Social constraints determine what is learned in the chimpanzee

Behavioural 0 1993

Processes, 28 (1993)

Elsevier Science

173-l

Publishers

173

80

B.V. All rights reserved

0376-6357/93/$06.00

BEPROC 00452

Social constraints

determine

what is learned

in the chimpanzee R. Chalmeau

and A. Gallo

Centre de Recherche en Biologie du Comportement, Toulouse, France

(Accepted

29 September

Universite’ Paul Sabatier,

1992)

Abstract A group of six chimpanzees was placed in a social learning situation, without training. The learning task was an operant conditioning situation; that is, a subject had to pull two handles simultaneously to cause a piece of fruit to fall into the cage. Only three individuals For the operant individuals, social influences on the acquired the operant behaviour. expression of the learning task were then examined; the dominant chimpanzee during feeding had an inhibiting effect when close to the operant subjects. Depending on the subject, social factors may influence not only the specific expression of what is learnt, but also the nature of what is learnt. Chimpanzees appear to experience situations differently: they develop an individual problem-solving strategy according to their social relationships even if the experimental

Key words: Operant

procedure

conditioning;

is the same for all.

Social influence;

Individual

strategy;

Chimpanzee

Introduction The term ‘social constraints on learning’ refers to social facilitating or social inhibiting, both mechanisms which act on the expression of an acquired behaviour (Bond and Titus, 1983). Other social influences act directly on the emergence of learning processes (mechanisms of observational learning, e.g. see Beck, 1974; Galef, 1976). In these studies, results are typically analysed in terms of individual performance in a learning task. In conventional learning studies, subjects undergo a standard procedure (Skinner, 1938). In other words, the experimental situation is the same for all subjects. However, if

Correspondence Paul Sabatier,

to:

R. Chalmeau,

Centre

de Recherche

(CNRS URA 6641, 118 route de Narbonne,

en Biologie 31062

du Comportement,

Toulouse,

France.

Universite

174

the learning task is performed in a social situation, then inter-individual

relationships

also

have to be taken into account because different individuals have neither the same skills nor the same social status. For Papio papio (Lepoivre and Pallaud, 19851, involved in discriminative tasks with an inversion, only three dominant animals performed the task. On the contrary, for discriminative tasks in Macaca rrwlatta (Bunnel et al., 1979) and Macaca fascicularis (Bunnel and Perkins, 19801, performance was better for subordinate animals than for dominant animals. Even if it is possible to explain differences in learning abilities according to the social status found in the social dynamics of the species under consideration (Strayer, 1976), individual skills cannot be fully revealed by performance which is partially affected by social constraints (Pallaud, 1990). In order to observe the influence of social constraints on a learning task, a problem was presented to a group of chimpanzees (fan troglodytes). As described in the first part of the paper, results were first analysed according to classical methods of measuring performance; in the second part, individual strategies used to attain this performance were studied and analysed.

Materials

and Methods

Subjects Six chimpanzees were tested in an operant conditioning task in a social situation. The group was housed in the zoo at Plaisance-du-Touch (near Toulouse, France). The group contained an adult male (Alfred, 21 years old), a sub-adult male (Alphonse, 7 years), an adult female with her infant (Amanda, 43 years and Amandine, one year), a sub-adult gravid female (Chloe, 11 years) and an adolescent female (Agathe, 6 years). They had been living together since 1986.

Priority

of access to food

In a preliminary

study

lasting

89

h, relationships

between the conspecifics

were

observed in order to determine the social structure of the group. When visitors threw some

TABLE 1 Priority of access to food Ad Ad

Am

Ch

As

A!??

E

33

40 11

46

14

76

13

11

3

10

16

11

8

15

Am

_

Ch

_

2

As

_ _

1 _

_ _

-

1

2

1

1

& E Ad = Alfred, n = 319. (columns).

Am = Amanda, Ch = Chlok,

As = Alphonse,

3 1

Ag = Agathe and E (Enfant) = Amandine;

Dashes represent the animals taking the food when lying close to one or more conspecifics

175

food into the cage, the dominance in priority of feeding was recorded (Table I>. The data reveal that when all the apes were present, only Alfred grasped the food even if it fell close to a conspecific (n = 209). However, when Alfred paid no attention to the food (during resting or some other occupation), then the feeding priority of the remaining individuals became apparent (n = 110). In some cases the visitor placed the food in the hand of a begging chimpanzee (not included in the table). Generally, the chimpanzee would eat it, except on two occasions when Alfred ‘stole’ the food from the animal’s hands (Amanda and Chloe). These observations indicate that Alfred was the dominant individual with priority in feeding, then came Amanda and Chloe (and sometimes the reverse>, then Alphonse, Agathe, and finally, Amandine. This pattern of interaction had been established over several years as was revealed by the animals’ behaviour during daily feeding (Toniutti, pers. corn.).

