“…Discovering new categories through unguided observation in the absence of explicit feedback or reinforcement is a fundamental ability that underlies much of human learning (see, e.g., Billman & Knutson, 1996;Clapper & Bower, 1991Mervis, 1987;Murphy, 2002;Nelson, 1974). This kind of self-directed pattern detection is often referred to as observational or unsupervised learning, in contrast to supervised learning, in which categories are defined in advance and participants receive corrective feedback from an external teacher (see, e.g., Bruner, Goodnow, & Austin, 1967;Medin & Schaffer, 1978;Posner & Keele, 1968, 1970Smith & Medin, 1981).…”