Building knowledge requires bricks, not sand: The critical role of familiar constituents in learning.

Despite vast efforts to better understand human learning, some principles have been overlooked; specifically, that less familiar stimuli are more difficult to combine to create new knowledge and that this is because less familiar stimuli consume more working memory resources. Participants previously unfamiliar with Chinese characters were trained to discriminate visually similar characters during a visual search task over the course of a month, during which half of the characters appeared much more frequently. Ability to form associations involving these characters was tested via cued recall for novel associations consisting of two Chinese characters and an English word. Each week performance improved on the cued-recall task. Crucially, however, even though all Chinese character pairs were novel each week, those pairs consisting of more familiar characters were more easily learned. Performance on a working-memory task was better for more familiar stimuli, consistent with the claim that familiar stimuli consume fewer working memory resources. These findings have implications for optimal instruction, including second language learning.