In this phase of the study investigation was directed primarily toward establishing the effect of marihuana on the subject's intellectual functioning. An attempt was made to determine what changes in mental ability occur under different amounts of the drug, what direction these changes take, when they are first measurable, and how long they persist.
Bellevue Adult Intelligence Test
This test was used to measure the general mental level of all the subjects. It was chosen in preference to other available scales because it is the only individual test of intelligence which has been standardized on an adult population, takes into account both verbal and performance abilities, and compares the individual with standards established for his particular age group. It consists of ten tests, five verbal and five performance. The verbal tests cover the fields of general information and general comprehension, draw on the individual's capacity for abstract reasoning and test his arithmetical ability and his rote memory. The performance tests also evaluate the subject's comprehension of social situations, but here the results are independent of language. There are also tests of the individual's ability to carry out a routine task, to organize parts into a meaningful whole, to distinguish between essential and unessential details, and to analyze and synthesize.
Army Alpha (Bregman Revision, Forms A, B, 5, 7 and Bellevue Revision)
This is a group test first used in the United States Army in 1917 and 1918 when it was given to more than a million recruits. It consists of eight tests: test 1, a direction test which was not used in this study since the item does not appear on all forms; test 2, a test of arithmetical reasoning; test 3, a test of common sense in which the subject indicates which he considers the best of three possible responses to a given question; test 4, a modified vocabulary test; test 5, in which the subject must mentally reorganize disarranged sentences and then indicate whether the resultant statement is true or false; test 6, a Wg of numerical relations in which the subject must supply the last two numbers in a numerical series on the basis of the relationship between the first six numbers; test 7, a test of analogies in which the subject determines the relationship between two given words and then underlines one of four words which is related to a third word in the same way; and test 8, which on Forms A and B and on the Bellevue Revision is a test of general information in which the subject is given a choice of five answers to a question. On Forms 5 and 7, this test is a test of directions.
Because this test has five alternate forms which are roughly of equivalent difficulty it could be repeated many times within a short time interval. It was therefore used to establish a curve showing at what time following ingestion the marihuana has an effect on general intelligence and on individual higher mental processes.
Pyle's Digit Symbol Test
In this test each number from 1 through 9 is associated with a specific symbol, as, for example, number 1 is associated with a square and number 2 with an asterisk. The numbers and their associated symbols appear at the top of the sheet of paper. Below the sample are rows of symbols, five symbols to a row, followed by five blank squares. The subject is expected to fill in each square with the number associated with the respective symbol. With practice the association bond between the number and the symbol becomes stronger and the subject depends less and less on the model at the top of the sheet. He is therefore able to work faster and his learning rate is reflected in the increased number of squares filled.
The subject is required to cross out a specific geometric form wherever it appears on a sheet which is covered with rows of geometric figures. This measures the individual's capacity for carrying out a routine task.
Form Board Test
The measurement of the ability to manipulate concrete material in contrast to the verbal or abstract ability determined by the Army Alpha test required the introduction of certain form board tests. These were the Seguin Form Board, the Two Figure Board, the Casuist Board, the Five Figure Board, Healy A, Triangle Test, Diagonal Test, all administered and scored according to the Pintner-Patterson Performance Series. The Seguin Form Board has ten blocks of various goemetric forms, to be put in their appropriate places as rapidly as possible. Three trials are given. The Two Figure Board has nine pieces which, when placed correctly, form a large cross and a large square. Time and the number of moves are recorded. The Casuist Board has twelve pieces which, when correctly placed, form three circles and an oval. Time and errors are recorded. The Five Figure Board has five geometrical figures which are formed by the correct placement of two or three pieces for each figure. Time and errors are recorded. Healy A has five' small rectangular pieces which, when placed correctly, form a large rectangle. Time and the number of moves are recorded. The Triangle Test consists of four triangular pieces which are fitted together in a board. Time and errors are recorded. The Diagonal Test has five pieces of various shapes which must be fitted together in a rectangular frame. Time and moves are recorded.
Kohs Block Design Test
This is a performance test which is less a test of manual dexterity and more dependent on abstract intelligence than are the form board tests. It correlates more highly with intelligence than do most performance items and yet it is entirely independent of language. Therefore, the individual who cannot express himself well or who suffers from a language handicap is not penalized as he is on verbal scales.
