Measuring human Pavlovian appetitive conditioning and memory retention

While a body of literature has addressed quantification of aversive conditioning, there is a dearth of systematic work comparing different conditioned responses during human reward learning and its retention. In consequence, it is unclear how to best measure reward conditioning in humans. Here, we sought to fill this gap by investigating heart period response (HPR), skin conductance response (SCR), pupil size (PS), and respiration amplitude response (RAR) during Pavlovian appetitive conditioning. We conducted two independent experiments (N1 = 37, N2 = 34) with an acquisition phase and a recall phase after a 7-day interval, in which a visual conditioned stimulus (CS+) predicted fruit juice reward (unconditioned stimulus, US), while a second CS- predicted US absence. In experiment 1, only HPR distinguished CS+/CS-, both during acquisition (Hedge’s g = 0.56) and recall (Hedge’s g = 0.40). As an out-of-sample generalisation test, experiment 2 confirmed this result during acquisition (Hedge’s g = 0.78) and recall (Hedge’s g = 0.55). We conclude that in a Pavlovian appetitive conditioning paradigm, HPR is a sensitive measure of reward learning and the retention of reward memory, and we provide robust and replicable measurement methods to this end.