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Comparison of the delay in response of normals and retardates to a choice reaction time task-a pilot… Gatley, Lyle Daryle 1971

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A COMPARISON OF THE DELAY IN RESPONSE OF NORMALS AND RETARDATES TO A CHOICE REACTION TIME TASK - A PILOT STUDY by LYLE DARYLE GATLEY B.Ed., University of B r i t i s h Columbia, 1963 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS i n the Department of Educational Psychology We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA June, 1971 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f 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 C o l u m b i a , I a g r e e t h a t t h e L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and s t u d y . I f u r t h e r a g r e e t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Depa rtment The U n i v e r s i t y o f B r i t i s h C o l umbia Vancouver 8, Canada Abstract 5 normal subjects randomly selected from the entire grade 8 male population at Vancouver Technical Secondary School, and 5 retarded subjects from the spe c i a l class at the same school were exposed to a series of 5 reaction time experiments involving a button press response to a series of stimulus l i g h t s , and varying i n complexity from simple reaction time to an 6* choice s i t u a t i o n . The object was to test the effect of the decision mechanism involve-ment on reaction time. It was hypothesized that the retar-dates would be s i g n i f i c a n t l y slower than the normals on the reaction time tasks, and that a l i n e a r equation would describe the best f i t t i n g l i n e of the normals when the speed of response was plotted against the informational load of the stimulus, while a non-linear equation would best describe the retardates' scores. The resu l t indicated that there was no s i g n i f i c a n t difference between the mean values of the reaction time scores of the retarded and the normal groups, but a p r o b a b i l i t y l e v e l of .075 was obtained. There was no s t a t i s t i c a l l y s i g n i f i c a n t evidence to indicate which equation was the best f i t to the retarded and normal scores; however, v i s u a l inspection indicated that the observed trends were i n agreement with the prediction. It was concluded that although the evidence presented was not s t a t i s t i c a l l y s i g n i f i c a n t , enough evidence has been presen-ted to suggest that retardates do not react to a l e v e l of information beyond 2 b i t s i n a l i n e a r fashion that t y p i f i e s the normals, and that further research i s required to ascer-t a i n the causal factor i n the retardates' i n a b i l i t y to react at a normal l e v e l on a reaction time task. S e r i a l Subject Page(s) 1 Abstract i - i i 2 Table of Contents i i i 3 L i s t of Tables i v 4 L i s t of Figures v 5 Acknowledgement v i 6 Problem 1 - 5 7 Method 5 - 1 0 g Results 10 - IS 9 Discussion 19 - 21 10 Bibliography 22 - 27 11 Appendix A 261 - 32 L i s t of Tables Subject Characteristics of the Subjects Mean Scores For Retarded and Normal Subjects Results of the Wilcoxon Matched-Pairs Signed-Ranks Test Results of the Mann-Whitney U Test The Squared Multiple Cor-r e l a t i o n C o e f f i c i e n t s for Simple and Multiple Regres-sion Equations of Normals and Retardates Raw Scores for Normal and Retarded Subjects L i s t of Figures Figure Subject Page(s) 1 R.T. as a function of information given, retarded vs" normal: Best f i t t i n g l i n e of l i n e a r form 17 2 R.T. as a function of information given, retarded vs normal: Best f i t t i n g l i n e of quadratic form 13 Acknowledgement I wish to express my gratitude to Dr. Wilson E. Schwann and Dr. Ronald G. Marteniuk f o r t h e i r continued assistance and encouragement during the writing of t h i s t h e s i s . I would also l i k e to thank Dr. Douglas McKie and Mr. Dale Russnell fo r t h e i r invaluable assistance during the analysis of the data, and Dr. N. E l l i s and the Vancouver School Board for t h e i r assistance i n the procuring and testing of subjects. A Comparison o f the Delay i n Response o f Normals and Retardates to a Choice R e a c t i o n Time Task - A P i l o t Study Problem There i s as y e t an u n r e s o l v e d i s s u e concerning the r e l a -t i o n s h i p between mental a b i l i t y and motor performance, the d e t e r