The test consists of sixteen cubes each with a red, a white, a blue, a yellow, a red-and-white, and a blue-and-yellow side. A colored design which can be reproduced with the cubes is placed before the subject and he is expected to make it. Results are rated numerically, depending upon the time consumed in execution. In this experiment two sets of designs of equivalent difficulty were required; Designs IV, VI, and XIV were selected for one series and V, VII, and XII for the other.
Although memory in itself cannot be considered a measure of intelligence, it is essential to any intelligent functioning and must therefore be included in any estimate of intelligence. Three aspects of memory, namely rote memory, the ability to recall presented objects, and visual memory were tested. The rote memory test requires the repetition of digits in forward and reverse order as given on the Bellevue Intelligence Test.
Object memory was tested by exposing ten small objects for three seconds and recording the number of articles the subject was able to recall. Visual memory or the ability to reproduce designs after a ten-second exposure was estimated by using the designs and scoring technique from the Army Performance Test.
The Bellevue Adult Intelligence Test
Each subject was given the Bellevue Adult Intelligence test within two or three days after his admission to the hospital and before any marihuana had been administered.
The Army Alpha, Pyle's Digit Symbol, and Cancellation Tests
These tests were given as group tests to a total of 20 subjects. The Army Alpha and Pyle's Digit Symbol tests were given every half-hour, beginning a half-hour after drug ingestion. The Army Alpha was continued for seven hours and Digit „Symbol for five hours. The Cancellation test was given every hour for six hours, beginning one hour after drug administration. Eleven users and 9 non-users took the Army Alpha and the Digit Symbol tests, while 9 users and 11 non-users took the Cancellation test.
Tests 2 through 8 of the Army Alpha require twenty and a half minutes for actual performance while such preparations as the distribution of papers and the reading of directions consume almost ten minutes more, so that had the entire Alpha been given at each half-hourly session, the subjects would have gone from test to test with no intermittent rest period. For this reason the tests were divided and the following schedule arranged:
* Although one and a half minutes is the usual time allotment for this test, two minutes were used for it in this study.
Each subject took three test series, one without the drug, one with 2 cc. and one with 3, 4, 5, or 6 cc., depending on individual tolerance. A test series consisted of fourteen half-hour sessions for the Alpha, ten half-hour sessions for the Digit Symbol and seven hourly sessions for the Cancellation tests. Because of the time factor, a series required two days for its completion.
The halves of a series were given on successive days, and the different series a week apart. Thus for example, a subject might take his first test series with 2 cc. on Monday and Tuesday of one week; the following Monday and Tuesday the series would be repeated with the subject in a different drug state (no drug or 5 cc.); and a final series would be given the third week with the subject in still another drug condition.
An effort was made to obviate practice effect by giving the first test series to one third of the subjects without drug, to one third with 2 cc., and to one third with 3, 4, or 5 cc. However, because of the necessity of increasing dosage gradually this ideal presentation was not actually obtained. The following gives the amount of drug administered to users and non-users at each test series.
Since the various forms of the Army Alpha are not absolutely equivalent in difficulty, their order of presentation for any one group had to be identical in each of the three drug states. However, for each of the three groups tested the order of presentation was different so that all the difficult forms did not come at the same interval, as is shown on the following page.
* 5 cc. is used to indicate large doses although the amount ranged from 3 cc. to 6 cc. depending on individual tolerance. In the non-user group no maximum dose for this test was more than 4 cc.
** Entered experiment too late to take more than two series.
t Patient took initial series with 5 cc. but became so ill test was discontinued and only two subsequent series given.
# Patient discharged from experiment before third series was given.
Kohs Block Design, Form Board, and Memory Tests
Administration of these tests differed markedly from those discussed above in that no attempt was made to give them at regular successive time intervals. Rather, they formed part of a battery of individual tests given to various subjects under specific drug conditions. For example, 5 cc. of marihuana would be ordered for a patient for 8:00 A.m., and testing began as soon thereafter as the patient appeared "high," the state of "highness" being judged by the subject's own statement, his pulse rate, the condition of his pupils and other physiological signs.
Kohs Block Design was given to each subject twice, once without the drug and once with 5 cc. The test was taken by a total of 21 subjects, 10 users and 11 non-users. Five users took the test first without the drug, 5 had their first trial with 5 cc. Of the non-user group 8 had their first trial without marihuana, 3 with 4 cc. The average time at which the test was given to the user group was three and a half hours after drug administration, with range from two to five and a half hours. For the nonuser group, the average time of administration of the test was also three and a half hours after the drug was given, range two and half to five and a half hours.
