cooperative problem solving in rats

8/9/2019 Cooperative Problem Solving in Rats

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COOPERATIVE PROBLEM SOLVING IN RATS

1

WILLIAM J. DANIEL

The Psychological Laboratory of the University of North Carolina

Received May 20,1942

INTRODUCTION

Several experiments (2-5) have been presented which have more or less suc-

cessfully dem onstrated cooperative behavior in the higher apes. A few experi-

ments (1, 6, 7), observational in character, have indicated this behavior in

children. Only one experiment, th at of Wolfle and Wolfle (9) has attem pted to

study cooperative behavior genetically by comparing the behavior of apes and

children in nearly identical experimental situations.

It has generally been believed tha t a study of cooperative behavior in animals

as far down the evolutionary scale as the ra t is rathe r fruitless. Only one such

experiment (8) has come to the writer's atten tion . One of the three experiments

which constitutes tha t monograph w as designed to te st for cooperative behavior

in the rat. This experiment was neg ative; and aside from the films of Mow rer,

no other attem pt to obtain cooperative behavior in rats has been reported. The

experiment reported here represents an a pparen tly successful atte mp t at obtain-

ing cooperation and one which relies primarily on q uan titative da ta.

PROBLEM

In the experiment described below we wanted to know if it is possible to

arrange an experimental situation in such a manner that two animals can assist

one another in o btaining food and at the sam e time escape electric shock.

The experimental situation consisted of a grid box with an electrically insulated

platform at one end which, when a rat stepped on it, would remove the charge

from th e grid. There was also a food crock flush with the grid and beyond th e

reach of a rat on the platform. This situation is represented schematically in

figure

1.

Our problem is concerned w ith the behavior oftworats in this situation. Will

one rat go to the platform and rema in on it, thu s enabling the other ra t to feed?

Will the feeding rat leave the food crock and go to the platform, enabling the

rat to leave the platform an d feed? fina lly, w ill they exchange positions in

such a manner th at b oth are adeq uately fed and bo th escape or minimize shock?

In short, will cooperative behavior be obtained when two rats are put into a

double motive situation if the satisfaction of bo th of these motives is contingent

upon the behavior of both animals?

1

A report of part of this work was presented at the Chicago meetings of the American

Psychological A ssociation in Evan ston, 111., Sept. 1941.

This study represents the substance of a thesis subm itted to the faculty of the Univer sity

of North Carolina in partial fulfillment of the requirements for the degree of Doctor of

Philosophy in the d epartment of Psychology and was done under the direction of Dr. A. G .

Bayroff of that department.

361


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6

WILLIAM J. DANIEL

ANIMALS

Heterozygous albino rats were used, ten males and two females ranging from

9 to1 7days of age at the sta rt of the experiment.

APPARATUS

The experimental situation {fig

1)

The experimental situation consisted of

a

paraffined wood cage

22 |*

long x 12

widex4\ high withagrid floor andaglass top. Inthe centerofthe cagea

Pivot -

Grid floor1/8 brass

rods $

apart

4

4

Wall atop 2

Platform

y

\

*

12

*.

Fig*

1.

Diagram

of

apparatus*

F

s

Food crock

Scale - Inch 1 Inch

food crock, flush with the grid, was placed 8 from th e edge of the platform thu s

making

it

impossible for

a rat to

feed from the platform.

This grid cage was mou nted o n

a

se t

of

stilts thu s facilitating th e replenishing

and replacing

of

the food-crock.

A

small wooden wall stop was mounted over

the platform

at

the end

of

the cage forcing all rats

to

remain beyond its center

of gravity an d m aking it impossible for

a

rat to adm inister shock withou t leaving

the platform.

Theilting

of the platform also completed

a

light circuit so tha t a

40 wa tt bulb Sashed whenever

a rat

received

a

shock. This facilitated

an

ob-

jective countingofthe numberofshocks adm inisteredbyeachrat.


