An Experimental Study of the Suggestibility of Twelve and Fifteen-Year-Old Boys
The Psychological Clinic Copyright, 1916, by Lightner Witmer, Editor. Vol. X, No. 1 March 15, 1916 :Author: Clara Harrison Town, Ph.D.,
Psychologist, Orthogenic Clinic, Rush Medical College, Chicago.
The study here reported is the first step in a research which seems to be forced upon the writer by a very definite need for knowledge on the subject. In clinical and educational work with under-average individuals, extreme suggestibility is an ever present problem. There is an immediate and urgent demand for educational methods which will develop a critical power able to cope with the strong suggestions playing upon an individual from all sides. Such methods must grow from a knowledge of the psychological factors involved in suggestibility and its causes, and this knowledge is still to be built up on a sound experimental basis. The term suggestion has been used with such diverse meanings,?been stretched by some writers to include so much that it loses all significance, while limited by others to abnormal phenomena,?that it seems well to state that for the purposes of the present study suggestion means a mental influence which causes the person influenced to think and to act without the guidance of his own reason. Persons peculiarly open to such influence are called suggestible.
The experimental studies thus far made on suggestion fall into two groups, those concerned with hypnosis, and those concerned with suggestion in the waking state. This study considers suggestion in the waking state only. One of the first men to investigate experimentally suggestion in the waking state was the zoologist, Professor E. Yung, of Geneva. He believed (and all later experiments sustain his opinion) that suggestibility, in the sense used in this study, is common to all men. It might be said just as truly that an excessive suggestibility is common to most men. This fact is impressed upon us constantly by our contact with average as well as with under-average persons. A couple of years ago, at the University of Pittsburgh, Professor O’Shea was invited to give a talk on what he considered the most serious omission in the curriculum of the Pittsburgh schools. He gave a most illuminating talk, pointing out the utter lack in the course of anything that would tend to counteract the super-suggestibility of the young people. To illustrate this prevalent supersuggestibility he cited the incredible ease with which fakers lead their audiences to believe them capable of reading letters hidden in pockets, numbers hidden in watch cases, and events buried in the past or still more deeply in the future, and even to believe that dogs and horses perform arithmetical feats that would be impossible for a bright school boy. Professor O’Shea did not dictate a remedy, but he suggested one by explaining then and there, how many popular and baffling tricks are performed, and by incidently stating that he was at that time threatened with suit for as much as he possessed, for destroying by such public explanations one faker’s means of livelihood. Suggestion is clearly over prominent in the lives of both the average and the under-average individual. With the average person certain moral and ethical standards limit the realm where suggestion rules; with the feebleminded these standards are absent, and in consequence, the most essential acts of life are but the blind realization of the suggestions of others.
With suggestion a dominant factor in conduct, it surely is important that those undertaking to guide the conduct of others find out as much as possible about this condition, about its causes and about methods of controlling it. The work so far published furnishes comparatively little information along these lines. The experimental studies on suggestion in the waking state group themselves into the many studies on the psychology of testimony; and laboratory studies on the effect of suggestions of various kinds on sensation, on judgments of sensory stimuli, on motor ability, and on imagination. The studies in the latter group have been quite varied in character. The methods used are:?the production of hallucinations by the careful preparation of an expectant attention; the production of a variation in judgment by the presentation of a second stimulus either immediately before or immediately after the stimulus to be judged; the production of a variation in judgment by an expressed judgment of the experimenter; the production of a variation in judgment by suggestions of ability or inability; the production of a variation in motor achievement by suggestions of ability and inability; the production of a variation in imaginal activity by the presentation of an immediately preceding stimulus. The subjects have varied much in age, being drawn from primary and high school pupils, college students and teachers, and suggestibility has been found in persons of all ages. Binet,2 Yung,22 Guido Guidi,8 Vitali2 and Small17 all consider suggestibility a function of age, finding that it decreases as age increases. Binet,2 and Guido Guidi8 also consider it a function of school grade, and Lippman and Guido Guidi8 a function of culture. Pearse,12 Binet,2 and Vitali,2 all found that suggestibility increased with the repetition of the suggestion experiments.
