o a d , (b) elbow f l e x i o n w i t h 15 pound weight l o a d , and i (c) elbow ex t ens io n downward w i t h no r e s i s t a n c e . 2. RL i n c r e a s e d as the length of the movement i n c r e a s e d . Two movements, s i x inches and 18 i n c h e s , were the c r i t i c a l d i s t a n c e s used . 3 . RL i n c r e a s e d when movements were under s t r i c t d i r e c t i o n a l c o n t r o l , e . g . , s t r i k i n g a r e s t r i c t e d t a r g e t . 4. One r e v e r s a l of d i r e c t i o n o n l y , was i n s u f f i c i e n t to i n c r e a s e RL i n comparison to a cont inuous movement ( suppor t ing Henry, 1961) . G lencross suggests that at l e a s t two r e v e r s a l s i n d i r e c t i o n are r e q u i r e d j befo re RL i s a f f e c t e d . 5 . RL i n c r e a s e d as the number of response u n i t s r e q u i r e d i n c r e a s e d . RL f o r a one arm task was s i g n i f i c a n t l y f a s t e r than f o r the same task performed w i t h both arms s i m u l t a n e o u s l y . The speed w i th which s u b j e c t s responded l e d G lencross to argue i n support o f Henry and Rogers ' n e u r a l o r g a n i z a t i o n a l hypothes i s (memory drum t h e o r y ) , s t a t i n g " i t i s ev ident tha t they are beyond immediate sensory mon i to r ing and must be under c e n t r a l c o n t r o l of some f o r m " . However, G lencross quest ioned why a more complex motor programme has a longer RL than a s imple programme i f RL i s a measure o f the onset o f the programme and not the length of the programme. Assuming complex i ty of the programme does i n f l u e n c e RL, G lencross proposed t h a t the i n c r e a s e i n RL of a more complex task cou ld be the r e s u l t of the o r g a n i z a t i o n of a response r e q u i r i n g two p r o c e s s e s , a compi le r o r assembly phase and a runn ing phase. The more complex programme, due to an i n c r e a s e i n task c o m p l e x i t y , would account f o r an i n c r e a s e i n RL i n the compi le r o r assembly phase , independent o f the execut ion s t a g e . STIMULUS-RESPONSE PROBABILITY The r e l a t i o n s h i p between RL and s t i m u l u s - r e s p o n s e (S-R) occurrence has been e x t e n s i v e l y examined i n psycho-motor r e s e a r c h . I t i s w e l l e s t a b l i s h e d that i n CRT experiments i n v o l v i n g t a s k s o f equal c o m p l e x i t y , RL i s i n v e r s e l y r e l a t e d to S-R p r o b a b i l i t y ( B e r t e l s o n and B a r z e e l e , 1965; Falmagne, 1965; Hyman, 1953; Laming, 1969; Theios et a l . , 1973) . What i s not c l e a r l y d e f i n e d i s which component, s t i m u l u s i d e n t i f i c a t i o n or response s e l e c t i o n , i s r e s p o n s i b l e f o r the observed p r o b a b i l i t y e f f e c t . On the b a s i s of t h e i r r e s u l t s , s e v e r a l researchers have supported the s t i m u l u s expectancy e f f e c t ( B e r t e l s o n and T i s s e y r e , 1966; H i n r i c h s and K r a i n z , 1970; O r e n s t e i n , 1970). Converse l y , o ther s t u d i e s have concluded tha t response u n c e r t a i n t y was the major i n f l u e n c e on CRT (Kee le , 1969; M o r r i n and F o r r i n , 1963) . S t i l l o ther s t u d i e s have i m p l i c a t e d both processes ( B e r t e l s o n , 1965; Blackman, 1972; La Berge and Tweedy, 1964). To account f o r these c o n f l i c t i n g r e s u l t s , H i n r i c h s and K r a i n z (1970) have proposed the e f f e c t s o f TC as a confounding v a r i a b l e . They observed t h a t i n s t u d i e s which i n d i c a t e d a s t rong s t i m u l u s f a c t o r , the 28 degree of response d i f f i c u l t y of the exper imenta l tasks was m i n i m i z e d . Response b i a s e f f e c t s became apparent i n s t u d i e s i n which the exper imenta l t a s k s were made more d i f f i c u l t by (a) i n c r e a s i n g the number of responses , (b) reduc ing S-R c o m p a t i b i l i t y , and (c) reduc ing the i n t e r - t r i a l i n t e r v a l . Another c o n t r i b u t i n g f a c t o r which has been o f f e r e d t o p a r t i a l l y account f o r the c o n f l i c t i n g S-R p r o b a b i l i t y data i s the d i s t i n c t i o n between s e r i a l and d i s c r e t e CRT tasks (Goodman, 1975; Hawkins and Hosk ing , 1969; H i n r i c h s and K r a i n z , 1970; Schutz , 1972) . An observed phenomenon i n s e r i a l CRT tasks o n l y , has been the r e p e t i t i o n e f f e c t . Th is r e f e r s to the f a c t t h a t RLs f o r immediately repeated responses are f a s t e r than f o r changed responses . Accord ing to B e r t e l s o n (1965) the r e p e t i t i o n e f f e c t i s a r e s u l t o f response r e p e t i t i o n and not s t i m u l u s r e p e t i t i o n . A c c o r d i n g l y , s t u d i e s employing s e r i a l CRT t a s k s have l i k e l y accounted f o r changes i n RL due to p r o b a b i l i t y as a r e s u l t o f response f a c t o r s , w h i l e d i s c r e t e CRT t a s k s are more l i k e l y to e x h i b i t a s t i m u l u s expectancy b i a s . Blackman (1972) u s i n g a d i s c r e t e task i n a 4 :2 S -R mapping examined the s t i m u l u s -response p r o b a b i l i t y e f f e c t i n three exper imenta l c o n d i t i o n s . H i s r e s u l t s agreed w i t h those r e s e a r c h e r s s u p p o r t i n g a s t i m u l u s b i a s f a c t o r . However, an i n t e r e s t i n g r e s u l t s b e a r i n g d i r e c t re levance to t h i s p resent study occur red when the c o n t r o l c o n d i t i o n (CC) was compared to the s t i m u l u s -response imbalance c o n d i t i o n (SRI) to t e s t f o r a response b i a s e f f e c t . The mean RLs f o r the low frequency p a i r s i n the SRI c o n d i t i o n p.05 had a s i g n i f i c a n t l y f a s t e r RL than i n the CC which had a p r o b a b i l i t y f i v e t imes g r e a t e r p . 2 5 . Blackman concludes that l a r g e p r o b a b i l i t y d i f f e r e n c e s g rea te r than or equal to 90 percent are l i k e l y to produce a response b i a s 29 e f f e c t . For the purposes of t h i s i n v e s t i g a t i o n , the locus of the p r o b -a b i l i t y e f f e c t i s not of paramount importance as a 1:1 S-R p a i r i n g i s used To e x p l a i n the observed i n f l u e n c e of p r o b a b i l i t y e f f e c t (a l so run leng th and p r e d i c t i o n outcome) on CRT G e l l e r and P i t z (1970) and H i n r i c h s and K r a i n z (1970) have in t roduced the expectancy h y p o t h e s i s . Th is hypo-t h e t i c a l c o n s t r u c t assumes; (a) tha t CRT i s f a s t e s t to the s t i m u l u s which i s a n t i c i p a t e d or expected , (b) expectancy f o r a g iven s t i m u l u s i n c r e a s e s d i r e c t l y w i t h p r o b a b i l i t y , and (c) s u b j e c t s p r e d i c t expected events . These assumptions of the expectancy hypothes is account f o r s e v e r a l f i n d i n g i n CRT exper iments . F i r s t l y , tha t CRTs to c o r r e c t l y p r e d i c t e d events are f a s t e r than to i n c o r r e c t l y p r e d i c t e d events ( G e l l e r and P i t z , 1970; G e l l e r and Whitman, 1972; G e l l e r , Whitman and P o s t , 1973; G e l l e r et a l . , 1971; H i n r i c h s and K r a i n z , 1970; K e e l e , 1969) . Secondly , tha t CRT i s f a s t e s t to the more probable s t i m u l u s - r e s p o n s e p a i r (Blackman, 1972; La Berge and Tweedy, 1964; Laming, 1969). Cor rec t p r e d i c t i o n s o f S-R p a i r s , has been g iven as an e x p l a n a t i o n of the p r o b a b i l i t y e f f e c t on CRT ( H i n r i c h s and K r a i n z , 1970; K e e l e , 1969) , however, G e l l e r , i n c o n j u n c t i o n w i t h s e v e r a l r e s e a r c h e r s ( G e l l e r and P i t z , 1970; G e l l e r and Whitman, 1972; G e l l e r , Whitman and P o s t , 1973; G e l l e r et a l . , 1971) , have proposed tha t p r e d i c t i o n outcome (PO) and s t i m u l u s p r o b a b i l i t y (SP) have independent e f f e c t s on CRT. Accord ing t o G e l l e r and P i t z (1970) , s u b j e c t s p r e d i c t the more f r e q u e n t l y o c c u r r i n g s t i m u l u s more o f t e n , consequent l y , f a s t e r r e a c t i o n s to the more probable s t i m u l u s might be a t t r i b u t a b l e to the l a r g e number of c o r r e c t p r e d i c t i o n s of the more probable s t i m u l u s , r a t h e r than the r e l a t i v e f requency o f s t i m u l u s 30 occur rence . From r e s u l t s obta ined i n t h i s s tudy , they concluded t h a t PO and SP acted independent ly on CRT. In a subsequent study u s i n g a 3 :2 S-R mapping to examine PO and s t imu lus versus response a n t i c i p a t i o n , G e l l e r and Whitman (1972) found t h a t RL was s i g n i f i c a n t l y i n f l u e n c e d by the s u b j e c t ' s PO on the t r i a l p reced ing the observed i d e n t i f i c a t i o n response . They concluded tha t e i t h e r s t i m u l u s or response b i a s cou ld a f f e c t CRT, however, the s t i m u l u s e f f e c t was more pronounced. Response^ e f f e c t s became more ev ident on a p a r t i c u l a r t r i a l when the PO to the p reced ing t r i a l i n v o l v e d i n c o r r e c t l y p r e d i c t i n g the s t i m u l u s w h i l e c o r r e c t l y p r e d i c t i n g the response . In a f u r t h e r s t u d y , G e l l e r , Whitman and Post (1973) examined s e v e r a l p r o c e d u r a l c o n s i d e r a t i o n s and t h e i r e f f e c t on CRT and PO. Of p a r t i c u l a r re levance to t h i s p resent i n v e s t i g a t i o n was the amount o f p r o b a b i l i t y i n f o r -mation p rov ided to the s u b j e c t p r i o r to t e s t i n g . S p e c i f i c a l l y , one h a l f of the group (20 s u b j e c t s ) was t o l d of the s p e c i f i c p r o b a b i l i t y r a t i o (70:30) between the two t a s k s , w h i l e the remain ing 20 s u b j e c t s were not in fo rmed . T h e i r r e s u l t s showed t h a t s u b j e c t s informed of the r e l a t i v e s t i m u l u s p r o b -a b i l i t i e s reac ted s i g n i f i c a n t l y f a s t e r than s u b j e c t s who had not been g iven t h i s knowledge p r i o r to t e s t i n g . They concluded t h a t e i t h e r the added p r o b a b i l i t y i n f o r m a t i o n reduced the task u n c e r t a i n t y and f a c i l i t a t e d the s u b j e c t s ' r e a c t i o n s , or the i n c r e a s e of u n c e r t a i n t y due to l a c k of s t i m u l u s i n f o r m a t i o n i n h i b i t e d CRT. As observed by G e l l e r et a l . (1973) , the e f f e c t o f p r i o r p r o b a b i l i t y i n f o r m a t i o n on RL does not appear to have been an important c o n s i d e r a t i o n i n some p r e v i o u s exper iments , and i n f a c t , s e v e r a l v s t u d i e s d i d not repor t whether s u b j e c t s were g iven s t i m u l u s p r o b a b i l i t y i n f o r m a t i o n (La Berge and Tweedy, 1964) . V 31 TASK COMPLEXITY BY RESPONSE PROBABILITY Only two s t u d i e s have been found which have examined the j o i n t e f f e c t s of TC and RP on RL. Schutz (1972) used f i v e exper imenta l c o n d i t i o n s to t e s t h i s proposed theory o f motor memory r e t r i e v a l . As a consequence of s e v e r a l unexpected r e s u l t s from S c h u t z ' s d a t a , Ryan (1972) used S c h u t z ' s model to p rov ide f u r t h e r t e s t s o f the motor memory r e t r i e v a l t h e o r y . The r e s u l t s of these two r e s e a r c h e r s w i l l be reviewed together i n the f o l l o w i n g d i s c u s s i o n . Task Complex i ty Both s t u d i e s hypothes i zed and v e r i f i e d tha t an i n c r e a s e i n TC i n the SRT c o n d i t i o n , r e s u l t e d i n an i n c r e a s e i n RL. From S c h u t z ' s model i t was proposed that a more complex task (TC2) r e q u i r e d a longer read out t ime d u r i n g the response search and r e t r i e v a l stage r e s u l t i n g i n a s lower RL. . A l though h y p o t h e s i z e d , r e s u l t s from both s t u d i e s d i d not support a p o s i t i v e monotonic r e l a t i o n s h i p between TC and RL i n the CRT c o n d i t i o n . * In f a c t , i n S c h u t z ' s exper iment , Exper imenta l C o n d i t i o n s 3 , 4 , and 5 , and C o n d i t i o n s B and C i n Ryan's study (CRT c o n d i t i o n s i n v o l v i n g equal and unequal S-R p r o b a b i l i t i e s ) , the more complex task had a f a s t e r RL than the s imple task (TCI ) . The task complex i t y main e f f e c t was not s i g n i f i c a n t i n e i t h e r s tudy . Both researchers found the e f f e c t o f TC a l o n e , was m i n i m a l . From t h e i r r e s u l t s , a l though the data were not c o n c l u s i v e , the e f f e c t of response read iness (RR), i . e . , p l a c i n g a p a r t i c u l a r programme i n t o s e l e c t i v e a t t e n t i o n , appeared to be of paramount importance i n the type of search and r e t r i e v a l s t r a t e g y employed. 