m i n a t i o n o f which has c r i t i c a l i m p l i c a t i o n s f o r educa-t i o n a l p r a c t i c e as w e l l as f o r l e a r n i n g theory. A c c o r d i n g to Welford's Information Model (1959) man r e a c t s to i n p u t i n f o r m a t i o n as i f he embodied t h r e e separate but i n t e r r e l a t e d mechanisms. In a task such as a R e a c t i o n Time (R.T.) experiment, the P e r c e p t u a l Mechanism (P.M.) accepts the sensory i n p u t and i d e n t i f i e s and c l a s s i f i e s i t , the D e c i s i o n Mechanism (D.M.) s e l e c t s the a p p r o p r i a t e r e s -ponse, and the E f f e c t o r Mechanism (E.M.) makes t h a t response. R e a c t i o n time to any response, then, can be c o n s i d e r e d a sum-mation o f the time r e q u i r e d to p e r c e i v e a s t i m u l u s , decide upon a response, and e f f e c t t h a t response. Numerous R.T. experiments d e a l i n g w i t h normal s u b j e c t s have shown t h a t R.T. i s l i n e a r l y r e l a t e d to the number o f s t i m u l i p resented, or more s p e c i f i c a l l y , R.T. i s a l o g a r i t h -mic f u n c t i o n o f the amount o f i n f o r m a t i o n presented i n the stimulus a r r a y (Hick, 1952: B r a i n a r d et a l , 1962: F i t t s and Peterson, 1963: Hilgendorf, 1966). R.T. studies dealing with retarded subjects have revealed that R.T.s of retarded subjects are s i g n i f i c a n t l y slower than the R.T.s of normal subjects for both simple R.T. tasks and more complex or choice R.T. tasks (Scott, 1940: E l l i s and Sloan, 1957: Dingman and S i l v e r s t e i n , 1964). One of the f i r s t to d i s -cover t h i s was Scott (1940), who employed a series of four tasks ranging i n complexity from simple R.T. to a f i v e choice s i t u a t i o n . Although no tests of significance were employed, his data showed that high I.Q. subjects were fas-t e r than low I.Q. subjects at a l l levels of complexity. Berkson (I960 a,b, 1961) performed a series of studies on R.T.s of normals and varying degrees of retarded youths, using, among other tasks, simple and choice R.T. tasks involving a button press response to one or more stimulus l i g h t s . He discovered differences between i n t e l l i g e n c e groups, but also noted that the differences were less for the R.T. tasks than for those tasks which also included bal-l i s t i c movements. He concluded from t h i s that: ..." no information from the present series of experi-ments supports the b e l i e f that I.Q. i s related to the speed of v i s u a l information reception, the making of a choice, or the planning of a movement, but that I.Q. i s related to functions involved i n the speed of performance of response." The discrepancy i n response time between retardates and normals may seemingly be attributed to any one or any combin-a t i o n of the three mechanisms suggested by Welford, Berkson (1961), however, a t t r i b u t e s the R.T. discrepancy to an e f f e c t o r breakdown, d i s r e g a r d i n g both the perceptual and d e c i s i o n mechanisms. Berkson's study employed a button press task with a maximum stimulus a r r a y of f i v e items, the task being designed to i s o l a t e the d e c i s i o n mechanism in v o l v e d and examine i t s e f f e c t on R.T. to an increased i n f o r m a t i o n a l l o a d . On t h i s task he found that although the retardates were g e n e r a l l y i n f e r i o r , they were not d i f -f e r e n t i a l l y disadvantaged by increased task complexity. This r e s u l t may have been due to a task which was not of s u f f i c i e n t i n f o r m a t i o n a l load t o a l l o w f o r an i n t e r a c t i o n . I t i s p o s s i b l e that i f Berkson had increased the task com-p l e x i t y beyond the f i v e choice s i t u a t i o n , a s i g n i f i c a n t i n t e r a c t i o n may have been shown between i n t e l l i g e n c e and D.M. involvement on the R.T. t a s k . The author questions Berkson*s conclusion as a r e s u l t of h i s own experiences i n d e a l i n g w i t h educably retarded youths (I.Q. 60-80) i n a Secondary School.?shop environ-ment. The author has observed that retarded youths i n t h i s I.Q. range were much more capable m a n i p u l a t i v e l y than Berkson's r e s u l t s might suggest. With p r a c t i c e , edu-cably retarded youths were observed to be capable of per-forming compound manipulative tasks to a high