Running Head: INTERNALIZATION OF STIMULUS CONTROL Internalization of Stimulus Control during Skill Learning: An Animal Model

In order to quantify the internalization of stimulus control during skill learning, 20 rats were trained to complete a left-right sequence of lever presses guided by the onset and offset of panel lights over the respective levers. Once sequence accuracy was high and stable, the rats were divided into two groups. For the No-Lights group, the lights were eliminated without changing the response requirements. Sequence accuracy decreased in all subjects, but accuracy was higher than that predicted by random chance, implying internalization of stimulus control. The Reversed-Lights group controlled for potential generalization decrement by presenting the lights in reversed order without changing the response requirements. Sequence accuracy immediately plummeted and did not recover. S-R associations involving external stimuli apparently overshadowed internal cues. This study provides a method (an animal model) for the quantitative measurement of the degree of internalization of stimulus control during skill learning in a well-controlled environment.