By the mid-1960s, the concept that drugs can function as reinforcing stimuli through response-reinforcer contingencies had created a paradigm shift in drug abuse science. Steve Goldberg's first several publications focused instead on stimulus-stimulus contingencies (respondent conditioning) in examining Abraham Wikler's two-factor hypothesis of relapse involving conditioned withdrawal and reinforcing effects of drugs. Goldberg provided a compelling demonstration that histories of contingencies among stimuli could produce lasting withdrawal reactions in primates formerly dependent on opioids. Other studies conducted by Goldberg extended the analysis of effects of stimulus-stimulus contingencies on behavior maintained by opioid reinforcing effects and showed that withdrawal-inducing antagonist administration can produce conditioned increases in self-administration. Subsequent studies of the effects of stimuli associated with cocaine injection under second-order schedules showed that the maintenance of behavior with drug injections was in most important aspects similar to the maintenance of behavior with more conventional reinforcers when the behavior-disrupting pharmacological effects of the drugs were minimized. Studies on second-order schedules demonstrated a wide array of conditions under which behavior could be maintained by drug injection and further influenced by stimulus-stimulus contingencies. These schedules present opportunities to produce in the laboratory complex situations involving response- and stimulus-stimulus contingencies, which go beyond simplistic pairings of stimuli and more closely approximate those found with human drug abusers. A focus on the response- and stimulus-stimulus contingencies, and resulting quantifiable changes in objective and quantifiable behavioral endpoints exemplified by the studies by Steve Goldberg, remains the most promising way forward for studying problems of drug dependence.
Keywords: Conditioned reinforcement; Drug abuse; Drug self-administration; Opioid withdrawal; Respondent conditioning; Second-order schedules; Stimulus-stimulus contingencies.