Several investigators have endeavored to find out whether there is a correlation between suggestibility for different kinds of stimuli. Professor Scott14 using suggestions of color and of heat found a very low correlation and decided that the degree of suggestibility is related to the sense stimulated. Pearse12 reached the same conclusion carrying it further. He concluded from his studies with visual, auditory, and tactual suggestions that there is a constant ratio between the degrees of suggestibility for the different senses. Pearse also finds that the highest degree of suggestibility for all the tests was attained by the same subject, an inevitable result if the ratio hypothesis is a true one.
Arthur Chojecki,4 also looking for correlations, used three tests, one suggested heat sensation, one suggested a magnetic influence, and one suggested a judgment of length of line. Sixty subjects were used, thirty men and thirty women. Twice as many subjects were influenced by the judgment suggestion as by the sensory suggestions. The two sensory suggestions were successful with the same number of persons but the persons were not the same ones in all instances. The men were more suggestible than the women. A fact brought out in the studies of Binet,2 Brand,3 and Bell1 is that a suggestion often has an effect just the opposite of the intended one. If the suggestion “warmer” is given the stimulus is judged colder, if the suggestion “heavier” is given the stimulus is judged lighter. Were the suggestion ineffectual, the subject would be free to judge from the sensational content alone; in reality he resists the suggestion just enough to oppose it but not enough to ignore it. MacDougal11 writes of this tendency and considers it a transition state between uncritical acceptance and critical judgment. It is interesting to find this tendency toward negativism, which is such a constant factor of conduct in certain insane and feebleminded types, so prominent in the reactions of average persons.
The present study is an attempt to discover something definite about the relation of suggestibility to age. It aims to find out whether there is any marked difference in the suggestibility of average boys of twelve and fifteen years of age. Forty twelve-year-old boys and thirty fifteen-year-old boys were used as subjects. Age and average performance in school were the only requirements. Apart from these two constant factors the groups were quite heterogeneous, quite representative of the Chicago populace?the seventy boys represented many races and many social conditions. Some boys were pupils of the Glenwood Manual Training School, Glenwood, Illinois, which is a school for dependent boys; these boys, before their Glenwood experience, had enjoyed few if any environmental advantages. Some boys were attending the Grammar School at Hinsdale, Illinois, where the pupils are drawn from families of education and means.*
The conditions with the exception of the time of day and the place of testing were quite constant. The majority of the tests were made at the two schools mentioned. As the tests were all made by the writer who lived at a distance from the schools, it was impossible to keep the time of day constant. The personal equation, an important factor in suggestion experiments, was as constant as possible, all tests being made by the same person, who was a stranger to all the boys. Each boy was tested individually, and was put through the series of five tests at one sitting.
Five tests were used, all devised by Binet, all of the judgment controlling type. In two tests the personal element is practically eliminated?the suggestion is given by the arrangement of the test material; in two the suggestion is purely personal; and in one there is a combination of the suggestive arrangement of material with the personal element. This last is the test made familiar by incorporation in the “Measuring Scale of Intelligence.” The other four tests with tabulated results of experiments, are presented by Binet2 in his volume entitled La Suggestibilite.
Binet’s subjects were pupils of the elementary primary school, varying in age from seven to fourteen years, and pupils of the superior primary school, averaging sixteen or seventeen years of age. For test 1 of our series Binet used 36 subjects, 24 elementary school pupils, and 12 superior school pupils; for test 3 of our series Binet used as subjects 25 elementary pupils; for test 4 of our series he used 54 subjects, 42 from the elementary school and 12 from the superior school; for test 5 he used 35 subjects, 25 from the elementary and 10 from the superior school. As among Binet’s subjects there were not many of any one age, his results do not give definite information concerning the degree of suggestibility usual at certain ages. They show in a general way that his older subjects were less suggestible than his younger ones.
I wish to express to Mr. Leo A. Philips, Superintendent of the Glemwood Manual Training
School, and to Mr. Douglass, Superintendent of the Hinsdale High School, my sincere appreciation of the cordial and generous co-operation which made this study possible.
The results attained by any one individual, in the different tests are compared by Binet in a study of order of individual achievement in the large groups, or in smaller groups representing different grades of achievement. For instance, if subject A attained the highest suggestibility coefficient in test 1 and also in test 2 there would seem to be a correlation; if subject B’s suggestibility coefficient appeared among the first ten in test 1 (number 2) and among the first ten in test 2 (number 9) there would still be a correlation, but one of less degree.