degree of p r o f i c i e n c y . A l s o , to adopt a c o n c l u s i o n i n v o l v i n g an e f f e c t o r breakdown would obligate educators of retardates to assume methods of i n s t r u c t i o n and remediation contrary to those methods required i f acceptance of a decision breakdown were considered. The inherent dangers to the retarded c h i l d of accepting a wrong conclusion are reason enough to i n s i s t upon further research i n t h i s area. It i s , therefore, the purpose of t h i s study to i s o l a t e the decision mechanism involvement on an R.T. task, and test the degree to which the R.T. of normals and educable retardates i s affected by the D.M.. A button press task si m i l a r to Berkson's but involving an increased informa-t i o n a l load of 3 b i t s (1 to $ choices) was u t i l i z e d . Iso-l a t i o n of the decision mechanism was achieved by elimina-t i n g any perceptual discrepancies and standardizing a l l ef f e c t o r involvement. The stimulus l i g h t s were designed so that t h e i r i n t e n s i t y was equal and well above threshold l e v e l for a l l subjects, thereby a l l e v i a t i n g any confounding by the perceptual mechanism. The e f f e c t o r involvement was kept constant by recording the same response f o r a l l tests, namely the response of the d i g i t finger of the subject's preferred hand. It i s hypothesized that the discrepancy i n R.T. between normal and educably retarded subjects i s a resu l t of an ever increasing breakdown of the decision mechanism of the retar-ded subject as the. informational load i s augmented. Some s p e c i f i c predictions from t h i s hypothesis are: a. Reaction time of both normal and retarded sub-jects would increase as the information load on the decision mechanism i s increased. b. Reaction times of the retarded subjects would increase at a greater rate than that of the normals. c. The best f i t t i n g l i n e f o r the plotted points of the normal scores (R.T. vs information) would be a l i n e a r equation. d. The best f i t t i n g l i n e for the plotted points of the retarded scores (R.T. vs information) would be a non-linear equation. It i s believed that the demonstration of t h i s r e l a t i o n -ship would serve to i d e n t i f y the mechanism which actually d i f f e r e n t i a t e s between i n t e l l i g e n c e l e v e l s i n performing psycho-motor tasks of t h i s kind, thereby enlightening educa-tors as well as t h e o r i s t s as to the true strengths and weak-nesses of the educable retardates i n t h i s respect, so that appropriate expectations and tasks may be set f o r them i n a l l relevant educational s i t u a t i o n s . Method Subjects. Five mentally d e f i c i e n t boys were compared with f i v e normal boys on a series of simple and choice reaction time t e s t s . The c h a r a c t e r i s t i c s of the subjects are presen-ted i n Table 1. I n t e l l i g e n c e Quotients (I.Q.) were deter-mined by use of the performance t e s t s of the Weschler I n t e l -l i g e n c e Test f o r C h i l d r e n (WISC). The mental ages of the re t a r d a t e s were computed from the WISC scores, but the Men-t a l a z e s (M.A.) of the normals were not considered r e l i a b l e , and t h e r e f o r e were not recorded. The retarded subjects were drawn from a " s p e c i a l " c l a s s at Vancouver Technical School. They were chosen d i s c r i m i n -a t e l y by observing t h e i r case h i s t o r i e s , since the c l a s s was too small and v a r i e d i n a b i l i t y to choose from randomly. The retarded subjects had a mean I.Q. of 69 (S.D. : 6.6) and an M.A. of 8" years, 11 months (S.D. : 9.3 mo.). The mean Chrono l o g i c a l Age (C.A.) was lk years (S.D. : 2 y r s . 11 mo.). None of the retarded subjects showed any d e f i n i t e n e u r o l o g i c a l a b n o r m a l i t i e s or v i s u a l d e f o r m i t i e s and a l l were r i g h t handed The normal subjects, were chosen randomly from the e n t i r e grade 8" population e n r o l l e d i n the r e g u l a r classes at Van-couver T e c h n i c a l Secondary School. Their mean I.Q. was 99.2 (S.D. : 7.2) and t h e i r C.A.s averaged 13 years, 7 months (S.D. : 5.2 mo.). A l l normal subjects had normal a c u i t y i n both eyes, and none showed any n e u r o l o g i c a l a b n o r m a l i t i e s . A l l but one normal subject were r i g h t handed. Apparatus. The R.T. apparatus, which was designed and con-s t r u c t e d by the author, c o n s i s t e d of a metal chassis c o n t a i n -.TABLE 1 .CHARACTERISTICS OF THE SUBJECTS SUBJECT C A. M.A. I.Q. HAND yrs./mo. yrs/mo. DOMINANCE NORMAL 1. 