Generalization decrements: further support for flexibility in stimulus processing.

Thorwart and Lachnit (2009) found reliable symmetrical decrements in two generalization tasks: Removing an already trained component from a compound did not result in larger decrements than adding a new one did. In two contingency learning experiments, we investigated first whether time pressure during stimulus processing, as well as the degree of perceptual grouping, was effective in controlling the symmetry of the decrements (Experiment 1); and second, whether the symmetry was affected by the causal versus predictive nature of the relationship between the cue and the outcome (Experiment 2). The experiments generated unexpected results, since both revealed asymmetrical decrements independent of the manipulations introduced. They therefore demonstrate that more research is needed in order to understand the variables influencing stimulus representation in human associative learning.