IV

OBJECTIVES, PLAN OF WORK, AND LIST OF EXPERIMENTS

The primary objective in continuing observation of the gorilla was completion of general account of the psycho-biological traits of the individual, but as secondary aim appeared the desire to observe the changes in reactive tendency and capacity associated with growth and development. It is hoped now that it may be possible to observe Congo periodically until she is physically mature. Assuming that she was approximately five years old when first observed, she was in her sixth year during the last period of observation. There are evidences, later recorded, which suggest approach to adolescence, so it is possible that I have under-estimated her age. Mr. Ben Burbridge, however, disagrees with me in that he believes she is at least a year younger than I have estimated.

In the winter of 1927 I attempted to verify, correct, and supplement previous observations, to follow the development of processes previously observed, and to note the appearance and characteristics of others. Since the general survey of traits originally contemplated was well advanced, it was possible to work somewhat more intensively on certain problems. It was decided to concentrate attention on behavior involving representational processes, and especially on memory reactions.

As a most natural means of obtaining a measure of the behavioral development of Congo during the year I decided to re-present most of the types of problematic situation in which she had been given opportunity to work the previous winter. In many instances this required little time, because of immediate perfect adaptation to the situation, but in other cases solution of problems continued to be difficult or impossible and often observations were continued over several days.

Wherever opportunity offered in connection with repetition of experiments, promising forms of variation were introduced and former experiments were supplemented by new ones. As the work advanced the new experiments came to predominate, and in the final weeks of work, attention was devoted almost wholly to experiments on mnemonic processes.

The methods employed were, as formerly, crude and capable of yielding with few exceptions only qualitative results.2 Certain progress, however, was made toward the development and application of more exact methods. Especially in the study of memory responses, quantitative data were obtained. Naturally it was impossible to make other than rough measurements of the changes in reactive tendency exhibited by the gorilla. Yet in many instances these changes were so marked as to justify dogmatic statement.

For the convenience of the reader in seeing at a glance the program of experiments and essential facts concerning the presentation of each of the several problematic situations, a chronological list, comparable with that of the previous report (Yerkes, 1927, pp. 38-40), is offered herewith. By consultation of this list one may discover in order, on the first line, the number, name or title, relation to the series of 1926, and location of the experiment. Beneath follow in sequence the number (figure in parenthesis), date, hour, and duration of each trial. In a few instances the duration of trial lacks significance and is omitted.

For some experiments a number of variations or forms are indicated. Thus, for example, no. 7, box and pole, is recorded as a new experiment, that is, one not presented to Congo the previous winter, which was used in three forms: first, as offering the animal opportunity for solution by its own initiative, and therefore indicated, following (a), as initiative; second, as presented with imitative copy set by the experimenter, and therefore designated, following (b), as imitation, and third,

'Acknowledgment should be made to Hobhouse (1915) for suggestion of several forms of problematic situation.

with tuitional aid supplied by the experimenter, designated as (c), tuition. Similarly, in certain other experiments there appear two or three variations. Where in addition to initiative, imitation or tuition appeared, the first form of experiment. is regularly designated by the term initiative, the second by imitation, and the third by tuition; but in other cases, for example, no. 14, wound chain, the word variation, with appropriate letter, is employed. Thus, in the instance cited, the initial form of the experiment is recorded as no. 14 (a), and a modification thereof as no. 14 (b), variation A.

Following the title of each experiment is a number or the word new in parenthesis. The number indicates the experiment of the original report which is identical with the present experiment or most closely resembles it. Use of the word new indicates an experiment not previously presented.

Experiments were conducted in so many different locations about Shady Nook, and location is so obviously important by reason of associated successes or failures, that it has seemed desirable to adopt a system of symbols and to indicate, both in the following list of experiments and in text descriptions of problems, the observational location. The following definitions of abbreviated designations are here presented for reference: Tree 1 designates the home tree, that to which Congo was regularly moored when taken from her cage for fresh air and exercise. Tree 2 designates an oak adjacent to Tree 1 and some five yards northerly of it. Tree 3 designates one some ten yards northerly of the cage. It was the site of many of the out-of-doors experiments in 1926 and 1927. Tree 4 designates an oak some twenty-five yards northerly of the cage under which during 1927 the box problems were arranged.