The limitation of subjects to two ages in the present study makes it possible to compare group instead of individual results. The first test in the series aims to influence the judgment of differences of weight, and to do this entirely by the suggestive arrangement of material. Fifteen wooden weights, alike in size and appearance, and conspicuously numbered from one to fifteen, are placed in a row. The first weight weighs 20 grams, the second 40 grams, the third 60 grams, the fourth 80 grams, the fifth and each succeeding weight 100 grams. The subject is told that we wish to find out how well he can judge of weights, and is instructed to lift each weight in turn once, with his right hand (if right handed), and to state for each whether it is heavier or lighter than, or just the same as, the weight that just preceded it. The habit of expecting a heavier weight each time is established by the time the fifth weight is reached, and suggestibility is measured by the number of weights in the last ten which are judged heavier. This is followed by a repetition of the lifting; this time the subject is allowed to lift the weights as often as he chooses. Finally, the weights are lifted for the third time, and the subject required to estimate the actual weight after being told that the first weight is 20 grams. Introspections are then brought out by questions and recorded.
Binet compared the results of the three trials and found the suggestibility decreased in the second and increased again in the third proceeding, and that it was greatest of all by the first method. The suggestibility was less with older children than with the younger ones. In adopting this test we limited the procedure to Binet’s first series, a single lifting of the weights; Ave recorded no introspections* and we included as suggested judgments the judgments of “lighter,” considering them due to suggestibility of the negative type. Binet discusses this point but finally excludes the negative judgments from the results. The writer feels strongly that they should be included, and the mathematical treatment of the results seeins to support this view, as the probable error, the probable error of means and the coefficient of variability are all reduced by including them. The mean, the average deviation (A. D.), the standard deviation (S. D.), the probable error (P. E.), and the coefficient of variation (C.) have been worked out for the twelve and the fifteen-yearold groups. As the mean for each group is nearly six times its probable error both means would seem to be reliable. As the number of cases was but forty and thirty for the respective groups the probable error of means (P. E.m) or the probable error of the group mean compared with the mean for a very large number of cases, was P. E. computed by the formula ? which gave a P. E.m of about oneVn thirtieth of the mean.
The mean suggestibility for the twelve year group was 8.2 of a possible 10, and for the fifteen year group it was 7.5 of a possible 10. The difference in suggestibility was thus only 0.7 in favor of the fifteen year group. The probable error of this difference was also found by the formula P. E.d = -^(P. E.ml)2+(P. E.m2)2. The result was 0.341 which is less than half the difference. The difference is too small and its P. E. too large to indicate a definite age difference. The results are presented in table I, Group Results. TABLE I.?GROUP RESULTS?AGE GROUPS CONTRASTED. Test I Test I o O co J- ID C3 > a ?? “S o o Test II o ti ,2 3 ? rS C U> S CO O ?I >< ? Test III c3 m 0) O ^ tt ?O D m Test IV O -g m l. cd aj s (5 -ii ^ . “3 N o o rH O CTest V - O a m O si 53 Mean A. D. S.D. I’.E. C…. P. E. .. m. D. M P. E. . d. 8.2 1.825 2.287 1.54 0.27 0.243 7.5 1.56 1.955 1.318 0.021 0.240 0.7 0.341 7.0 1.97 2.44 1.647 0.346 0.260 6.5 2.06 2.58 1.74 0.397 0.317 0.5 0.419 2.0 0.85 1.065 0.718 0.532 0.113 1.0 1.0 1.2533 0.8453 1.2533 0.154 1.0 0.191 1.2 0.82 1.02 0.687 0.85 0.108 0.5 0.63 0.789 0.532 1.579 0.097 0.7 0.148 142.0 21.9 27.44 18.50 0.193 128.0 13.8 17.295 11.665 0.135 31.3 9.57 11.994 2.92 2.12 30.0 7.3 9.149 8.089! 6.171 0.383 0.304 1.27 1.12 14.0 j 1.3 3.6 I 1.69
The second test in the series is that used in “The Measuring Scale of Intelligence.” The results are here treated quite differently in order to make them comparable with the results of the other tests of the series. The test aims to influence the judgment of the length of lines. Six pairs of lines are used, each pair drawn on a separate card. The lines are drawn in line with each other and one centimeter apart. The first pair measure four and five centimeters each, the second pair five and six centimeters, the third pair six and seven centimeters; the longer line in all three cases being drawn to the right. All the lines on the last three cards measure seven centimeters. The subject is shown each pair separately; as he is shown each of the first three pairs he is asked “Which is the longer line there?” and as shown each of the last three pairs “And there?”