The two series of designs (one series being Designs IV, VI and XIV, the other V, VII and XII) were presented in such manner that half of the subjects were tested on one series and half on the other series while they were under the influence of marihuana. Thus any difference in degree of difficulty between the two sets of designs was cancelled out. The weighted scores given on the Arthur Point scale were used in evaluating the results.
Form Board Tests were divided into three batteries, each battery consisting of the Seguin Form Board, one of the three larger boards (Two Figure, Five Figure, or Casuist) and one of the three smaller boards. Various combinations of boards were used under various drug conditions in order to make the results as comparable as possible. The following indicates the number of times the various boards were used with different dosages of marihuana.
From the results it appears that Gwyn Triangle was used too often with 5 cc. and Healy A was not used often enough.
Aside from the Triangle and the Healy A, the distribution of boards in different drug stages was such as to obviate any differences in degree of difficulty. Nineteen subjects, 10 users and 9 non-users, took this test. The results were scored for time and errors according to the Pintner-Patterson Performance series.
Memory tests. The first digit span test was always given before marihuana had been administered, since the Bellevue Scale was given each patient during the first two or three days of the study. The trials under 2 cc. and 5 cc. were alternated. In all, 28 subjects, 17 users and 11 non-users, took this test before and after the ingestion of marihuana. The final score equaled the number of digits recalled.
To test Object Memory, ten small articles such as a key, a ring, a pill box, and a crayon were placed on a flat, neutral surface and exposed for three seconds. An attempt was made to vary some of the articles at each presentation so that six or seven were the saine and three or four were different. Twenty-six subjects, 11 users and 15 non-users, took this test. They were so divided that 10 of them took the test the first time without drug, 10 with 2 cc., and 6 with 5 cc.
To test Visual Memory, Army designs were given each subject three times, once prior to the administration of marihuana, once under 2 cc., and once under 5 cc. The test was given to a total of 28 subjects, 16 users and 12 non-users.
Because there is no alternative form for this test, results were definitely influenced by practice. Here, therefore, more than with any other test, it became important to arrange the order of administration. The following indicates the dosage of marihuana at the first test.
It is obvious that the initial examination was given slightly more often when the subjects were not under the influence of the drug. Improvement derived from practice is therefore more of a factor in the tests which were performed under marihuana.
Bellevue Adult Intelligence Test
General Intelligence. The results of the Bellevue Adult Intelligence Test which was administered to 60 subjects, 40 users and 20 non-users, are shown in Table 5. As has been pointed out elsewhere, these findings indicate that both the user and the non-user groups may be classified as of average intelligence.
Mental Deterioration. Studies of mental deterioration due to toxic, organic or psychotic factors, as given in the literature, reveal that in such cases the subtest scores on the Bellevue Adult Intelligence Test show marked irregularity, depending upon. the functions involved in the deteriorative process. As a group, the marihuana users tested show very even functioning, and what little irregularity occurred can be explained on the basis of language and racial factors.4 From this we may conclude that the marihuana users had suffered no mental deterioration as a result of their use of the drug.
Army Alpha Test
Total Mental Functioning. The total scores obtained from this test at the successive testing periods are shown in Table 6. Those recorded before the administration of the drug give a picture like that seen in any learning curve, that is, there is a gradual increment in test scores at each testing interval, interspersed with plateau periods. Thus, without drug the test score for the second testing interval showed a 2 per cent gain over the initial score, the score for the third testing interval showed a 4 per cent gain over the initial score, and so on up to the last testing period when there was a 13 per cent gain over the initial test score.
Between two and a half and three hours after ingestion of 2 cc. of the drug there appeared to be a possible very slight falling off in mental ability. Otherwise the results paralleled the findings obtained in the undrugged condition except that toward the end of the day the increments were larger than those which occurred when the subjects were undrugged. This may be due to complications in the experimental procedure or may be an indication of accelerated mental functioning resulting from drug ingestion. This point is discussed more fully when the effect on different mental functions is considered.
