How does the peak-end rule smell? Tracing hedonic experience with odours

The peak-end rule predicts that retrospective evaluations of affective events heavily depend on their most intense and last moment and imply duration neglect. It was originally proposed for negative experiences such as painful medical procedures. It is unclear, however, to what degree it also applies to positive experiences. Previously, rigorous comparisons between the two domains were limited due to the use of qualitatively different stimuli. Hence, it is not clear if the peak-end rule holds for short positive and negative experiences alike. To address these questions in a genuinely emotional domain, we conducted two experiments (n = 48 each) in which we used odours as stimuli. Participants repeatedly evaluated continuous odour sequences delivered into their noses via an olfactometer. The sequences differed in valence (positive vs. negative), length (36 vs. 72 s), and trajectory (increasing, decreasing, U-shaped, and inverse U-shaped). Results provide evidence for the peak-end rule for both positive and negative experiences alike. Results further show an overweighting of intense negative experiences for sequences that contain both pleasant and unpleasant episodes but provide little evidence for an effect of the trajectory manipulation.峰终定律（peak-end rule）指出，人们对情感事件的回溯性评价在很大程度上取决于该事件中最强烈的时刻与最终时刻，且会忽略事件的持续时长。该定律最初针对疼痛性医疗操作等负面体验提出。然而目前尚不清楚，该定律在多大程度上也适用于正面体验。此前由于两类研究使用的刺激在性质上存在差异，导致对正面与负面体验这两个领域的严谨对比研究受限，因此尚不明确峰终定律是否同样适用于时长较短的正面与负面体验。为在真实情感领域解答上述问题，本研究开展了两项实验（每组被试n=48），实验以气味作为刺激材料。被试需通过嗅觉仪（olfactometer）将连续的气味序列吸入鼻腔，并反复对其进行评价。这些气味序列在情绪效价（valence）（正面vs.负面）、时长（36秒vs.72秒）以及变化轨迹（递增、递减、U型与倒U型）上均存在差异。实验结果为峰终定律适用于正面与负面体验提供了实证支持。此外，结果还显示，当序列同时包含愉悦与不愉悦片段时，被试会过度重视其中强度较高的负面体验，但未发现轨迹操纵存在显著效应的可靠证据。