Theory of Mind in Humans & Primates

1. Theory of Mind in Humans & Primates Yee-Ann Soong and Bob Same

2. False Belief Tasks • Children begin to conceptualize thought • ~4 or 5 years old • Seems to be a link between language and ability to conceptualize thought • What about primates? • Predictions: • If language is important, they will fail the false belief test • If language is not important, they will pass

3. Previous Studies • Woodruff & Premack (1979) • Used two different trainers • One would locate the food and give it to the primate • Other would locate the food and eat it himself • Can primates understand the intentions of the trainers? • Took many trials for primates to master the task Simply learning how to get the food?

4. Previous Studies • Povinelli, Nelson & Boysen (1990) • Can primates distinguish a knowledgeable vs. ignorant human? • Tested primates with trainers who had/had not seen a hiding event • Took many trials for primates to master the task Simply learning how to get the food? *Couldn’t replicate results using younger chimps in 1994

5. Comparing Humans to Apes • Must be nonverbal

6. Experimental Setup A B

7. Experimental Conditions • Understanding of task • 3 control tests • 1. Visible Displacement • 2. Invisible Displacement • 3. Ignore Communicator • Mastery of all 3 control tests is necessary for passing the false belief task (and a requirement for participation)

8. Results: Children & Control Tests

9. Results: Children and False Belief

10. Interpretation • Most 4 and 5 year olds can pass the control tests • Most 5 year olds clearly pass the false belief test • Ability increases with age!

11. ToM – Ability and Age

12. Testing Primates

13. Modified Tests • Instead of removing the marker after 1-2 s, the marker was left on the box • How do you know that the ape isn’t just equating the marker with food? • Answer: Invisible displacement non-marker test (where there was no marker)

14. Results: Primates and Control Tests

15. Results: Primates and False Belief *Total 4 trials

16. Theory of Mind • Follow up tests ensure that the Primates still understood the control tasks • Primates failed the false belief test regardless of age • Primates failed differently from 4 year olds • Primates knew the answer: the wrong one! • 4 year olds were guessing • (Not overwhelmingly choosing the wrong answer)

17. Comparison: Humans and Primates

18. Conclusion? “Apes do not have a ‘theory of mind’ in the sense of understanding the false beliefs of others.” -Call & Tomasello • Are all apes created equal? • Is the task too hard?