Deleterious effects were apparent an hour after the ingestion of 5 cc. of marihuana. There was a 3 per cent drop from the initial score at this one-hour period and this first attainment is not surpassed until four and a half hours after drug ingestion. From the four-and-a-half-hour period on to the end of the testing there were gradual increments in score.
Different Mental Functions. A very elaborate study was made of the scores made on the subtest (Table 7). Some irregularities occurred even in the undrugged state, and these may be attributed primarily to chance factors, as, for example, the difference in difficulty of the various test forms. On the whole, the findings were in line with those which one would expect in any situation where constant repetition increases efficiency.
The effects of 2 cc. of marihuana on the different mental functions were variable. Tests involving number concepts gave clear-cut, consistent findings and revealed that impairment occurred an hour after the drug was taken and continued for from two and a half to three hours after ingestion. Results of other tests showed that there was little if any loss in ability, and some of them, especially those done toward the end of the day, showed gains which exceeded the ones made in the undrugged state. It is not possible on the basis of the present data to ascertain whether these large increments indicate that small amounts of the drug serve as stimulants in situations dependent primarily upon verbal facility or whether they are due to certain complications in the test technique. The former theory coincides with the increased verbosity noted on other tests as well as with the clinical impression, but the latter also cannot be overlooked. Further investigation of this point is definitely indicated.
The effect of the 5 cc. dosage on each function was in line with that reported for total scores, that is, there was a falling off in efficiency one hour after the drug was taken and this impairment continued for anywhere from three and a half to six and a half hours after ingestion. Here too the scores on tests involving number concepts were most severely affected, recovery for them taking place from six to six and a half hours after drug administration.
Degree and Duration of Drug Eflect. In general it may be ,stated that marihuana has a deleterious effect on mental functioning, the extent, time of onset, and duration of the impairment being related to the amount of drug taken.
The adverse effect of the 2 cc. dosage on global intelligence was slight (about 3 per cent to 4 per cent impairment in efficiency) and of sort duration, occurring at about two and a half hours after ingestion and lasting little longer than a half-hour or an hour. Certain mental functions, especially those dealing with number concepts, appear to have been affected much earlier than others, the effect on the number test scores being measurable as early as one hour after ingestion and continuing until two and a half hours after ingestion. For other functions, in particular those involving verbal facility, the results were variable, in some instances showing no adverse effect and even a slight acceleration.
The effect of 5 cc. of marihuana on global intellectual functioning was apparent within an hour from the time the drug was taken and was operative until four and a half hours after ingestion. All mental functions showed this early impairment but for some of them recovery from the adverse effect was earlier than for others. Those most severely impaired from point of view of duration were the ones dealing with number concepts.
The testing program was continued for only seven hours after the drug was taken and, therefore, any estimate of the effect of marihuana after this time is purely a subjective one. However, both the subject and the examiner felt that the drug produced a "hang-over" which in most cases continued into the following day. The subject complained of being headachy, sleepy, and unable to work at his usual level, and the examiner also noted that the subject did not work as well or as quickly when called upon to do something on a day following marihuana ingestion.
The impairment reported here is not entirely representative of the maximum impairment which occurs under the influence of marihuana. Two opposing variables account for the results obtained in the drugged condition. One variable is practice effect which tends to increase test scores with each succeeding trial. The other variable, the drug, tends to lower test scores. In the earlier sessions there was evidence that the marihuana, especially when given in large doses, is the more potent force, as seen by the continuing downward trend of the curve during the first few hours. In these earlier phases, in spite of repetition, results were lower with each succeeding trial, or if there was no actual loss, the increments made were never comparable to those made in the undrugged state. Three or four hours after drug administration there was a general trend toward rising scores. Some of this gain must be attributed to increased practice effect which was counteracting, in part at least, the deleterious effect of the marihuana. For this reason it is not certain that the drug was less effective at later points in the curve than it was at the moment of seemingly greatest impairment. This seems particularly plausible because, beginning with the third hour, the subject was no longer working on new tasks but was actually repeating identical tasks that he performed earlier in the day. Thus, at the third hour the test form used was the same as the one given at the initial session; at the end of the three-and-a-half-hour period the form was the same as the one-hour examination, and so on. What is shown in the curves is the effect of marihuana on intellectual tasks with which the subject has become very familiar. For practical purposes the test situation has the advantage of being comparable with daily living since the tasks performed in daily routine are usually relatively familiar ones.