List of problems with dates of presentation

1. Shelf and stick (1). In cage.

(1) Jan. 17, 12:07, 3'; (2) 18, 9:32, 3'.

2. Hooked rope (3). In cage.

(1) Jan. 18, 12:15, 30′′; (2) 19, 9:16, 1'; (3) 20, 9:39, 1'; (4) 21, 10:04, 10"; (5) 22, 12:05, 5".

3. Platform and stick (4). In cage.

(1) Jan. 19, 9:30, 1′ 30′′, (2) 12:15, 7′; (3) 20, 9:44, 2'; (4) 21, 10:07, 20′′; (5) 22, 12:06, 20'.

4. Suspended food and stick (8). Under Tree 3.

(1) Jan. 19, 10:40, 16′; (2) 20, 10:20, 5′; (3) 21, 9:19, 1'; (4) 22, 11:11, 10', (5) 11:53, 8'.

5. Pipe and stick or rod (9); (a) initiative, (b) imitation. Under Tree 3.

(a) (1) Jan. 21, 9:25, 30'; (2) 22, 11:22, 30'. (b) (1) Jan. 23, 10:32, 30'; (2) 24, 10:25, 30'. 6. Suspended food and auxiliary stick (new). Under Tree 3. (1) Jan. 23, 9:40, 56'; (2) 24, 9:40, 41'; (3) 25, 9:35, 41'; (4) 26, 9:38, 41′; (5) 28, 9:25, 24'; (6) 29, 9:27, 20'; (7) 30, 10:11, 25′; (8) 31, 9:55, 13′; (9) Feb. 1, 9:41, 40'; (10) 2, 9:21, 17' 30"; (11) 3, 9:42, 4'; (12) 4, 10:13, 2'; (13) 5, 10:50, 2'; (14) 6, 10:15, 2'; (15) 11, 10:56, 3'.

7. Box and pole (new); (a) initiative, (b) imitation, (c) tuition. Under Tree 3.

(a) (1) Jan. 25, 10:25, 30'; (2) 26, 10:24, 30'; (3) 28, 10:00, 30'; (4) 29, 9:53, 30'; (5) 30, 10:43, 30'; (6) 31, 10:13, 30'.

(b) (1) Feb. 1, 10:24, 23'; (2) 2, 10:20, 25'; (3) 3, 9:52, 26'; (4) 4, 10:20, 25'; (5) 5, 10:58, 12'; (6) 6, 10:25, 13′; (7) 7, 9:43, 22′; (8) 8, 9:56, 22'.

(c) (1) Feb. 9, 9:20, 16', (2) 9:45, 33"; (3) 10, 9:22, 11'; (4) 11, 9:48, 13'; (5) 12, 9:52, 18', (6) 10:12, 15', (7) 10:34, 12', (8) 10:50, 12′; (9) 13, 9:55, 16', (10) 10:12, 16', (11) 10:30, 11', (12) 10:43, 11'; (13) 14, 9:44, 6'; (14) 15, 9:32, 14', (15) 9:48, 11', (16) 10:06, 1', (17) 10:09, 2′, (18) 10:15, 2′; (19) 17, 9:13, 5′, (20) 9:20, 30′′, (21) 9:24, 2', (22) 9:27, 28".

