Sixteen Experimental Investigations from the Harvard Psychological Laboratory, Hugo Münsterberg [top fiction books of all time TXT] 📗

100 preliminary tests, trained by 250

experiences to escape by the Right-hand passage. Now, in Groups III.

to VII., the subject’s usual manner of getting out of the closed

passage, when by a wrong choice it happened to get into it, was to

draw back on the curled abdomen, after the antennae and chelæ had

touched the glass plate, and then move the chelæ slowly along the

Right wall of the partition until it came to the upper end; it would

then walk around the partition and out by the open passage. Fig. 3

represents such a course. In Group VIII. the Right passage was closed,

instead of the Left as previously. The first time the animal tried to

get out of the box after this change in the conditions it walked

directly into the Right passage. Finding this closed it at once turned

to the Right, _as it had been accustomed to do when it came in contact

with the glass plate_, and moved along the side of the box just as it

did in trying to get around the end of the partition. The path taken

by the crawfish in this experiment is represented in Fig. 4. It is

very complex, for the animal wandered about more than fifteen minutes

before escaping.

 

The experiment just described to show the importance of the tendency

to turn in a certain direction was the first one of the first series

after the change in conditions. When given its second chance in this

series the subject escaped directly by the Left passage in 33 seconds,

and for the three following trips the time was respectively 25, 25 and

30 seconds.

 

Upon the experimental evidence presented we base the conclusion that

crawfish are able to profit by experience in much the same way that

insects do, but far more slowly.

 

[Illustration: FIG. 4. Path taken by crawfish which had been trained

to avoid the Left passage, when the Right passage was closed. Showing

turning to the right as in Fig. 3.]

 

It was thought that a study of the way in which crawfish right

themselves when placed upon their backs on a smooth surface might

furnish further evidence concerning the ability of the animals to

profit by experience.

 

Dearborn[3] from some observations of his concludes that there is no

one method by which an individual usually rights itself, and,

furthermore, that the animals cannot be trained to any one method. His

experiments, like Bethe’s, are too few to warrant any conclusions as

to the possibility of habit formation.

 

[3] Dearborn, G.V.N.: ‘Notes on the Individual Psychophysiology

of the Crayfish,’ Amer. Jour. Physiol., Vol. 3, 1900, pp.

404-433.

 

For the following experiments the subject was placed on its back on a

smooth surface in the air and permitted to turn over in any way it

could. Our purpose was to determine (1) whether there was any marked

tendency to turn in a certain way, (2) whether if such was not the

case a tendency could be developed by changing the conditions, and (3)

how alteration in the conditions of the test would affect the turning.

 

A great many records were taken, but we shall give in detail only a

representative series. In Table III., 557 tests made upon four

subjects have been arranged in four groups for convenience of

comparison of the conditions at different periods of the training

process. Each of these groups, if perfect, would contain 40 tests for

each of the four subjects, but as a result of accidents II., III., and

IV. are incomplete.

 

TABLE III.

 

RETURNING OF CRAWFISH.

 

Group. Number of L. R. Time in Tests.

Animal. Per cent. Seconds.

I. 2 22.5 77.5 14.6 40

3 42.5 57.5 2.6 40

4 52.8 47.2 4.3 38

16 44.5 55.5 22.5 45

— –- –- –- –

40.6 59.4 10.8 163

 

Group. Number of L. R. Time in Tests.

Animal. Per cent. Seconds.

II 2 28 72 50 43

3 32 68 6.2 50

4 — 100 6.8 40

16 31.3 68.7 39.3 42

— –- –- –- –

22.8 77.2 25.6 175

 

Group. Number of L. R. Time in Tests.

Animal. Per cent. Seconds.

III 2 2.5 97.5 46.5 40

— — — — —

4 20 80 5.5 40

16 41 59 15 49

— –- –- –- –

21.2 78.8 22 129

 

Group. Number of L. R. Time in Tests.

Animal. Per cent. Seconds.

IV. 2 2 98 41 50

— — — — —

4 32.5 67.5 7.3 40

— –- –- –- –

17 83 24 90

 

Group I., representing 163 tests, shows 59 per cent. to the right,

with a time interval of 10.8 seconds (i.e., the time occupied in

turning). Group II. shows 77 per cent. to the right; and so throughout

the table there is an increase in the number of returnings to the

right. These figures at first sight seem to indicate the formation of

a habit, but in such case we would expect, also, a shortening of the

time of turning. It may be, however, that the animals were gradually

developing a tendency to turn in the easiest manner, and that at the

same time they were becoming more accustomed to the unusual position

and were no longer so strongly stimulated, when placed on their backs,

to attempt to right themselves.

 

All the subjects were measured and weighed in order to discover

whether there were inequalities of the two sides of the body which

would make it easier to turn to the one side than to the other. The

chelæ were measured from the inner angle of the joint of the

protopodite to the angle of articulation with the dactylopodite. The

carapace was measured on each side, from the anterior margin of the

cephalic groove to the posterior extremity of the lateral edge. The

median length of the carapace was taken, from the tip of the rostrum

to the posterior edge, and the length of the abdomen was taken from

this point to the edge of the telson. These measurements, together

with the weights of three of the subjects, are given in the

accompanying table.