Apparatus

and procedure

In the second phase, the group was presented with an operant conditioning task, involving a specially constructed, fruit distribution apparatus (Jegat and Chalmeau, 1992). The distributor was located outside the animals’ outdoor cage. Two ropes linked to counterweights, with a handle on the other end of each rope, extended from the distributor to the interior of the cage. An operant response (OR) was defined as a simultaneous pull on both handles, which caused a piece of fruit to fall through a 2-m long gutter into the cage in front of the apparatus. An individual alone could produce an operant response (or with difficulty, two animals could do so). The distributor was set to release fruit, at a maximum rate of one piece per 15 s. Subsequent pulls on the handles during this 15-s delay did not result in a fruit drop. The learning phase lasted 20 days over a period from 1 st June to 7th July 1991 (on rainy days the chimpanzees remained indoors). The duration of each session was limited by the number of rewards (R) available (between 30 and 40 pieces of fruit each day) so as not to alter the group’s normal food intake. Throughout the sessions, any individual near the handles was videotaped and his or her behaviour quantified.

Results and Discussion

Performance

and rewards

As shown in Table 2, only four individuals produced operant responses. Amandine was too young and not strong enough to pull the handles which were linked to counterweights. Alfred, the dominant chimpanzee in terms of priority in feeding, never produced an operant response and touched the handles the least of all. Approximately midway through the experiment, Chloe produced three operant responses, one per session, and no more throughout the remainder of the experiment. This low performance rate could be linked to the fact that she often deliberately isolated herself because of her pregnancy. Amanda produced her first responses on the seventeenth day, Alphonse on the eleventh day, and Agathe on the second day.

176 TABLE

2

Frequency (F), percentage (%) of operant responses (OR) and rewards obtained (R) by each subject. Subjects

OR (F)

Alfred

OR (%)

0

R (%)

0

38

Alphonse

240

60

35

Amanda

44

11

9

3

1

3

111

28

13

0

0

ChloC Agathe Amandine

2

-__

The total number of operant responses was 398 and the number of rewards 391. This difference was due to 7 ‘cooperative’ responses between Amanda and Agathe: each of them pulled on one handle at the same time. This

unusual behaviour was counted as one operant response for each ‘cooperat-

ing’ subject.

Alfred

obtained

most of the pieces of fruit, even though

he never produced

responses (Table 21, because conspecifics ‘voluntarily’ retreated Amandine collected very few pieces of fruit, slightly more than came second in terms of pieces of fruit obtained, but he was the responses, followed by Agathe. For Alphonse and Agathe, half

any operant

in front of him. Chloe and they produced. Alphonse main producer of operant of their productions was

taken by others, especially by Alfred. Finally, Amanda’s production was approximately equal to her number of rewards. This analysis reflects both individual efficiency when using the apparatus, and the importance of relative dominance in priority of access to food among the subjects. The level of overall individual performance (Table 3) was assessed using an index calculated over the 20 days of experimentation (Global Index: Cl). The Cl differed significantly among the subjects (Kruskall-Wallis test, H = 21.67, P < 0.05). The other two indices could not be calculated for Chloe because of her low number of OR. A second index expressed the average performance when subjects were alone at the apparatus (Alone Index: Al). The Al represents the average frequency of the ratio OR/min, and individual Als were significantly different (Kruskall-Wallis test, H = 13.04, P < 0.05). In

TABLE

3

Average frequency of operant responses (OR/min)

for all sessions

(Global Index),

for trials when

subjects were alone (Alone Index), or in Alfred’s presence (Presence Index) Global Index

Alone Index

Presence Index

(OR/min)

(OR/min)

(OR/min)

Alfred

0

0

0

Alphonse

0.56

1.58

0.04

Amanda Chloe

0.21 0.07

0.53 _

0.19

Agathe

1.57

3.31

0.26

Amandine

0

0

0

_

Cl expresses the ratio between the number of OR and the total time spent at the apparatus for all sessions.

