I s awareness necessar y for true inference?

context-dependent relations and to make inferences about untrained relations. In a typical TI task, participants are trained on a set of overlapping two-item discriminations or premise pairs (e.g., A B, B C, C D, D E; “A B” denotes a forced choice between A and B in which A is the correct choice). An efficient representation of these simultaneous context-dependent relations is A B C D E. At test and without reinforcement, the capacity for inference is tested with an untrained pair, B? D. The capacity for correct inference has been observed in numerous nonhuman animal species (Davis, 1992; Gillan, 1981; Weaver, Steirn, & Zentall, 1997) and in humans (Greene, Spellman, Dusek, Eichenbaum, & Levy, 2001; Heckers, Zalesak, Weiss, Ditman, & Titone, 2004; Nagode & Pardo, 2002; Preston, Shrager, Dudukovic, & Gabrieli, 2004). In humans, inference is possible with or without explicit awareness of the contingencies (Frank, O’Reilly, & Curran, 2006; Greene, 2007; Greene, Gross, Elsinger, & Rao, 2006; Greene et al., 2001; van Elzakker, O’Reilly, & Rudy, 2003). If participants are not informed of a hierarchy at the outset, TI task awareness either is independent of task performance (Greene et al., 2006; Greene et al., 2001) or may occur in the absence of task awareness (Frank, Rudy, Levy, & O’Reilly, 2005). That learned contingencies may support inference without awareness is of particular interest because it suggests a level of flexibility previously believed to require conscious memory processes (Clark, Manns, & Squire, 2002; Reber, Knowlton, & Squire, 1996; Smith & Squire, 2005). One possibility is that implicit versions of TI are not really demonstrating flexibility, but instead are solved using pseudoinference (Frank, Rudy, & O’Reilly, 2003; Siemann & Delius, 1994; van Elzakker et al., 2003; Zentall & Sherburne, 1994). Consider a five-item TI task (e.g., A B C D E). If the A item is present, it is always the correct choice; likewise, E is always incorrect. The middle items B–D are each correct only 50% of the time. Van Elzakker et al. argued that end items cause a blocking effect that is responsible for differential associative strength among items. Accordingly, the perfect predictive value of the end items causes them to be treated as atomic discriminations (select A, avoid E), and so blocking leads one to ignore B in the AB pairing and to ignore D in the DE pairing. This has the consequence that B is ignored when it would be an incorrect choice (A B) and is attended to only when it is the correct choice (B C). Similarly, D is ignored when it would be the correct choice (D E) and is attended to only when it is the incorrect choice (C D). According to this view, the novel pairing at test, B? D, is solved only because B has a more positive t associative strength than does D, so true inference is no required (Frank et al., 2005; Frank et al., 2003; van Elzakker et al., 2003). Another proposed mechanism is value transfer theory (VTT; Siemann & Delius, 1994; Zentall & Sherburne, 1994), in which item B gains positive strength by repeated association with item A, and likewise item D receives some of E’s negative value by repeated association. According to VTT, the selection of B D at test merely reflects that B has been paired with a positive stimulus (A) and that D has been paired with a negative stimulus (E), so B has more positive associative strength than does D. VTT differs from the blocking approach only in the means by which differential associative strength is imparted to items B and D; both approaches argue that the differential associative values of B and D result in choices that resemble inference (pseudoinference) but are not