32 Response P r o b a b i l i t y In the CRT c o n d i t i o n o f equal response p r o b a b i l i t y , i t was hypo-t h e s i z e d tha t the RL f o r the complex task would be g r e a t e r than the s imple t a s k , but t h a t the d i f f e r e n c e between the two t a s k s would be l e s s than i n the SRT c o n d i t i o n . The p r o p o s a l t h a t the d i f f e r e n c e between the two tasks would be l e s s i n the CRT c o n d i t i o n was supported by both r e s e a r c h e r s as g iven i n Table 1 below: Table 1 Mean RLs f o r TCI and TC2 i n the SRT and CRT Cond i t ions i n Experiments by Ryan and Schutz SRT CRT (p.50) TCI TC2 TC2 - TCI TCI TC2 TC2 - TCI Schutz 159 177 18 245 243 - 2 Ryan 221 253 32 330 315 - 1 5 However, the negat i ve d i f f e r e n c e i n d i c a t i n g tha t the complex task had a f a s t e r RL than the s imple task was not expected i n e i t h e r s t u d y . Con-s e q u e n t l y , the main hypothes is tha t TC2 i s g r e a t e r than TCI i n the CRT c o n d i t i o n of equal p r o b a b i l i t i e s was not suppor ted . Accord ing to S c h u t z ' s model , i t appeared sub jec ts were p l a c i n g the complex task i n t o SA more o f t e n than the s imple task to compensate f o r the i n c r e a s e d c o m p l e x i t y . In so d o i n g , thei amount of t ime r e q u i r e d f o r the response search more than compensated f o r the d i f f e r e n c e due to response r e l e a s e t i m e , thus 33 y i e l d i n g a f a s t e r RL f o r TC2. TC seemed to be the on ly f a c t o r a f f e c t i n g RR when the p r o b a b i l i t i e s between the two t a s k s were e q u a l . Task Complex i ty by Response P r o b a b i l i t y I n t e r a c t i o n Schutz hypothes i zed t h a t average CRT i s n e g a t i v e l y r e l a t e d to RP, i . e . , an i n c r e a s e i n RP r e s u l t s i n a decrease i n CRT. He found t h a t t h i s r e l a t i o n s h i p h e l d f o r tasks of equal complex i t y o n l y . Because the r e l a -t i o n s h i p d i d not h o l d t rue f o r tasks of unequal c o m p l e x i t y , Schutz r e v i s e d t h i s theorem which p r e d i c t e d tha t i n a CRT s i t u a t i o n , the e f f e c t o f RP i s a d e c r e a s i n g f u n c t i o n of T C ' As TC i s i n c r e a s e d the e f f e c t RP has on RL i s decreased , and c o n v e r s e l y , a decrease i n TC w i l l i n c r e a s e the e f f e c t RP has on RL. For very complex t a s k s , RP would have very l i t t l e e f f e c t . A f t e r examining S c h u t z ' s r e s u l t s , Ryan attempted to s u b s t a n t i a t e t h i s r e v i s e d theorem and hypothes i zed t h a t i n a CRT c o n d i t i o n w i th v a r y i n g RPs, d i f f e r e n c e s i n CRT due to TC are an i n c r e a s i n g f u n c t i o n of RP, i . e . , the more complex the t a s k , the l e s s w i l l be the e f f e c t o f i n c r e a s i n g the RP on RL. In Exper imenta l C o n d i t i o n C, w i t h RP f o r TCI , TC2 at . 7 5 , .25 r e s p e c t i v e l y , Ryan hypothes i zed tha t because o f the h i g h RP of TCI , task complex i t y would have l i t t l e e f f e c t on the s t r a t e g y the s u b j e c t u s e d , and the h i g h l y p robable TCI would be p l a c e d i n t o SA most o f t e n . I t was found , however, tha t TC2, w i t h the low p r o b a b i l i t y , had a f a s t e r RL than the h i g h l y probable TCI. S i m i l a r l y , i n C o n d i t i o n D w i t h the p r o b a b i l i t y of occurrence f o r TCI , TC2 reversed ( . 2 5 , . 7 5 ) , i t was proposed t h a t TC2 ' would be i n SA more o f t e n because of the e f f e c t o f TC and p a r t i a l l y due to RP. Again r e s u l t s d i d not support the h y p o t h e s i s , as TCI , the low p r o b a b i l i t y t a s k , had a f a s t e r RL than the h i g h l y probable TC2. 34 From Ryan's r e s u l t s , i t seems apparent tha t the c r i t i c a l f a c t o r f o r response read iness was a low p r o b a b i l i t y l e v e l i n both exper imenta l c o n d i t i o n s . Both Schutz and Ryan found t h a t a decrease i n RP had a g r e a t e r e f f e c t on response s t r a t e g i e s and consequent ly on RL when u s i n g tasks of d i f f e r e n t c o m p l e x i t i e s . In both s t u d i e s , the number of d i f f e r e n t p r o b -a b i l i t y l e v e l s examined was r e l a t i v e l y few, consequent ly , i d e n t i f i c a t i o n o f a c r i t i c a l low RP l e v e l was not determined. From the above l i t e r a t u r e r e v i e w , i t i s apparent tha t the r e s u l t i n g data from s t u d i e s examining the j o i n t e f f e c t s o f TC and RP on RL do not concur w i t h the l i t e r a t u r e d e a l i n g w i t h these two v a r i a b l e s s e p a r a t e l y . Consequent ly , the f o l l o w i n g exper iment , o u t l i n e d i n Chapter 3 , has been designed to p rov ide a f u r t h e r t e s t of the j o i n t e f f e c t s of TC and RP on RL. The subsequent r e s u l t s w i l l be i n t e r p r e t e d i n terms o f the t h e o r e t i c a l framework of CRT as proposed by Schutz as o u t l i n e d e a r l i e r i n t h i s rev iew . Chapter 3 METHODS AND PROCEDURES Subj e c t s S i x t e e n students from undergraduate and graduate s t u d i e s at the U n i v e r s i t y of B r i t i s h Columbia were used as s u b j e c t s . A l l s u b j e c t s were male , between the ages of 20 and 28 , w i t h a mean age o f 22 .6 y e a r s . No r e s t r i c t i o n s were p l a c e d on handedness, r e s u l t i n g i n one l e f t handed and f i f t e e n r i g h t handed students v o l u n t e e r i n g to serve as s u b j e c t s . Apparatus x The apparatus used i n t h i s experiment was a r e a c t i o n t ime apparatus which c o n s i s t e d of a s u b j e c t ' s console and an exper imente r ' s c o n s o l e . S u b j e c t ' s c o n s o l e . The s u b j e c t ' s c o n s o l e , a 33 x 45 cm. box, c o n s i s t e d o f s i x red s t i m u l u s l i g h t s s i t u a t e d h o r i z o n t a l l y 8 cm. d i r e c t l y above s i x response keys (see F igure 4 ) . The c r i t i c a l s t i m u l u s l i g h t s used i n t h i s study were c o n f i n e d to l i g h t s 3 and 4 of the s t i m u l u s a r r a y . The index f i n g e r of each hand was p o s i t i o n e d on the response key d i r e c t l y below the cor responding s t i m u l u s l i g h t . At the beg inn ing o f each t r i a l the two f i n g e r s r e s t e d g e n t l y , but d i d not depress the response keys p r i o r t o the onset of the s t i m u l u s l i g h t . A depress ion of 4 mm. was r e q u i r e d to te rminate the d i g i t a l c l o c k i n i t i a t e d by the p r e s e n t a t i o n of the s t i m u l u s l i g h t . Three l a r g e movement response keys (MRK) 5 cm. long and 2 .5 cm. wide were s i t u a t e d at the top of the conso le 23 cm. from the response keys 35 36 Movement Response Keys o o o O Green Warning L igh t Red O O O S t imulus L i g h t s O O White Response Keys O O o o L e f t Index F inger Right Index F inger gure 4. P i c t o r i a l d e s c r i p t i o n of the S u b j e c t ' s console apparatus . and spaced 6 . 5 cm. a p a r t . The middle MRK, when depressed , stopped the d i g i t a l c l o c k complet ing one t r i a l . To mask extraneous n o i s e , a l l s u b j e c t s were r e q u i r e d to wear earphones d u r i n g the t e s t i n g s e s s i o n s . The s u b j e c t ' s conso le and the exper imente r ' s console were s i t u a t e d approx imate ly four f e e t apar t and were separated by a non-diaphanous c u r t a i n . Exper imente r ' s c o n s o l e . The exper imente r ' s console c o n s i s t e d of a programmer, a r e a c t i o n t ime i n t e r f a c e , and a d i g i t a l p r i n t e r . The programmer, React ion Time Module 1973, a l lowed the exper imenter t o s e l e c t e i t h e r of the two c r i t i c a l s t i m u l u s l i g h t s f o r p r e s e n t a t i o n and r e s e t the t i m i n g apparatus i n p r e p a r a t i o n f o r the next t r i a l . No warning l i g h t or predetermined i n t e r - s t i m u l u s i n t e r v a l were used d u r i n g the t e s t i n g . The r e a c t i o n t ime i n t e r f a c e (manufactured by Canadian Dynamics Instrument C o r p o r a t i o n ) , and the d i g i t a l p r i n t e r (manufactured by Un i ted Systems C o r p o r a t i o n ) , were w i red to r e c o r d response l a t e n c y and movement t ime i n m i l l i s e c o n d s . The apparatus recorded RL as the t ime between the onset of the s t i m u l u s l i g h t on the s u b j e c t ' s conso le to the depress ion of the cor responding response key . Movement time (MT) was recorded as the t ime e l a p s i n g between the depress ion of a response key and the d e p r e s s i o n of the middle MRK at the top of the c o n s o l e . Dur ing the 1600 t r i a l s f o r each s u b j e c t , a method o f i d e n t i f y i n g TCI from TC2 as p r i n t e d out by the d i g i t a l p r i n t e r was adopted. The p r i n t e r was w i red so t h a t a l l RLs and MTs f o r TCI were recorded on one h o r i z o n t a l l i n e , w h i l e the response t imes f o r TC2 were recorded on two h o r i z o n t a l l i n e s . Th is a d a p t a t i o n ensured tha t d u r i n g coding of the d a t a , the response t imes recorded f o r 38 the two tasks would not be confused. At the same t i m e , i f an i n a p p r o -p r i a t e response key was depressed d u r i n g any t e s t t r i a l , the d i g i t a l p r i n t e r recorded the cor responding t ime i n red p r i n t . A l l c o r r e c t responses were recorded i n b l a c k . Procedures Response t a s k s . Subjects were seated i n f r o n t of the apparatus and the i n s t r u c t i o n s , as appear i n Appendix A, were r e a d . Subjects were r e q u i r e d to respond to one of two p o s s i b l e s t i m u l u s l i g h t s w i t h i t s a s s o c i a t e d movement response r e f e r r e d to as TCI or TC2. TCI r e q u i r e d the s u b j e c t , upon s t imu lus p r e s e n t a t i o n , to depress the cor responding response key d i r e c t l y below the l i g h t , and then move as q u i c k l y as p o s s i b l e to depress the middle MRK des ignated MRK2. TC2 r e q u i r e d the sub jec t to depress the a p p r o p r i a t e response key w i t h the index f i n g e r and then move to h i t the MRKs i n a predetermined o r d e r . E i g h t s u b j e c t s performed TC2 w i t h the r i g h t hand and were r e q u i r e d to h i t MRKs 2 - 3 - 1 - 2 i n r a p i d s u c c e s s i o n , w h i l e the remain ing e i g h t s u b j e c t s performed TC2 w i t h the i l e f t hand and were i n s t r u c t e d to respond w i t h movement s e r i e s 2 - 1 - 3 - 2 . Procedures f o r r e c o r d i n g RL and MT f o r TC2 were i d e n t i c a l to those f o r TCI . RL f o r TC2 was te rminated by the depress ion of the c o r r e c t response key , w h i l e MT was te rminated when the s u b j e c t depressed MRK2 at the beg inn ing of the movement s e r i e s . Only the i n i t i a l phase of MT was r e c o r d e d , ensur ing i d e n t i c a l movement sequences f o r the two t a s k s . The remain ing p a r t of the movement sequence was not t i m e d , but merely i n c l u d e d to p r o v i d e a more complex t a s k . Subjects were informed they were be ing t imed f o r the t o t a l movement. 