13/5 - 108 R 2. .13/6 - 106 R 3 . 13/3 - 100 R 4 . 13/6 - 92 L 5. 13/9 - 90 R 1 13/7 - 99.2 S.D. 5.2 mo. - 7.2 RETARDED 1. 15/5 8/6 64 R 2. 15/4 8/6 6$ R 3 . 14/5 8/6 67 R 4. 14/9 8/10 67 R 5. 14/2 10/6 82 R X 14/10 8/11 69 S.D. 2/11 9.3 mo. 6.6 i n g e i g h t red stimulus lights., e i g h t black response huttons, and one y e l l o w warning l i g h t . The apparatus was pl a c e d a t mid-chest l e v e l to the s u b j e c t when seated, and c l o s e enough so t h a t the stimulus l i g h t s were no f u r t h e r than e i g h t e e n inches from the eyes. The subject sat at one end of a t e n f o o t t a b l e , d i r e c t l y o p posite and f a c i n g the examiner. A l a r g e blank panel was p l a c e d two f e e t i n f r o n t of the s u b j e c t to minimize v i s u a l d i s t r a c t i o n s . A m i r r o r was pl a c e d above the s u b j e c t and t i l t e d at an angle, a l l o w i n g t h e examiner to observe the s u b j e c t without d i s t u r b i n g h i s c o n c e n t r a t i o n . The s u b j e c t ' s apparatus was completely s i l e n t - r u n n i n g , and a l l l i g h t s were of equal and high i n t e n s i t y , and in s t a n t a n e o u s . The experimenter's c o n t r o l s c o n s i s t e d of a Hunter Klock-ounter (Model 120 A, s e r i e s D) and a c o n t r o l panel c o n s i s t i n g of a switch capable of s e l e c t i n g any one of the e i g h t s t i m u l i , a push button t o a c t i v a t e the warning l i g h t , and one to a c t i -vate the r e l a y f o r the st i m u l u s l i g h t . The e l e c t r o n i c c l o c k and the st i m u l u s l i g h t were a c t i v a t e d simultaneously by the experimenter with the same push button, and were both t e r m i n -ated when the c o r r e c t response button was pressed by the s u b -j e c t . The warning l i g h t remained on only as long as the push button a c t i v a t i n g i t was depressed. The experimenter was i n s t r u c t e d to leave the warning l i g h t on u n t i l the stimulus l i g h t was a c t i v a t e d . A l l r e a c t i o n times were recorded to the nearest m i l l i s e c o n d . Procedure. A l l subjects were exposed to each of the f i v e stimulus conditions i n a counter-balanced order. P r i o r to tes t i n g , each subject was given verbal instructions and a demonstration to describe the task and explain the use of the apparatus. The subject was allowed to proceed only when he was capable of manipulating the apparatus c o r r e c t l y and understood the instructions f u l l y . The subject was informed that the object of the t e s t i n g was to increase his speed of response. A rest period of from one to f i v e minutes was interspersed between each condition, the length depending on the i n d i v i d u a l subject and the judgement of the experimen-te r . During the t h i r d rest period the subject was given a chocolate bar as an added incentive. P r i o r to each new con-d i t i o n , a dditional instructions were given as well as a prac-t i c e period of s u f f i c i e n t length to ensure complete under-standing. During each t r i a l the subject was warned "ready" by the experimenter. On answering "yes", the warning l i g h t was immediately presented and followed within one to four seconds by the stimulus l i g h t . This foreperiod was randomly varied i n one second i n t e r v a l s by use of a table of random numbers. The warning l i g h t remained on u n t i l presentation of the stimulus l i g h t , which remained on u n t i l the subject depressed the correct response button. The selection of the stimulus l i g h t was also randomized. The t r i a l s were contin--ued u n t i l ten reaction times were recorded for the right d i g i t finger (or l e f t d i g i t finger f o r the l e f t handed subjects). The f i v e stimulus conditions employed were as follows: Condition 1: A single known response to a known stimulus (simple R.T.). The index finger of the preferred hand was used f o r the response. Condition 2: Two sti m u l i , two responses. The index fingers of each hand were used f o r the response. Condition 3 : Four s t i m u l i , four responses, employing the f i r s t and second fingers of each hand (coun-t i n g from the index f i n g e r ) . Condition 4 : S i x s t i m u l i , six responses, employing the f i r s t three fingers of each hand. Condition 5 : Eight s t i m u l i , eight responses, employ-ing a l l the fingers. The subjects were tested i n d i v i d u a l l y , and a l l f i v e con-d i t i o n s were completed i n one session. No subject had p r i o r experience with t h i s or si m i l a r apparatus, and none was informed of the experiment u n t i l just p r i o r to being tested. A l l subjects were cautioned not to discuss the experiment with anyone. Results The means of the R.T.s of each subject displayed i n Table 2 were employed i n a l l analysis of the data, with a c r i t i c a l region f o r rej e c t i o n of the n u l l hypothesis set at the .05 p r o b a b i l i t y l e v e l . Because of the small sample size (n=5) and the unequal variances, non-parametric tests were considered to be the most v a l i d means of analysis. The r e s u l t s of the Wilcoxon Matched-Pairs Signed-Ranks Test of Table 3 reveals that a l l conditions are 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 with the exception of condition 4 and 5, which are not. In Table 4 the Mann-Whitney U Test reveals that the retardates did not respond at a s i g n i f i c a n t l y d i f -ferent l e v e l than the normals when t h e i r mean scores were analysed simultaneously across a l l conditions. However, i t i s worth noting that the .075 p r o b a b i l i t y l e v e l obtained with t h i s small a sample size i s at least approaching the .05 c r i t i c a l region previously accepted as s i g n i f i c a n t . The same table displays the p r o b a b i l i t y l e v e l s of the normals and retardates compared under each of the f i v e conditions, and reveals that none of the p r o b a b i l i t y values are s i g n i f i -cant although conditions 4 and 5 approach significance with values of .061 and .075 respectively. In order to observe any l i n e a r or c u r v i l i n e a r trends which might be representative of either the normals or r e t a r -dates, best f i t t i n g l i n e s were plotted using simple and mul-t i p l e regression techniques.^" In both Figures 1 and 2 i t can be seen that the regression l i n e s representing the The University of B r i t i s h Columbia Computing Center, "Triangular Regression Package" SIMREG, STBREG Dec. 1970. TABLE 2 MEAN SCORES FOR RETARDED A ( A l l Values Recorded i SUBJECT NORMALS 1 2 Simple RT 2 Choice 1 198 275 2 212 337 3 201 255 4 210 261 5 178 246 X 200 275 SD 13.54 36.33 RETARDED 1 341 308 2 273 390 3 184 267 4 184 280 5 152 264 X 227 302 SD 78.16 52.28 ND NORMAL SUBJECTS n Milliseconds) GONDITION 3 4 5 4 Choice 6 Choice 8 Choice 292 320 325 523 573 570 421 493 467 333 480 448 292 338 410 372 441 444 99 .40 108.3 89.08 457 647 572 480 719 986 420 507 351 285 573 523 418 470 583 412 583 603 75.63 101.5 233.4 RESULTS OF THE WILCOXON MATCHED-PAIRS SIGNED-RANKS TEST Conditions T value Signi f icance P 1 x 2 3 s <.005 2 x 3 0 s < .005 3 x 4 0 s < ,005 4 x 5 29 N/S > .05 1 x 3 0 S < .005 1 x 4 0 s <.005 1 x 5 0 s <.005 2 x 4 0 s <.005 2 x 5 0 s <.005 3 x 5 0 s < .005 RESULTS OF THE MANN-WHITNEY U TEST Source U Value Pro b a b i l i t y -Group x Condition 1 13 .579 2 6 .111 3 9 .274 4 4/5(Tie) .061 5 5 .075 Between Groups 5 .075 retarded group has a greater slope than that of the normal group, and that the reaction time of the retardates becomes increasingly greater as the stimulus information i s increased, with the greatest differences occuring on Condition 4 and 5 . According to the multiple regression equations of Figure 2, when observing the best f i t t i n g l i n e s beyond 3 b i t s of i n f o r -mation, the equation representing the normal group w i l l even-t u a l l y reach an asymptote, a f t e r which i t becomes a slow, 2 negatively decreasing function when the negative x term 2 becomes larger than the x term. (Y = 194.7 * 94.6x - 2.29x ) . N Conversely the equation symbolizing the retarded group contin-u a l l y remains a p o s i t i v e l y increasing function. 2 (Y * 222.9 * 58.2x + 25.6x ). Consequently the distance R between the two equations tends to become increasingly grea-t e r as the information i s increased. Table 5 reports the squared multiple correlation c o e f f i -2 cients (R ) for both the simple and multiple regressions of 2 the normals and retardates. This R term i s a statement of the proportion of the t o t a l observed variance accounted f o r by each of the regression equations. The difference between the R^  terms of the normals from simple to multiple regres-sion i s 0 . 