Speed Versus Power. Intellectual impairment under the influence of marihuana resulted from a loss in both speed and efficiency. There was a slowing up in output indicated by the difference in the number of items done before and after the administration of the drug. On the whole the number of test items attempted tended to increase at each succeeding examination period even when the subject was under the influence of marihuana, but the percentage of increase in the drugged state practically never equaled that attained for the corresponding time interval when the subject had not ingested the drug. The findings for the number of items done in the drugged and undrugged condition follow very closely the findings in respect to the number of items correctly done. From this it may be concluded that under the influence of marihuana an individual functions less rapidly and also less efficiently than when he has had no drug.
Careful analysis of what causes the loss in efficiency reveals that certain factors not necessarily related to mental ability per se were accountable for the reduced scores in the drugged state. For example, under the influence of the drug the subject felt dizzy, had blurred vision, or exhibited other handicapping physiological disturbances. These impeded his efficiency in putting his answer on the correct line, or marking a cross in the right box. Men were observed running their fingers across the page in an effort to keep their place. On the other hand, much of the intellectual loss can be ascribed to an impairment in the thinking processes, and there seemed to be a general confusion of ideas and inability to maintain a fixed goal. Some subjects reported that the reason they accomplished so little was that, by the time they had finished reading a question, they no longer remembered what their purpose in reading it had been. Occasionally perseveration of a form of response specific to one test was found in a subsequent test. For example, some forms of the Same-Opposite test require the subject to mark the answer S or O. In a later test requiring a plus or minus response occasional irrelevant S's or O's appeared.
Comparison of the Effect of Marihuana on User and Non-User. When the group is divided into marihuana users and nonusers certain interesting and suggestive differences are revealed (Table 8). Although the general findings for total intelligence scores for the two groups follow similar curves, the deleterious effects were not as great on the user as on the non-user. Thus under 2 cc. of marihuana the user showed no real intellectual impairment except for a very short interval beginning about two and a half hours after ingestion and lasting for an hour or an hour and a half. In contrast to this he made gains both at the beginning of the testing and toward the end of the day which exceeded those made in the undrugged state. The non-user who had ingested 2 cc. of marihuana showed a definite drop in score beginning about two and a half hours after ingestion, and for a period from one and a half to two and a half hours after this time he did not make increments comparable to those which he made in the undrugged state. Following this, during the last two hours of testing he, like the user, obtained scores which showed an acceleration not paralleled in the undrugged state.
Under 5 cc. of marihuana both the user and the non-user showed a 3 per cent loss in efficiency within an hour of the time that the drug was taken. Although recovery was slow for both groups, the user was less severely affected, as is indicated by the fact that at the next testing interval his score was only 1 per cent below his initial score as compared with a 7 per cent loss on the part of the non-user. The disparity in the degree of impairment for the two groups continued for several hours. The more marked drug effect in the case of the non-user was further evidenced by the fact that the user showed recovery four or four and a half hours after ingestion (as measured by the time when his scores approach those made when in the undrugged state) while the non-user, even at the end of seven hours of testing, did not approximate his undrugged performances.
No simple explanation of this difference is available. The most probable reason seems to be that previous use of the drug in some way serves to ameliorate that anxiety and inevitable disorganization which the use of any drug may have on an individual who has never taken it before. Another explanation may lie in possible physiological adaptation to the drug which, though not identical with tolerance in the ordinary pharmacological sense, seems to act in the same direction.
Variability. The results reported here are all in terms of averages. A study of individual scores indicates that there was marked variability in the effect of the drug on different subjects. In one case the drug action came early and soon disappeared. Another subject experienced no reaction until after he had eaten his lunch, at which time a very definite effect was apparent. A third subject showed impairment late in the day when the drug effect on almost all the other subjects had worn off. There were some hardy souls who did not appear to be affected by even large quantities of marihuana, while a few (mainly non-users) became so ill that they could not , continue with the examinations.
Pyle's Digit Symbol Test
Comparison of the results obtained on this test when the subject was in the undrugged condition and when he had had 2 cc. of marihuana reveals that small amounts of the drug did not interfere with his ability to carry out the appointed task (Table 9). In fact, as was noted above for certain other tests, the improvement in score at the end of two and a half or three hours was greater after the ingestion of 2 cc. of marihuana than it was when no drug had been administered, and at the end of the five-hour testing period there was a 32 per cent increase in score as against a 22 per cent increase in the undrugged condition.
