FIGURE 13.--Multiple-choice apparatus, showing observer's bench
and writing stand.
FIGURE 14.--Apparatus as seen from observer's bench.
FIGURE 15.--Entrances to multiple-choice boxes as seen from
the response-compartment.
FIGURE 16.--Apparatus as seen from the rear, showing exit
doors, food receptacles, and covers for same.
The apparatus was built in room A (figure 12), this room having been
especially planned for it with respect to lighting as well as dimensions
and approaches. It was unfortunately impossible to obtain photographs
showing the whole of the apparatus, but it is hoped that the four
partial views of plate IV may aid the reader who is unfamiliar with
previously described similar devices to grasp readily the chief points
of construction. In this plate, figure 13 shows the front of the
complete apparatus, with the alleyway and door by way of which the
experimenter could enter. The investigator's observation-bench and
record-table also appear in this figure, together with weighted cords
used to operate the various doors and the vertically placed levers by
means of which each pair of doors could be locked. Figure 14 is the view
presented to the observer as he stood on the bench or observation stand
of figure 13 and looked over the entire apparatus. Three of the entrance
doors are shown at the right of this figure as raised, whereas the
remainder of the nine entrance doors of the apparatus are closed. Figure
15 is a view of the entrance doors from below the wire roof of the
apparatus. Again, two of the doors are shown as raised, and three
additional ones as closed. The rear of the apparatus appears in figure
16, in which some of the exit doors are closed and others open. In the
latter case, the food receptacles appear, and on the lower part of the
raised doors of the corresponding boxes may be seen metal covers for the
food receptacles projecting at right angles to the doors, while on the
lower edge of each door is an iron staple used to receive a sliding bar
which could be operated from the observer's bench as a means of locking
the doors after they had been closed. The space beyond the exit doors
was used as an alleyway for the return of the animals to the starting
point.
It will be necessary at various points in later descriptions to refer to
these several figures. But further description of them will be more
readily appreciated after a careful examination of the ground plan of
the apparatus presented as figure 17 In accordance with the labelling of
this figure, the experimenter enters the apparatus room through doorway
16, passes thence through doorways 17 and 10 to the large cage Z, from
which he has direct access to the animals and can bring them into the
apparatus. The multiple-choice mechanism proper, consisting of nine
similar boxes (nine were used instead of twelve as a matter of
convenience of construction, not because this smaller number is
otherwise preferable) is labelled F. These boxes are numbered 1 to 9,
beginning at the left. This numbering was adhered to in the recording of
results throughout the investigation. The other important portions of
the apparatus are the runway D, from which the subject at the
experimenter's pleasure could be admitted through doorway 12 to the
large response-chamber E; the alleyways G, H, and I, by way of which
return to the starting point was possible; the observation bench C, with
its approach step 13; and the observer's writing table A.
In the construction of this large apparatus, it was necessary to make
provision for the extremely destructive tendencies of monkeys and
anthropoid apes,--hence the apparent cumbersomeness of certain portions.
It was equally necessary to provide for the protection of the observer
and the prevention of escape of the subjects by completely covering the
apparatus and alleyways with a heavy wire netting.
Each of the eighteen doors of the multiple-choice boxes, and in addition
doors 11, 12, and 15 of the runway D, were operated by the observer from
his bench C by means of weighted window cords which were carried by
pulleys appropriately placed above the apparatus. Each weight was so
chosen as to be just sufficient to hold its door in position after the
experimenter had raised it. For the convenience of the experimenter in
the rapid operation of the twenty-one doors, the weights for the doors
of runway D were painted gray, those for the entrance doors, white, and
those for the exit doors, black.
In each entrance door, as is shown in figure 15 of plate IV, a window
was cut so that the experimenter might watch the animal after it had
entered a given box, and especially note when it left the box after
having received its reward. This window was covered with wire netting.
No such windows were necessary in the exit doors, but to them were
attached heavy galvanized iron flanges which served to cover the food
receptacles. One of these flanges is labelled o in figure 17. The food
receptacles were provided by boring holes in a 2 by 4 inch timber
securely nailed to the floor immediately outside of the exit doors. Into
these holes aluminum cups fitted snugly, and the iron flanges, when the
doors were closed, fitted so closely over the cups that it was
impossible for the animals to obtain food from them.