0 0 0 3 , while the difference f o r the retarded group i s 0 .0151 . Since the sample size was small, the differences between simple regression and multiple regression were not found to be s t a t i s t i c a l l y s i g n i f i c a n t for either the normals or the retardates. TABLE 5 THE SQUARED MULTIPLE CORRELATION COEFFICIENTS FOR SIMPLE AND MULTIPLE REGRESSION EQUATIONS OF NORMALS AND RETARDATES R2 Simple Regression Multiple Regression Normals 0.6343 0.6346 Retardates 0.5958" 0.6109 .^ . . . . . . . . . - 17 - . FIGURE 1 R.T. AS A FUNCTION OF INFORi-iATION GIVEN, RETARDED VS. NORMAL: BEST FITTING LINE OF LINEAR FORM. i t . i . (msec.) 700 . MEAN SCORES RETARDATE = X NORMAL = ® 600 500 . 400 . 300 y„= 197-5 + 1 3 4 * : . •® y/s«= 197+ 87- 94 *<• NORMAL 200 . 0 .5 1 1.5 INFORMATION (Bits! 2 2.5 ... . . .... - 18 - . .. . ; FIGURE 2 R.T. AS.A FUNCTION OF INFORMATION GIVEN, RETARDED VS. NORMAL: BEST FITTING LINE OF QUADRATIC FORM. R.T. (msec.) 700 MEAN SCORES RETARDATE. = X NORMAL ' = 0 0 .5 1 1.5 . 2 INFORMATION (Bits) 2.5 Discussion The results of both the normal and retarded subjects support e a r l i e r research findings that R.T. increases proportionally as the information load i s increased. (Hick, 1952: Brainard et a l , 1962: F i t t s and Peterson, 1963: Hilgendorf, 1966). The r e s u l t s also indicate that no s i g n i f i c a n t difference existed between normal and edu-cably retarded children'-jon a choice R.T. task i n which R.T. increases are dependant on the D.M. involvement. However, the .075 p r o b a b i l i t y l e v e l obtained with the small sample size observed i s evidence that the decision mechanism i s l i k e l y a factor i n determining the discrepancy i n R.T. between normals and retardates. In t h i s study as well as i n Berkson's (1961) the r e s u l t s d e f i n i t e l y do not show a s i g n i f i c a n t R.T. difference between zero and 2 b i t s of information (Cond. 1, 2, 3). It i s within the region of 2.5 to 3 b i t s of information (Cond. 4, 5) that the r e s u l t s approach sign i f i c a n c e . Although conditions 4 and 5 are not 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, they are s i g n i f i -cantly d i f f e r e n t from conditions 1, 2 and 3, therefore i t i s apparent that the educable retardate begins to react d i f f e r e n t l y than normal to a display of more than 2 bits of information. Although the evidence supporting a D.M. breakdown as the causal factor i s weak, nevertheless, i t i s evident. Since the differences i n the R values of both the quadratic and the l i n e a r equation were small, and since the number of subjects were few, i t was not possible to provide s t a t i s t i c a l l y s i g n i f i c a n t evidence concerning which of the regression equations i s the best f i t . Visual inspection of the best f i t t i n g l i n e s and the-raw scores as well as consid-eration of the values, reveals that the l i n e a r equation describes the best f i t f o r the normal scores, since the R^ values of.the l i n e a r equation i s v i r t u a l l y the ssame as the quadratic equation (Difference .0003), even though a l i n e a r trend i s by d e f i n i t i o n a more d i f f i c u l t f i t to a series of points. The best f i t t i n g l i n e to the retarded scores by observation of Figures 1 and 2 i s the quadratic equation, which also has a larger R value. The observed trends are c l e a r l y i n agreement with the prediction, and i t i s a l t o -gether possible that with the use of a larger sample size, the c u r v i l i n e a r trend would have been a s i g n i f i c a n t l y better f i t to the retarded scores than the l i n e a r equation, as would the l i n e a r trend have been to the normal scores. Examination of the quadratic equation describing the retarded scores beyond 3 b i t s of information reveals a steadily increasing function. If t h i s equation i s an hon-est p rediction of the retardates' c a p a b i l i t i e s on an R.T. task, then i t i s reasonable to conclude that the retardate does not react to an increase i n information i n the l i n e a r fashion t y p i f y i n g themormals. Instead the decision mechan-ism breakdown i s greatly increased as the informational load i