Associations and propositions: the case for a dual-process account of learning in humans.

We review evidence that supports the conclusion that people can and do learn in two distinct ways - one associative, the other propositional. No one disputes that we solve problems by testing hypotheses and inducing underlying rules, so the issue amounts to deciding whether there is evidence that we (and other animals) also rely on a simpler, associative system, that detects the frequency of occurrence of different events in our environment and the contingencies between them. There is neuroscientific evidence that associative learning occurs in at least some animals (e.g., Aplysia californica), so it must be the case that associative learning has evolved. Since both associative and propositional theories can in principle account for many instances of successful learning, the problem is then to show that there are at least some cases where the two classes of theory predict different outcomes. We offer a demonstration of cue competition effects in humans under incidental conditions as evidence against the argument that all such effects are based on cognitive inference. The latter supposition would imply that if the necessary information is unavailable to inference then no cue competition should occur. We then discuss the case of unblocking by reinforcer omission, where associative theory predicts an irrational solution to the problem, and consider the phenomenon of the Perruchet effect, in which conscious expectancy and conditioned response dissociate. Further discussion makes use of evidence that people will sometimes provide one solution to a problem when it is presented to them in summary form, and another when they are presented in rapid succession with trial-by trial information. We also demonstrate that people trained on a discrimination may show a peak shift (predicted by associative theory), but given the time and opportunity to detect the relationships between S+ and S-, show rule-based behavior instead. Finally, we conclude by presenting evidence that research on individual differences suggests that variation in intelligence and explicit problem solving ability are quite unrelated to variation in implicit (associative) learning, and briefly consider the computational implications of our argument, by asking how both associative and propositional processes can be accommodated within a single framework for cognition.

Striatal sensitivity to personal responsibility in a regret-based decision-making task.

Regret and relief are complex emotional states associated with the counterfactual processing of nonobtained outcomes in a decision-making situation. In the "actor effect," a sense of agency and personal responsibility is thought to heighten these emotions. Using fMRI, we scanned volunteers (n = 22) as they played a task involving choices between two wheel-of-fortune gambles. We examined how neural responses to counterfactual outcomes were modulated by giving subjects the opportunity to change their minds, as a manipulation of personal responsibility. Satisfaction ratings to the outcomes were highly sensitive to the difference between the obtained and nonobtained outcome, and ratings following losses were lower on trials with the opportunity to change one's mind. Outcome-related activity in the striatum and orbitofrontal cortex was positively related to the satisfaction ratings. The striatal response was modulated by the agency manipulation: Following losses, the striatal signal was significantly lower when the subject had the opportunity to change his/her mind. These results support the involvement of frontostriatal mechanisms in counterfactual thinking and highlight the sensitivity of the striatum to the effects of personal responsibility.

Differential effects of insular and ventromedial prefrontal cortex lesions on risky decision-making.

The ventromedial prefrontal cortex (vmPFC) and insular cortex are implicated in distributed neural circuitry that supports emotional decision-making. Previous studies of patients with vmPFC lesions have focused primarily on decision-making under uncertainty, when outcome probabilities are ambiguous (e.g. the Iowa Gambling Task). It remains unclear whether vmPFC is also necessary for decision-making under risk, when outcome probabilities are explicit. It is not known whether the effect of insular damage is analogous to the effect of vmPFC damage, or whether these regions contribute differentially to choice behaviour. Four groups of participants were compared on the Cambridge Gamble Task, a well-characterized measure of risky decision-making where outcome probabilities are presented explicitly, thus minimizing additional learning and working memory demands. Patients with focal, stable lesions to the vmPFC (n = 20) and the insular cortex (n = 13) were compared against healthy subjects (n = 41) and a group of lesion controls (n = 12) with damage predominantly affecting the dorsal and lateral frontal cortex. The vmPFC and insular cortex patients showed selective and distinctive disruptions of betting behaviour. VmPFC damage was associated with increased betting regardless of the odds of winning, consistent with a role of vmPFC in biasing healthy individuals towards conservative options under risk. In contrast, patients with insular cortex lesions failed to adjust their bets by the odds of winning, consistent with a role of the insular cortex in signalling the probability of aversive outcomes. The insular group attained a lower point score on the task and experienced more 'bankruptcies'. There were no group differences in probability judgement. These data confirm the necessary role of the vmPFC and insular regions in decision-making under risk. Poor decision-making in clinical populations can arise via multiple routes, with functionally dissociable effects of vmPFC and insular cortex damage.

Disrupted prediction-error signal in psychosis: evidence for an associative account of delusions.

Delusions are maladaptive beliefs about the world. Based upon experimental evidence that prediction error-a mismatch between expectancy and outcome--drives belief formation, this study examined the possibility that delusions form because of disrupted prediction--error processing. We used fMRI to determine prediction-error-related brain responses in 12 healthy subjects and 12 individuals (7 males) with delusional beliefs. Frontal cortex responses in the patient group were suggestive of disrupted prediction-error processing. Furthermore, across subjects, the extent of disruption was significantly related to an individual's propensity to delusion formation. Our results support a neurobiological theory of delusion formation that implicates aberrant prediction-error signalling, disrupted attentional allocation and associative learning in the formation of delusional beliefs.

Stimulus-outcome interactions during instrumental discrimination learning by rats and humans.

The associative structure mediating goal-directed action was investigated using congruent and incongruent conditional discriminations. The stimulus was the same as the outcome in each component of the congruent discriminations, whereas the stimulus of one component of the incongruent discriminations was the same as the outcome of the other component. Humans, but not rats, learned the congruent discrimination more rapidly than the incongruent discrimination, a difference that the authors attribute to the fact that outcome-response associations caused response conflict in the incongruent discrimination. Moreover, responding was resistant to outcome devaluation following incongruent, but not congruent, training, suggesting that both humans and rats adopted a stimulus-response strategy to resolve the incongruent discrimination.

Diazepam produces disinhibitory cognitive effects in male volunteers.

RATIONALE: Diazepam has well known amnestic and sedative effects but effects on fronto-executive function remain largely uninvestigated, especially on neuropsychologically validated tests of risk taking and orbitofrontal cortex function. OBJECTIVES: We aimed to determine the impact of diazepam on a variety of executive tasks. METHODS: The effects of 5, 10 and 20 mg of diazepam on a battery of neuropsychological tests were investigated using a randomised, double blind, placebo-controlled design. Seventy-five adult men were recruited. The Rogers et al. (1999b) test of risk-taking was given along with tasks from the CANTAB battery. RESULTS: Diazepam impaired performance on the Tower of London test of planning, without influencing visual pattern recognition memory. Subjects who had taken diazepam made more risky choices on the risk-taking task. On two speeded reaction time tasks diazepam impaired discrimination sensitivity and increased the bias to respond. CONCLUSIONS: In contrast to the well-known sedative effects of diazepam, we demonstrate disinhibitory effects on two speeded reaction time tasks. Our results show that diazepam can impair performance on reaction time tasks both by impairing sensitivity and by increasing the bias to respond. Furthermore diazepam impaired performance on tests of planning and risky decision making that depend predominantly on dorsolateral and orbitofrontal regions of the prefrontal cortex, respectively.