Under the influence of 5 cc. of marihuana, however, there was a decrease in ability occuring within an hour after the time the drug was administered. Although the scores show no actual loss as compared with the initial score, the increments did not equal those made in the undrugged condition until from four to four and a half hours after ingestion.
It may therefore be concluded that certain types of learning ability are not affected by small amounts (2 cc.) of marihuana, but are impaired when larger amounts (5 cc.) are ingested.
The results of this test are shown in Table 10.
With 2 cc. of marihuana, there was a slight falling off in the subject's efficiency occurring about three hours after drug ingestion. At that time he was 3 per cent less efficient than he had been an hour previous. With 5 cc. of marihuana there was a slowing up in the subject's ability to carry out the appointed task, which was apparent two hours after drug ingestion (and possibly earlier). At that time there was only a 4 per cent increment over his initial score as compared with a 10 per cent increment in the undrugged state and a 12 per cent increment when the 2 cc. dosage had been administered. He improved only slightly at the three- and four-hour testing interval, and only at the five-hour interval did he show an appreciable improvement.
Apparently, the carrying out of a simple routine task is adversely affected to a slight degree and for a short period of time as the result of the ingestion of 2 cc. of marihuana, while the ingestion of 5 cc. of the drug produces adverse effects which are more severe and more lasting.
Seguin Form Board. For adults of average intelligence this test is primarily one involving speed of reaction time. The average time taken by the subjects when they were not under the influence of marihuana was 12.8 seconds. This was increased to 14.0 and 14.1 seconds under doses of 2 cc. and 5 cc. respectively. Thus, ingestion of marihuana in 2 cc. and 5 cc. doses caused a 9 per cent delay in performance time.
Form Boards. The time scores for this test remained practically the same whether no drug, 2 cc. or 5 cc. of marihuana had been administered, the average scores in terms of mental age being respectively 11.7, 11.7 and 11.9 years. The error scores also showed little change as a result of drug ingestion, the averages in terms of mental age being 9.7 years (no marihuana), 9.9 years (2 cc.) and 10.2 years (5 cc.), and what change occurred was in a positive direction, that is, there was a very slight improvement in the subject's performance when he was under the influence of marihuana.
Kohs Block Design. This test correlates more highly with abstract intelligence than do any of the other performance tests. Here the drug had a definitely deleterious effect when it was administered in large amounts. The average score was 17.6 when the subjects were not under the influence of marihuana and 14.8 after they had ingested the drug; that is, under 5 cc. of marihuana there was a 16 per cent loss in score as compared with undrugged results.
In general it appears that those functions most closely associated with higher intellectual processes are more impaired by the drug than are the simpler functions.
Rote Memory. As measured by the ability to repeat digits forward there were no changes in rote memory as a result of drug ingestion, the average scores under no drug, 2 cc. of marihuana, and 5 cc. of marihuana being in each case 7.1.
Digits Reversed. Although the giving of digits in reverse order is always grouped with memory tests, this task actually requires something over and above mere recall. It demands a mental control not necessary in tests dependent purely upon rote memory. Although simple rote memory, as measured by the ability to repeat digits forward, was not affected by the ingestion of marihuana, the repetition of digits reversed was affected adversely. In the undrugged state the average for the group was 5.4, with 2 cc. the average was 5.0, and with 5 cc. it was 4.8. The impairment was comparatively small but it seems to have been related to the amount of drug taken.
Object Memory. The average scores under no drug, 2 cc. of marihuana, and 5 cc. of marihuana were respectively 6.2, 5.6, and 5.9; that is, there was a loss of about 9 per cent in the subject's ability to recall objects which had been exposed to his vision for three seconds when he took the test under the influence of 2 cc. of marihuana, while after the ingestion of 5 cc. the impairment was less, being only about 5 per cent. This seemingly contradictory result is probably due to the fact that by the time the subjects took the test under the influence of 5 cc. most of them had already had it two times previously. The loss in terms of absolute number of remembered articles was slight.
Visual Memory. In this test as in the case of digits reversed something over and above simple memory function is involved. A capacity for analysis and synthesis which correlates well with intelligence is required for the successful execution of this task, and it is this function which is adversely affected by the ingestion of marihuana. The average scores were 10.3 (no drug), 9.7 (2 cc.) and 7.8 (5 cc.); that is, after the ingestion of 2 cc. of marihuana there was a 6 per cent drop in score, while under 5 cc. there was a 24 per cent drop.