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COOPERATIVE PROBLE M SOLVING IK BATS 363

The rats were dropped onto the grid through a small glass door on the top

of the appa ratus . Directly benea th this door a small entrance alley 6 long and

4 | wide served to orient the animals in the proper direction, that is, facing

directly towards the food-crock and platform.

The shocking circuit

The grid was wired in series with a high resistance shocking circuit and the

platform automatically shorted out th e grid when a rat stepped on it.

The essential problem here was to apply an electrical stimulus to the rats,

the physical constancy of which we could be reasonably assured. Our circuit

was of such a high external resistance tha t th e added resistance of one or two ra ts

gave the same meter reading as when a copper wire was placed across the grid.

The transformer of this shocking circuit applied 3,750 volts to the rectifier tube

and th e cu rrent at the shock grid terminals could be varied from 100 microamps

to5milliamps. The average shock intensity of25 microamps required a circuit

resistance of 3,400,000 ohms.

PROCEDURE

The preliminary training

The aims of the preliminary training were three-fold:

1. To train th e rats to feed in the experimental situation.

2. To train the ra ts to go to the platform when the g rid was electrified.

3.

To develop this discrimination, basic to the solution of the problem to be

presented in the social situation, to the point at which the rats immediately

made the response appropriate to the situation when the situations were varied

in an irregular order.

The following schedule was maintained:

1. The rats were unfed for 24 hours.

2. One rat w as placed in the grid cage alone with th e shock off an d th e food-

crock in place. It remained there for two 450-second trials, and was weighed

before and after each day 's trials. This procedure was continued through th e

8th day for each rat.

3. At the end of the 8th d ay's run the sated ra t was put in the grid cage with

the grid electrified at 100 microamps. It was not removed until it had reached

the platform and remained on it for3

seconds.

This procedurewasrepeated for

20 trials on this day.

4. From th e 9th through the 13th day the ra t was run for 20 irregularly mixed

trials with electrified and non-electrified grid.

On the shock trials the rat ha d to learn to go to the platform and to remain on

it for 30 seconds. The time it took the ra t to make the approp riate response,

i.e., going to the platform, was recorded.

On the food trials the grid was not electrified and the rat was left in the ap-

para tus for 100 seconds. If by the end of this time it had not mad e th e ap-

propriate response (feeding) it was removed from the apparatus and given the

next trial. The time it took the ra t to. commence feeding was recorded and if


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3 6 4 WILLIAM J. DANIEL

the ra t did feed it was allowed to do so for 30 seconds so long as it start ed some-

time within this 100 second interval.

By the end of the 13th day of the preliminary training the ra ts had mastered

this discrimination. When dropped on a cold grid the ra t imm ediately went to

the food-crock and fed; when dropped on a hot grid the rat immediately went to

the platform and remained on it for 30 seconds. It m ade this discrimination in

less than a second or before the experimenter could get to his stop watch to

start timing the rat.

Thu s at th e conclusion of the prelim inary training each animal had learned to

escape from shock or to feed in the app aratu s depending upon the situ ation and

it had learned this individually and in isolation.

The experimental trials

At the end of the preliminary training the rats were divided into pairs of as

nearly equal weight as possible.

In the experimental trialstworats were put into the cage with the grid electri-

fied and the food-crock in place. The y remained in the experimental cage for

one trial of

12

seconds dura tion. They were run

12

trials a day , a tota l of 1440

seconds, which, on the basis of preliminary experimentation, was adequate for

the hunger satiation of both anim als. The trial was timed by an electric stop -

clock and the individual feeding times by a manually operated stop-watch.

Throughout the experimental trials the apparatus operated automatically.

W ith one or both ra ts on the platform t he shock was off. W ith the grid not

charged, a rat could feed at the food-crock. Thus at least on e rat hadalways

to be on the platform if the other was to get to the food-crock. Occasionally

both rats would leave the platform and attempt to feed and take shock simul-

taneously. If this behavior persisted for 5 consecutive times the shock was

increased 50 microamps, and this double feeding stopped.

