A key aspect of theory of mind is the ability to reason
about other people's desires. As adults, we know that desires
and preferences are subjective and specific to the individual.
However, research in cognitive development suggests that a
significant conceptual shift occurs in desire-based reasoning
between 14 and 18 months of age, allowing 18- but not 14-
month-olds to understand that different people can have
different preferences (Lucas et al., 2014; Ma & Xu 2011;
Repacholi & Gopnik, 1997). The present research investigates
the kind of evidence that is relevant for inducing this shift and
whether younger infants can be trained to learn about the
diversity of preferences. In Experiment 1, infants younger
than 18 months of age were shown demonstrations in which
two experimenters either liked the same objects as each other
(in one training condition) or different objects (in another
training condition). Following training, all infants were asked
to share one of two foods with one of the experimenters –
they could either share a food that the experimenter showed
disgust towards (and the infants themselves liked) or a food
that the experimenter showed happiness towards (and the
infants themselves did not like). We found that infants who
observed two different experimenters liking different objects
during training later provided the experimenter with the food
she liked, even if it was something they disliked themselves.
However, when infants observed two experimenters liking the
same objects, they later incorrectly shared the food that they
themselves liked with the experimenter. Experiment 2
controlled for an alternative interpretation of these findings.
Our results suggest that training allows infants to overturn an
initial theory in the domain of Theory of Mind for a more
advanced one.