Substituting one set of discriminative stimuli for another (or, as a process, the stimulus control maintained after such a substitution). Transfer may be based on common properties of two sets of stimuli or on similar correlations of the two sets of stimuli with differential contingencies. In verbal learning, transfer from one task to another is usually assessed with reference to a control group that did not learn the first task; it is positive if the first task enhances performance on the second anci negative if it does the opposite.