Statistical learning is a powerful mechanism that allows us torapidly extract structure from the environment. However,nuances of what structure is extracted—for example, whetherreliable groups are stored without knowledge of theirconstituent item order—are not well understood, leaving uswith open questions about how this mechanism supportsbehaviour. Here, we extend prior work on the representation ofstatistical structure by asking what specific aspects of structurematter for memory judgments. We consider three candidatesfor memory representation: transitional probability, order-independent group information, and position tags. Participantswatched a stream of shape triplets and then completed arecognition memory test designed to isolate contributions oftransitional probability, group, and position. We demonstratethat although memory for transitions alone would be sufficientfor knowledge of triplets, participants showed evidence ofrepresenting both transitional probability and group. Our datahighlight statistical learning as a mechanism enablinggeneralization across experiences.

In the United States, the difference in academic achievement between higher- and lower-income students (i.e., the income-achievement gap) is substantial and growing. In the research reported here, we investigated neuroanatomical correlates of this gap in adolescents (N = 58) in whom academic achievement was measured by statewide standardized testing. Cortical gray-matter volume was significantly greater in students from higher-income backgrounds (n = 35) than in students from lower-income backgrounds (n = 23), but cortical white-matter volume and total cortical surface area did not differ significantly between groups. Cortical thickness in all lobes of the brain was greater in students from higher-income than lower-income backgrounds. Greater cortical thickness, particularly in temporal and occipital lobes, was associated with better test performance. These results represent the first evidence that cortical thickness in higher- and lower-income students differs across broad swaths of the brain and that cortical thickness is related to scores on academic-achievement tests.