Disgust acquisition in Pavlovian conditioning: A systematic review and meta-analysis

The acquisition of disgust through Pavlovian conditioning is thought to be a crucial mechanism underlying the development of mental disorders such as obsessive-compulsive disorder and eating disorders. The present systematic review and meta-analysis aims to enhance our understanding of disgust conditioning by examining research using psychophysiological (autonomic) and self-report measures (disgust, valence, expectancy). Furthermore, the role of characteristics of the unconditioned stimulus (UCS), i.e., modality and number of different stimuli paired with a single conditioned stimulus, was analyzed based on 44 studies (total N = 3832). In addition, findings from studies using facial electromyography, electroencephalography, and functional magnetic resonance imaging as well as research in clinical samples were systematically reviewed. Regarding differential conditioned responses, our results indicate medium effect sizes for valence and disgust ratings and very large effect sizes for expectancy ratings, whereas effect sizes for psychophysiological measures were small. We found no evidence for a moderator effect of UCS modality or UCS number on self-report indices, despite high between-study heterogeneity. In contrast, larger effect sizes for psychophysiological outcomes emerged for (audio-)visual UCS (as compared to olfactory UCS) and with increasing number of disgust-related UCS. Evidence for publication bias was low. In conclusion, there is robust evidence for disgust acquisition through Pavlovian conditioning based on self-report and psychophysiology. However, potential factors influencing the depth and speed of acquisition remain to be examined. Furthermore, additional research using psychophysiological and neural measures, in healthy and clinical samples, is required to gain a deeper understanding of disgust conditioning and its underlying neurobiological processes.