The curse of knowledge: Mistaking your beliefs for those of others

[This post was originally published in September, 2007]

ResearchBlogging.orgHere's a task that four-year-olds can do but three-year-olds have some trouble with. Imagine Sally in the picture below is playing with a ball. She puts the ball in the box and goes to the kitchen to get a drink. While she's gone, Bill takes the ball out of the box and puts it in the bucket. When Sally returns, where does she look for the ball?


Most three-year-olds will say Sally would look in the bucket, apparently failing to realize that Sally doesn't know anything about what Bill did while she was gone. Some researchers have explained this phenomenon by speculating that young children haven't yet formed a theory of mind; they don't understand that other people can have thoughts independent of their own.

But Susan Birch and Paul Bloom believe they have found a scenario where adults make a similar error.

Consider this:


This is Sally. She finishes playing with the ball and puts it in the box. Then she goes outside to play. While Sally is outside playing, her sister Denise moves the ball to another container. Then, Denise rearranges the containers in the room until they look like the picture below.


When Sally returns, she wants to play with the ball again. What are the chances Sally will look first for her ball in each of the above containers?

Here is how the adults given this test responded, as you might expect:


Another group of adults was shown the same set of pictures, but with a key difference in the text. this time they were told that "Denise moves the ball to the bucket." The remainder of the instructions were the same. Now look at the results:


This time significantly more people said Sally would look for the ball in the bucket -- despite the fact that Sally had the same information in each scenario. Birch and Bloom call this phenomenon the curse of knowledge -- now that they know the ball is in the bucket, even adult respondents are more likely to say Sally will look there for it.

Birch and Bloom are careful to point out that this study doesn't disprove the notion that three-year-olds are unable to take the perspective of others, but it does make it clear that other factors are in play. And it's possible that, rather than being unable to understand the thoughts of others, younger children are simply more susceptible to the curse of knowledge.

Birch, S., & Bloom, P. (2007). The Curse of Knowledge in Reasoning About False Beliefs Psychological Science, 18 (5), 382-386 DOI: 10.1111/j.1467-9280.2007.01909.x

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I think this has a lot to do with people's representation of uncertainty. Unlike the scenario presented to the toddlers, Sally knows that something is different. It has been shown many times through other experiments that responses depend very heavily on how information is presented. I am clearly speculating, but one possibility is that most people (myself included) can't really decide if Sally will look in the same container or in the same physical location. This makes representing Sally's uncertainty very difficult, and can easily be influenced subconsciously by outside factors. So, in a sense, I don't think the adults are falling for the same pitfall. In both situations, both the basket and vase have lower subjective probabilities assigned to them and the result is some combination of the bucket and the box. Perhaps Sally knows something about her friend. Since we are unable to completely represent Sally's uncertainty, we let other information creep in.

Rereading my own comment, I don't think I was completely clear. My point is that both the bucket and the box are plausible places to look (either the same container or the same place). Yes, the presentation of information sways the subjective probabilities one way or another, but I would argue that the distribution of responses is not an appropriate measure here.

A lot of arguments have occurred because one person had information that doing 'x' was a bad idea, and _assumed_ that the person who was doing 'x' also had that information and was - therefore - a 'bad person' or 'acting with malice'.

By Oscar Zoalaster (not verified) on 18 Aug 2009 #permalink

As I recalled from a class on cognitive science, there exists two models explaining the False Belief task. The first model proposes that what happens cognitively is a theory of mind system, where the theory of mind allows the subject to construct a view of the world from someone else's perspective. The second model proposes that there's a second system on top of it, the self-inhibition system, which exists to suppress one from projecting one's own knowledge onto the situation presented. This experiment with moving the boxes and known vs unknown locations seems to lend credence to the 2nd.

IIRC, the self-inhibition hypothesis was created based on studies of patients with TPJ lesions (temporo-parietal junction), where the effect was that they failed the false belief task, and it was subsequently discovered that they passed equivalent setups of the false belief task as long as they themselves didn't know where the object actually is.