In scoring this test for the “Intelligence Scale” resistance to suggestion is recorded, not suggestibility, and resistance is credited whether two or three of the equal pairs is judged correctly. In order to compare the results with the results of the other four tests in this study it is necessary to record suggestibility, not power of resistance, and also to credit each response.
It is interesting to note that in both the twelve and fifteen year groups, the line to the left in the last pairs was judged “longer” more than twice as often as the line to the right. That the judgment of “longer” for the line to the left is a negative response is not quite clear. Two suggestions are given by the test, a personal, verbal one of difference in size by the words “Which is the longer line?” and one of position by a suggestive arrangement of material which establishes a habit of choosing the line at the right as the longer. It may be that in the left line judgments the personal, verbal suggestion of size holds, while the material suggestion of position does not. In either case the left judgments are suggestions and are counted as such. They are implicitly so counted by Binet who accepts nothing but equal judgments as resistances. In the treatment of the results obtained from the use of this test, in the manner already described for test 1, it developed that the P. E. is so large for each group that the group averages are practically worthless. The results of test 2 are therefore omitted from our final comparative analysis. The results are presented in table I, Group Results.
Test 3 aims to influence the judgment of the length of line, this time by a purely personal, verbal suggestion. A series of 24 parallel vertical lines are drawn from a base line on a piece of paper. The shortest of these lines measures 12 millimeters and the longest 104 millimeters. The lines are arranged from left to right on the paper each one being 4 millimeters longer than the one to the left of it. These lines are plainly numbered from 1 to 24. On separate cards three other lines are drawn, one like line 6 of the series, one like line 12, and one like line 18. The subject is shown the line like line 6, allowed to look at it for several seconds, and then is asked to pick out from the series of lines the line of the same length. When he has finally determined upon one, the experimenter says, “Do you not think it is a little longer, as long as this next line?” If this suggestion succeeds the suggestion is repeated with the next longer line. The entire proceeding is repeated with lines 12 and 18. The mathematical treatment of the results-obtained from the use of this test again shows such large probable errors that neither of the group averages is reliable; they are therefore omitted from the final analysis. The results are presented in table I, Group Results.
Test 4 also attempts to influence the judgment of length of lines, but by the arrangement of material only. The method is the same as that of test 1, lines being substituted for weights. A series of thirty-seven lines are shown, one at a time. The first line measures one inch, the second two inches, the third three inches, the fourth four inches, the fifth and each of the succeeding lines five inches. The subject looks carefully at a line, estimates its length, and indicates this length by placing a dot at the proper distance from a margin on a sheet of quadruled paper. He is then shown another line, and the process repeated until the last of the thirty-seven lines has been judged. It is assumed that the habit of expecting each succeeding line to be longer will be established by the time the fifth line is estimated. Not only can one tell by the record the number of times the suggestion has held, but one can also measure the lines and discover the amount of the suggested error. Binet’s method of treating the results is to measure the estimate of line 5 and also measure the longest estimate in the series, multiply the latter by 100 and divide by the former, and thus secure a coefficient of suggestibility. By this method 100 indicates an absence of suggestibility, and this must be remembered in judging of the significance of the probable error. Binet’s method is followed in this study. In addition the length of each of the thirty-two estimates was measured, and a coefficient of average positive suggestibility, a coefficient of average negative suggestibility, and a coefficient of average total suggestibility (positive-negative) calculated. Binet’s coefficient of greatest positive suggestibility seems to be the best index of suggestibility, as it is the only one whose probable error is small enough to justify its use. It may be questioned whether this P. E. is small enough (a little more than one third the mean. The coefficient of greatest positive suggestibility for the twelve-year group is 142 (P. E. 18.5), that for the fifteen-year group 128 (P. E. 11.6). The difference in means is quite large?14. Its probable error (P. E.m) is 3.60. It seems correct to infer that there is an age difference in favor of the fifteen-year group for this test. The results are presented in table I, Group Results.
