Harvard Psychological Studies Part 23

Five days' interval instead of two.

In the following summary the recall after two days is combined from Tables I. and II. for the three subjects _M_, _S_ and _Hu_, there being no important difference in the conditions of experimentation.

For the three other subjects this summary is merely a resume of Table II. The recall after nine and sixteen days in Table II. is omitted, and will be taken up later. The figures are in all cases based on the remainders left after those couplets in which indirect a.s.sociations occurred were eliminated both from the total number of couplets learned and from the total number correctly recalled. _E.g._, in the case of nouns, _M_ learned, in all, 42 couplets in the _A_ and _B_ sets, but since in 3 of them indirect a.s.sociations occurred, only 39 couplets are left, of which 21 were correctly recalled. This gives 54 per cent.

SUMMARY OF RECALL AFTER TWO DAYS.--FROM TABLES I. AND II.

N. O. V. M.

M. 54 per cent. 62 per cent. 63 per cent. 61 per cent.

S. 8 " 21 " 7 " 12 "

Hu. 11 " 30 " 5 " 59 "

B. 19 " 57 " 13 " 27 "

Ho. 33 " 30 " 17 " 58 "

Mo. 57 " 94 " 13 " 85 "

Av. 30 per cent. 49 per cent. 20 per cent. 50 per cent.

Av. gain in object couplets, 19 per cent.

" " " movement couplets, 30 per cent.

The first question which occurs in examining the foregoing tables is concerning the method of treating the indirect a.s.sociations, _i.e._, obtaining the per cents. The number of couplets correctly recalled may be divided into two cla.s.ses: those in which indirect a.s.sociations did not occur, and those in which they did occur. Those in which they did not occur furnish us exactly what we want, for they are results which are entirely free from indirect a.s.sociations. In them, therefore, a comparison can be made between series using objects and activities and others using images. On the other hand, those correctly recalled couplets in which indirect a.s.sociations _did_ occur are not for our purposes pure material, for they contain not only the object-image factor but the indirect a.s.sociation factor also. The solution is to eliminate these latter couplets, _i.e._, subtract them both from the number correctly recalled and from the total number of couplets in the set for a given subject. By so doing and by dividing the first remainder by the second the per cents, in the tables were obtained.

There is one exception to this treatment. The few couplets in which indirect a.s.sociations occurred but which were nevertheless _incorrectly_ recalled are subtracted only from the total number of couplets in the set.

The method by which the occurrence of indirect a.s.sociations was recorded has been already described. It is considered entirely trustworthy. There is usually little doubt in the mind of a subject who comprehends what is meant by an indirect a.s.sociation whether or not such were present in the particular series which has just been learned. If none occurred in it the subjects always recorded the fact.

That an indirect a.s.sociation should occasionally be present on one day and absent on a subsequent one is not strange. That a second term should effect a union between a first and third and thereafter disappear from consciousness is not an uncommon phenomenon of a.s.sociation. There were thirteen such cases out of sixty-eight indirect a.s.sociations in the _A_, _B_ and _C_ sets. In the tables they are given as present because their effects are present. When the reverse was the case, namely, when an indirect a.s.sociation occurred on the second, ninth or sixteenth day for the first time, it aided in later recall and was counted thereafter. There were eight such cases among the sixty-eight indirect a.s.sociations.

Is it possible that the occurrence of indirect a.s.sociations in, _e.g._, two of the four couplets of a series renders the retention of the other two easier? This could only be so when the intervals between two couplets in learning were used for review, but such was never the case. The subjects were required to fill such intervals with repet.i.tions of the preceding couplet only.

The elimination of the indirect a.s.sociation couplets and the acceptance of the remainders as fair portrayals of the influence of objects and movements on recall is therefore a much nearer approach to truth than would be the retention of the indirectly a.s.sociated couplets.

The following conclusions deal with recall after two days only. The recall after longer intervals will be discussed after Table III.