39 The two t a s k s u t i l i z e d i n t h i s p resent study were s i m i l a r t o the t a s k s employed i n the experiments conducted by Ryan (1972) and Schutz (1972) . In both exper iments , the s imple task was found to have a s i g n i -f i c a n t l y f a s t e r RL than the complex t a s k . In a d d i t i o n , TC2 as o u t l i n e d above, conformed to the f i n d i n g s o f G lencross (1973) i n tha t TC2 r e q u i r e d a longer movement than TCI and a l s o i n v o l v e d th ree r e v e r s a l s of d i r e c t i o n te rminated by the s t r i k i n g of a t a r g e t a f t e r each r e v e r s a l . Upon complet ion of each t r i a l , the sub jec t re tu rned to the ready p o s i t i o n by p l a c i n g h i s index f i n g e r s on the cor responding response keys i n p r e p a r a t i o n f o r the next s t i m u l u s p r e s e n t a t i o n . Sub jects were i n s t r u c t e d to respond as q u i c k l y as p o s s i b l e w i t h emphasis a l s o p l a c e d on accuracy i n order to min imize e r r o r s . The sequence f o r each t e s t t r i a l was as f o l l o w s : 1. Subject i n the ready p o s i t i o n . 2 . S t imulus l i g h t on . 3 . Subject responds w i t h e i t h e r TCI or TC2. 4 . RL and MT recorded . 5 . Sub ject r e t u r n s to ready p o s i t i o n as the exper imenter r e s e t s t imer and s e l e c t s s t i m u l u s l i g h t (3 or 4 ) . Exper imenta l C o n d i t i o n s E i g h t exper imenta l c o n d i t i o n s (ECs) c o n s i s t i n g of 200 t r i a l s each , were performed d u r i n g f o u r t e s t i n g s e s s i o n s , two ECs per day. In each EC, two s t i m u l i and two responses were p a i r e d i n a 1:1 S-R mapping. A summary o f the e i g h t ECs w i t h t h e i r a s s o c i a t e d response p r o b a b i l i t i e s and number of t r i a l s per task i s g iven i n Table 2 . For e i g h t of the s u b j e c t s , TCI 40 Table 2 Response P r o b a b i l i t y and Number of T r i a l s f o r each Exper imenta l C o n d i t i o n f o r TCI and TC2 Tasks Exper imenta l Cond i t ions EC1 EC2 EC3 EC4 EC5 EC6 EC 7 EC8 TCI RP 1.0 T r i a l s 100 TC2 RP 1.0 T r i a l s 100 .90 180 . 10 20 .75 150 .25 50 .60 120 .40 80 .50 100 .50 100 .40 80 .60 120 .25 50 .75 150 .10 20 .90 180 was performed w i th the dominant hand and TC2 w i t h the non-dominant hand. For the remain ing e i g h t s u b j e c t s , TC2 was performed w i t h the dominant hand and TCI w i th the non-dominant hand. An 8 x 8 L a t i n Square r e p l i c a t e d tw ice was used to determine the order i n which each s u b j e c t performed the e i g h t ECs (see Table 1 , Appendix A ) . The L a t i n Square was m o d i f i e d to prevent two ECs w i t h the same p r o b a b i l i t y r a t i o s from o c c u r r i n g d u r i n g any one t e s t i n g s e s s i o n . For example, EC2 and EC8, w i t h p r o b a b i l i t y r a t i o s of 9 : 1 and 1:9 f o r TCI and TC2 r e s p e c t i v e l y , were never presented i n the same t e s t i n g s e s s i o n . P r i o r to t e s t i n g , a t a b l e of random numbers was used to determine the order o f p r e s e n t a t i o n o f TCI and TC2 f o r each p r o b a b i l i t y r a t i o which occur red between the two t a s k s . For each p a i r o f ECs w i t h reve rsed p r o b a b i l i t y r a t i o s , i n c l u d i n g EC2 - EC8, EC3 - EC7, and EC4 - EC6, on ly one s t i m u l u s p r e s e n t a t i o n sequence per p a i r was des igned . To accommodate both ECs w i t h i n the p a i r , the order i n which the s t i m u l u s l i g h t s occur red was s imply reversed f o r the oppos i te EC. I f opposing ECs occur red d u r i n g the same t e s t i n g s e s s i o n , i t was thought that s u b j e c t s cou ld p o s s i b l y i d e n t i f y s i m i l a r i t i e s between the two sequences and u t i l i z e t h i s knowledge i n t h e i r responses . Only EC1 and EC5 were p a i r e d w i t h a l l o ther ECs wi thout r e s t r i c t i o n . The L a t i n Square was ba lanced as c l o s e l y as p o s s i b l e so that d u r i n g the 64 i n d i v i d u a l t e s t i n g s e s s i o n s each EC occur red e q u a l l y w i t h the remain ing n o n - r e s t r i c t e d ECs. A f u r t h e r r e s t r i c t i o n was p l a c e d on the number o f r e p e t i t i o n s the s t i m u l u s l i g h t w i t h the h i g h e s t p r o b -a b i l i t y o f occurrence cou ld be repeated d u r i n g any g iven EC. I t was f e l t t h a t s u b j e c t s might not b e l i e v e the p r e s e t p r o b a b i l i t y l e v e l s i f the r e p e t i t i o n s f o r one s t imu lus l i g h t were u n u s u a l l y l o n g . The maximum 42 number of r e p e t i t i o n s a l lowed i s g iven i n Table 2 , Appendix A. The hypothes i zed r e s u l t s f o r TCI and TC2 have p r e v i o u s l y been expressed i n terms of RP (see F i g u r e - 1 , page 11). F igure 5 below i l l u s t r a t e s these same r e s u l t s f o r TCI and TC2 t ransposed from RP and presented i n terms of ECs. Subjects were r e q u i r e d to complete f o u r t e s t i n g s e s s i o n s w i t h i n a f i v e day p e r i o d , one s e s s i o n per day. Each sub jec t was r e q u i r e d to arrange the f o u r t e s t i n g s e s s i o n s at approx imate ly the same time of day ( w i t h i n two hours) f o r each s e s s i o n . Dur ing each of the f o u r t e s t i n g s e s s i o n s , s u b j e c t s performed 10 p r a c t i s e and 400 t e s t t r i a l s i n the f o l l o w i n g o r d e r : 10 p r a c t i s e t r i a l s (CRT c o n d i t i o n ) , 60 t e s t t r i a l s , a 30 second r e s t , 40 t r i a l s , a one minute r e s t , 60 t r i a l s , a 30 second r e s t , 40 t r i a l s , a two minute r e s t . Th is sequence was repeated f o r the second EC e x c l u d i n g the 10 p r a c t i s e t r i a l s . The t o t a l t ime f o r one t e s t i n g s e s s i o n was approx imate ly 30 minutes . To f a m i l i a r i z e the s u b j e c t s w i th the two t a s k s , a p r a c t i s e s e s s i o n c o n s i s t i n g of 15 t r i a l s f o r each task i n the SRT c o n d i t i o n and 15 t r i a l s t o t a l i n the CRT c o n d i t i o n (p.50) preceded the a c t u a l t e s t i n g on Day 1 . Subjects were g iven no p r i o r knowledge as to the order o f s t i m u l u s p r e s e n t a t i o n , but were t o l d of the p r e s e t p r o b a b i l i t i e s o f occurrence f o r each s t imu lus l i g h t f o r a l l e igh t ECs as they were p r e s e n t e d . No knowledge of r e s u l t s was g iven dur ing the t e s t i n g s e s s i o n s . I f a sub jec t responded w i t h the i n c o r r e c t movement t a s k , he was i n s t r u c t e d to r e t u r n to the ready p o s i t i o n and prepare f o r the next t r i a l . 43 EC1 EC2 EC3 EC4 EC5 EC6 EC7 EC8 Exper imenta l Cond i t ions F igure 5 . The hypothes i zed r e s u l t s f o r TCI and TC2 over Exper imenta l C o n d i t i o n s . 44 Exper imenta l Design In a n a l y s i n g the d a t a , the exper imenta l des ign was t r e a t e d as an 8 x 8 x 2 complete f a c t o r i a l w i t h repeated measures on. two f a c t o r s . The th ree independent v a r i a b l e s were: order of p r e s e n t a t i o n (e ight l e v e l s ) , response p r o b a b i l i t y (e igh t l e v e l s ) , and task complex i t y (two l e v e l s ) . The one dependent v a r i a b l e , RL, was measured i n m i l l i s e c o n d s . For each s u b j e c t , a t o t a l o f 1600 RL t r i a l s was r e c o r d e d . The mean RL f o r each task over each o f the e i g h t ECs was then c a l c u l a t e d , p roduc ing 16 measures of the dependent v a r i a b l e f o r f u r t h e r data a n a l y s i s . A n a l y s i s of Data In the i n i t i a l d e s i g n , i t was proposed t h a t the data cou ld be t r e a t e d as an 8 x 2 a n a l y s i s of v a r i a n c e w i t h repeated measures on both f a c t o r s . The r e s u l t s from t h i s a n a l y s i s , i n c o n j u n c t i o n w i t h the preplanned com-p a r i s o n s would have p rov ided a p p r o p r i a t e t e s t s of the s p e c i f i c hypotheses . However, examinat ion of the c e l l mean RLs over days suggested the presence of a Days e f f e c t (see Table 2 and F igure 1 , Appendix B ) . Thus the data were ana lysed as Tasks by Days, and as suspec ted , a s i g n i f i c a n t Days e f f e c t was found. In the p rev ious 8 x 2 a n a l y s i s , t h i s Days e f f e c t would have been r e f l e c t e d i n the Subject by C o n d i t i o n s , and Subject by C o n d i t i o n s by Task i n t e r a c t i o n s . As these two e r r o r terms are c r i t i c a l i n the c a l c u l a -t i o n s of the preplanned comparisons f o r a l l the hypotheses , t h i s would have r e s u l t e d i n an o v e r l y c o n s e r v a t i v e t e s t and an i n c r e a s e i n the p o s s i b i l i t y o f committ ing a Type I I e r r o r . In an attempt to reduce t h i s b i a s , the data were ana lysed as an 8 x 8 x 2 a n a l y s i s of v a r i a n c e , i n c l u d i n g a t h i r d independent v a r i a b l e , 45 order of c o n d i t i o n p r e s e n t a t i o n (non- repeated measures) . By t a k i n g out the order e f f e c t , the Days e f f e c t was p a r t i a l l y accounted f o r and the e r r o r terms reduced. S i n g l e degree of freedom preplanned comparisons were then admin is te red to t e s t the s p e c i f i c hypotheses . Test of Hypothes is 1. Hypothesis 1 p r e d i c t e d tha t the RL f o r TCI would be f a s t e r than f o r TC2 i n the SRT c o n d i t i o n . A preplanned c o n t r a s t between TCI and TC2 i n EC1 t e s t e d f o r a s i g n i f i c a n t d i f f e r e n c e between the two RL. The s p e c i f i c we igh t ing c o e f f i c i e n t s f o r a l l preplanned com-p a r i s o n s are g iven i n Table 3 . Test of Hypothesis 2 . Hypothes is 2 p r e d i c t e d the d i f f e r e n c e between TC2 and TCI i n a CRT c o n d i t i o n of equal response p r o b a b i l i t i e s would be l e s s than the d i f f e r e n c e between TC2 and TCI i n the SRT c o n d i t i o n . A preplanned comparison was used to t e s t the d i f f e r e n c e between TC2 and TCI i n EC! as compared to the d i f f e r e n c e between TC2 and TCI i n EC5. Test of Hypothes is 3 . Hypothes is 3 p r e d i c t e d tha t RL i s d i r e c t l y r e l a t e d to RP f o r p r o b a b i l i t i e s l e s s than p . 5 0 . A s e r i e s o f s i x Helmert c o n t r a s t s (Table 3) was used to t e s t Hypothes is 3 . The f i r s t th ree com-p a r i s o n s , S e r i e s A, determined i f RL, when averaged over the two l e v e l s of task c o m p l e x i t y , decreased m o n o t o n i c a l l y from p.50 to p . 1 0 . The second s e r i e s of th ree compar isons, S e r i e s B, t e s t e d whether the e f f e c t of RP on RL was the same under each l e v e l of TC. A s i g n i f i c a n t RP main e f f e c t ( S e r i e s A) and n o n - s i g n i f i c a n t TC x RP i n t e r a c t i o n (Ser ies B) were p r e d i c t e d . 