Test 5 aims to affect the judgment of length of lines by a purely personal suggestion. Forty lines are presented to the subject one at a time, and he is directed to indicate their length on quadruled paper just as in the previous test. Each of the forty lines is five inches in length. The first line is presented without comment, just before showing the second line the experimenter says in a casual way “The next line is a little longer,” and before showing the third, “And the next is a little shorter.” These remarks are repeated, longer and shorter on alternate lines, until forty have been shown. Binet used only eighteen lines. He recorded the estimated length of the first line, and the differences in the estimated length of succeeding lines, noting whether the difference was or was not in accordance with the suggestion given; he also recorded the number of resistances. He called resistances, not only a judgment of “equal” but also all judgments which were the opposite of the suggestion. This is contrary to his practice in test 2, where only equal judgments were considered resistances. The writer is strongly of the opinion that the contrary judgments are suggestions of a negative character, and by so considering them the probable error is again materially reduced. Binet finds by averaging the errors for each line separately, that the group of children of the elementary primary school made less errors on the last lines than on the first, but that this did not occur with the group made up of children from the superior primary school. This difference between the group results he accounts for by the fact that the older children made more accurate judgments from the first. Binet finally established his classification upon the number of resistances, explaining that the measure is a conventional one. With his subjects of the elementary primary schools, 25 in number, the resistances range from 0 to 14, with the pupils of the superior primary school, 10 in number, the resistances range from 0 to 12. In the present study the estimated length of the original line has not been recorded, neither have the differences in amounts of the suggested error with the succeeding lines. The judgment of each line is recorded by a plus sign if it follows the suggestion, by a minus sign if it contradicts the suggestion, and by an equal, sign if it entirely ignores the suggestion and estimates the line as equal to the preceding line. The number of suggested judgments are found by adding the plus and minus judgments. The mean, the A. D., the S. D., the P. E., the C. and the P. E.m have been calculated for each age group for positive, negative and total suggestibility, and the D. M. and P. E.a have also been calculated for both kinds of suggestibility as well as their sum. Negative or contrary judgments are more frequent among the fifteen-year-old than among the twelve-year-old boys, but the probable errors are so large that they invalidate any averages. The probable error is proportionally smaller for the positive suggestion averages, but only when positive and negative judgments are combined are the probable errors reduced sufficiently to support the means in a claim to consideration. The total suggestibility for the twelve and fifteen-yearold groups is 31.3 and 30 respectively. The small difference of 1.3 in favor of the fifteen-year-old group has a P. E.a of 1.69 which, of course, invalidates it. There is practically no age difference for the two groups in this test.
In the present study 40 lines were used instead of 18 and an attempt was made to ascertain whether the force of suggestion increased or diminished as the experiment progressed. The number of suggested judgments on each of the thirty-nine lines for each group was found, and curves plotted for these sums. It was seen that 35 of the 40 subjects in the twelve-year group succumbed to the first suggestion and 31 to the last, and that the number varied between, never rising beyond 36 nor falling below 29. The curve for the fifteen-year group showed that 24 of the 30 subjects yielded to the first suggestion and 23 to the last. The number fell to 20 on the ninth line and rose to 26 on the twenty-sixth and thirty-first line, never exceeding these limits. Repetition in this experiment seemed to have little effect upon the force of the suggestion. Curves representing the number of suggested judgments on each of the last ten weights in test 1 for each group were also plotted. Of the twelve-year group 31 of 40 proved suggestible on weight number 6 and 33 on weight number 15. The limits were 29 suggested judgments for weight 10 and 36 suggested judgments for weight 8. Of the fifteen-year group 20 of 30 subjects were suggestible for both weight 6 and weight 15; the limits were 19 suggested judgments for weight 6 and 26 for weight 10. Not one of the four curves plotted indicates that repetition either increases or diminishes the force of a suggestion.
The sifting out process has left results which seem reliable from three of the five tests used, tests 1, 4, and 5. An age difference in suggestibility is indicated in only one of these, test 4. To discover whether suggestibility for one of these tests indicates suggestibility for the others, the twelve and fifteen-year groups for each test were merged into one group of Seventy subjects, and the correlation coefficients for tests 1 and 4, tests 1 and 5, and tests 4 and 5 were calcuX xv lated by the “Product-Moments” Method of Pearson (r=n Oj o2).
The probable errors of each of these coefficients were also found? (P. E.r = 0.6745 V n The results are: Tests 1 and 4 r = 0.085 P. E.r = 0.079. Tests 1 and 5 r = 0.043 P. E.r = 0.080. Tests 4 and 5 r = 0.448 P. E.r = 0.064. The only coefficient with a sufficiently small probable error is that between tests 4 and 5.