The summary from Tables I. and II. shows that when objects and nouns are coupled each with a foreign symbol, four of the six subjects recall real objects better than images of objects, while two, _M_ and _Ho_, show little or no preference. The summary also shows that when body movements and verbs are coupled each with a foreign symbol, five of the six subjects recall actual movements better than images of movements, while one subject, _M_, shows no preference. The same subject also showed no preference for objects. With the subjects _S_ and _B_ the preference for actual movements is not marked, and has importance only in the light of later experiments to be reported.

The great difference in the retentive power of different subjects is, as we should expect, very evident. Roughly, they may be divided into two groups. _M_ and _Mo_ recall much more than the other four. The small percentage of recall in the case of these four suggested the next change in the conditions of experimentation, namely, to shorten with them the intervals between the tests for permanence. This was accordingly done in the _C_ set. But before giving an account of the next set we may supplement these results by results obtained from other subjects.

It was impossible to repeat this set with the same subjects, and inconvenient, on account of the scarcity of suitable words, to devise another set just like it. Accordingly, the _B_ set was repeated with six new subjects. We may interpolate the results here, and then resume our experiments with the other subjects. The conditions remained the same as for the other subjects in all respects except the following.

The tests after nine and sixteen days were omitted, and the remaining test for deferred recall was given after one day instead of after two.

In learning the series, each series was shown four times instead of three. The results are summarized in the following table. The figures in the left half show the number of words out of sixteen which were correctly recalled. The figures in parentheses separate, as before, the correctly recalled indirect-a.s.sociation couplets. In the right half of the table the same results, omitting indirect-a.s.sociation couplets, are given in per cents, to facilitate comparison with the summary from Tables I. and II.

TABLE III.

SHOWING RECALL AFTER ONE DAY.

N. O. V. M. N. O. V. M.

Bur. 6 10(1) 7(1) 5(4) 38 67 44 31 W. 5(3) 12(1) 6 9 31 75 38 56 Du. 1 11(1) 8 9 6 69 50 56 H. 9(1) 14 8 12 56 88 50 75 Da. 1(3) 7(4) 3(1) 9(3) 7 44 20 56 R. 7(2) 3(3) 5 5(1) 44 19 31 31 Total, 29(9) 57(10) 37(2) 49(8) Av., 30 60 39 51

Av. gain in object couplets, 30 per cent.

" " " movement couplets, 12 per cent.

The table shows that five subjects recall objects better than images of objects, while one subject recalls images of objects better.

Similarly, three subjects recall actual movements of the body better than images of the same, while with three neither type has any advantage.

THE _C_ SET.

In the _C_ set certain conditions were different from the conditions of the _A_ and _B_ sets. These changes will be described under three heads: changes in the material; changes in the time conditions; and changes in the method of presentation.

For lack of monosyllabic English words the verbs and movements were dissyllabic words. The nouns and objects were monosyllabic, as before.

All were still concrete, and the movements, whether made or imaged, were still simple. But the movements employed objects, instead of being merely movements of the body.

For two of the subjects, _M_ and _Mo_, the time intervals between the tests remained as in the _A_ and the _B_ sets, namely, two days, nine days, and sixteen days. With the four other subjects, _S, Hu, B,_ and _Ho_, the number of tests was reduced to three and the intervals were as follows:

The I. test, which as before was a part of the learning process, was not counted. The II. test followed from 4 to 6 hours, or an average of 5-3/8 hours, after the I. test. The III. test was approximately 16 hours after the II. test for all four subjects.

The series were learned between 10 a.m. and 1:30 p.m., the II. test was the same day between 4:30 and 5:10 p.m., and the III. test was the following morning between 8:30 and 9:10 a.m. Each subject of course came at the same hour each week.

Each series was shown three times, as in the _B_ set.

A change had to be made in the length of exposure of each couplet in the movement series. For, as a rule, movements employing objects required a longer time to execute than mere movements of the body.