In general one may conclude that simple memory functions are not affected by the administration of marihuana while the more complex memory functions are affected adversely, the extent of the impairment being related to the amount of drug taken.
Throughout the examination of subjects on individual tests, the same difference was observed in intensity of the effect upon user and non-user as was noted in group tests.
Experiments with Marihuana Cigarettes
In addition to the tests made to determine the effect of the ingestion of marihuana on various intellectual functions, several experiments were tried with marihuana cigarettes. The tests used in this part of the study were the Bellevue Adult Intelligence Test; the Woody McCall Mixed Fundamentals Test, Form I, which consists of thirty-five examples requiring addition, subtraction, multiplication or division; a cancellation test in which the subject is required to cross out a specific number (in this instance the number 8) wherever it appears on a sheet covered with rows of numbers; the Kohs Block Design Test; and the test for rote, object, and visual memory.
The subjects took the test series and individual tests twice, once without the drug and once after having smoked marihuana cigarettes. They were not given a specific number of cigarettes but were told to smoke until they felt "high." The number of cigarettes smoked to produce this effect ranged from two to seven.
The Mixed Fundamentals and cancellation tests were given as group tests and were repeated at half-hour intervals for two and a half hours. In the series given when the subjects were "high," the first test was taken as soon as the cigarettes had been smoked. Time limit on each test was one and a half minutes.
The Bellevue Adult, Kohs, and memory tests were given as individual tests and were administered only twice, once before the subject had smoked marihuana cigarettes and once after he had become "high" from smoking them. If during the course of the examination he wanted another cigarette or the examiner had reason to suspect that he was no longer under the influence of the drug, more cigarettes were smoked. The number of cigarettes used during a three-hour testing period ranged from six to twelve.
In the cancellation, Kohs, and memory tests the subjects were so divided that half took the tests for the first time before they had smoked and half after they had smoked. In the Woody McCall Mixed Fundamentals Test more non-users had their first tests before they had smoked. The Bellevue Adult Intelligence Test was always given first without the drug during the two or three days immediately following the subject's admission. Four weeks later the test was repeated on 10 subjects while they were under the influence of marihuana cigarettes.
Bellevue Adult Intelligence Test
Ten subjects, 5 users and 5 non-users, repeated this test under the influence of marihuana. The results are shown in Table 11.
Since the test taken when the subject was "high" was always his second experience with it, some allowance must be made for practice effect. Without drug the average I.Q. of these subjects was 101.6, while after they had smoked cigarettes it was 104.4. This increase of only 2.8 points is smaller than one would probably get with repetition occurring after such a short time interval. It may be concluded, therefore, that smoking marihuana cigarettes has some negative effect on intellectual functioning, in that the subject benefits less from previous experiences than he would if he had not smoked.
Woody McCall Mixed Fundamentals Test, Form 1
This test was given to 24 subjects, 10 users and 14 non-users. From the results which are shown in Table 12 it may be concluded that when the subject was "high" after smoking marihuana cigarettes there was a slowing up in his ability to do simple arithmetic calculations. This lag occurred within the first half-hour after smoking and continued for at least an hour. The deleterious effect was not such as to cause an actual loss in ability but the increments resulting from repeated practice were never as great in the drugged as in the undrugged state. Thus, the initial increment was 10 per cent in the test given before smoking and only 4 per cent in the one administered after the subject had become "high." The final increment at the end of two and a half hours was 20 per cent without drug, 13 per cent with drug.
This test measures the subject's ability to use acquired knowledge. Under the influence of marihuana cigarettes the capacity for using such an acquired skill is not lost but is slowed down. The adverse effect of smoking marihuana in cigarette form occurs almost immediately in contrast to the delayed action of the pills.
Sixteen subjects, 8 users and 8 non-users, took this test, the results of which are shown in Table 13. As a result of smoking marihuana cigarettes the subject worked a little slower in his execution of a routine task than he did when he had not smoked. The increment over the initial score in the test score made a half-hour after he became "high" was only 7 per cent as against an increment of 9 per cent when the cigarettes had not been smoked. His performance was slowed up for one hour after smoking and possibly longer.
