"the ability to attribute mental states -beliefs, intents, desires, pretending, knowledge, etc.- to oneself and others and to understand that others have beliefs, desires and intentions that are different from one's own."

It is hard to imagine any (social) activity in which we do not rely heavily on our theory of mind (imagine enjoying even the lamest movie plot without an adequate theory of mind...), and taking into consideration that others may not automatically know everything that we know - after a certain age (generally 4 - 6 years) - comes effortless to us; (Note: Some humans even appear capable of considering that other people may know things they themselves do not know...but this is rather seldom).

In fact, constructing other people's minds in our own head is so pervasive in our everyday lives and appears to require so little attention, effort and conscious thought, that psychologists have often assumed the process to be near automatic; saying that once you've learned that other people have minds of their own, this simply becomes the way your mind works; regardless of what else may be going on with you.

More and more experimental evidence, however, is beginning to question this assumption of an automated theory of mind module; most of which relies on the finding that people become less efficient at constructing theory of mind when they are under time pressure or distracted; thus implying that theory of mind construction does involve some (although apparently small) level of effort, and that even adults may sometimes draw conclusions about others that are equivalent to the child's assumption that Annika shares its knowledge of where the chocolate is hidden.

A further argument against an automated theory of mind can now be made based on a series of experiments that show how our mood influences how good we are at inferring other people's knowledge and intentions.

The hypothesis that emotions may influence theory of mind usage is not surprising, given that feelings of happiness and sadness are known to promote different ways of information processing. Happiness - so the current state of our knowledge - promotes heuristic-based thinking, which in turn interferes with the more deliberate processing that is usually associated with sadness.

To learn more about the potential linkage between emotions and theory of mind, a group of Psychologist at the University of Chicago set up a round of experiments including the following: As a means of inducing feelings of happiness (or sadness) participants were made to listen to a selection of happy (or sad) music. After listening to the music, the now measurably mood altered, participants were presented with an adult version of Annika's chocolate situation; which is summarized in the picture below:

Participants in the blue box condition do not know whether or not Vicki's sister moved the violin, while those in the red box condition know where the violin is. Regardless of whether participants knows where the violin is, theory of mind should lead them to infer that Vicki knows only where she put the violin, and that now the boxes have moved. Hence, any guess for where Vicki will look first should be irrespective of whether a participant is in the red-box or blue box condition.

For the group that listened to sad music at the outset of the experiment, this is also exacly what happens. For the group that listened to happy music, however, a more egocentric thought pattern emerges: People who listened to happy music and knew that the violin was in the red box, also assigned a significantly greater likelihood to the event that Vicki would look inside the red box (as compared to the happy people, who did not know where the violin was placed).
As the authors state it:

"These data suggest that participants were less likely to employ their theory of mind in the happy condition than in the sad condition."

Using this finding and those from another experiment (which can be found in the same publication), the authors come to the conclusion that

"mood states have important consequences for mental-state inferences, such that those in a happy mood may be less likely to utilize their theory of mind than those in a sad mood. These results are important [...] for the theoretical insights into how people make mental state inferences [...]. In particular, these results suggest that theory of mind requires deliberative processing to inhibit an egocentric assessment that is often more readily accessible than is specific knowledge about others. Happy people tend to rely on this egocentric default, whereas sad people incorporate knowledge about others more deliberately. These differential effects of mood are inconsistent with a purely automatic account of theory-of-mind use."

As a slight disclaimer they add that

"It is important to clarify that these results do not demonstrate that happiness will always increase egocentric bias, nor that egocentric bias will necessarily decrease accuracy"

One final question that this leaves me with now is this: When your spouse thinks that you should have known what he or she meant although he or she (and I am being overly p.c. here!) did not explicitly say what was meant, does that mean your spouse is happy or sad?

Main Reference:
Converse, B., Lin, S., Keysar, B., & Epley, N. (2008). In the mood to get over yourself: Mood affects theory-of-mind use. Emotion, 8 (5), 725-730 DOI: 10.1037/a0013283

<Cross-Posted with Ingenious Monkey>