Five seconds was found to be a suitable length of exposure. To keep the three other types of series comparable with the movement series, if possible, their exposure was also increased from 3 to 5 secs. The interval of 2 secs, at the end of a presentation was omitted, and the interval between learning and testing reduced from 4 secs, in the _B_ set to 2 secs.

In the movement series of the _A_ and _B_ sets, movements of parts of the body were chosen. But the number of such movements which a person can conveniently make while reading words shown through an aperture is limited, and as stated above no single word was ever used in two couplets. These were now exhausted. In the _C_ set, therefore, movements employing objects were subst.i.tuted. The objects lay on the table in a row in front of the subject, occupying a s.p.a.ce about 50 cm.

from left to right, and were covered by a black cambric cloth. They were thus all exposed at the same moment by the subject who, at a signal, laid back the cloth immediately before the series began, and in the same manner covered them at the end of the third presentation.

Thus the objects were or might be all in view at once, and as a result the subject usually formed a single mental image of the four objects.

With this kind of material it was no longer necessary for the operator to show the subject in advance of the series what the movements were in order to avoid hesitation and confusion, for the objects were of such a nature as obviously to suggest in connection with the words the proper movements.

TABLE IV.

SHOWING RECALL AFTER TWO, NINE AND SIXTEEN DAYS FOR TWO SUBJECTS, AND AFTER FIVE HOURS AND TWENTY-ONE HOURS FOR FOUR OTHER SUBJECTS.

Days. Two. Nine. Sixteen Two. Nine. Sixteen N. O. N. O. N. O. V. M. V. M. V. M.

Series _M._ C^{1-4} 4 4 4 4 3 2 3 2 2 2 1 1 C^{5-8} 2 2 2 2 2 1 1 1 1 2 1 0 C^{9-12} 3 2 3 1 3 0 2 4 3 2 2 1 C^{13-16} 4 3(1) 4 2(1) 4 2(1) 3 4 2 3 2 3 Total 13 1(1) 13 9(1) 12 5(1) 9 11 8 9 6 5 Per cent. 81 73 81 60 75 33 56 69 50 56 38 31

_Mo_ C^{1-4} 2 4 1 1 1 1 1 4 1 2 1 2 C^{5-8} 3 2 4 1 3 1 4 3(1) 4 3(1) 2 2(1) C^{9-12} 0 1 0 1 0 1 0 3 0 1 0 2 C^{13-16} 0 0(1) 0 0(1) 0 0(1) 1(1) 4 1(1) 2 0(1) 0 Total 5 7(1) 5 3(1) 4 3(1) 6(1) 14(1) 6(1) 8(1) 3(1) 6(1) Per cent. 31 46 31 20 25 20 40 93 40 53 20 40

Hours. Five. Twenty-one. Five. Twenty-one N. O. N. O. V. M. V. M.

Series _S._ C^{1-4} 1 3 1 1 0 1 0 1 C^{5-8} 0(1) 3 0 2 0 1 0 1 C^{9-12} 0(1) 3 0(1) 4 3 4 3 4 C^{13-16} 1 3 1 3 2 3(1) 3 3(1) Total 2(2) 12 2(1) 10 5 9(1) 6 9(1) Per cent. 14 75 14 63 33 60 40 60

_Hn._ C^{1-4} 1 4 1 4 0 4 1 4 C^{5-8} 0(2) 1 0(2) 1 0(1) 2 1(1) 2(2) C^{9-12} 3 4 3 4 2 4 2 4 C^{13-16} 1 3 3 3 0 3(1) 0 2(1) Total 5(2) 12 7(2) 12 2(1) 13(3) 4(1) 12(3) Per cent. 36 75 50 75 14 100 29 92

_B._ C^{1-4} 3 4 3 4 3 4 3 4 C^{5-8} 3 2 3 3 2 2 2 4 C^{9-12} 2 4 2 3 2 1 2 2 C^{13-16} 3 4 3 4 2 4 2 4 Total 11 14 11 14 9 11 9 14 Per cent. 69 88 69 88 56 69 56 88