Harvard Psychological Studies Part 34

The greater ease of vertical as compared with horizontal movements recalls an observation of Ladd,[3] in which the idioretinal light was willed into the shape of a cross. Ladd says: "The vertical bar of the cross seems much easier to produce and to hold steadily in the field."

This present observation is also in accord with that described above in the case of movements of a single image.

[3] Ladd, G.T.: 'Direct Control of the Retinal Field,' PSYCH.

REV., 1894, L, pp. 351-355.

On several occasions G. reported that the crossing movement was the easiest, and that the return to the original places was not easier than the other movements. In one experiment he reported the field at the center cloudy, so that it was a relief to get away from it. G.'s time records on these occasions did not support his feeling with regard to the return to the original places, but they show that the crossing movements were, in two or three instances, quicker than the 'left-and-right' movement, and the impression of promptness thus made persisted to the end of the experiment. The four movements in which both images moved uniformly were easier than the four in which movements in different directions were involved.

All the subjects were frequently conscious of eye movements, and more frequently conscious of a tendency to eye movement, which was, however, inhibited. That the strain in the eyes was practically constant during all the movements away from the original places, seems evident from the unanimous reports of a sense of relaxing and relief in the eyes, attending the movement of returning to the original places. The distance to which the images were moved was a powerful factor in producing this sense of strain. When the two images were moved and held but a few inches apart there was no sense of strain and no conscious alternation of attention. Practice increased greatly the distance at which the images could be held apart without conscious alternation of attention, but the strain of holding them apart and of inhibiting eye movement increased with the distance.

In the movements for which the time was recorded the distances varied, according to the subject, from six to eighteen inches, and varied at times with each subject. In the experiments without time record, A., B., C., E., F. and H. reported that they were able to move the images apart to ceiling and to floor, or to the opposite ends of the room, and to hold them there both in consciousness at the same time without either alternation of attention or eye movement, a tendency to which was felt but was inhibited. I. held them two feet apart without fluctuation of attention. A. reported: "I tend to turn my body to left or to right when I move the images in either of these directions." C., H. and I. said: "The eyes diverge when one image moves slowly to the right and one to the left." D. found a slight movement of the eyes which could be detected by the fingers placed lightly on the lids, when the attention was alternating between the images. K. had convergence and divergence of the eyes for crossing and separation respectively and he was accustomed to run his eye over the outline of the image. Strain in the scalp muscles was reported by A., B., E., F.

and G. The up-and-down movements were universally characterized by a feeling as if one eye tended to move up and the other down. C.

unconsciously inclined his head to the left in such movements as if to make the line of the two eyes parallel with the direction of the movement.

E., when holding the images two feet apart, had a strong feeling of difference of accommodation when alternating in observation and so judged the two to be in different planes.

When the movement seemed difficult the strain was greater, and when an image became dim the effort to restore its brightness or its distinctness of outline was accompanied by a feeling of bringing it nearer by accommodation and near focusing. J. found that the two images approached each other when he attempted to secure greater vividness. An a.n.a.logous instance is that of A.G.C., a subject quoted in 'Mental Imagery of Students,' by French.[4] In calling up the image of a die this subject held up his hand as if it held the die. When there was no sense of strain the hand was fourteen inches from his face, but when effort was made to image all the sides of the die at once he unconsciously moved his hand to within four inches of his eyes. French says in this connection: "Situation depends on the attention involved and the inference is near that this phenomenon may be connected with feelings of convergence and accommodation which so often accompany concentrated visual attention."

[4] French, F.C.: PSYCH. REVIEW, 1902, IX., p. 40.

The movements were a.s.sisted by mentally saying, 'this image is here, that image is there,' in the case of D., G., H., I. and K.; or, at times, by articulating the names of the image, or of the color when the image was of a colored object. I. found it easy to hold outlines, but in order to retain colors in the movements of separation, he had to speak the names continually. H. also repeated the names continually, as, for example, 'violet here, orange there.'

A. represented the line of vision as going to each of the two images, which seemed connected by a line, thus making a triangle, and then pictured himself as standing off and seeing himself looking at the images. When the two objects were solid and the images were to be crossed, B. carried one image above or below the other, but when the objects were colored surfaces he conceived them as pure colors so that there was no sense of impenetrability to interfere with their crossing and they glided by each other. In the up-and-down movements he moved one at a time. C. and D. had to construct some support for the images.