46 Test of Hypothesis 4. Hypothesis 4 stated that above a p r o b a b i l i t y l e v e l of p.50, RL was independent of RP for tasks of unequal complexity. As i n Hypothesis 3, a series of s i x Helmert contrasts was used. S i m i l a r l y , Series A, Contrasts 1, 2, and 3, tested whether a s i g n i f i c a n t RP main ef f e c t existed from p.50 to p.90 when averaged over the two lev e l s of task complexity. According to Hypothesis 4, a non-significant RP main e f f e c t was expected, supporting no change i n RL above a p.50 l e v e l . The second serie s of three contrasts, Series B, was used to test i f the differe n c e between TCI and TC2 remained constant over the four p r o b a b i l i t y l e v e l s . Again, a non-significant TC x RP i n t e r a c t i o n was expected. In the series of preplanned comparisons used to test the s p e c i f i c hypotheses, i t was not possible to make a l l contrasts orthogonal to each other. Hypothesis 1 i s orthogonal to Hypotheses 3 and 4, and the sets of singl e degree of freedom contrasts associated with both Hypothesis 3 and Hypothesis 4 are orthogonal within themselves. Hypotheses 3 and 4 both include contrasts with the p.50 p r o b a b i l i t y l e v e l and thus could ynot be made orthogonal to each other. S i m i l a r l y Hypothesis 2, which compares the 1.0 p r o b a b i l i t y l e v e l with the .50 p r o b a b i l i t y l e v e l , i s not orthogonal to either Hypothesis 1 or to Hypotheses 3 and 4. It i s acknowledged that the experiment-wise error rate w i l l consequently be s l i g h t l y larger than the per comparison error rate used f o r each contrast. 47 Table 3 Specific Weighting Coefficients of the Preplanned Comparisons For Hypotheses 1 to 4 Inclusive Hypotheses TCI TC2 4 Probability Levels 1.0 .90 .75 .60 .50 .40 .25 .10 1.0 .90 .75 .60 .50 .40 .25 .1( -1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 -1 0 0 0 1 0 0 0 1 0 0 0 -1 0 0 0 1 0 0 0 0 3 -1 -1 -1 0 0 0 0 3 -1 -1 -1 Series A 2 • 0 0 0 0 0 2 -1 -1 0 0 0 0 0 2 -1 -1 RP Main 3 0 0 0 0 0 0 1 -1 0 0 0 0 0 0 1 -1 1 'o 0 0 0 3 -1 -1 -1 0 0 0 0 -3 1 1 1 Series B 2 • 0 0 0 0 0 2 -1 -1 0 0 0 0 0 -2 1 1 TC x RP 3 interaction 0 0 0 0 0 0 1 -1 0 0 0 0 0 0 -1 1 1 0 3 -1 -1 -1 0 0 0 0 3 -1 -1 -1 0 0 0 Series A 2 • 0 0 2 -1 -1 0 0 0 0 0 2 -1 -1 0 0 0 RP Main 3 0 0 0 1 -1 0 0 0 0 0 0 1 -1 0 0 0 1 '0 3 -1 -1 -1 0 0 0 0 -3 1 1 1 0 0 0 Series B 2 • 0 0 2 -1 -1 0 0 0 0 0 -2 1 1 0 0 0 TC x RP 3 interaction 0 0 0 1 -1 0 0 0 0 0 0 -1 1 0 0 0 Chapter 4 RESULTS AND DISCUSSION Data Reduction P r i o r to data reduction, an examination of each subject's t r i a l by t r i a l scores showed that no appreciable fatigue or learning e f f e c t occurred during any one i n d i v i d u a l t e s t i n g session. Consequently, a l l t r i a l s were included in. the c a l c u l a t i o n of the mean which was used as the measure of central tendency. For each EC as outlined i n Table 2, page 40, the mean score was calculated according to the number of t r i a l s f o r each task i n that p a r t i c u l a r EC. For example, to determine the mean RL for a s p e c i f i c subject i n EC2, the number of scores used i n the c a l c u l a t i o n of the mean RL for TCI was 180 t r i a l s (less e r r o r s ) , while 20 scores (less errors) were used i n the c a l c u l a t i o n of the mean RL for TC2. Programme Datasnif (Goodman and Schutz, 1975) was used to calculate subjects' i n d i v i d u a l mean scores, c e l l means and standard deviations for TCI and TC2 under the eight ECs. Subjects' i n d i v i d u a l reduced data are given i n Table 1, Appendix B. Tables 4 and 5, which follow, present a tabulation of the resultant mean RLs together with the marginal means for each task. In addition, Figure 6 (a and b) i l l u s t r a t e s the mean RL values as presented i n Tables 4 and 5. 48 \ 49 Table 4 Mean Response L a t e n c i e s (msec.) and Standard Dev ia t ions f o r TCI and TC2 Under E igh t Exper imenta l Cond i t ions Tasks Exper imenta l Cond i t ions 1 2 3 4 5 6 7 8 X TCI RP 1.0 .90 .75 .60 .50 .40 . .25 .10 X 221 254 272 282 296 294 304 334 282 Sd 22 .5 33.9 36 .4 26 .8 49 .6 36.0 15.9 34.2 TC2 RP 1.0 .10 .25 .40 .50 .60 .75 .90 X 232 313 295 300 299 291 285 281 287 Sd 18 .1 4 5 . 6 35 .7 21 .6 46 .7 34 .5 37 .2 28 .8 Mean 227 284 284 291 298 293 295 308 Table 5 Mean Response L a t e n c i e s (msec.) f o r TCI and TC2 Under E i g h t P r o b a b i l i t y Cond i t ions Tasks Response P r o b a b i l i t y 1.0 .90 .75 .60 .50 .40 .25 .10 X TCI 221 254 272 282 296 294 304 334 282 TC2 232 281 285 291 299 300 295 313 287 Mean 227 268 279 287 298 297 300 324 Figure 6a. The empir ica l r e s u l t s for TCI and TC2 over Experimental Condi t ions . F igure 6b. The e m p i r i c a l r e s u l t s f o r TCI and TC2 over Response P r o b a b i l i t y l e v e l s . 51 Table 3 and Table .4, Appendix B, p resent the e r r o r data f o r each task under the e i g h t ECs and e i g h t RP l e v e l s r e s p e c t i v e l y . Subject e r r o r s , i . e . , responding w i t h the i n c o r r e c t t a s k , were r e l a t i v e l y low f o r a l l c o n d i t i o n s , w i t h the o v e r a l l e r r o r r a t e at approx imate ly 1.00%. I n c o r r e c t responses were recorded as b lanks on the F o r t r a n coding sheets and were not i n c l u d e d i n the a n a l y s i s of the d a t a . Computer programme BMD:P2V (Dixon, 1975) was used to c a l c u l a t e the 8 x 8 x 2 a n a l y s i s of v a r i a n c e , the r e s u l t s o f which are g iven i n Table 6 below: Table 6 A n a l y s i s of Var iance f o r the E f f e c t s of Order of P r e s e n t a t i o n , Exper imenta l Cond i t ions and Task Complexi ty on Response Latency Source df MS F P r o b a b i l i t y F Exceeded Order (0) 7 27831.60 1.09 0.444 SwO 8 25352.56 Cond i t ions 7 19522.35 25.79 <0.001 0 x C 49 2033.24 2.68 <0.001 SwO x C 56 756.81 Task Complex i ty (TC) 1 1482.24 3 .63 0.093 0 x TC 7 478.10 1.17 0.411 SwO x TC 8 408.13 C x TC 7 8461.54 59.60 <0.001 0 x C x TC 49 207.65 1.46 0.084 SwO x C x TC 56 141.96 T o t a l 255 52 Task Complex i ty E f f e c t s The task complex i ty main e f f e c t measured whether the mean RL f o r TCI was s i g n i f i c a n t l y d i f f e r e n t from the mean RL f o r TC2 when averaged over the e i g h t ECs. Contrary to the p r e d i c t e d r e s u l t s , the cor responding F r a t i o f o r the TC main e f f e c t f a i l e d to approach s i g n i f i c a n c e . The task complex i ty by c o n d i t i o n s i n t e r a c t i o n was h i g h l y s i g n i f i c a n t (F=59.60, p<.001) . The hypothes i zed r e s u l t s , as i l l u s t r a t e d i n F igu re 5 (see Chapter 3 , page 43) p r e d i c t e d a s i g n i f i c a n t TC x EC i n t e r a c t i o n would occur over c o n d i t i o n s EC1 and EC2. I t was expected tha t the s u b j e c t s ' RLs to TC2 would be f a s t e r than to TCI i n the CRT c o n d i t i o n EC2, i n comparison to the SRT c o n d i t i o n EC1, account ing f o r the s i g n i f i c a n t TC x RP i n t e r a c t i o n . For a l l CRT c o n d i t i o n s , EC2 - EC8, the d i f f e r e n c e between the two t a s k s was expected to be r e l a t i v e l y constant and no s i g n i f i c a n t i n t e r a c t i o n was p r e d i c t e d . However, the e m p i r i c a l r e s u l t s i l l u s t r a t e d i n F igu re 6a show a n o n - s i g n i f i c a n t TC x C i n t e r a c t i o n o c c u r -r i n g between EC1 and EC2 and a c l e a r l y d e f i n e d s i g n i f i c a n t i n t e r a c t i o n i n the CRT c o n d i t i o n s . The n o n - p a r a l l e l l i n e s between EC2 and EC8 i n d i c a t e tha t the d i f f e r e n c e between the two tasks was not constant over the seven CRT c o n d i t i o n s as was o r i g i n a l l y h y p o t h e s i z e d . Exper imenta l C o n d i t i o n E f f e c t s The c o n d i t i o n s (C) main e f f e c t t e s t e d whether s u b j e c t s responded d i f f e r e n t l y to the e i g h t exper imenta l c o n d i t i o n s when averaged over the two l e v e l s of TC. As expected , the c o n d i t i o n s main e f f e c t was h i g h l y s i g n i f i c a n t (F=25.79, p<.001) . However, an examinat ion of Table 4 shows t h a t the mean RLs (averaged over TCI and TC2) were r e l a t i v e l y constant 53 f o r the CRT c o n d i t i o n s EC2 - EC7. The on ly CRT c o n d i t i o n to show an a p p r e c i a b l e i n c r e a s e i n RL was EC8. From Table 4 i t can be seen t h a t a mean RL of 334 msec, f o r TCI accounted f o r the c o n d i t i o n mean i n c r e a s i n g from EC7 to EC8 (see the d i s c u s s i o n of Hypothes is 3 f o r a d e t a i l e d examin-a t i o n of the above r e s u l t ) . I t would appear t h a t the s i g n i f i c a n t F r a t i o of the c o n d i t i o n s main e f f e c t was p r i m a r i l y due to the i n c l u s i o n o f the SRT c o n d i t i o n (EC1) i n the data a n a l y s i s . Order E f f e c t s The order main e f f e c t t e s t e d whether the order i n which s u b j e c t s performed the e i g h t ECs had a s i g n i f i c a n t e f f e c t on the mean RLs f o r any one EC. By u t i l i z i n g a L a t i n Square i n the Exper imenta l Design (see Table 1 , Appendix A ) , the order of ECs was not expected to produce a s i g -n i f i c a n t F r a t i o . In agreement w i th the hypothes i zed r e s u l t s , the o rder main e f f e c t was n o n - s i g n i f i c a n t . The r e s u l t i n g low F va lue of 1.09 would seem to i n d i c a t e tha t the order of c o n d i t i o n s main e f f e c t was not a confounding v a r i a b l e i n s u b j e c t s ' response s t r a t e g y . However, i t can be seen from Table 6 , tha t a l a r g e v a r i a b i l i t y between s u b j e c t s , s t a t i s t i c a l l y represented by a mean square e r r o r o f 25,352 was r e s p o n s i b l e f o r the non-s i g n i f i c a n t order main e f f e c t . The d i f f e r e n c e i n orders was due l a r g e l y to t h i s v a r i a b i l i t y between s u b j e c t s . A l though the order main e f f e c t was not s i g n i f i c a n t , the order by c o n d i t i o n s i n t e r a c t i o n was s i g n i f i c a n t , w i th a cor responding F va lue of 2 . 6 8 , p<001. S p e c i f i c a l l y , the 0 x C i n t e r a c t i o n examined whether the d i f f e r e n c e which e x i s t e d between con -d i t i o n s was r e l a t e d to the order i n which s u b j e c t s performed the c o n d i t i o n s . In order to i n t e r p r e t the s i g n i f i c a n t i n t e r a c t i o n , TCI and TC2 were 54 graphed s e p a r a t e l y w i t h response p r o b a b i l i t y as the a b s c i s s a and RL as the o r d i n a t e . To i l l u s t r a t e the manner i n which TCI and TC2 were graphed, F igure 2 (a and b) , which shows the i n t e r a c t i o n of th ree orders on ly (05, 0 6 , and 0 7 ) , has been i n c l u d e d i n Appendix B. Note tha t f o r TCI , i n f l a t e d RL scores (high p o i n t s on the graph) occur red under 06 at the p .50 and p.25 l e v e l s , and under 07 at the p .50 and p.10 l e v e l s . Each of the cor responding ECs f o r the above p r o b a b i l i t y l e v e l s (EC5 and EC7 f o r 0 6 , and EC5 and EC8 f o r 07) occur red on Day 1 o f the t e s t i n g s e s s i o n s (see Table 1, Appendix A ) . S i m i l a r l y , f o r TC2, the h i g h p o i n t s under 07 at p .90 and p .50 and p.50 f o r 06 were a l l performed on Day 1. A f t e r examining a l l e igh t orders i n t h i s manner, i t was found that the c o n d i t i o n s performed on Day 1 l a r g e l y accounted f o r the 0 x C i n t e r a c t i o n be ing s i g n i f i c a n t . However, not a l l s u b j e c t s were e q u a l l y a f f e c t e d , and i n f a c t on ly th ree of the e igh t orders (02, 06 , and 07) showed any marked i n c r e a s e i n RL on Day 1. The s u b j e c t s w i t h i n the remain ing f i v e orders showed r e l a t i v e l y l i t t l e i n c r e a s e i n RL due to a Days e f f e c t . For example, as i l l u s t r a t e d i n F igu re 2b, Appendix B, 05 performed EC1 and EC4 on Day 1. Only at p .40 f o r TC2 (EC4) was any i n c r e a s e i n RL noted which cou ld be a t t r i b u t a b l e to a Days e f f e c t . I t i s o f i n t e r e s t to note t h a t i n the three orders most a f f e c t e d by Day 1 (RLs g rea te r than 350 m s e c ) , the m a j o r i t y of s u b j e c t s w i t h i n these orders had the s lowest RLs f o r both TCI and TC2 when averaged over the e i g h t ECs. I t would appear that s lower r e a c t i n g s u b j e c t s were more, a f f e c t e d by the Days f a c t o r than those s u b j e c t s w i t h r e l a t i v e l y f a s t e r RLs . The remain ing i n t e r a c t i o n s , order by task complex i t y (0 x TC) and order by c o n d i t i o n s by task complex i t y (0 x C x TC) were n o n - s i g n i f i c a n t . 