s expanded beyond 3 b i t s of information. This would suggest that to f a c i l i t a t e learning with educable retar-dates i t i s necessary to keep the information load at a workable l e v e l — below a maximum of 2 b i t s of information. If the results of t h i s study have not shown a s i g n i f i -cant i n t e r a c t i o n betweeniitype of subject and the decision mechanism, i t i s at least evident that the realm .beyond 2 b i t s of information must be investigated i n d e t a i l to ascer-t a i n the true nature of the relationship between information load and the retardates' a b i l i t y to respond. Such an inves-t i g a t i o n might best be employed by designing a p a r a l l e l study which would account f o r a l l the aspects of the decision mech-anism as well as for those of the e f f e c t o r mechanism, with-out confounding one with the other. Bibliography Baumeister, A.A. & F.M. Berry. D i s t r i b u t i o n of practice and s p e c i f i c i t y of learning i n normals and retar-dates. Amer. J. Men. Def... 72: 227-31. September, 1967. ., W.F. Hawkins, & J. Holland. Motor learning and knowledge of r e s u l t s . Amer. J. Men. Def., 69: 590-594, 1965. & G. Kellas. D i s t r i b u t i o n of reaction times of retardates and normals. Amer. J. Men. Def., 72: 715-13, March, 1968. ., et a l . Reaction times of normals and retardates under d i f f e r e n t stimulus in t e n s i t y changes. Amer. J. Men. Def., 69: 126-130, March, 1964-., & L.C. Ward. Effects of reward on reaction time of the mentally d e f i c i e n t . Amer. J. Men. Def., 71: 55-9, July, 1966. Berkson, G. An analysis of reaction time i n normal and mentally d e f i c i e n t young men I. Duration threshold experiment. J. M|n. DJf. Res., 4: 51-58, I960. . An analysis of reaction time i n normal and men-t a l l y d e f i c i e n t young men I I . V a r i a t i o n of complex-i t y i n reaction time tasks. J. Men. Def. Res., 4: 59-67, I960. . An analysis of reaction time i n normal and mentally d e f i c i e n t young men I I I . Variation of stimulus and response complexity. J . Men. Def. Res. 4 : 69-77, 1961. Bertelson, P . S-R relationships and reaction times to new versus repeated signals i n a s e r i a l task. J. Exp_. Psych. , 65 : 478-484, 1963. Brainard, R.W., et a l . Some variables influencing the rate of gain of information. J. Exp. Psych., 63: 105-110, 1962. Brengelmann, J . C , & J. L. Standon. Task d i f f i c u i t y ^ a n d response time i n the retar-date. Tr. Sch • Bui. , 1964. Carron, A.V. Ef f e c t s of practice upon i n d i v i d u a l d i f f e r -ences and i n t r a - v a r i a b i l i t y i n a motor s k i l l . Res. Quart., 3 9 : 470-5 , October, 1968. Cratty, B.J. Development sequence of perceptual motor  tasks. Educational A c t i v i t i e s Inc. , 1967. . Movement behaviour and motor learning. Second Ed. Philadelphia: Lea and Febiger, 1967. . Perceptual motor behaviour and educational processes. S p r i n g f i e l d : Charles C. Thomas, 1969. E l l i s , N.R. (ed). Handbook of mental.deficiency: psycho- l o g i c a l theory and research. New York: McGraw-Hill, 1963. . International review of research i n mental ret a r - dation. Vol. 1-3. New York: Academic Press, 1966, 1968. . , & W. Sloan. Relationship between i n t e l l i g e n c e and simple reaction time i n mental defectives. Pere. and Motor S k i l l s . . 7> 65-67, 1957. F i t t s , P.M. Cognitive aspects of information processing:? I I I . Set f o r speed versus accuracy. J . Exp. Psych., 71: 849-857, 1966. ., & I. Biederman. S-R compatibility and information reduction. J . Exp_. Psych.. 69: 408-12, 1965. ., & R. L. Deinger. S-R compatibility: correspon-dence among paired elements within stimulus and response codes. J . Exp. Psych. 48: 483-92, 1964. ., J . R. Peterson, & G. Wolpe. Cognitive aspects of information processing I I . Adjustments to stimulus redundancy. J . Exp_. Psych.. 65: 423-32, 1963. ., & M.I. Posner. Human performance. Belmont, C a l i -f o r n i a : Brooks-Cole Publishing Co., 1967-& C.M. Seeger. S-R compatibility: s p a t i a l charac-t e r i s t i c s of stimulus and response codes. J . Exp. Psych.. 46: 199-210, 1953-., & G. Switzer. Cognitive aspects of information processing I. The f a m i l i a r i t y of S-R sets and subsets. 1- Psvch.. 