In most of the experiments H. first moved the images to a greater distance away, somewhat higher up and a little farther apart. In this new position the images appeared smaller and the suggested movements were made more easily. Sometimes in crossing two colored images he observed a partial mixture of the colors. J. found that a sharp movement of the head in the required direction aided materially in moving the images, and when the objects were colored surfaces fastened to the same card he found it necessary either to conceive the card as of rubber or to picture it as cut in two before he could make the movements of the images.

With A., B., C. and D. there were instances of unwilled movements of the images, in the experiments where the movements were not timed.

These were much more frequent with D. than with the others, and to check them required prolonged effort. The more common movements of this sort were rotation of the image, change of its position, separation of its parts (if detachable in the object) and change of shape. E. had a return of the two images of a preceding experiment which persisted in staying a few seconds and which were as vivid as the two legitimate occupants of the mental field.

The images were duplicated five times on different days with A., and once each with C., F. and K.

A.'s cases were these. The 'wraith' of a small box whose image was out at the right, appeared above the other image off at the left and it was turned with a corner to the front. Again, at the central position each image was duplicated, the true pair being of full size, bright and distinct, the false pair small, dim and on a more distant plane, _i.e._, behind the others. One of the extra images persisted against all effort to banish it, for fifty-five seconds. Again, when twelve inches apart each image was similarly duplicated. In the fourth instance the images were at the center of the field. In the fifth, the right image, eight inches from the center, was duplicated, the extra image being still farther away and above. This second image was very dark, dim and vague in outline, and came and went slowly. The right image of C., when seven feet from the center, had a dim double above it. F. had moved the right-hand image (a violet disc) close to the left when a blue disc also appeared above it. Though repeating the word 'violet' he had imaged the violet disc as blue. K. was holding the two images a foot and a half apart when an extra pair appeared at the center. Both pairs persisted for sixty seconds and then the outer pair vanished, and the inner, the false pair, grew brighter.

As was said in the case of a single image, so with double images, the motion could be traced and often was traced when the movements were away from the original positions, but on the return to the original positions the images were not usually seen _in transitu_. For ten of the subjects, the image moved downward uniformly on an arc whose center was at the eye; and often the right and left movements were likewise on an arc. With E. the ends of the arc for motion right and left were higher also. H., I. and J. reported that all the movements were in the same plane. The upward movement was always to a less distance and the downward movement to a greater distance than the horizontal movements.

In most cases the images were the size of the percepts, in a number of cases smaller, and in a few cases larger. This was determined by comparison between the image and the percept immediately on opening the eyes and seeing the object at the end of the five minutes occupied by the experiment. A similar mode of comparison showed that, in about half of the experiments, the images were at the end of five minutes approximately equal to the percept in clearness and distinctness of outline. A comparison of these results with those obtained in a series of experiments involving pa.s.sive observation of the image seems to indicate that active manipulation of the image tends to maintain the qualitative fidelity of the image when at its original position.

During the progress of the experiments the reports were almost unanimous and constant that at its original position the image was vivid and distinct, but lost in both respects when away from that position, the loss being greater the greater the distance to which it was moved. Frequently there was fluctuation,--a loss of vividness and then a restoration,--which A. frequently found to be rhythmical, while in general it was evident that an increase of effort or of attention was successful in restoring lost vividness and distinctness.

D., after three minutes, read the time in the image of a watch. In superposing green on yellow, in two instances, the yellow shone through, making a mixed color, and again, in moving a green disc and a yellow disc, the green became suffused with yellow, so that the two discs were one yellow and the other greenish-yellow. For C., similarity in the two objects presented tended to make both images less vivid and distinct and to render more difficult their retention and manipulation. When one of the two objects partially overlapped the other it was difficult to separate the two images, and the area of contact was very vague in the image of the under one, and when the scrutiny reached that portion the other image returned to its original overlapping position.

IV. SUPPRESSION OF ONE OF TWO IMAGES.

The next tables (V. and VI.) give the results of experiments in suppressing one of two images, the objects presented being saturated color squares, discs, triangles, etc., placed side by side, one above the other, or a smaller one superposed on a larger. The time of perception was five seconds. After the disappearance of after-images, if there were any, the subject was directed to suppress one of the two memory images, the one to be suppressed being indicated by the director. The subject reported as soon as the indicated image disappeared, and reported any return of the suppressed image and its later disappearance in consequence of his efforts. Also he reported any disappearance and reappearance of the retained image. Five minutes was the limit of the time for the experiments with a few exceptions.

