Compound Summation and Attenuation of Conditioned Suppression

Abstract

<p> In six conditioned suppression experiments with rats, two conditioned stimuli (CSs) were individually trained and then tested as a compound. In one set of experiments, the suppressing effect of the compound was greater than that of either CS presented alone. This result is referred to as compound summation. In a second set of experiments, the suppressing effect of the compound was less than that of the "stronger" suppressing individual CS. This result is referred to as compound attenuation. The combination of summation and attenuation makes it possible to determine whether CSs with unknown properties are weakly excitatory (i.e., weak suppressors) or inhibitory (i.e., conditioned characteristics that are opposite the excitatory suppressing effect). If an unknown CS is tested in compound with a second CS known to be excitatory, summation indicates that the unknown stimulus is excitatory, while attenuation indicates that the unknown stimulus is inhibitory. In a final set of experiments, this compound test procedure was used to examine extinction and differential conditioning as inhibitory training procedures. Extensive extinction of a previously trained CS, even far beyond the point at which suppression vanished, was found to be an ineffective inhibitory training procedure. Rather, compound tests showed that the stimulus retained excitatory properties. Differential conditioning was found to be a very effective inhibitory training procedure, regardless of whether presentations of a previously trained CS and shock, shook alone, or the previously trained CS - alone accompanied the unreinforced CS undergoing inhibitory conditioning. These findings are discussed in terms of current theories of conditioning and unresolved issues surrounding the acquisition and maintenance of inhibitory properties.</p>