It is of considerable interest that the only correlation coefficient found is that between two tests which, while they both aim to produce a variation in judgments of visual stimuli, differ profoundly in method of effecting the suggestion. In test 4 the suggestion is made simply by an arrangement of material, in test 5 it is made by a verbal suggestion of the experimenter. On the other hand there is no correlation between the results of test 1 and test 4 in which different sense fields are involved, although the method of effecting the suggestion depends entirely upon a similar arrangement of the material in the two tests. This lack of correlation might be partly due to the fact that the amount of suggested error is considered in scoring test 4 and is not considered in scoring test 1. To eliminate this difference test 4 was scored by the same method used with test 1, ignoring entirely the amount of suggested error, and calculating the correlation coefficient on this basis. There was still an absence of correlation. These findings are in accord with those of Scott and of Pearce, that there is a relation between the degree of suggestibility and the sense stimulated.
The results of the present study lead to the following conclusions:?that average boys of twelve and fifteen years of age are highly suggestible; that the difference in suggestibility due to the age difference between twelve and fifteen in average boys is slight; that to secure an estimate of an individual’s suggestibility it would be well to use a series of tests each effecting the suggestion through stimulation of different senses; that repetition has little if any effect on the strength of a suggestion.
Bibliography.
1. Bell, J. Carleton. The Effect of suggestion on the reproduction of triangles and of point distances. Amer. Jour, of Psychol, 1908, 19, 504-18. 12 THE PSYCHOLOGICAL CLINIC. 2. Binet, Alfred. La Suggestibilite. Paris: Schleicher Freres, 1900, 391pp. (Contains historical review.) 3. Brand, John E. The Effect of verbal suggestion upon the estimation of linear magnitudes. Psychol. Rev., 1905, 12, 41-9. 4. Chojecki, Arthur. Contribution h l’6tude de la suggestibilite. Archiv. de Psychol, 1911, 11, 183-86. 5. Edwards, A. E. An Experimental study of sensory suggestion. Amer. Jour, of Psychol., 1915, 26, 99-129. 6. Elst-Gaume, Robert van der. La Suggestion. Rev. de Philos., 1910, 17, 476-95. 7. Feingold, Gxtstave A. The Influence of suggestion on the imagination. Amer. Jour, of Psychol., 1915, 26, 540-49. 8. Guidi, Guido. Recherches exp6rimentelles sur la suggestibilite. Archiv. de Psychol., 1908, 8, 49-54. 9. Hartenberg, Paul. Die zwei Hauptformen der Suggestibilitat. Zsch. f. Psychother. u. Psychol., 1910, 2, 44-47. 10. Jones, Grace Milard. Experiments in the reproduction of distance as influenced by suggestion of ability and inability. Psychol. Rev., 1910, 17, 269-78. 11. MacDougal, Robert. Contrary Suggestion. Jour, of Abnormal Psychol. 1912, 6, 368-91. 12. Pearce, Haywood J. Experimental observations upon normal motor suggestibility. Psychol. Rev. 1902, 9, 329-56. 13. Powelson, Inez, and Washburn, Margaret F. The Effect of verbal suggestion on judgments of the affective value of colors. Amer. Jour, of Psychol., 1913, 24, 267-69. 14. Scott, Walter Dill. Personal differences in suggestibility. Psychol. Rev., 1910, 17, 147-54. 15. Seashore, C. E. Measurements of illusions and hallucinations in normal life. Studies from Yale Laboratory, 1895, 3, 1-66. 16. Sidis, Boris. The Psychology of suggestion. New York: D. Appleton Co., 1910, 386 p. 17. Small, Maurice H. Suggestibility of Children. Pedagogical Seminary, 1897, 4, 176-220. 18. Starch, D. Unconscious imitation in handwriting. Psychol. Rev., 1911, 18, 223-8. 19. Strong, E. K. The Effect of various types of suggestion upon muscular activity. Psychol. Rev., 1910, 17, 279-93. 20. Triplett, Norman. The Psychology of conjuring deceptions. Amer. Jour. of Psychol, 1900, 11, 439-510. 21. Washburn, Margaret F. An Instance of the effect of verbal suggestion on tactual space perception. Amer. Jour, of Psychol., 1909, 20, 447-8. 22. Yung, Emile. Contribution & l’6tude de la suggestibility a l’etat de veille. Arch, de psychol, 1909, 8, 263-85.
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