8. Hasp and padlock (11). In cage.

(1) Jan. 24, 10:58, 15'; (2) 25, 11:05, 15'; (3) 26, 9:21, 15'; (4) 28, 10:40, 15'; (5) 29, 10:41, 15'; (6) 30, 11:35, 38", (7) 11:37, 55"; (8) 31, 11:20, 1'27", (9) 11:25, 48"; (10) Feb. 1, 11:22, 4', (11) 11:27, 27"; (12) 2, 11:12, 19′′, (13) 11:14, 4"; (14) 3, 11:25, 49′′; (15) 4, 11:52, 30"; (16) 5, 12:16, 15"; (17) March 2, 12:35, 3"; (18) 3, 9:45, m. p. r.3

9. Spring snap (new); (a) initiative, (b) imitation. Under Tree 3 or in cage.

M. p. r. stands for motion picture record.

(a) (1) Jan. 25, 10:25, 30'; (2) 26, 10:24, 30'; (3) 28, 10:00, 30′; (4) 29, 9:53, 30′; (5) 30, 10:43, 30′; (6) 31, 10:13, 30'; (7) Feb. 1, 10:24, 23′; (8) 2, 10:20, 25', (9) 10:55, 3′′, (10) 10:56, 15'; (11) 3, 11:09, 15'; (12) 4, 11:35, 15'; (13) 5, 12:00, 15'.

(b) (1) Feb. 7, 10:33, 10'; (2) 8, 10:38, 10'; (3) 9, 10:20, 10′; (4) 10, 10:05, 10′; (5) 11, 11:06, 10'; (6) 12, 11:29, 10'; (7) 13, 11:34, 10'; (8) 15, 10:27, 10'; (9) 17, 10:26, 10'; (10) 18, 11:12, 10'; (11) 19, 10:55, 10′; (12) 20, 9:14, 55"; (13) 21, 9:13, 11'; (14) 22, 8:54, 14'; (15) 23, 9:47, 9'; (16) 25, 8:44, 21"; (17) 26, 8:55, 56"; (18) 27, 9:15, 14′′; (19) 28, 8:50, 8′′; (20) March 2, 12:30, 32′′. M. p. r. Feb. 21 and March 3.

10. Greatest dimension of box (23). Trials 1 and 2 under Tree 3; trial 3 under Tree 4.

(1) Jan. 26, 11:21, 9'; (2) 28, 10:35, 45′′; (3) Feb. 28, 9:52, 1'.

11. Diagonal rope (2). In cage.

(1) Jan. 28, 11:15, 5′′. M. p. r. March 3.

12. Box stacking with two boxes (23). Trial 1 under Tree 3; trial 2 under Tree 4.

(1) Jan. 29, 10:30, 1'; (2) March 1, 9:27, 4′52′′.

13. Box stacking with three boxes (new). Under Tree 4, except preliminary trial, which was under Tree 3.

(Preliminary trial) Jan. 30, 11:20, 10'; (1) Jan. 31, 10:46, 30'; (2) Feb. 1, 10:50, 30′; (3) 2, 9:45, 30′; (4) 3, 10:28, 30'; (5) 4, 9:40, 30'; (6) 5, 9:45, 60'; (7) 6, 9:33, 21'; (8) 7, 10:10, 2′10′′; (9) 8, 10:20, 15′; (10) 11, 10:20, 30′; (11) 13, 11:05, 8'; (12) March 2, 9:29, 3′12′′. 14. (a) Wound chain (20), under Tree 2; (b) Variation A, under Tree 1.

(a) (1) Feb. 3, 11:33, 1'; (2) 4, 10:55, 30'; (3) 5, 11:25, 30′; (4) 6, 10:55, 30'; (5) 9, 10:52, 30′; (6) 10, 9:38, 10'; (7) 11, 11:22, 30′; (8) 12, 11:54, 30'; (9) 13, 11:55, 30'; (10) 15, 10:43, 30'; (11) 17, 10:39, 30'; (12) 18, 11:59, 30'; (13) 19, 10:02, 7'; (14) 20, 10:39, 20"; (15) 21, 11:23, 30'; (16) March 5, 12:30, 30'.

(b) (1) Feb. 7, 10:52, 30"; (2) 8, 10:51, 10′′; (3) 9, 10:41, 12", (4) 11:25, 9′′; (5) 10, 9:49, 1'; (6) 11, 11:53, 1'; (7) 12, 12:28, 1'; (8) 13, 12:43, 14'; (9) 17, 11:10, 1'; (10) 18, 11:50, 6'; (11) 19, 1:01, 20"; (12) March 5, 1:20, 7'.