Theory of Mind Theory of Mind in Humans & in Humans &

PrimatesPrimatesYee-Ann Soong and Bob SameYee-Ann Soong and Bob Same

False Belief TasksFalse Belief Tasks

Children begin to conceptualize thought Children begin to conceptualize thought ~4 or 5 years old~4 or 5 years old

Seems to be a link between language and Seems to be a link between language and ability to conceptualize thoughtability to conceptualize thought

What about primates?What about primates? Predictions:Predictions:

If language is important, they will fail the false belief If language is important, they will fail the false belief testtest

If language is not important, they will passIf language is not important, they will pass

Previous StudiesPrevious Studies

Woodruff & Premack (1979) Woodruff & Premack (1979) Used two different trainersUsed two different trainers

One would locate the food and give it to the primateOne would locate the food and give it to the primate Other would locate the food and eat it himself Other would locate the food and eat it himself

Can primates understand the intentions of the Can primates understand the intentions of the trainers?trainers?

Took many trials for primates to master Took many trials for primates to master the taskthe task

Simply learning how to get the Simply learning how to get the food?food?

Previous StudiesPrevious Studies

Povinelli, Nelson & Boysen (1990)Povinelli, Nelson & Boysen (1990) Can primates distinguish a Can primates distinguish a

knowledgeable vs. ignorant human? knowledgeable vs. ignorant human? Tested primates with trainers who had/had not Tested primates with trainers who had/had not

seen a hiding eventseen a hiding event

Took many trials for primates to master Took many trials for primates to master the taskthe task

Simply learning how to get the Simply learning how to get the food?food?

*Couldn’t replicate results using younger chimps in 1994*Couldn’t replicate results using younger chimps in 1994

Comparing Humans to Comparing Humans to ApesApes

Must be nonverbalMust be nonverbal

Experimental SetupExperimental Setup

A B

Experimental ConditionsExperimental Conditions

Understanding of taskUnderstanding of task 3 control tests3 control tests

1. Visible Displacement1. Visible Displacement 2. Invisible Displacement2. Invisible Displacement 3. Ignore Communicator3. Ignore Communicator

Mastery of all 3 control tests is Mastery of all 3 control tests is necessary for passing the false belief necessary for passing the false belief task task

(and a requirement for participation)(and a requirement for participation)

Results: Children & Results: Children & Control TestsControl Tests

Results: Children and Results: Children and False BeliefFalse Belief

InterpretationInterpretation

Most 4 and 5 year olds can pass the Most 4 and 5 year olds can pass the control testscontrol tests

Most 5 year olds clearly pass the Most 5 year olds clearly pass the false belief testfalse belief test

Ability increases with age!Ability increases with age!

ToM – Ability and AgeToM – Ability and Age

Testing PrimatesTesting Primates

Modified TestsModified Tests

Instead of removing the marker after Instead of removing the marker after 1-2 s, the marker was left on the box1-2 s, the marker was left on the box

How do you know that the ape isn’t How do you know that the ape isn’t just equating the marker with food?just equating the marker with food?

Answer: Invisible displacement non-Answer: Invisible displacement non-marker test (where there was no marker test (where there was no marker)marker)

Results: Primates and Results: Primates and Control TestsControl Tests

Results: Primates and False Results: Primates and False BeliefBelief

*Total 4 trials

Theory of MindTheory of Mind

Follow up tests ensure that the Follow up tests ensure that the Primates still understood the control Primates still understood the control taskstasks

Primates failed the false belief test Primates failed the false belief test regardless of ageregardless of age

Primates failed Primates failed differentlydifferently from 4 year from 4 year oldsolds

Primates knew the answer: the wrong one!Primates knew the answer: the wrong one! 4 year olds were guessing 4 year olds were guessing

(Not overwhelmingly choosing the wrong answer)(Not overwhelmingly choosing the wrong answer)

Comparison: Humans and Comparison: Humans and PrimatesPrimates

Conclusion?Conclusion?

““Apes do not have a ‘theory of mind’ in Apes do not have a ‘theory of mind’ in the sense of understanding the false the sense of understanding the false beliefs of others.”beliefs of others.”

--Call & TomaselloCall & Tomasello

• Are all apes created equal?Are all apes created equal?

• Is the task too hard?Is the task too hard?