Kohs Block Design Test
This test, which measures performance ability, was given to a total of 9 subjects, 6 users and 3 non-users. The average score without the drug was 18.5, and after cigarettes had been smoked 14.7. This difference in score of 3.8 points indicates a loss in efficiency of 21 per cent.
Rote Memory. Thirteen users and 9 non-users took this test. Neither in repeating digets forward nor in giving them in reverse did the subjects show any disadvantageous effects from the use of marihuana cigarettes, the average scores before and after smoking being 6.9 and 7.1 respectively for the digits forward test and 5.2 and 5.1 for the digits reversed test. The only explanation for this deviation from the results obtained when marihuana was taken in pill form is the inability to control the dosage when marihuana is given in cigarette form.
Object Memory. Thirteen subjects took this test. Object memory was not impaired by the smoking of marihuana, the average scores being 6.8 before the cigarettes were smoked and 7.1 when the subjects were "high."
Visual Memory. There was an .8 point loss (from 10.5 to 9.7) in the average score of the 20 subjects, 11 users and 9 non-users, who took this test. This represents an impairment of about 8 per cent.
Effect of Marihuana Cigarettes on Users and Non-Users
The difference in intensity of effect of marihuana cigarettes on the user and on the non-user was not the same as the difference in the effect of the marihuana concentrate on these two groups. The user was usually more affected by smoking marihuana than was the non-user, probably because the nonuser did not smoke as much or as intensely as the user and was not as much under the influence of the drug.
EFFECTS ON WOMEN
Five women were used in this experiment, 1 marihuana user and 4 non-users. The group as a whole was of average intelligence, with an I.Q. of 101.3, range 85 to 115, on Bellevue Adult Intelligence Test. Verbal I.Q. was 101.0, range 89 to 116; performance 1.Q. 101.5, range 83 to 117. Average age for the group was 30.3 years, range 28 to 34.
The tests used and the procedure employed were the same for the women as for the men with the following exceptions: (1) the Army Alpha test was given every hour instead of every half-hour; (2) no form board tests were given; (3) no group tests with cigarettes were given.
Test results for the female subjects were not entirely like those obtained for the men. In the case of the women, intellectual impairment, as measured by Army Alpha total scores, was more severe and lasting under 2 cc. of marihuana than it was under 3 to 5 cc. This was also true of learning ability as measured by Pyle's Digit Symbol test. The ability to carry out a routine task showed impairment only when tested under the influence of 3 to 5 cc. of the drug. The ingestion of the drug in either dosage brought about an improvement in rote memory (digits forward), while in the digits reversed test there was an impairment under 2 cc. and no change under 5 cc. Object memory remained unchanged when the subject had had 2 cc. of marihuana, and was slightly impaired with 3 to 5 cc. and cigarettes. There was a drop in score for visual memory (Army Designs Test) under both 2 cc. and 5 cc. of the drug. Kohs Block Design Test (a performance test which requires integrative functioning at higher intellectual levels) was given only twice, once without the drug and once with 5 cc. There was a loss in efficiency on this test when taken under marihuana which was comparable to that reported for the men.
It should be noted that the performance of the female subjects showed great variability. The variability may have been due either to the small number of subjects employed, or to their special selection, or both, and the findings can only be considered suggestive of possible trends. The fact that in some tests the subjects were more adversely affected by 2 cc. of marihuana than by larger doses is probably due to the fact that the 2 cc. dose was always administered before the larger dosage, and possibly also to the seemingly greater suggestibility of this particular group of women.
1. Marihuana taken either in pill or in cigarette form has a transitory adverse effect on mental functioning.
2. The extent of intellectual impairment, the time of its onset, and its duration are all related to the amount of drug taken. Small doses cause only slight falling off in mental ability while larger doses result in greater impairment. The deleterious effect is measurable earlier with large doses than with small ones, and the impairment continues for a greater length of time with large doses than with small ones.
3. The degree of intellectual impairment resulting from the presence of marihuana in the system varies with the function tested. The more complex functions are more severely affected than the simpler ones.
4. In general, non-users experience greater intellectual impairment for longer periods of time than the users do. This suggests the possibility of an habituation factor.
5. The falling off in ability which occurs when an individual has taken marihuana is due to a loss in both speed and accuracy.
6. Indulgence in marihuana does not appear to result in mental deterioration.
4 The age factor does not affect the result since the groups were well equated in this respect.