The times were recorded, and those given for the first suppression include the time between the director's command and the subject's report 'now' or 'gone,' and include, therefore, two reaction times.

The later suppressions include but one reaction time.

TABLE V.

SUMMARY OF ALL SUPPRESSIONS. AVERAGE TIME IN SECONDS.

[Label 1: Image Suppressed]

[Label 2: No of Exper.]

[Label 3: Time of First Supp.]

[Label 4: Time of Ab. of Supp. Im.]

[Label 5: No. of Later Supp.]

[Label 6: Time of Later Supp.]

[Label 7: No. of Ab. of Supp. Im.]

[Label 8: Time of Ab. of Supp. Im.]

[Label 9: Time of All Supp.]

[Label 10: Time of All Absence of Supp. Im.]

[1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Right. 46 11.59 82.39 221 8.43 216 35.74 8.94 43.93 Left. 43 11.89 79.34 175 7.79 173 44.86 8.60 51.26 Upper. 22 11.67 49.77 150 6.26 147 29.75 6.95 32.35 Lower. 17 14.23 64 71 7.88 70 46.68 9.11 50.04 Central. 42 18.24 96.93 357 3.90 352 18.13 5.41 26.54 Marginal. 20 14.25 181.57 24 8.93 24 78.08 11.35 125.12 Sundry. 7 8.71 127.21 19 13.34 19 47.27 12.09 68.78 Averages. 13.48 91.25 6.46 32.14 7.60 41.86

TABLE VI

SUPPRESSIONS GROUPED BY SUBJECTS. AVERAGE TIME IN SECONDS.

[Label 1: Subject]

[Label 2: No. of Exp.]

[Label 3: Time of First Supp.]

[Label 4: Time of Ab. of Supp. Im.]

[Label 5: No. of Later Supp.]

[Label 6: Time of Later Supp.]

[Label 7: No. of Ab. of Supp. Im.]

[Label 8: Time of Ab. of Supp. Im.]

[Label 9: Time of All Supp.]

[Label 10: Time of All Ab. of Supp. Im.]

[1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

A. 11 28.32 11.29 117 14.90 114 10.35 16.05 10.44 B. 29 5.79 270.44 5 0.25 5 138.80 4.98 251.08 C. 18 7.88 43.08 64 3.94 63 67.49 4.81 62.07 D. 14 23.28 190.07 6 31.66 5 204.60 25.80 193.89 F. 10 12.67 86.07 230 1.95 230 67.92 2.40 10.09 G. 21 21.88 20.39 190 9.97 184 19.37 11.15 19.47 H. 21 15.27 73.27 47 10.30 47 84.48 11.84 81.02 I. 26 9.77 53.83 96 5.06 94 61.34 6.06 59.72 J. 26 3.59 32.18 209 1.40 208 31.69 1.64 31.75 K. 21 21.63 71.90 53 14.75 51 70.04 16.70 31.83 Averages. 13.48 91.25 6.46 32.14 7.60 41.86

There were ten subjects in most of the experiments, and the marked differences in the individual records which were evident in the previous experiments did not exist here except in the case of A., for whom alone the time required to obtain the suppression exceeded the time of absence of the suppressed image.

In several experiments the subjects were unable to suppress the indicated image, which in five cases was the image at the center of a disc and in two cases the outer portion of the disc. Further, five failures were by one subject, D., and one each by A. and F. The statistical report here given includes only the results of the successful experiments. Forty-four of the one hundred and ninety-seven were completely successful, as the suppressed image did not return throughout the entire period. The following table shows the grouping of the experiments according to the recurrence of the suppressed image:

Returned 0 times, 44 " 1 " 26 " 2 " 18 " 3 " 25 " 4 " 16 " 5 " 16 " 6 to 10 " 28 " more than 10 times, 24 Total, 197

Seventy-three and three fifths per cent. of all the experiments have five or fewer returns of the suppressed images.

The subjects suppressed the image as soon as possible after each return, the average time taken to accomplish these later suppressions being 6.46 sec., while the average time of absence of the suppressed image was 32.14 sec.

Including the first efforts and the first absences of the suppressed image, the average time required to suppress the image was 7.60 sec., and the average time of absence of the suppressed image was 41.86 sec.

Arranging the subjects according to the average time they required to accomplish a suppression, we have the following order. J. and F. had more recurrences of the suppressed image than any of the other subjects.

J. 1.64 sec.