 

TABLE IV.

 

MEASUREMENTS OF CRAWFISH.

 

Chelæ. Carapace. Abdomen. Weight.

Left. Right. Left. Right. Median.

 

No. 2, 9.8 10.0 38.2 38.7 47.3 48.1 29.7

No. 4, 7.7 7.7 33.6 33.8 39.4 42.3 17.7

No. 16, 12.5 12.4 37.6 37.6 46.4 53.2 36.2

 

Since these measurements indicate slightly greater size on the right

it is very probable that we have in this fact an explanation of the

tendency to turn to that side.

 

To test the effect of a change in the conditions, No. 16 was tried on

a surface slanted at an angle of 1° 12’. Upon this surface the subject

was each time so placed that the slant would favor turning to the

right. Under these conditions No. 16 gave the following results in two

series of tests. In the first series, consisting of 46 turns, 82.6 per

cent. were to the right, and the average time for turning was 17.4

seconds; in the second series, of 41 tests, there were 97.5 per cent,

to the right, with an average time of 2.5 seconds. We have here an

immediate change in the animal’s method of returning caused by a

slight change in the conditions. The subject was now tested again on

a level surface, with the result that in 49 tests only 59 per cent.

were toward the right, and the time was 15 seconds.

 

SUMMARY.

 

1. Experiments with crawfish prove that they are able to learn simple

labyrinth habits. They profit by experience rather slowly, from fifty

to one hundred experiences being necessary to cause a perfect

association.

 

2. In the crawfish the chief factors in the formation of such habits

are the chemical sense (probably both smell and taste), touch, sight

and the muscular sensations resulting from the direction of turning.

The animals are able to learn a path when the possibility of following

a scent is excluded.

 

3. The ease with which a simple labyrinth habit may be modified

depends upon the number of experiences the animal has had; the more

familiar the animal is with the situation, the more quickly it changes

its habits. If the habit is one involving the choice of one of two

passages, reversal of the conditions confuses the subject much more

the first time than in subsequent cases.

 

4. Crawfish right themselves, when placed on their backs, by the

easiest method; and this is found to depend usually upon the relative

weight of the two sides of the body. When placed upon a surface which

is not level they take advantage, after a few experiences, of the

inclination by turning toward the lower side.

 

*

 

THE INSTINCTS, HABITS, AND REACTIONS OF THE FROG.

 

BY ROBERT MEARNS YERKES.

 

PART I. THE ASSOCIATIVE PROCESSES OF THE GREEN FROG.

 

I. SOME CHARACTERISTICS OF THE GREEN FROG.

 

The common green frog, Rana clamitans, is greenish or brownish in

color, usually mottled with darker spots. It is much smaller than the

bull frog, being from two to four inches in length ordinarily, and may

readily be distinguished from it by the presence of prominent

glandular folds on the sides of the back. In the bull frog, _Rana

catesbeana_, these folds are very small and indistinct. The green frog

is found in large numbers in many of the ponds and streams of the

eastern United States, and its peculiar rattling croak may be heard

from early spring until fall. It is more active, and apparently

quicker in its reactions, than the bull frog, but they are in many

respects similar in their habits. Like the other water frogs it feeds

on small water animals, insects which chance to come within reach and,

in times of famine, on its own and other species of frogs. The prey is

captured by a sudden spring and the thrusting out of the tongue, which

is covered with a viscid secretion. Only moving objects are noticed

and seized; the frog may starve to death in the presence of an

abundance of food if there is no movement to attract its attention.

Most green frogs can be fed in captivity by swinging pieces of meat in

front of them, and those that will not take food in this way can be

kept in good condition by placing meat in their mouths, for as soon as

the substance has been tasted swallowing follows.

 

The animals used for these experiments were kept in the laboratory

during the whole year in a small wooden tank. The bottom of this tank

was covered with sand and small stones, and a few plants helped to

purify the water. An inch or two of water sufficed; as it was not

convenient to have a constant stream, it was changed at least every

other day. There was no difficulty whatever in keeping the animals in

excellent condition.

 

Of the protective instincts of the green frog which have come to my

notice during these studies two are of special interest: The

instinctive inhibition of movement under certain circumstances, and

the guarding against attack or attempt to escape by ‘crouching’ and

‘puffing.’ In nature the frog ordinarily jumps as soon as a strange or

startling object comes within its field of vision, but under certain

conditions of excitement induced by strong stimuli it remains

perfectly quiet, as do many animals which feign death, until forced to

move. Whether this is a genuine instinctive reaction, or the result of

a sort of hypnotic condition produced by strong stimuli, I am not

prepared to say. The fact that the inhibition of movement is most

frequently noticed after strong stimulation, would seem to indicate

that it