177

terms of these two indices, Agathe’s performance was the highest, followed by Alphonse’s, and then Amanda’s. Operant performance here was inversely correlated to the usual ranking during feeding. The AI can then be compared with another index, the Presence Index (PI), which refers to the effect of Alfred’s presence at the apparatus (within a 3-m zone) on individual performance. The PI represents the ratio between the number of ORs and the time spent at the apparatus in the presence of Alfred. For all individuals, performance was poorer when Alfred was present than when they were alone at the apparatus. Thus, Alfred may be considered to be an inhibitor (Mann-Whitney U test, U = 164, z = - 2.72, P < 0.05). Of all the rewards delivered following an operant response, 50% were eaten by a subject other than the operator. Alfred obtained 74% of those rewards, and his approach toward operant subjects was enough to stop all activities at the apparatus.

Individual

strategies

After this traditional approach, an alternative analysis considering behaviour patterns other than operant responses was undertaken. Emergence (session in which the first OR appeared) and rapidity in expression of operant responses (frequency and duration of OR per session) differ among individuals. Social constraints may effect not only operant performance, but also the manner in which this performance is carried out, i.e. behaviour patterns before the operant response is made. The frequency of operant responses is not sufficient enough to explain all behavioural differences between individuals. However, consideration of individual strategies can provide some important clues for understanding inter-individual differences in performance. For example: (i) an individual may learn to produce an operant response only when alone. Agathe, for instance, had to be very quick in order to have a chance to collect her reward before another member of the group got it. Therefore she worked at the apparatus mainly when it was unoccupied. The average time each subject spent per visit illustrates individual strategies: Agathe showed the shortest time per visit, both in visits when she performed an operant response (38 + 8 s, n = 54) and in visits without operant response (mean: 22 + 3 s,n = 92). Alphonse used another strategy: he spent significantly more time (Wilcoxon test, z = - 5.44, P < 0.05) on visits with operant responses (350 + 128 s, n = 72) than on visits without operant response (63 f 7 s, n = 139). In fact, when Alphonse was near the apparatus, he appeared to be waiting for an opportunity to produce an operant response. He kept a constant watch over the others and especially over Alfred. Whenever he was near the handles and had some chance of obtaining his reward (i.e. when he was alone), he produced an operant response. (ii) an individual could produce several successive operant responses: Amanda, like Alphonse, spent much more time at the apparatus for visits producing operant responses (281 + 46 s, n = 12) than for visits without operant response (54 + 9 s, n = 129; Wilcoxon test, z = - 1.96, P < 0.05). Apart from Alfred, no subjects disturbed Amanda when she was there, so Amanda developed a peculiar technique. She seized one handle with one hand, the other handle with the contralateral foot, and holding both handles, simultaneously pulled. She then collected several successive rewards (at 15 s intervals) with her free hand. (iii) an individual could pull on one handle while the other handle was being pulled on by a conspecific: we observed this ‘cooperation’ seven times, always between Amanda and

178 Agathe. During the seventeenth session, Amanda had still not mastered the operant-response task, but while she pulled on one handle, Agathe came several times to pull on the other handle and thus produced a reward. (iv) an individual

could learn to collect a reward obtained by a conspecific: Chloe and

Amandine learned to associate the behaviour of an ‘operant individual’ at the apparatus with the possibility of obtaining fruit, but only when Alfred was not around. At first, Alfred learned the same thing, but when he stayed near the apparatus, nobody else approached to produce an operant response because they had learnt that Alfred might take their reward. Consequently, Alfred used another strategy, associating the sound of the platform’s rotation (which meant that a piece of fruit was about to fall) with the reward itself. Then he remained at a distance, only approaching the apparatus rapidly when he heard the rotation of the platform. It appears that Alfred learned to associate the behaviour of a conspecific with a possible food reward, without realizing that he could perform an operant response by himself. In conclusion, the type of learning in a given situation differs between individuals who produce many operant responses and those who never, or only rarely produce one. Three individuals learnt the operant-response task, i.e. they conformed to rules fixed by the experimenter. The others learnt something different according to their own understanding of the situation. This study shows that a problem is not perceived in the same way by all members of a group, even if it has been defined by the experimenter as a single task. Even though a ‘problem’ is presented by the experimenter, each individual constructs his or her own problem. This could provide an explanation for the observed diversity of individual strategies. These variable learning strategies, shaped by the relationships with conspecifics, might constitute a significant source of variation in problem-solving at the individual level.

Acknowledgements We would like to thank J.M. Toniutti, Director at the Plaisance-du-Touch Zoo, for permission to conduct research there, and F. Marche for his help in installing the apparatus. We would also like to thank R. Jegat for making the apparatus, and finally, S. Becker, D. Dracos and C. Melan for help in linguistics, and 1. Medioni, J.R. Anderson and an anonymous referee for helpful comments on the manuscript.

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