The rats were fed pulverized purina dog chow mixed with water in the ratio

of 5:6 respectively. At no tim e did the rat s receive food other than th at ob-

tained in the experimental situation. This procedure was continued for 40 days

at which time it appeared th at the ra ts were doing as well as they ever would.

RESULTS

The m ost significant fact in th e da ta is tha t th e rat s exchanged positions from

food-crock to platform an d from platform to food-crock. Ma ny of these ex-

changes were accompanied by shock and many shocks were administered in

between these exchanges. It will be remembered th at whenever there was any

shock both r ats received it, bu t itwasadministered only by one rat (the platform

ra t) stepping off the platform and thu s electrifying th e entire grid. As the ex-

periment progressed more and more of the position shifts were accomplished

wit hou t shock. Also fewer and fewer shocks were administered which did not

result in an alternation. This data for 6 pairs of rats are presented in table 1.

Since we are most interested in the final stage of this behavior th e da ta are given


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COOPERATIVE PBOBLEM SOLVING IN BATS

65

in terms of the mean performances for the last 5 days of the experiment as com-

pared with the mean performances for the first 5 days of the experiment.

Notice th at with th e exception of pairs 1-2 and 9-10 the critical ratios indicate

that there is a marked and statistically significant decrease in the number of

shocks not resulting in an alternatio n. The shock seems to have been qu ite

effectively reduced.

The natur e of the alternations is also impo rtant. Let us call one of these rats

A and the other B . Now if rat A is feeding at the food-crock he ma y return t o

the platform and the n again retu rn immediately to the food-crock. We shall

call this exchange in position an indiv idual alternation since it is accomplished

only by one ra t. When r at B exhibits this behavior we shall also call this ex-

change in position an individual alternatio n. When ra t A is at th e food-crock

and returns to the platform an d rat

B comes

off th e platform and

goes

to th e food-

TABLE 1

MEAN

SHUTSJOK

LAST 5DAYS

PEB CENT OF TOTAL SHUTS

WITHOUT

SHOCK

C I

1 2

3 4

6 6

7 8

9 10

11 12

18

15

92

14

25

95

14

68

89

92

89

93

1.33

4.64

8.92

6.04

1.29

8.89

TABLE 2

Total number of alternations

Percentage which the mutual alternations are of

the total

PAHS

1-2

947

97

3- 4

863

94

5-6

3748

97

7-8

957

94

9-10

1201

95

11-12

3271

99

crock we refer to thi s kind of a shift as a m utu al exchange in position. The

question is, then, w hat percentage of th e tota l exchanges in position is m utual

and wh at percentage is individual? These data are presented in table 2.

These data support the conclusion tha t for the entire group the ra ts a lternate

in amutualmanner in at least 94 per cent of the total alternations. We can say

then tha t they are taking tur ns 94 to 99 per cent of the time.

Our next question is, how well do these rats ge t fed while they are eliminating

shock and exchanging positions in the experimental situation? Table 3 gives

the mean weights for the first 5 days and the last 5 days of the experiment.

It is clear from this table that every rat gained weight during the experiment

and these gains ranged from 24 to 140 grams. This, along with the fact of their

general healthy and vigorous appearance, further support the conclusion that

rats w ere adequately fed through out th e experiment.


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66

WILLIAM J. DANIEL

Another factor of importance is the extent to which the animals use the total

available time in the appa ratu s. Means of this dat a for the entire experiment

are given in table 4. Since the y were run for 12 two-m inute trials a day th e

tota l available feeding time for each pair of rats is 1440 seconds a day. Oc-

casionally both rats would go to the platform and rem ain on it together. This

is considered time w asted in as much as it is time during which food w as available

for one or the other animal but was taken by neither. We can see tha t the r ats

used practically all of the available feeding tim e. This speaks well for our final

choice of time interval and also indicates tha t th e rat s were actively working on

TABLE 3

SAT

1

2

3

4

5

6

7

8

9

10

11

12

O R A H S E A T E N P E S

DA V

21

21

25

. 20

25

27

27

23

30

21

32

31

W E I G H T B E F O R E I H E

E X P E R I M E N T

96

113

109

121

118

126

127

140

121

158

182

161

W K XG HT A FT R TH E

E X P E R I M E N T

153

253

144

179

205

189

170

211

160

230

250

231

W EIG H T G A D i ZD

57

140

35

58

87

24

43

71

39

72

68

70

TABLE 4

the problem set by th e experimental situation practically all of the tim e tha t t hey

were in the apparatus.

