“…Experiment 2 provides another avenue for assessing the conditions under which infants discriminate faces engaged in dynamic activities and for evaluating the attentional salience hypothesis. Consistent with research traditions in the areas of concept formation, categorization, and invariant detection, presenting multiple exemplars of a category, opportunities for variable training, or information that is invariant across transformation has been found to facilitate attention, habituation, learning, and memory of information that is common or invariant across presentations and to facilitate generalization across aspects that vary, for both infants and adults (e.g., Bomba & Siqueland, 1983; Gibson,1969; Hayne, 1996; Mandler, 1998; Mervis & Rosch, 1981; Needham, Dueker, & Lockhead, 2005; Quinn, 1987; Rovee-Collier & Gulya, 2000). For example, Needham et al (2005) found that infants required three exemplars to form a category, and variability in the exemplar set was necessary.…”