[Illustration: FIGURE 17.--Ground plan of multiple-choice apparatus in
experiment room A. Scale 1/60
A, record stand; C, bench for observer; B, step as approach to C; D,
alleyway leading to E, response-compartment; F, one of the nine (1-9)
similar multiple-choice boxes; G, H, alleyways leading from boxes to
starting point at D; I, alleyway used by experimenter as approach to
rear of apparatus; W, W, windows; P, alleyway; Z, large cage; 16,
entrance to room A; 17, entrance to apparatus and thence via 10 to
cages; 18, entrance to alleyway 1; 11, 15, entrances to D; 12, entrance
to E; 13, entrance door of box 5; 14, exit door of box 5; o, cover for
food receptacle.]
As originally constructed, no provision was made in the apparatus for
locking the entrance and exit doors of the several boxes when they were
closed. But as two of the subjects after a time learned to open the
doors from either outside or inside the boxes, it became necessary to
introduce locking devices which could be operated by the experimenter
from the observation bench. This was readily accomplished by cutting
holes in the floor, which permitted an iron staple, screwed to the lower
edge of each door, to project through the floor. Through these staples
by means of a lever for each of the nine boxes, the observer was able to
slide a wooden bar, placed beneath the floor of the room, thus locking
or unlocking either the entrance door, the exit door, or both, in the
case of any one of the nine boxes.
Since figure 17 is drawn to scale, it will be needless to give more than
a few of the dimensions of the apparatus. Each of the boxes was 42
inches long, 18 inches wide, and 72 inches deep, inside measurements.
The alleys D, I, and H were 24 inches, and G 30 inches wide, by 6 feet
deep. The doors of the several boxes were 18 inches wide, by 5 feet
high, while those in the alleyways were 24 inches wide by 6 feet high.
The response-compartment E of figure 17 was 14 feet 4 inches, by 8 feet,
by 6 feet in depth. In order that the apparatus might be used with adult
human subjects conveniently, if such use should prove desirable, the
depth throughout was made 6 feet, and it was therefore possible for the
experimenter to walk about erect in it.
The experimental procedure was briefly as follows: A small quantity of
food having been placed in each of the food cups and covered by the
metal flanges on the exit doors, the experimenter raised door 11 of
figure 17 and then opened door 10 and the door of the cage in which the
desired subject was confined. After the latter, in search of food, had
entered the runway D, the experimenter lowered door 11 to keep it in
this runway, and immediately proceeded to set the reaction-mechanisms
for an experiment (trial). Let us suppose that the first setting to be
tried involved all of the nine boxes. Each of the entrance doors would
therefore be raised. Let us further suppose that the right door is
defined as the middle one of the group. With the apparatus properly set,
the experimenter next raises door 12, thus admitting the animal to the
response-compartment E. Any one of the nine boxes may now be entered by
it. But if any except number 5, the middle member of the group, be
entered, the entrance door is immediately lowered and both the exit and
entrance doors locked in position so that the animal is forced to remain
in the box for a stated period, say thirty seconds. At the expiration of
this time the entrance door is raised and the animal allowed to retrace
its steps and make another choice. When the middle box is chosen, the
entrance door is lowered and the exit door immediately raised, thus
uncovering the food, which the animal eats. As a rule, by my monkeys and
ape the reward was eaten in the alleyway G instead of in the
multiple-choice box. As soon as the food has been eaten, the exit door
is lowered by the experimenter, and the animal returns by way of G and H
to runway D, where it awaits its next trial.
As rewards, bananas and peanuts were found very satisfactory, and
although occasionally other foods were supplied in small quantities,
they were on the whole less constantly desired than the former.
Four problems which had previously been presented to other organisms
were in precisely the same form presented to the three primates. These
problems may be described, briefly, by definition of the right reaction
mechanism, thus: problem 1, the first mechanism at the subject's left;
problem 2, the second mechanism at the subject's right (that is, from
the end of the series at the subject's right); problem 3, alternately,
the first mechanism at the subject's left and the first at its right;
problem 4, the middle mechanism of the group.
It was my intention to present these four problems, in order, to each of
the three animals, proceeding with them as rapidly as they were solved.
But as it happened, only one of the three subjects got as far as the
fourth problem. When observations had to be discontinued, Sobke was well
along with the last, or fourth problem; Skirrl was at work at the third
problem; and Julius had failed to solve the second problem.
For each of the problems, a series of ten different settings of the
doors was determined upon in advance. These settings differ from those
employed in a similar investigation with the pig only in that the
numbering of the doors is reversed. In the present apparatus, the boxes
as viewed from the front (entrance) are numbered from the left to the
right end, whereas those of the pig apparatus were numbered from the
right end to the left end.
Below are presented for each of the several problems (1) the numbers of
the settings presented in series; (2) the numbers of the doors open; (3)
the number of doors open in each setting and for the series of ten
settings; and (4) the number of the right door.