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This research focused on the changes in stimulus control that influence an animal�s ability to master a behavioral skill. We assessed stimulus control by (a) predictive environmental cues (panel lights) and (b) practice cues resulting from the subject�s own behavior, as rats learned to complete a left�right lever-press sequence. Following a demonstration of overshadowing by Reid, Nill, and Getz (Behavioural Processes 84: 511�515, 2010), in which stimulus control by the panel lights overshadowed control by practice cues, four additional experiments replicated and assessed this overshadowing effect. In Experiment 1, we discovered a powerful asymmetry: Rats failed to adapt to a lights ? reversed-lights transition, but adapted immediately to a reversed-lights ? lights transition. Experiment 2 was designed to measure the interactions between these stimulus conditions and practice cues. In Experiment 3, we measured the effect of these stimulus conditions on acquisition rates. Finally, in Experiment 4 an ABA design was used to assess the effects of prior exposure to condition A on B ? A transitions, and we found that prior exposure generally reversed the effects observed in B ? A transitions presented first or in isolation. We discuss feature-positive bias and spatial S�R compatibility as potential explanations of the observed insensitivity to cues that should be, at face value, highly predictive of food during the acquisition of a behavioral skill. Perfectly predictive cues in behavior chains do not always guide behavior.
