The informational properties of S1, S2, and the S1–S2 sequence on conditioned suppression

The Egger-Miller information hypothesis was tested in a nonoverlapping compound stimulus CER situation. During CER training, S2, the so-called redundant stimulus, acquired greater suppression qualities than S1. However, following CER training, subjects were exposed to test situations in which the independent suppression qualities of S1 and S2 were assessed. S1 was followed by a trace interval, S2 was presented alone, or the S1–S2 sequence was reversed. Results of all test conditions showed minimal suppression to S2, while suppression to S1 was maintained or facilitated. It was suggested that S2, although a redundant predictor of shock occurrence, provides information as to “when” shock is due.