63: 321-329, 1962. Gardner, W.I. Effects of f a i l u r e on i n t e l l e c t u a l l y retarded and normal boys. Amer. J. Men. Def., 70: 899-902, May, 1966. Hawkins, W.F., et a l . Simple and disjunctive reaction times of normals and retardates. Amer. J. Men• Def., 69: 536 - 40, May, 1964. Hick, W.E. On the rate of gain of information. Quart. J . Exp. Psych.. 4 : 11-26, 1952. Hilgendorf, L. Information input and response time. Ergonomics, 9: 1, 31-37, January, 1966. Hyman, R. Stimulus information as a determinant of reaction time. J. Exp_. Psych.. 45: 188-196, 1953. . The information hypothesis and non-repetitions. Attention and performance I I . (W.G. Koster ed.) Amsterdam: North Holland Pub. Co., 1969. John, I.D. Mediating processes i n choice reaction tasks, Attention and performance I I . (W.G. Koster ed.) Amsterdam: North Holland Pub. Co., 1969. Kahn, H. & A.D. Burdett. Interaction of practice and rewards on motor performance of adolescent mental retardates. Amer. _J. Men. Def., 72: 4 2 2 - 7 , November, 1967. Kornblum, S. Choice R.T. f o r repetitions and non r e p e t i t i o n s : a re-examination of the information hypothesis. Atten t i o n and performance. (A.F. Sanders ed.), Acta Psycho logi c a , 2 7 : 178-187, 1967. . Serial-choice reaction time: inadequacies of the information hypothesis. Science, 159: 432-434, 1963. . Sequential dependencies as a determinant of choice reaction time: A summary. Attention and performance I I . , pp. 54-57, Amsterdam: North Holland Pub. Co., 1969. Krinchik, E.P. 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Toronto: McGraw-Hill, 1962. - r 2$ -APPENDIX A TABLE 6 RAW SCORES FOR NORMAL AND RETARDED SUBJECTS (Results i n Milliseconds) - CONDITION I Retarded X^ 1 679 484 3 0 0 292 306 281 349 276 226 218 341 2 333 300 308 234 250 273 2 4 9 277 258 225 292 3 191 227 185 201 183 184 159 184 211 126 175 4 265 200 216 175 168 184 159 176 159 165 165 5 143 148 126 158 157 157 184 163 146 142 152 Normal 227 1 224 150 210 177 182 198 235 208 190 390 210 2 218 234 250 252 191 217 231 283 243 200 212 3 200 184 173 268 201 201 200 197 201 180 201 4 199 250 226 235 266 210 230 172 192 165 167 5 184 190 175 174 191 178 174 201 173 175 141 . TABLE B RAW SCORES FOR NORMAL AND RETARDED SUBJECTS (Results i n Milliseconds) CONDITION II Retarded X. 1 290 227 266 323 622 308 317 393 363 543 359 2 405 449 416 306 434 390 501 302 308 359 418 3 209 218 218 432 264 267 364 227 183 333 218 4 191 300 317 323 250 280 259 234 376 324 226 5 285 266 266 288 227 264 226 340 201 279 242 X 302 Normal 1 242 265 259 424 241 275 226 300 310 234 251 2 384 301 332 224 350 337 326 334 368 374 376 3 194 249 269 316 309 255 318 232 217 233 211 4 341 233 214 233 193 261 380 248 340 216 209 5 236 225 231 224 226 246 249 249 348 208 259 TABLE 6 RAW SCORES FOR NORMAL AND RETARDED SUBJECTS (Results i n Milliseconds) CONDITION III Retarded 4 1 746 418 592 507 742 455 376 304 410 103 457 2 534 667 743 783 733 557 556 476 72 5 507 480 3 267 365 318 267 508 642 532 383 460 460 420 4 264 260 251 292 321 293 398 242 193 290 285 5 516 466 349 476 367 260 413 348 490 334 418 412 Normal 1 2 3 4 5 X 268 318 268 293 285 301 276 282 335 291 292 538 433 472 483 571 534 494 590 563 449 523 514 418 476 317 461 434 400 535 380 335 421 280 399 424 368 498 244 219 313 296 291 333 260 344 368 498 424 358 26? 232 293 224 292 RAW SCORES FOR NORMAL AND RETARDED SUBJECTS (Results i n Milliseconds) CONDITION IV Retarded . X 6 647 719 507 573 1 634 643 643 771 425 832 402 591 751 773 2 743 839 911 6 3 2 551 433 860 533 952 684 3 481 509 558 621 483 817 376 293 493 435 4 626 525 540 591 575 630 368 485 841 551 5 594 308 492 491 375 568 568 451 407 440 Normal 1 2 3 4 5 357 283 289 369 259 393 267 3 4 2 336 307 558 427 668 643 489 764 501 493 551 634 425 454 534 616 565 524 559 376 493 384 547 513 537 410 5 4 2 3 59 369 352 628 516 418 267 376 310 3 9 2 365 288 309 318 333 470 583 320 573 480 338 X 441 TABLE 6 RAW SCORES FOR NORMAL AND RETARDED SUBJECTS (Results i n Milliseconds) -CONDITION V -Retarded X M g 1 592 439 577 558 533 764 627 602 518 510 2 712 941 992 878 1.356 1.115 656 775 1.258 1.167 3 271 576 416 250 253 291 327 235 200 416 4 500 587 540 484 509 608 505 495 955 579 5 629 615 627 721 630 X 687 724 544 630 642 Normal 1 299 343 272 301 360 468 323 235 395 243 2 549 501 484 559 632 825 543 509 500 593 3 474 466 526 339 533 600 352 512 377 493 4 433 519 426 609 457 610 526 334 452 493 5 450 417 488 419 353 310 439 433 409 386 572 351 523 583 603 325 570 467 448 410 444 

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