People often know things about their sisters. Maybe subjects guess that Sally might know that her sister usually moves balls from boxes to buckets.

Too much information makes the mind clouded. People are not perfectly rational thinking machines. I think this is the reason for these results.

It's probably a trait of intelligence to be able to focus your mind on the relevant details. You know, people get along in their day to day life without it.

This really confuses me. What earthly reason would Sally have for looking anywhere other than the place she put the ball in the first place? *she* doesn't know it's been moved...

Am I missing something here?

@LabRat: She knows _something_ has happened, because all the containers have moved around.

If I wandered into a room where I'd put something in a box (say) I'd very likely first look in the spot where the box was - when I discovered the box was now a bucket, I'd glance in it simply because it's effectively free to do (since I'm there) and because I'm a nosey bastard. :)

I suspect if you really did this experiment, a significant proportion of people wandering back into the room would look in the bucket first just out of sheer confusion...

To avoid all these issues, it'd be better to have the ball in the vase, say, and avoid the possible location of container vs shape of container thing.

I seem to recall reading a study where young children will more often associate the last known physical location of an object with the objects location, regardless of the container the object was in. I believe the scientists played some sort of shell game with different colored containers and the biggest contributing factor was original location.

It could be that this is merely something people have picked up on over time, so they assume the child will base the guess on physical location. So I have to agree with poster Sam K, when I say that there is something more than just container shape going on here.

To Lab Rat: The question is whether or not Sally was really paying attention to the type of container she placed the ball in. She put it in the box, yet some adults believe that she would look for it in the bucket. They may have answered in that way because the bucket was moved to the location where the box was originally. If Sally wasn't paying attention to the type of container she placed the ball in, then she might logically return to the same physical location to look for the ball.

Yet, it is interesting that the percentage of adults who answered "the bucket" increased (in the second scenario) just because someone moved the ball to the bucket without Sally's knowledge of that action.

I ponder the age of Sally. I can see a child under 2 or 3 going to the place they left the ball, ignoring the shape of the container. At 4 children begin to reason beyond themselves and then the container would become more attractive than the place/position. Variables don't seem clear enough to make this a valid study.

In retrospect I feel rather foolish for thinking so, but I just assumed the bucket given that its open top (larger than the box's viewing aperture) appears to make it easy to see into.

This would be a perfect experiment to actually carry out, with parents of young children. The difference between the hypothetical situation and the complex, real-life scenario could tell us a lot about how the mind works. This kind of pairing of traditional single-variable experiments with parallel field observations not only makes possible a productive critique of the original experimental conditions, but challenges and hopefully strengthens the viability of the scientific method.

Also, if, in the future, we live side by side with AI beings, and these beings are programmed not to make this kind of mistake, they will have great difficulty in understanding us, and the kind of disagreements that come about as a result of this artifact of our way of thinking. This could be problematic.

I am surprised that most adults would know what you were asking for with the question: "What are the chances Sally will look first for her ball in each of the above containers?

I think we should be careful at making broad generalizations with data collected from two groups of people in one study.
You use the word "significant" to describe the number of people who chose the bucket the second time. Looking at the same data, however, I see a relatively small change with a trend being almost identical to the first study.
What are the sizes of each group? One person could have picked "bucket" instead of "box" the second time and altered the graph if the group size was small enough. And I would not call that a "significant" change. Speaking purely as a statistician, of course.
I'd like to see some numbers before I consider these findings significant and not just a result of individual variation.

is there a chance that they thought she would look in the bucket because it is in the same place in the room where the box originally was? that is why I was going to say she looked there first. I would probably move towards where I last left it.


I think that the subjects assumed that Sally just threw the ball into the container in one corner of the room without paying attention to what type of container it was. She returns to look for the container in the same place as the container where she placed the ball.

I'd love to see them try the other half of this experiment.

Go get some balls, some buckets, and see what happens.