We describe a very interesting computational model of social-learning mechanisms proposed by Lopes, Melo, Kenward and Santos-Victor (2009). The authors distinguish between imitation ("adhere to inferred intention, replicate observed actions and effect") and emulation ("replicate observed effect") taking into account the agent´s preferences for different actions and the information available from the demonstration. There is a module addressing the baseline preferences of the agent, evaluating actions in terms of energy consumption. With this module is associated the utility function Qb ranking possible action sequences according to their overall energy consumption. A utility function Qe evaluates the actions in terms of their probability of reproducing the observed result/effect. For the intention replicating module, the utility function Qi assumes the demonstrator is goal-oriented. The module operates by considering all the possible goals in the current system, calculating for each one the relative probability that it would give rise to the demonstrated behaviour, and choosing the one that maximises the probability. In cases that are equally likely to produce the observed demonstration, goals with tied probability are ranked randomly which leads to stochasticity in the final behaviour.
The model of Lopes and collaborators can replicate the tendency to interpret and reproduce observed actions in terms of the inferred goals of the action in line with the experiments of Malinda Carpenter and colleagues (2005): a demonstrator moved a toy mouse across a table from one point to another; in one condition, the final point of the move was inside a little house, and in the other condition, no house was present: infants showed a much grater tendency to replicate the specific mouse moving action observed when there was no house to move the mouse into. The results of the simulation reproduce the findings of Carpenter et al. (2005), confirming the standard interpretation of the experiment: the infant infers what the demonstrator´s intention was.
Other simulation replicates the famous experiment of Meltzoff (1988) in which 14-month olds were exposed to a demonstrator who performed unusual actions on objects (there was a box with a panel that lit up when the demonstrator touched it with his forehead, and most infants copied the use of the forehead rather than using their hand): the infants reproduced the actions with a delay of a week. According to Lopes and collaborators, the simulation confirms the imitation in terms of the inferred intention and of sensitivity to the constraints on the demonstrator.
To investigate what happens when the learner does not have complete knowledge of the world dynamics, they model a type of experiment based on Horner and Whiten (2005) experiment in which presented preschoolers and chimpanzees with two identical boxes, one opaque and one transparent. The demonstration consisted of inserting a stick into a hole on the front of the box, with the latter step generating a reward. The insertion of the stick into the top hole was unnecessary in order to obtain the reward, but the causal physical relations were only visible with the transparent box. The results showed that 3 and 4-year-old children imitated both actions no matter whether they had observed and were tested on the transparent or opaque box, but chimpanzees were more able to switch between emulation and imitation after having observed demonstrations with a transparent box and reduced tendency to insert the stick into the ineffective hole.
The simulation designed by Lopes, Melo, Kenward and Santos-Victor replicate the results from both children and chimps when the weight of the intention replicating module was increased, confirming that the difference occurs because chimps are primarily motivated to select the most efficient method they know to achieve the end effect.
Following the taxonomy proposed by Call and Carpenter (2002), Lopes et al. (2009) build a unifying mathematical model of types of social influence on behaviour, mainly imitation and emulation, concluding that a switch between imitation and emulation might be triggered by changing the value (to the learning) of the social interaction or of the effect. So, the greater utilization of imitation by children might be explained by a stronger focus on others´intentions, mediated by social cues.
