A series of four experiments is reported using a CER procedure with rats as subjects. The first three experiments provide demonstrations of second-order fear conditioning and suggest that second-order conditioning is unaffected by extinction of the first-order stimulus upon which it was based. A fourth experiment indicates that in the analogous sensory preconditioning procedure, extinction of the first-order stimulus does affect responding to the secondary stimulus. The results are interpreted as inconsistent with an interpretation of second-order conditioning in terms of associations between the first-and second-order stimuli.

providing the computer program for the co variance analyses of Experiments 1 and 2. The authors especially want to thank Augustus Lumia for providing many stimulating comments and criticisms at various stages of this research. Thanks are also due to M. Ray Denny. David Linden, and J. Bruce Overmier for their criticisms of an earlier draft of this paper.2 Requests for reprints shou'd be sent to James

Acquisition and extinction of rat avoidance was unaffected by relative shock and nonshock compartment confinement and retention of avoidance, although statistically significant, was an impotent factor for the Holtzman strain, but a potent factor for Sasco rats. In general, Holtzman rats were more resistant to extinction than Sasco rats.

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