Premack and Woodruff tried to address this question with a simple experiment:
Sarah (their chimpanzee) was shown eight short videos, each of which showed a human actor in a difficult situation e.g. being locked in a cage. Sarah was then shown photographs of objects, one of which could present a solution to the actor’s dilemma. E.g a spigot and hose , a key, a match and a power socket. For each of the videos, Sarah pointed most often to the photograph which could offer a solution. Premack and Woodruff argued that for Sarah to be able to do this she must have understood what the actor intentions were, and that she therefore had theory of mind.
Many people believe that Sarah may have completed the task using ‘matching’ skills. For example; when presented with a video of an actor shivering in front of a broken heater, instead of knowing that the actor was cold and offering a solution she may have chosen the burning roll of paper because she associates the colour orange with both the heater and the flames.
Since Premack and Woodruff’s experiment many people have tried to design experiments that will prove definitively whether or not chimpanzees have a theory of mind. Most of the experiments have focused on individual cognitive abilities associated with theory of mind. For example;
- Machiavellian intelligence.(deception)
- The ability to determine what others are and are not aware of. (sight)
- Self-recognition
For each of these I will discuss the successes and failures of the experiments and assess whether or not any conclusive evidence has been revealed.
Machiavellian Intelligence
Many scientists have reported observing deceptive behaviour in chimpanzees, but the evidence is anecdotal and very little experimental evidence has been gathered. The only investigation into intentional deception by chimpanzees was undertaken by Premack and Woodruff:
Four chimpanzees were tested. They were placed in front of several inaccessible containers, and food was placed in one of them whilst the chimpanzee was watching. A human trainer would then enter the room and retrieve look in whichever container the chimpanzee gestured toward or touched. When a trainer dressed in green entered the room, (the ‘cooperative’ trainer) the food would be given to the chimpanzee if he pointed to the correct container. When the trial was repeated with a trainer dressed in white (the ‘competitive’ trainer) the chimpanzee was only given food if he indicated the incorrect box. The results showed that after 120 trials the chimpanzees were able to indicate the container which resulted in them being rewarded with both the ‘cooperative’ and ‘competitive’ trainer.
The results of this experiment can be interpreted in two ways: It is possible that the chimpanzees are actively deceiving the ‘competitive’ trainer thus demonstrating their ability to understand another’s perception. It is also possible however, that the chimpanzees may have merely learnt over the course of the experiment that signalling toward an empty box in the presence of a trainer in green would lead to them receiving a reward. (Dennett 1983; Heyes 1993).
Sight
In an attempt to prove whether or not chimpanzees have a theory of mind several experiments have been designed which try to establish whether or not chimpanzees are aware of what others can and can’t see.
In one experiment chimpanzees were given apples or bananas as a reward every time they extended their arms toward a trainer . The chimpanzee and trainer were separated by a Perspex screen with arm holes in it. The experiment was then varied and the trainers had their view obscured. In one experiment one of the trainers had a blindfold over their eyes and the other trainer had a blindfold over heir mouth. In another variation one trainer presented her back to the chimp whilst the other wore a bucket over her head. It was discovered that the chimps would make begging gestures to trainers who had their eyes covered with the same frequency as they would to the trainer who could see. The chimps behaviour only changed when the trainer’s back was facing the chimp.(Povinelli et al. 1990 ) The results of this experiment seem to suggest that chimpanzees do not equate seeing with knowing, one of the principles of theory of mind.
Self-recognition
The capacity to recognise oneself in a mirror is said to imply:
“..the possession of a self-concept and the potential to imagine oneself as one is viewed by others.”
(Gallup 1982)
Considering this, self-recognition must also imply theory of mind. Several self-recognition experiments have been undertaken, but all have been disputed. For example:
A chimpanzee with previous experience of mirrors is anesthetised and marked on the head with a dye. After recovery, the chimpanzee is observes without a mirror present and the number of times the chimpanzee touch their head is recorded. A mirror is then introduces and the same observations are made. Chimpanzees have been seen to touch their heads more in the presence of a mirror, this could suggest that they are aware that the image they can see in the mirror is themselves. Unfortunately this evidence is not conclusive as the number of times the chimpanzee touches his/her head may be increased in the second situation because the anaesthetic has worn off further, thus increasing all activity.
Conclusion
All attempts to provide a concrete answer to the question of chimpanzee’s theory of mind have as yet been unsuccessful. The studies introduced above are a only a few of many, but the same challenges in designing a useful experiment have reoccurred in all attempts. Arguably the best experiment so far has been Premack and Woodruff’s initial study.
One of the most frequent problems has been creating an experiment in which the chimpanzee’s behaviour can not be attributed to ‘trial and error’: The chimpanzee may seem to have made an intelligent decision to complete a task, but it is always possible that the chimpanzee has managed to do so by use previously gained knowledge. This has prevented scientists being unable to determine whether behaviour is mentalistic or behaviouristic.
Before an answer to the initial question, “do chimpanzees have a theory of mind?”, can be given, a more reliable study will have to be undertaken.
Bibliography
McFarland, D (1993) Animal Behaviour (2nd edition) England:Longman Group
Tomasello, M., Call, J. & Hare, B. 2003. Chimpanzees understand psychological states – the question is which ones and to what extent. Trends in Cognitive Sciences 7, 153-156.
On-line Resources
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