Stimulus–response learning in long-term cocaine users: Acquired equivalence and probabilistic category learning

Abstract

Objective-The purpose of this study was to examine stimulus-response (S-R) learning in active cocaine users.Participants and Methods-Twenty-two cocaine-dependent participants (20 male and 2 female) and 21 non-drug using control participants (19 male and 2 female) who were similar in age and education were administered two computerized learning tasks. The Acquired Equivalence task initially requires learning of simple antecedent-consequent discriminations, but later requires generalization of this learning when the stimuli are presented in novel recombinations. The Weather Prediction task requires the prediction of a dichotomous outcome based on different stimuli combinations when the stimuli predict the outcome only probabilistically.Results-On the Acquired Equivalence task, cocaine users made significantly more errors than control participants when required to learn new discriminations while maintaining previously learned discriminations, but performed similarly to controls when required to generalize this learning. No group differences were seen on the Weather Prediction task.Conclusions-Cocaine users' learning of stimulus discriminations under conflicting response demands was impaired, but their ability to generalize this learning once they achieved criterion was intact. This performance pattern is consistent with other laboratory studies of long-term cocaine users that demonstrated that established learning interfered with new learning on incremental learning tasks, relative to healthy controls, and may reflect altered dopamine transmission in the basal ganglia of long-term cocaine users.

Learning and generalization from reward and punishment in opioid addiction

“…To our knowledge, this is the first study that has examined acquired equivalence in opioid-addicted individuals versus healthy controls. However, the absence of a group difference in generalization is similar to that previously observed in a prior study with long-term cocaine users (34), who were also impaired at learning but not at generalization. Given the body of prior work implicating the hippocampal region in generalization on acquired equivalence tasks (15, 18, 19, 23), the current findings do not provide evidence of impaired hippocampal function in the opioid-addicted patients.…”

“…By contrast, prior studies with the computer-based acquired equivalence task have reported much better performance particularly in control groups, with control groups often averaging at or below 10–15% errors on generalization pairs (20, 21, 34), although one prior study using an Australian sample found error rates of about 31% in healthy elderly subjects (41). These prior studies did not include separate reward- and punishment-based trials; rather, on each trial the subject received explicit reward (feedback and point gain) for a correct response or explicit punishment (feedback and point loss) for an incorrect response.…”

“…The start of a new stage was not signaled to the participant. Because training stages contain different number of trials for each participant, a simple percent error measure is not appropriate, because two participants could have similar numerators but very different denominators; instead, following convention for this type of acquired equivalence task (e.g., 15, 17, 18, 19, 22, 34, 36, 37), we report total errors to criterion on each stage for reward-based and punishment-based antecedents, as well as number of trials to criterion on each stage.…”

“…One prior study considered long-term cocaine users, and found that they were worse than non-addicted controls during the learning phase – specifically, on learning to map familiar antecedents to new consequents – but subsequently unimpaired on generalization (34). Conversely, abstinent individuals with a history of alcohol dependence showed the opposite pattern of spared learning but impaired generalization (35).…”

Differential sensitivity to learning from positive and negative outcomes in cocaine users

“…Cocaine users display impairments in probabilistic categorical learning compared to controls and alcohol/marijuana users (Vadhan et al, 2014). However, such impairments have not been consistently observed (Lane et al, 2014; Vadhan et al, 2008) and these prior studies have not dissociated the influence of positive and negative outcomes.…”