You cannot find what you are not looking for: Population differences in relational reasoning are sometimes differences in inductive biases alone.

Relational reasoning is a cornerstone of human cognition. Extensive work, drawing on the Relational Match to Sample paradigm (RMTS), has established that humans, at least above the age of five, are much more proficient relational reasoners than younger children or non-human animals. While sometimes differences between populations derive from differences in capacity (the capacity to create representations in a certain format or of a certain complexity, information processing capacity), other times such differences derive from different learning histories alone. Here we distinguish between two types of learning history explanations on the example of four-year-olds' failure on Premack's (1983) RMTS task: (1) that children four-year-olds have not yet created representations of the relations same and different with the properties need to support success on RMTS and (2) that four-year-olds have different inductive biases than do adults. Experiment 1 established that four-year-olds are at chance on the RMTS task we deploy as a transfer task in Experiment 2. Experiments 2A-C each provide children with a mere 8 trials of training on of one three MTS tasks (Number, Size and Identity MTS, respectively), none of which involves making matches of same to same or different to different. The very brief training (eight trials) on two of these tasks (Number MTS, Size MTS) leads to spontaneous success on RMTS in four-year-olds. Identity MTS has no effect on subsequent performance on RMTS. Given the brevity and non-relational nature of the training the successes after Number and Size MTS training must have resulted from changing inductive biases alone. Furthermore, the same two training tasks increased relational responding by adults on a related task (Kroupin & Carey, in press), whereas Identity MTS training did not, suggesting that the mechanisms through which the training changed inductive biases are at least partially continuous between ages four and adulthood.