55 The d i f f e r e n c e between TCI and TC2 Was expected to be constant over the e i g h t o r d e r s . This assumption was supported by the n o n - s i g n i f i c a n t 0 x TC i n t e r a c t i o n as g iven i n Table 6. The 0 x C x TC i n t e r a c t i o n examined whether the 0 x C i n t e r a c t i o n was the same f o r both TCI and TC2. From the graphs used i n the i n t e r p r e t a t i o n of the 0 x C i n t e r a c t i o n , i t appeared t h a t f o r p r o b a b i l i t y l e v e l . 1 0 , those s u b j e c t s who performed TCI at the .10 l e v e l on Day 1 had a s lower RL than those s u b j e c t s who performed TC2 at the .10 l e v e l on Day 1. However, t h i s t rend d i d not account f o r a s i g n i f i c a n t 0 x C x TC i n t e r a c t i o n . RESULTS AND DISCUSSION OF PREPLANNED COMPARISONS FOR HYPOTHESES 1 TO 4 In order to t e s t the s p e c i f i c hypotheses , the s i n g l e degree o f freedom preplanned c o n t r a s t s , o u t l i n e d i n Table 3 , Chapter 3 , were u s e d . The r e s u l t s are g iven i n Table 7. Table 8 p rov ides the mean RLs and t h e i r d i f f e r e n c e s account ing f o r the F r a t i o s as shown i n Table 7. 56 Table 7 Hypotheses 1 to 4: Hypothes ized R e s u l t s and C a l c u l a t e d F R a t i o s o f the Preplanned Cont ras ts Hypothes ized R e s u l t s Hypothes is S i g n i f i c a n c e (S) N o n - S i g n i f i c a n c e or (NS) C a l c u l a t e d F r a t i o P r o b a b i l i t y F exceeded 1 S 2.37 0.162 2 1 S 1.80 0.185 3 S e r i e s A (RP Main) Cont ras t CC) C l S 2.66 0.108 C2 S 5 .92* 0.018 C3 S 12.17** <0.001 S e r i e s B (TC x RP) -C l NS 5 .11* 0.027 C2 NS 24.85** <0.001 C3 NS 4 .05* 0.048 4 S e r i e s A (RP Main) C l NS 12.68** <0.001 C2 NS 5 .13* 0.027 C3 NS 2.55 0.115 S e r i e s B (TC x RP) C l NS 14.72** <0.001 C2 NS 2.76 0.102 C3 NS 1.01 0.319 **p<.001 *p<.05 57 Table 8 Response P r o b a b i l i t y Means and The i r D i f f e r e n c e s U t i l i z e d i n the Preplanned Cont ras ts of Hypotheses 1 to 4 Hypotheses Means D i f f e r e n c e s 3 r , Xp.50 C2 Xp.40 r ^ Xp.25 ^ Xp.10 4 r , Xp.90 X P ( .7< C2 r ^ Xp.60 Xp.50 TC2 TCI TC2 - TCI 232 221 11 (TC2_ - TCI) EC1 EC5 EC1 - EC5 11 3 S e r i e s 8 A c o n t r a s t s * S e r i e s B c o n t r a s t s r D i f f e r e n c e of Cont ras t D i f f e r e n c e TCI TC2 X Means of TCI - TC2 296 299 298 Q - 3 . 2 5 , .10) 311 302 307 - y 9* 294 300 297 - 1 5 * - 6 .10) 319 304 312 15** 304 334 295 313 300 324 - 2 4 * * 9 21* 254 281 268 - 2 0 * * - 2 7 . 6 0 , .50) 283 292 288 - 9 * * 272 285 279 - 1 3 * - 1 3 .50) 289 295 292 - 6 282 296 291 299 287 297 - 1 0 - 9 - 3 **p<.001 *p<.05 58 Hypothesis 1 A preplanned c o n t r a s t was used to determine i f , i n the SRT c o n d i t i o n (EC1), the mean RL of TC2 (232 msec.) was s i g n i f i c a n t l y g r e a t e r than the mean RL of TCI (221 m s e c ) . The s t a t i s t i c a l t e s t y i e l d e d a non -s i g n i f i c a n t F r a t i o (F=2.37, p=0.162) , consequent l y , the premise t h a t complex task TC2 would have a longer RL than TCI i n the SRT c o n d i t i o n was not suppor ted . The n o n - s i g n i f i c a n t r e s u l t s of Hypothesis 1 were t o t a l l y unexpected. In p rev ious experiments u t i l i z i n g s i m i l a r t a s k s , both Ryan (1972) and Schutz (1972) found the complex task y i e l d e d a s i g n i f i c a n t l y s lower RL than the s imple task i n the SRT c o n d i t i o n . As presented i n Table 1 , page 32, Schutz found tha t h i s complex task was 18 m i l l i s e c o n d s s lower than h i s s imple t a s k , w h i l e Ryan recorded a 32 m i l l i s e c o n d d i f f e r e n c e . Al though i n t h i s p resent study TC2 had a mean RL 11 m i l l i s e c o n d s s lower than TCI , the d i f f e r e n c e between the two t a s k s was not s u f f i c i e n t l y l a r g e enough to produce a s i g n i f i c a n t F r a t i o . When i n d i v i d u a l sub jec t data f o r EC1 were examined, i t was found tha t Subject 11 was the on ly sub jec t to r e c o r d a negat i ve d i f f e r e n c e between the two t a s k s , i . e . , the RL f o r TC2 was 40 m i l l i s e c o n d s f a s t e r than the RL f o r TCI (see Table 1 , Appendix B ) . Because o f the extreme e f f e c t such a d i s c r e p a n t score would have on the e r r o r v a r i a n c e , as w e l l as on the mean, a t t e s t was admin is te red to determine i f a s i g n i f i c a n t d i f f e r e n c e occur red between TCI and TC2 i n EC1 when Subject 1 1 ' s scores were exc luded . The r e s u l t s of the t t e s t are g iven i n Table 9 . 59 Table 9 Comparison Values f o r the Test of Hypothesis 1, I n c l u d i n g and E x c l u d i n g Subject IT 's R e s u l t s i n the SRT C o n d i t i o n TCI TC2 D i f f . F/t v a l u e Subject 11 i n c l u d e d 221 232 11 F = 2.29 Subject 11 excluded 216 230 14 t = 4.68* *p<.001 The r e s u l t i n g t va lue of 4 .68 was s i g n i f i c a n t at the .001 l e v e l , i n d i c a t i n g t h a t TC2 had a s i g n i f i c a n t l y s lower RL than TCI i n the SRT c o n d i t i o n as was o r i g i n a l l y h y p o t h e s i z e d . I t i s d i f f i c u l t to s p e c u l a t e why Subject 11 responded w i t h such incongruous r e s u l t s when compared to the o ther 15 s u b j e c t s . I t i s i n t e r e s t i n g to n o t e , t h a t i n a recent study u s i n g the i d e n t i c a l tasks TCI and TC2, R o l l o (1977) found tha t of the 40 s u b j e c t s t e s t e d i n the SRT c o n d i t i o n , e i g h t recorded a f a s t e r RL f o r the complex t a s k . Of the remain ing 15 s u b j e c t s , four recorded a minimal d i f f e r e n c e between TCI and TC2 of four m i l l i s e c o n d s or l e s s . I t would appear tha t i n the SRT c o n d i t i o n these four s u b j e c t s e i t h e r d i d not p e r c e i v e the two tasks as b e i n g of d i f f e r e n t c o m p l e x i t y , or tha t because of the s i m p l i c i t y of TCI and the number of consecut i ve r e p e t i t i o n s , i . e . , 60 t r i a l s , 30 second r e s t , 40 t r i a l s , s u b j e c t s , p o s s i b l y due to lack of a t t e n t i o n , d i d not respond w i t h maximum r a p i d i t y to the m a j o r i t y o f the t r i a l s . To determine i f a d e t e r i o r a t i o n i n performance occur red over the 100 t r i a l s , s u b j e c t s ' 60 i n d i v i d u a l data was examined and means were c a l c u l a t e d f o r each b l o c k o f 20 t r i a l s . Performance over the f i v e b l o c k s o f 20 t r i a l s e x h i b i t e d no i n c r e a s e i n RL and i n f a c t , s u b j e c t s ' scores remained r e l a t i v e l y constant throughout the 100 t r i a l s . In accordance w i t h the t h e o r i e s of CRT proposed by Falmagne (1965) and Schutz (1972) , these s u b j e c t s were unprepared f o r the p r e s e n t a t i o n of the s t i m u l u s l i g h t and t h e r e f o r e , RLs f o r these t r i a l s were i n f l a t e d . However, i t i s i n t e r e s t i n g to note t h a t of these f o u r s u b j e c t s i n d i s c u s s i o n , th ree recorded RLs f o r TCI and TC2 i n EC1 t h a t were f a s t e r than 12 other s u b j e c t s . In a d d i t i o n , these same th ree s u b j e c t s recorded mean RLs f o r each t a s k , when averaged over the e i g h t ECs, t h a t i ranked among the f o u r f a s t e s t recorded s c o r e s . This may i n d i c a t e tha t f o r these p a r t i c u l a r s u b j e c t s , responding w i t h the s imple task a repeated number of t imes i n the SRT c o n d i t i o n , was not o f s u f f i c i e n t complex i t y to warrant a t t e n d i n g to the o v e r a l l t a s k , t h e r e f o r e r e s u l t i n g i n longer RLs f o r the s imple t a s k . Th is e x p l a n a t i o n cou ld a l s o account f o r Subject 1 1 ' s SRT r e s u l t s . I f the 100 t r i a l s o f TCI i n the SRT c o n d i t i o n d i d not s u f f i c i e n t l y cha l lenge Subject 11 to the p o i n t where he would m e n t a l l y prepare f o r the s imple task p r i o r to s t i m u l u s o n s e t , then h i s RLs to TCI would c e r t a i n l y be s lower than i f he was prepared f o r each t r i a l . U n f o r t u n a t e l y these h y p o t h e t i c a l e x p l a n a t i o n s to account f o r i n d i v i d u a l s u b j e c t s and u l t i m a t e l y Hypothes is l ' s n o n - s i g n i f i c a n t r e s u l t s , cannot be v e r i f i e d from the data obta ined i n t h i s p resent s tudy . In a rev iew of s p e c i f i c l i t e r a t u r e d e a l i n g w i t h task complex i t y i n the SRT c o n d i t i o n ( G l e n c r o s s , 1973; Henry and Rogers , 1960) a n o n - s i g n i f i c a n t d i f f e r e n c e between two t a s k s has been s o l e l y a t t r i b u t a b l e to a lack o f d i f f e r e n t i a t i o n i n complex i t y between the two t a s k s , i . e . , one task was 61 not s i g n i f i c a n t l y more complex than the o t h e r . Consequent ly , the non-s i g n i f i c a n t r e s u l t s obta ined i n Hypothes is 1 may suggest t h a t the remain ing preplanned comparisons f o r Hypotheses 2 , 3 , and 4 are not v a l i d . I t i s p o s s i b l e , however, that those s u b j e c t s who recorded a d i f f e r e n c e of l e s s than f i v e m i l l i s e c o n d s between the two tasks i n the SRT c o n d i t i o n , may have p e r c e i v e d the tasks as d i f f e r e n t and responded a c c o r d i n g l y i n the CRT c o n d i t i o n . For the purpose of the remain ing th ree hypotheses , i t w i l l be assumed that s u b j e c t s d i d p e r c e i v e TC2 as a more complex task r e l a t i v e t o TCI . Hypothes is 2 The s t a t i s t i c a l t e s t a p p l i e d to Hypothesis 2 y i e l d e d a non-s i g n i f i c a n t F r a t i o (F=1.80, p=0.185) . S p e c i f i c a l l y , Hypothesis 2 proposed tha t the d i f f e r e n c e between TC2 - TCI i n EC5 would be l e s s than i n EC1. The r e s u l t i n g d i f f e r e n c e s of 3 msec, f o r EC5 and 11 msec, f o r EC1 were not l a r g e enough to produce a s i g n i f i c a n t F. r a t i o , and t h e r e f o r e , Hypothes is 2 was not suppor ted . I t was proposed t h a t i n a CRT c o n d i t i o n of equal p r o b a b i l i t i e s , s u b j e c t s , adopt ing a de fens i ve s t r a t e g y , would prepare f o r the complex task more o f t e n than the s imple t a s k , independent of the p r e s e t p rob -a b i l i t y l e v e l s . As TC2 would then be i n a s t a t e of RR w i t h i n c r e a s e d f requency , the search t ime r e q u i r e d would be reduced , o f f s e t t i n g the longer r e l e a s e t ime f o r the complex task (Schutz , 1972) . I t was t h e r e f o r e expected that the d i f f e r e n c e between TC2 - TCI i n EC5 would be l e s s than i n the SRT c o n d i t i o n (EC1). 