DISCUSSION AND INTERPRETATION

First of all let us re-emphasize the fact th at this was a double motive situation.

Our original intention was to arrange these m otives in an experimental situation

in such a mann er th at n either of them could be satisfied witho ut th e co-ordinated

efforts of oth animals.

Rather than put the organism into an experimental situation and observe if it

exhibits cooperative behavior we attem pt to put the animal through a pro-


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3 6 8 WILLIAM J . DANIEL

SUMMARY

AND

CONCLUSIONS

To investigate the development of cooperative behavior in rats 6 pairs of rats

were put into a double motive problem situation (feeding and avoiding shock)

requiring the co-ordinated efforts of both animals for its adequate solution.

Each ratwasin dividually trained t o feed when the gridfloorwas not electrified,

and when it was charged to go to a platform which shorted out the grid floor

when a rat stepped on it. The rats were then paired, and th e problem was to

discover if cooperative behavior would be obtained when two rats were put into

a double motive situation in which the satisfaction of both of these motives is

contingent upon th e behavior of both animals. One rat of a pair had to run t o

a platform which shorted out the electrified floor grid of a feeding box in order

that a second rat might feed.

From the data obtained in this situation we might draw the following con-

clusions:

1.

The rats learned to exchange positions in this situation and at the same

time allow sufficient feeding time for each rat to become adequately fed in the

course of the experimental session.

2.

They showed marked improvement in alternating without shock and in

eliminating the shocks which did not result in an alternation.

3. They learned to take turns at the food-crock and platform so that by the

end of the experiment they spent almost all of the available time in the ap-

paratus working on the problem and very little time together on the platform.

4.

And finally, in this situation, cooperative behavior has been apparently

established. In a food-shock situation both anim als exchange positions so th at

bo th are adequ ately fed. Furth ermo re, they exchange positions with sufficient

care and speed th at they avoid shock. They satisfy bot h conditions of th e ex-

periment in a situation in which the satisfaction of

both

conditions was con-

tingent upon the behavior of

both

animals.

RE F E RE NCE S

(1) BERNE, E .VANC.: An experimental investigation of social behavior patterns in young

children. Un iv. la . Stud. ChildWelf.,1930,4,61 pp .

(2) CRAWFORD, M. P . , AND NISSEN, H. W.: Gestures used by chimpanzees in cooperative

problem solving. (Silent film.) New York: Instructional Films, Inc., 30 Rocke -

feller Plaza, 1937.

(3)

CBAWFOBD,

M. P.: C ooperative behavior in chimpanzee. Psych ol. Bull., 1835,3 2,714 .

(4)

CRAWFORD,

M . P.: Cooperative solution b y chimpanzees of a problem requiring serial

responses to color cues. Psyc hol. Bull ., 1938,36,70S .

(5) CRAWFORD, M. P. : Further study of cooperative behavior in chimpanzee. Psycho l.

Bull., 1936,33, 809.

(6)

LEWIN,

K .,

AND LIPPITT,

R.: An experimental approach to the study of autocracy and

democracy: a preliminary not e. Sociometry, 1938,1 , 292-300.

(7) MOORE, E. S.: The development of mental health in a group of young children: An

analysis of factors in purposeful activit y. Univ . la . Stud. Child

Welf.,

1931,4,128 pp .

(8) WINSLOW,C. N. : A study of experimentally induced com petitive behavior in the white

rat. Comp. Psychol. Monogr., 1940,15, 35 pp.

(9)

WOLJXE,

D. L. , ANDWoLPtE, H. M .: The developmen t of coo perative behavior in

monkeys and young children. J. Genet. Psychol., 1939,65,137-75.

cooperative problem solving in rats

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