Cognitive control of sequential knowledge in 2-year-olds: evidence from an incidental sequence-learning and -generation task.

Under incidental instructions, thirty-eight 2-year-olds were trained on a six-element deterministic sequence of spatial locations. Following training, subjects were informed of the presence of a sequence and asked to either reproduce or suppress the learned material. Children's production of the trained sequence was modulated by these instructions. When asked to suppress the trained sequence, the children were able to increase generation of paths that were not from the training sequence. Their performance was thus dependent on active suppression of knowledge, rather than on a random generation strategy. This degree of control in 2-year-olds stands in stark contrast to 3-year-olds' failure to control explicitly instructed rule-based knowledge (as measured by the dimensional-change card-sort task). We suggest that the incidental nature of a learning episode enables the acquisition of a more procedural form of knowledge with which this age group has more experience prior to the onset of fluent language.