62 Table 10 below presents the mean RLs and t h e i r d i f f e r e n c e s f o r ECl and EC5: Table 10 Mean RLs and D i f f e r e n c e s f o r ECl and EC5 U t i l i z e d i n the S t a t i s t i c a l Test of Hypothesis 2 Task ECl (SRT C o n d i t i o n ECS (CRT, p.50) D i f f e r e n c e (ECl - EC5) TCI 221 296 75 TC2 232 299 67 D i f f e r e n c e 11 3 8 Al though the d i f f e r e n c e between TC2 and TCI i n ECl was l a r g e r than the d i f f e r e n c e i n EC5, the r e s u l t i n g 8 msec, d i f f e r e n c e between the two c o n d i t i o n s was not great enough to produce the r e q u i r e d F r a t i o o f 4 .00 f o r s i g n i f i c a n c e at the p .05 l e v e l . A g a i n , as i n Hypothes is 1 , a r e p l i c a t i o n of the r e s u l t s obta ined by Ryan (1972) and Schutz (1972) was expected due to the s i m i l a r i t i e s i n the tasks i n v o l v e d i n a l l th ree exper iments . Both researchers recorded a s i g n i f i c a n t l y l a r g e r d i f f e r e n c e i n the SRT c o n d i t i o n p r o v i d i n g support f o r S c h u t z ' s proposed theory r e g a r d i n g the reduced search t ime o f f s e t t i n g the longer r e l e a s e t ime f o r the complex task i n the CRT c o n d i t i o n of equal p r o b a b i l i t y . A subsequent c a l c u l a t i o n to t e s t i f the two d i f f e r e n c e s were i n f a c t s i g n i f i c a n t l y d i f f e r e n t from each other was performed a f t e r Subject 11 's 63 data were exc luded . A l though the F r a t i o o f 2 .13 approached the r e q u i r e d l e v e l of 4 . 0 0 , i t was s t i l l i n s u f f i c i e n t to support Hypothes is 2 and S c h u t z ' s proposed t h e o r y . j I t was f u r t h e r proposed tha t f o r the s p e c i f i c tasks TCI and TC2, the mean RL f o r TC2 would be l e s s than f o r TCI i n the CRT c o n d i t i o n o f equal RP. A d i f f e r e n c e of approx imate ly 20 m i l l i s e c o n d s between the two t a s k s was a n t i c i p a t e d i n the SRT c o n d i t i o n . In EC5, as a r e s u l t of TC2 b e i n g prepared f o r more o f t e n than TCI due to the complex i t y f a c t o r , the longer r e l e a s e t ime r e q u i r e d to respond w i t h TC2 would i n f a c t be reduced to the p o i n t where the RL f o r TC2 would be l e s s than f o r TCI. Both Ryan and Schutz r e p o r t e d f a s t e r RLs f o r the complex task i n the equal p r o b - . a b i l i t y CRT c o n d i t i o n (see Table 1 ) , a l though S c h u t z ' s d i f f e r e n c e of - 2 m i l l i s e c o n d s was not s i g n i f i c a n t . S i m i l a r l y , S idowski (1958) r e p o r t e d a s i g n i f i c a n t l y f a s t e r RL f o r the complex task ( three s w i t c h response) as compared to the s imple task ( f i n g e r w i t h d r a w a l ) . As d i s c u s s e d i n Chapter 2 , S idowski proposed tha t h i s s u b j e c t s , p r e p a r i n g f o r the complex task more o f t e n because of the d i f f i c u l t y of the t a s k , had to i n h i b i t t h e i r response to t h i s task and then i n i t i a t e a response to the s imple task r e s u l t i n g i n a s lower RL f o r the s imple t a s k . In t h i s p resent experiment a n e g a t i v e d i f f e r e n c e , i . e . , a f a s t e r RL f o r TC2 was not a c h i e v e d . These r e s u l t s suggest tha t the u n d e r l y i n g theory of s u b j e c t s adopt ing a de fens i ve s t r a t e g y by p r e p a r i n g f o r the more complex task i n the equal p r o b a b i l i t y c o n d i t i o n was not suppor ted . However, the reduced d i f f e r e n c e from 11 m i l l i s e c o n d s i n EC1 to t h r e e m i l l i s e c o n d s i n EC5 i n d i c a t e s tha t s u b j e c t s may have compensated f o r the g r e a t e r 64 complex i t y of TC2 r e l a t i v e to TCI , but tha t the e f f e c t s o f a d e f e n s i v e response s t r a t e g y were not o f the magnitude expected . Hypothes is 5 S i x Helmert c o n t r a s t s were used to determine i f RL was d i r e c t l y r e l a t e d f o r p r o b a b i l i t y l e v e l s l e s s than . 5 0 . S e r i e s A (Cont ras ts 1 , 2 , and 3) t e s t e d whether RL, when averaged over the two l e v e l s of task c o m p l e x i t y , decreased m o n o t o n i c a l l y from p.50 to p . 1 0 . The RP main e f f e c t , S e r i e s A, was not s i g n i f i c a n t f o r Cont ras t 1 , w h i l e Cont ras ts 2 and 3 were s i g n i f i c a n t (F=5.92, p< .05; F=12.17, p<.001 r e s p e c t i v e l y ) . However, a l though both Cont rast 2 and Cont rast 3 were s i g n i f i c a n t , i t was hypothes i zed that the d i f f e r e n c e s between the means at the c r i t i c a l p r o b a b i l i t y l e v e l s f o r each c o n t r a s t would be p o s i t i v e , i . e . , a decrease i n RP would r e s u l t i n a decrease i n RL. From Table 7 i t can be seen tha t Cont ras t 2 , which compared the mean RL at p .40 to the average of the mean RLs at p .25 and p . 1 0 , and Cont ras t 3 , which compared the mean RLs at the c r i t i c a l p r o b -a b i l i t y l e v e l s .25 and .10 both r e s u l t e d i n negat i ve d i f f e r e n c e s , i . e . , a decrease i n RP r e s u l t e d i n an i n c r e a s e i n RP. The s p e c i f i c va lues of - 1 5 f o r Cont ras t 2 and - 2 4 f o r Cont rast 3 (see Table 8) were s u f f i c i e n t l y l a r g e to g ive s i g n i f i c a n c e , however, these va lues were not i n the d i r e c t i o n p r e d i c t e d . The r e s u l t s of S e r i e s A, c o n t r a r y to Hypothes is 3 , i l l u s t r a t e the c l a s s i c a l p r o b a b i l i t y e f f e c t (as documented by S m i t h , 1968) , i . e . , a decrease i n RP r e s u l t s i n an i n c r e a s e i n RL. S tud ies examining the e f f e c t s of p r o b a b i l i t y upon RL have most o f t e n employed t a s k s o f equal complex i t y and g e n e r a l l y supported the above r e l a t i o n s h i p . However, Ryan (1972) , 65 u s i n g tasks o f unequal c o m p l e x i t y , found t h a t i n both o f h i s ECs of unequal RP, the mean RL to the l e s s probable task was s i g n i f i c a n t l y f a s t e r than the more probable t a s k , r e g a r d l e s s of the l e v e l o f TC (see Chapter 2 , page 33) . Consequent ly , Hypothes is 3 was proposed to t e s t i f i n f a c t , t a s k s of unequal complex i t y had an oppos i te e f f e c t on s u b j e c t s ' response s t r a t e g y i n c o n d i t i o n s of unequal p r o b a b i l i t y . From the r e s u l t s obta ined i n S e r i e s A, i t would appear tha t Hypothesis 3 i s c l e a r l y r e f u t e d . In order f o r S e r i e s A to support Hypothes is 3 , the d i f f e r e n c e of c o n t r a s t means (Table 8) must be s i g n i f i c a n t and a l s o p o s i t i v e i n numeric v a l u e . The negat i ve d i f f e r e n c e s obta ined i n each o f the th ree c o n t r a s t s i n d i c a t e s that the mean RL f o r the more probable task had a f a s t e r RL than the task w i t h the lower RP, c o n t r a r y to the p r e d i c t e d r e s u l t s . The TC x RP i n t e r a c t i o n , S e r i e s B (Cont rasts 1 , 2 , and 3 ) , t e s t e d whether the change i n RL over the f o u r l e v e l s of RP (p .50 to p.10) was the same under each l e v e l o f TC. A n o n - s i g n i f i c a n t i n t e r a c t i o n was p r e d i c t e d , however, a l l th ree compar isons, when t e s t e d , were s i g n i f i c a n t , not sup-p o r t i n g Hypothes is 3 . A l though the s i g n i f i c a n t F r a t i o s obta ined i n S e r i e s B showed t h a t the e f f e c t o f RP on TC was indeed d i f f e r e n t under each p r o b a b i l i t y l e v e l ( .50 to . 1 0 ) , c l o s e r examinat ion of the mean RLs f o r both tasks r e v e a l e d tha t t h i s was not p r e c i s e l y c o r r e c t . From Table 5 i t can be seen that f o r p r o b a b i l i t y l e v e l s . 5 0 , . 4 0 , and . 2 5 , very l i t t l e change occur red i n the mean RLs f o r e i t h e r t a s k . S p e c i f i c a l l y , a d i f f e r e n c e of on ly 10 m i l l i s e c o n d s f o r TCI and f i v e m i l l i s e c o n d s f o r TC2 i n d i c a t e s t h a t p r o b a b i l i t y does not appear to a f f e c t one task more than the other under these three p r o b a b i l i t y l e v e l s . However, under the p.10 66 l e v e l , s u b j e c t s responded very s l o w l y f o r TCI (334 m s e c . ) - I t was hypo- -t h e s i z e d t h a t a low p r o b a b i l i t y l e v e l (below .50) would cause the s u b j e c t to prepare f o r the l e s s probable t a s k . From these r e s u l t s i t can be seen t h a t s u b j e c t s d i d not adopt a d e f e n s i v e s t r a t e g y i n t h e i r responses to TCI at the p .10 l e v e l , and t h e r e f o r e a s lower RL was r e c o r d e d . S u b j e c t s ' responses to TC2 at the p .10 l e v e l were s l i g h t l y s lower (313 msec.) than at the p rev ious p r o b a b i l i t y l e v e l s below . 5 0 , but not as pronounced as f o r TCI . I t would appear tha t the combinat ion of low p r o b a b i l i t y and i n c r e a s e d TC d i d a f f e c t the s u b j e c t s ' response s t r a t e g y as p r e d i c t e d , w i t h s u b j e c t s more o f t e n prepared f o r TC2 under the p.25 and p .10 c o n d i t i o n s r e l a t i v e to TCI (see F igure 6b). The i n f l a t e d RLs under the p .10 l e v e l were l a r g e l y r e s p o n s i b l e f o r the n o n - s u p p o r t i v e r e s u l t s produced by the preplanned c o n t r a s t s o f S e r i e s A and S e r i e s B. These r e s u l t s i n d i c a t e d t h a t s u b j e c t s were f r e -quent l y unprepared to respond to events i n v o l v i n g a very low p r o b a b i l i t y of occurrence (p<_. 10) . Ryan's r e s u l t s and c o n c l u s i o n s were drawn from a p r o b a b i l i t y l e v e l of .25 f o r the l e a s t p robable t a s k . I t i s suggested tha t a c r i t i c a l p r o b -a b i l i t y l e v e l may e x i s t (approx imate ly .25) below which s u b j e c t s are no longer w i l l i n g to exchange a f a s t RL to the probable task f o r response read iness to the l e s s probable t a s k . I f we accept the premise tha t s u b j e c t s d i d i n f a c t t r e a t TC2 as a more d i f f i c u l t task than TCI i n the CRT c o n d i t i o n s , then based on the r e s u l t s o f the s i x Helmert c o n t r a s t s , l i t t l e support can be g iven to Ryan's f i n d i n g s and a r e j e c t i o n o f Hypothes is 3 i s i n o r d e r . 67 Hypothesis 4 A s i m i l a r s e r i e s of s i x Helmert c o n t r a s t s was designed to t e s t Hypothes is 4 , which p r e d i c t e d t h a t above a p .50 l e v e l , RL was independent o f RP f o r tasks of unequal complex i t y . S e r i e s A t e s t e d whether a s i g n i f i c a n t RP main e f f e c t e x i s t e d between p.50 to p .90 when averaged over the two l e v e l s o f task complex i t y . From Table 7, i t can be seen tha t w i t h i n S e r i e s A , Cont ras t 1 , which compared the mean RL at p .90 to the average of the means f o r p r o b a b i l i t y l e v e l s . 7 5 , . 6 0 , and . 5 0 , was s i g n i f i c a n t (F=12.68, p< .001) , and t h e r e f o r e not s u p p o r t i v e of the hypothes i zed r e s u l t s . S i m i l a r l y , Cont ras t 2 , which compared the mean RL at p.75 to the average of the means f o r p .60 and p.50 was a l s o s i g n i f i c a n t (F=5.13, p< .05) . Only Cont ras t 3 , which t e s t e d the d i f f e r e n c e between the mean RLs at p.60 and p.50 was n o n - s i g n i f i c a n t as p r e d i c t e d (F=2.55, p=0.115) . I t was proposed tha t f o r t a s k s of unequal c o m p l e x i t y , the percentage o f t ime a p a r t i c u l a r response programme cou ld be prepared f o r may reach a maximum at the p .50 l e v e l . Consequent ly , f o r a t w o - c h o i c e RT t a s k , an i n c r e a s e i n RP above p.50 f o r one task would not r e s u l t i n a s i g n i f i c a n t decrease i n RL f o r tha t p a r t i c u l a r t a s k . Schutz (1972) i n comparing the RLs f o r TC2 between EC3 (p.50) and EC4 (p.67) expected the i n c r e a s e d p r o b a b i l i t y l e v e l would have a s i g n i f i c a n t l y f a s t e r RL than at- the p .50 l e v e l . Th is was not the case as the mean RL f o r TC2 at p.50 was 243 msec, w h i l e at p .67 the mean RL e q u a l l e d 246 msec. Because o f t h i s n e g l i g i b l e d i f f e r e n c e , Schutz specu la ted t h a t the response programme f o r TC2 would a l r e a d y be i n S e l e c t i v e A t t e n t i o n (RR) due to the TC f a c t o r . A f u r t h e r i n c r e a s e i n RP d i d not cause an i n c r e a s e i n the number of t imes the 68 programme was prepared f o r . A comparable EC f o r TCI was not i n c l u d e d i n S c h u t z ' s exper iment . Ryan's f i n d i n g s (1972) a l s o supported a min imal d i f f e r e n c e i n RL when comparing the p.50 to the p .75 p r o b a b i l i t y l e v e l s . Data f o r these s p e c i f i c p r o b a b i l i t i e s presented a decrease o f 7 msec, f o r TCI from 330 msec, f o r p .50 to 323 msec, f o r p . 