Key result
Heart period responses reliably distinguish reward-predicting from non-rewarding stimuli during learning and recall.
Why the study?
Pavlovian reward conditioning with primary reinforcers and its recall after consolidation remain understudied, with few studies directly comparing conditioned response types.
Standardized Mean Difference: 0.56
Heart period responses and pupil size responses are valid physiological indices of reward learning and memory retention in human Pavlovian conditioning.
HPR may index human reward memory; leaves open extension to cardiovascular populations.
While a body of literature has addressed the quantification of aversive Pavlovian conditioning in humans, Pavlovian reward conditioning with primary reinforcers and its recall after overnight consolidation remain understudied. In particular, few studies have directly compared different conditioned response types and their retrodictive validity. Here, we sought to fill this gap by investigating heart period responses (HPR), skin conductance responses (SCR), pupil size responses (PSR), and respiration amplitude responses (RAR). We conducted two independent experiments ( N 1 = 37, N 2 = 34) with a learning phase and a recall phase 7 days later. A visual conditioned stimulus (CS+) predicted fruit juice reward (unconditioned stimulus, US), while a second CS− predicted US absence. In experiment 1, model‐based analysis of HPR distinguished CS+/CS−, both during learning (Hedge's g = 0.56) and recall ( g = 0.40). Furthermore, model‐based analysis of PSR distinguished CS+/CS− in early trials during recall ( g = 0.69). As an out‐of‐sample generalization test, experiment 2 confirmed the result for HPR during learning ( g = 0.78) and recall ( g = 0.55), as well as for PSR during recall ( g = 0.41). In contrast, peak‐scoring analysis of PSR yielded low retrodictive validity. We conclude that in our Pavlovian reward conditioning paradigm, HPR is a valid measure of reward learning, while both HPR and PSR validly index the retention of reward memory.
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Xia et al. (2025) studied Pavlovian reward conditioning (n=71). Visual conditioned stimulus (CS+) predicting fruit juice reward vs. Visual conditioned stimulus (CS-) predicting absence of reward was evaluated on Heart period responses (HPR) distinguishing CS+ from CS- during learning (Experiment 1) (Hedge's g 0.56). Heart period responses validly distinguished reward-predicting stimuli from non-rewarding stimuli during learning (Hedge's g = 0.56) and recall 7 days later (g = 0.40).
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