7 5 , w h i l e an i n c r e a s e of 7 msec, f o r TC2 from 315 msec, f o r p .50 to 322 msec, f o r p . 7 5 . From the above r e s u l t s repor ted by Ryan and Schutz , i t was proposed that RL, when averaged over the two l e v e l s of TC, would e x h i b i t a s i m i l a r r e s u l t and produce n o n - s i g n i f i c a n t F r a t i o s f o r a l l th ree c o n t r a s t s i n S e r i e s A, i . e . , the mean RLs at p . 5 0 , p . 6 0 , p . 7 5 , and p.90 would be r e l a t i v e l y constant when averaged over TCI and TC2. However, Cont ras ts 1 and 2 w i t h d i f f e r e n c e s o f c o n t r a s t means o f - 2 0 and - 1 3 r e s p e c t i v e l y (see Table 8 ) , were both s i g n i f i c a n t and t h e r e f o r e d i d not support the proposed r a t i o n a l e . As d i s c u s s e d i n Hypothes is 3 , the extreme p r o b a b i l i t y l e v e l s , i . e . , p .10 i n Hypothes is 3 and p.90 i n Hypothes is 4 , g r e a t l y e f f e c t e d s u b j e c t s ' response s t r a t e g i e s and consequent ly RLs when compared to the remain ing p r o b a b i l i t y l e v e l s w i t h i n each preplanned c o n t r a s t . For example, Cont ras t 1, S e r i e s A (see Table 8 ) , i n c l u d e d p.90 and was h i g h l y s i g n i -f i c a n t at the p .001 l e v e l due main ly to the RL o f 254 msec, f o r TCI , w h i l e Contrast - 2 , which d i d not i n c l u d e the mean RL at p . 9 0 , had a reduced F r a t i o s i g n i f i c a n t at the p.05 l e v e l o n l y . The extreme p r o b a b i l i t y l e v e l .90 a l s o e f f e c t e d the r e s u l t s of S e r i e s B, the TC x RP i n t e r a c t i o n . The th ree c o n t r a s t s w i t h i n S e r i e s B examined whether the e f f e c t o f RP on RL a f f e c t e d the two t a s k s d i f f e r e n t l y , above the p .50 l e v e l , and was hypothes i zed to be n o n - s i g n i f i c a n t . However, 69 Cont rast 1 which i n c l u d e d p.90 was s i g n i f i c a n t w i th an F r a t i o of 1 4 . 7 2 , p<.001 c o n t r a r y to Hypothes is 4 . Cont ras ts 2 and 3 which d i d not i n c l u d e the mean RL at p.90 were both n o n - s i g n i f i c a n t , i n d i c a t i n g tha t between p r o b a b i l i t y l e v e l s . 7 5 , . 6 0 , and . 5 0 , there was no s i g n i f i c a n t d i f f e r e n c e i n the e f f e c t of RP on TCI as compared to TC2. I t would appear that TCI was f a r more a f f e c t e d by the h igh RP l e v e l of p.90 than was TC2. A l though an i n c r e a s e i n RP was not expected to a f f e c t e i t h e r task above the p .50 l e v e l i t can be seen from Table 5 tha t the h i g h e s t p r o b a b i l i t y l e v e l r e s u l t e d i n a s u b s t a n t i a l l y f a s t e r RL f o r TCI (254 msec.) as compared to TC2 (281 m s e c ) . Schutz (1972) found tha t i n a t w o - c h o i c e RT experiment u s i n g tasks of unequal c o m p l e x i t y , the e f f e c t of RP was a d e c r e a s i n g f u n c t i o n of TC, b e i n g minimal f o r the very complex t a s k . A c c o r d i n g l y , an i n c r e a s e i n TC decreased the e f f e c t RP had on the RL to that t a s k . In terms o f response r e a d i n e s s , S c h u t z ' s hypothes i s would suggest t h a t as TC i n c r e a s e s , the amount of t imes a sub jec t would prepare f o r the complex task would a l s o i n c r e a s e r e g a r d l e s s of the RP l e v e l . The l e s s complex task would be more s u s c e p t i b l e to the e f f e c t s of RP and the number of t imes t h i s task would be prepared f o r would be determined by the p r e s e t p r o b a b i l i t y l e v e l f o r both t a s k s . From these present r e s u l t s , S c h u t z ' s s u p p o s i t i o n was indeed suppor ted . For both Hypothes is 3 and Hypothes is 4 , the s imple task (TCI) was no tab l y more a f f e c t e d by RP at the extreme p r o b a b i l i t y l e v e l s of .10 and .90 than was the complex task (TC2). The r e s u l t s obta ined from the preplanned c o n t r a s t s f o r S e r i e s A and B n e c e s s i t a t e r e j e c t i n g the t h e o r e t i c a l r a t i o n a l e f o r Hypothes is 4. RL was expected to be independent of RP above a p .50 l e v e l and non -s i g n i f i c a n t F r a t i o s were expected f o r S e r i e s A, Cont ras ts 1 , 2 , and 3 . 70 However, both Cont ras ts 1 and 2 were s i g n i f i c a n t i n d i c a t i n g tha t an i n c r e a s e i n RP r e s u l t e d i n a decrease i n RL. Only at the p.60 l e v e l (Contrast 3) d i d s u b j e c t s respond as h y p o t h e s i z e d . Summary of Hypotheses The r e s u l t s from the above four hypotheses are at bes t c o n f u s i n g . The s i m i l a r i t i e s i n exper imenta l t a s k s used by Ryan (1972) , Schutz (1972) and t h i s p resent exper iment , presupposed a r e p l i c a t i o n o f r e s u l t s f o r the SRT . c o n d i t i o n (Hypothesis 1) and the CRT p.50 c o n d i t i o n (Hypothesis 2 ) . However, n e i t h e r Hypothesis 1 nor 2 was s t a t i s t i c a l l y v e r i f i e d . As s t a t e d p r e v i o u s l y , the extraneous r e s u l t s of Subject 11 i n the SRT c o n d i t i o n accounted f o r the n o n - s i g n i f i c a n t F r a t i o of Hypothes is 1. Hypothes is 2 examined the premise of a de fens i ve s t r a t e g y i n which i n a two -cho ice r e a c t i o n t ime s i t u a t i o n , s u b j e c t s would prepare f o r the complex task w i t h g r e a t e r f requency than the s imple t a s k . For the s p e c i f i c t a s k s TCI and TC2, TC2 was expected to have a f a s t e r RL than TCI (at the p .50 l e v e l ) . Cont rary to the r e s u l t s obta ined by Ryan and Schutz , TCI was e s s e n t i a l l y equal to TC2, the th ree m i l l i s e c o n d d i f f e r e n c e b e i n g m i n i m a l . The e x i s t e n c e of a d e f e n s i v e s t r a t e g y was not supported by the r e s u l t s of Hypothes is 2. The assumption of a de fens i ve s t r a t e g y was paramount to both Hypotheses 3 and 4 . Hypothes is 3 proposed t h a t below a p r o b a b i l i t y l e v e l o f .50 RL would decrease as RP decreased (the l e s s probable task would then become the more d i f f i c u l t t a s k ) . In c o n j u n c t i o n , Hypothes is 4 p r e d i c t e d t h a t as RP surpassed the p .50 l e v e l , RL became independent of RP. As the p r o b a b i l i t y f o r one task i n c r e a s e d above the p.50 l e v e l the o ther task had a cor responding decrease i n RP and as Hypothes is 3 p r e d i c t e d 71 would be prepared f o r more o f t e n . N e i t h e r Hypothesis 3 nor Hypothes is 4 v e r i f i e d the e x i s t e n c e of a d e f e n s i v e s t r a t e g y when responding to' t a s k s of unequal c o m p l e x i t y . In f a c t the RP main e f f e c t f o r p r o b a b i l i t y l e v e l s .90 to .10 p rov ided f u r t h e r support f o r the w e l l documented i n v e r s e r e l a t i o n s h i p between RP and RL f o r tasks of equal c o m p l e x i t y . The TC x RP i n t e r a c t i o n i n d i c a t e d tha t the response s t r a t e g i e s s u b j e c t s adopted f o r TCI and TC2 were somewhat d i f f e r e n t . TCI showed a r e l a t i v e l y steady i n c r e a s e i n RL as RP decreased from p.90 to p .10 (see F igure 6 b ) , w i t h an i n f l a t e d RL score o c c u r r i n g at the p.10 l e v e l . TC2, however, tended to be l e s s respons ive to a decrease i n RP, as the t o t a l change i n RL between p r o b a b i l i t y l e v e l s .90 to .10 was on ly 32 msec, as compared to 80 msec, f o r TCI (see Table 5 ) . For p r o b a b i l i t y l e v e l s . 5 0 , . 4 0 , and . 2 5 , the RL f o r TC2 was r e l a t i v e l y c o n s t a n t . The decrease i n RP d i d not have a cor responding i n c r e a s e i n RL as would be expected from the r e s u l t s of the RP main e f f e c t . Al though there was no s i g n i f i c a n t decrease i n RL as was o r i g i n a l l y h y p o t h e s i z e d , s u b j e c t s tended to prepare f o r TC2 at the p .40 and p.25 l e v e l s as o f t e n as they had at the p.50 l e v e l . Consequent ly , there was no i n c r e a s e i n RL as the RP main e f f e c t would i n d i c a t e . The r e s u l t s f o r TC2 at these th ree p r o b a b i l i t y l e v e l s cou ld be viewed as tenuous support f o r the e x i s t e n c e of a d e f e n s i v e s t r a t e g y f o r TC2 o n l y . As i n TCI , TC2 a l s o had an i n f l a t e d RL at the p.10 l e v e l , however, the e f f e c t was not so pronounced as f o r TCI (see Table 5 ) . As p r e v i o u s l y d i s c u s s e d , i t would appear tha t at a very low p r o b a b i l i t y l e v e l p<_. 10 sub jec ts were t o t a l l y unprepared f o r the low p r o b a b i l i t y t a s k , r e s u l t i n g i n the i n f l a t e d RL s c o r e s . E r r o r score data presented i n Tables 4 and 5 and i n F igu re 3 (a and b ) , Appendix B, s u b s t a n t i a t e the d i f f i c u l t y 72 w i t h which s u b j e c t s responded at the p.10 l e v e l . As can be seen f r o m " F igure 3b, Appendix B, a s i g n i f i c a n t i n c r e a s e i n the percentage e r r o r r a t e occur red at the p .10 l e v e l f o r both tasks when compared to a l l o ther p r o b a b i l i t y l e v e l s . I t i s d i f f i c u l t to e x p l a i n why the percentage e r r o r r a t e f o r TC2 was comparat i ve l y l a r g e r than f o r TCI (11.3% to 5.6% r e s p e c t i v e l y ) and yet TC2 had a f a s t e r RL at t h i s p r o b a b i l i t y l e v e l than TCI (313 msec, to 334 msec, r e s p e c t i v e l y ) . Assuming that the e m p i r i c a l r e s u l t s of Hypothes is 1 (exc lud ing Subject l l ' s r e s u l t s ) are v a l i d , i . e . , TC2 had a s i g n i f i c a n t l y s lower RL than TCI , the premise that s u b j e c t s adopted a d e f e n s i v e s t r a t e g y when responding to tasks of unequal complex i t y must be r e f u t e d . The e x i s t e n c e of a d i r e c t r e l a t i o n s h i p between RP and RL f o r p r o b a b i l i t y l e v e l s below .50 was a l s o u n s u b s t a n t i a t e d . Hypotheses 2 , 3 , and 4 , which were fo rmula ted i n response to c o n c l u s i o n s drawn from the s t u d i e s by Ryan (1972) and Schutz (1972) were not suppor ted . At t h i s t i m e , no t h e o r e t i c a l e x p l a n a t i o n s of the j o i n t e f f e c t s of TC and RP on RL as presented by Ryan and Schutz can be o f f e r e d on the b a s i s of t h i s s tudy . Chapter 5 r SUMMARY AND CONCLUSIONS Summary The main purpose o f t h i s i n v e s t i g a t i o n was to study the j o i n t e f f e c t s of response p r o b a b i l i t y (RP) and task complex i t y (TC) on response l a t e n c y (RL) i n s imple and cho ice r e a c t i o n t ime t a s k s . Th is experiment was prompted by the e a r l i e r work of Ryan (1972) and Schutz (1972) and based i n p a r t , on S c h u t z ' s theory of motor memory r e t r i e v a l . E i g h t exper imenta l c o n d i t i o n s , one s imple and seven cho ice r e a c t i o n t ime c o n d i t i o n s were used i n the t e s t i n g of f o u r separate hypotheses . Response l a t e n c i e s f o r 1600 t r i a l s were obta ined from each o f the 16 male s u b j e c t s d u r i n g four o n e - h a l f hour t e s t i n g s e s s i o n s . Each s u b j e c t was t e s t e d i n a l l e i g h t exper imenta l c o n d i t i o n s . The exper imenta l t a s k s i n v o l v e d depress ing a s i n g l e key f o r the s imple task and depress ing a number of keys i n a predetermined order f o r the complex task i n response to one of two s t i m u l u s l i g h t s . Subsequent to an a n a l y s i s of v a r i a n c e , a s e r i e s o f preplanned com-p a r i s o n s was admin is te red to t e s t the s p e c i f i c hypotheses . Conc lus ions The c o n c l u s i o n s fo rmulated from t h i s i n v e s t i g a t i o n are as f o l l o w s : 1. That RL i s i n v e r s e l y r e l a t e d to RP i n a CRT experiment i n v o l v i n g tasks of unequal complex i t y . 73 2. That s u b j e c t s do not adopt a d e f e n s i v e s t r a t e g y when presented w i t h tasks o f unequal c o m p l e x i t y , and t h e r e f o r e the c o n c l u s i o n s of Ryan (1972) and Schutz (1972) are not suppor ted . 3 . That the more complex task i s l e s s a f f e c t e d by RP than the s imple t a s k . S p e c i f i c a l l y , the e f f e c t o f RP on RL i s a d e c r e a s i n g f u n c t i o n of TC. 4. That f o r extremely low p r o b a b i l i t y l e v e l s p<_. 10 s u b j e c t s are unprepared f o r the s t i m u l u s occur rence . Th is r e s u l t i s r e f l e c t e d i n the h igh percentage e r r o r r a t e i n c u r r e d at the low p r o b a b i l i t y l e v e l s , and the r e l a t i v e l y h i g h RLs . SUGGESTIONS FOR FURTHER RESEARCH The r e s u l t s o f Hypothes is 1 n e c e s s i t a t e some p r o c e d u r a l changes be fo re any c o n c l u s i v e support or r e j e c t i o n of the deduct ions made from the f i n d i n g s o f Ryan (1972) and Schutz (1972) can be accepted . I t i s suggested t h a t a p r e t e s t be admin i s te red to a l l p o s s i b l e s u b j e c t s i n which both s imp le and complex tasks are t e s t e d i n the SRT c o n d i t i o n . Only those s u b j e c t s r e c o r d i n g a s i g n i f i c a n t l y f a s t e r RL (approx imate ly 20 msec.) f o r the s imple task be p e r m i t t e d to cont inue w i t h the CRT c o n d i t i o n s . A l s o , an i n c r e a s e i n the number o f p r a c t i s e t r i a l s p r i o r to the exper imenta l t e s t i n g i s recommended. Th is i n v e s t i g a t i o n c o u l d be en larged to i n c l u d e (a) a c o n t r o l group i n which no s p e c i f i c knowledge o f the p r e s e t p r o b -a b i l i t y l e v e l s i s g iven o u t , and (b) CRT tasks i n v o l v i n g more than two c h o i c e s . 75 76 B e r t e l s o n , P. S e r i a l cho ice r e a c t i o n - t i m e as a f u n c t i o n of response versus s i g n a l - a n d - r e s p o n s e r e p e t i t i o n . Nature , 1965, 206, 217 -218. B e r t e l s o n , P . , § B a r z e e l e , J . 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P . , § G e l l e r , E. S . P r e d i c t i o n outcome and cho ice r e a c t i o n t i m e : St imulus versus response a n t i c i p a t i o n . J o u r n a l o f  Exper imenta l Psycho logy , 1972, 9 3 , 193-197. W i l d i n g , J . M. The r e l a t i o n s h i p between l a t e n c y and accuracy i n the i d e n t i f i c a t i o n of v i s u a l s t i m u l i . I. The e f f e c t of task d i f f i c u l t y . A c t a P s y c h o l o g i c a , 1971, 35_, 378 -398. APPENDICES \ 80 r APPENDIX A Procedures 82 I n s t r u c t i o n s This experiment i s designed to t e s t your response t i m e , t h a t i s , how q u i c k l y you can r e a c t to a prearranged s i g n a l w i t h a s p e c i f i c movement. There are a t o t a l of e igh t d i f f e r e n t t e s t c o n d i t i o n s i n t h i s experiment and you w i l l perform two dur ing each of the four t e s t i n g s e s s i o n s . The s p e c i f i c d e t a i l s of the e i g h t c o n d i t i o n s w i l l be g iven j u s t p r i o r to each t e s t i n g s e s s i o n . In f r o n t of you i s a console u n i t w i t h s i x red s t i m u l u s l i g h t s which we w i l l number 1 to 6 from the l e f t hand s i d e . L i g h t s 3 and 4 w i l l be the on ly two l i g h t s used i n t h i s exper iment . D i r e c t l y below l i g h t s 3 and 4 are two whi te keys . P l a c e the index f i n g e r of your r i g h t hand on the whi te key below s t i m u l u s l i g h t 4 , and the index f i n g e r o f your l e f t hand on the whi te key below s t i m u l u s l i g h t 3 . I t i s important to keep both hands l e v e l w i t h your w r i s t s down. There are two d i f f e r e n t movements or tasks to per form d u r i n g t h i s exper iment . One task i s a s s o c i a t e d w i t h s t i m u l u s l i g h t 3 and the other task w i t h s t i m u l u s l i g h t 4 . Once you have learned the two t a s k s , the t e s t i n g s e s s i o n s w i l l b e g i n . The b a s i c i d e a i s to respond as q u i c k l y as p o s s i b l e to whichever s t i m u l u s l i g h t i l l u m i n a t e s . I w i l l now o u t l i n e the two t a s k s f o r you. TCI: Requires that you depress the index f i n g e r o f your r i g h t / l e f t hand and then move upward to depress the middle l a r g e b l a c k response key at the top of the c o n s o l e . The th ree b l a c k response keys are a l s o numbered from l e f t to r i g h t , the middle key cor responding to key 2. Now t r y the movement r e q u i r e d f o r TCI - depress the whi te response key w i t h your index f i n g e r and then move to h i t the b l a c k response key 2. Any ques t ions about TCI? TC2: Requires tha t you depress the index f i n g e r o f your l e f t / r i g h t hand and then move to h i t the b l a c k response keys 2 - 1 - 3 - 2 / 2 - 3 - 1 - 2 i n r a p i d s u c c e s s i o n . Now t r y the movement r e q u i r e d f o r TC2, s t a r t i n g w i t h your index f i n g e r on the whi te response key . Depress i t , now move q u i c k l y to h i t keys 2 - 1 - 3 - 2 / 2 - 3 - 1 - 2 . Try TC2 a g a i n , depress the whi te key and, move to h i t 2 - 1 - 3 - 2 / 2 - 3 - 1 - 2 . Any ques t ions about TC2? This experiment i s t e s t i n g your r e a c t i o n and movement t i m e , t h e r e f o r e i t i s important tha t you respond as q u i c k l y as p o s s i b l e on each t r i a l . I t i s a l s o important tha t you i d e n t i f y each s t i m u l u s l i g h t c o r r e c t l y and respond w i t h the a p p r o p r i a t e t a s k . Your emphasis should be on both speed and accuracy . Try to make as few e r r o r s as p o s s i b l e . Now that you are f a m i l i a r w i t h the apparatus and the r e q u i r e d movement tasks we w i l l b e g i n w i t h some p r a c t i s e t r i a l s o f each t a s k . P l a c e your index f i n g e r s on keys 3 and 4 w i t h your w r i s t s down. We w i l l beg in w i th 15 t r i a l s of TCI o n l y . Watch f o r s t i m u l u s l i g h t 3/4 to appear. As soon as i t goes on respond as q u i c k l y as p o s s i b l e w i t h TCI. R e a d y . . . 84 We w i l l now t r y 15 t r i a l s of TC2. Again watch f o r s t i m u l u s l i g h t 4/3 to appear , then respond q u i c k l y w i t h TC2. R e a d y . . . Now you are ready to respond to a cho ice s i t u a t i o n i n which e i t h e r l i g h t 3 or 4 may go on . Watch c a r e f u l l y , and when e i t h e r s t i m u l u s l i g h t appears r e a c t q u i c k l y w i t h the a p p r o p r i a t e movement. R e a d y . . . Now we are ready to beg in the a c t u a l exper imenta l t e s t i n g . Dur ing each o f the f o u r s e s s i o n s you w i l l perform two exper imenta l con -d i t i o n s . Each exper imenta l c o n d i t i o n c o n s i s t s of 200 t r i a l s w i t h shor t r e s t p e r i o d s d u r i n g the s e s s i o n . A response to e i t h e r s t i m u l u s l i g h t counts as one t r i a l . I f d u r i n g a p a r t i c u l a r t r i a l you a c c i d e n t a l l y respond w i t h the wrong movement t a s k , s imp ly prepare y o u r s e l f f o r the next t r i a l . Remember, r e a c t as q u i c k l y and a c c u r a t e l y as p o s s i b l e . Any ques t ions? 85 Table 1 Order o f P r e s e n t a t i o n of E i g h t Exper imenta l Cond i t ions Order (0) T e s t i n g Sess ions - Two Exper imenta l Cond i t ions per Sess ion Subjects (S) 1 2 3 4 01 S I , S9 1 2 Exper imenta l 3 4 Cond i t ions 5 6. 7 8 02 S2, S10 2 3 4 8 6 1 5 7 03 S 3 , S l l 8 4 7 1 2 5 6 3 04 S4, S12 3 6 2 7 1 8 4 5 05 S5 , S13 4 1 5 3 7 2 8 6 06 S6, S14 7 5 1 6 8 3 2 4 07 S7, S15 5 8 6 2 4 7 3 1 08 S8, S16 6 7 8 5 3 4 1 2 '86 Table 2 Maximum Number of R e p e t i t i o n s For P r o b a b i l i t y Leve ls p . 5 0 , p . 6 0 , p . 7 5 , p .90 P r o b a b i l i t y Leve l Maximum Number o f R e p e t i t i o n s p .50 7 p.60 10 p.75 12 p.90 16 APPENDIX B R e s u l t s 87 88 Table 1 Reduced Data : Mean;.RL f o r 16 Subjects Over 8 Exper imenta l Cond i t ions For TCI , TC2 Cond i t ions Subjects TCI 1 2 5 4 5 6 7 8 .9 10 11 12 13 14 15 16 X EC1 203 271 241 183 224 211 205 183 210 193 295 200 226 264 228 204 221 EC2 227 339 252 220 240 237 222 194 276 252 293 229 262 290 288 251 255 EC3 251 380 260 214 316 263 240 201 285 265 282 246 273 331 289 251 272 EC4 278 368 313 235 245 279 246 205 282 305 337 243 290 311 308 271 282 EC5 280 364 275 214 247 304 324 228 262 232 318 249 285 476 388 288 296 EC6 265 394 281 252 327 297 300 229 270 245 288 270 279 386 309 315 294 EC7 267 373 305 268 298 338 309 223 279 247 320 279 301 428 318 305 304 EC8 285 435 340 318 309 330 351 250 318 345 402 289 291 358 412 317 334 X 257 366 283 238 276 282 275 214 273 261 317 251 276 356 318 275 282 TC2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 X EC1 205 305 254 193 240 253 221 187 218 201 255 204 238 264 241 230 232 EC2 223 422 302 261 297 325 300 248 309 304 335 326 280 331 397 343 313 EC3 259 420 288 232 313 313 300 233 277 274 295 278 259 334 342 303 295 EC4 269 391 345 255 277 317 264 230 280 325 343 254 310 329 330 284 300 EC5 262 356 300 242 252 313 353 208 266 225 287 228 287 492 437 277 299 EC6 257 367 284 265 332 316 284 227 278 242 278 260 272 374 319 308 291 EC7 246 340 305 244 285 321 256 214 254 224 319 256 269 435 306 297 285 EC8 248 353 317 242 267 276 251 215 250 279 335 230 267 327 370 266 281 X 246 369 299 242 283 304 279 220 267 259 306 255 273 361 343 289 287 Hypothes is 1 TC2-TC1 i n EC1 2 34 13 10 16 42 16 4 8 8 - 4 0 4 14 0 13 26 89 Table 2 Tasks by Days Tasks Days (Response Latency i n M i l l i s e c o n d s ) TCI 304 284 274 266 TC2 310 288 276 273 Mean 307 286 275 270 91 Table 3 E r r o r s : T o t a l Number and Percent E r r o r s , Tasks by Exper imenta l Cond i t ions Tasks Exper imenta l Cond i t ions TCI T o t a l Percent TC2 T o t a l Percent T o t a l (TCI, TC2) 2 3 4 5 6 7 8 T o t a l 1 20 10 10 19 8 17 18 103 0% .7% .4% .5% 1.1% .6% 2.1% 5.6% 7 . 36 20 23 22 19 23 5 155 4% 11.3% 2.5% 1.7% 1.3% .9% .9% .2% 8 56 30 33 41 27 40 23 258 T o t a l E r r o r s = 258 T o t a l T r i a l s = 25,600 Percent E r r o r s = 1.00% Table 4 E r r o r s : T o t a l Number and Percent E r r o r s , Tasks by Response P r o b a b i l i t y Tasks Response P r o b a b i l i t y 1.0 ,90 ,75 .60 .50 .40 ,25 .10 TCI T o t a l Percent 1 .0% 20 .7% 10 .4% 10 .51 19 1.1% .6% 17 2.1% 18 5.6% TC2 T o t a l Percent 7 .4% 5 .21 23 .9% 19 .9% 22 1.3% 23 1.7% 20 2.5% 36 11.3% T o t a l (TCI, TC2) 8 25 33 29 41 31 37 54 EC1 EC2 EC3 EC4 EC5 EC6 EC7 EC8 Exper imenta l C o n d i t i o n s F igure 3a . The Percentage E r r o r r a t e s f o r TCI and TC2 over Exper imenta l C o n d i t i o n s . Response P r o b a b i l i t y F i g u r e 3b. The Percentage E r r o r r a t e s f o r TCI and TC2 over Response P r o b a b i l i t y l e v e l s . 94 Response P r o b a b i l i t y F igu re 2a . Response La tenc ies f o r TCI under orders of p r e s e n t a t i o n 0 5 , 06 , and 0 7 . Response P r o b a b i l i t y F igure 2b. Response L a t e n c i e s f o r TC2 under orders of p r e s e n t a t i o n 0 5 , 06 and 0 7 . 

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