Abstract:
Aversive conditioning serves as a key model for studying human aversive learning, with fear conditioning representing its central form. Despite extensive research, two core questions remain unresolved in this field. The first is whether contingency awareness, defined as the conscious recognition of the relationship between the conditioned stimulus (CS) and the unconditioned stimulus (US), constitutes a necessary condition for the acquisition of conditioned responses (CRs) in fear conditioning. This question has important implications for theories of fear learning and is also relevant to understanding the development of anxiety- and fear-related disorders as well as the design of targeted interventions. The second question concerns how the sensory modality of the US influences CRs across multiple response systems, including evaluative (subjective), autonomic, and neural domains. Clarifying this relationship can deepen understanding of aversive learning and inform the selection of US modalities when targeting specific CRs in experimental design.
To address these questions, two complementary empirical studies were conducted. Study 1 employed a large-scale online design with 895 participants assigned to 12 experimental groups. It examined how procedural parameters and individual differences, such as personality traits and cognitive functioning, influence the emergence of contingency awareness in fear conditioning. It also tested whether contingency awareness is necessary for the emergence of evaluative CRs, as measured by affective ratings of the CSs. The results showed that several procedural factors, including online fear ratings, US-expectancy ratings, engagement in concurrent tasks, the sensory modality of both the CS and the US, and the instructions provided, significantly influenced the emergence of contingency awareness. Moreover, only participants who demonstrated awareness of the CS-US relationship showed clear evaluative differentiation between CS+ and CS-. This finding suggests that contingency awareness plays a critical role in the formation of evaluative CRs during fear learning.
Building on these findings, Study 2 was conducted in a controlled laboratory setting to further examine the role of contingency awareness and to investigate how different US modalities shape CRs across evaluative, autonomic, and neural systems. Participants were randomly assigned to receive electric shocks, airpuffs to the eye, or aversive images as the US. CRs were measured using affective ratings, skin conductance responses (SCRs), heart rate (HR), and electroencephalographic (EEG) activity. The results showed that electric shocks elicited the most robust and consistent CRs across all systems, including higher fear and arousal ratings, lower
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valence ratings, elevated SCRs, HR deceleration, more negative stimulus-preceding negativity (SPN) amplitudes, enhanced late positive potential (LPP) amplitudes, and greater alpha-band power suppression for CS+ compared to CS-. Airpuffs evoked reliable HR deceleration and more negative SPN amplitudes for CS+ relative to CS-, but evaluative CRs were weak and no SCR effects emerged. In contrast, aversive images elicited robust evaluative CRs but did not produce detectable autonomic or neural CRs. Importantly, within the image group, contingency awareness modulated evaluative CRs but showed no impact on autonomic responses. Taken together, these findings underscore the pivotal role of US modality in shaping the strength and the response profile of aversive learning. They further suggest that contingency awareness is primarily linked to evaluative CRs, whereas its influence on autonomic systems remains less conclusive.
Overall, these findings provide robust evidence that both cognitive factors such as contingency awareness and stimulus-related features such as US modality play critical roles in human aversive learning. Contingency awareness appears especially important for the emergence of evaluative CRs, whereas the sensory modality of the US shapes both the strength of learning and the specific response systems involved, including evaluative, autonomic, and neural domains. In addition, the emergence of contingency awareness was influenced by several procedural factors. These findings contribute to a more nuanced understanding of the mechanisms underlying human aversive conditioning and carry important implications for clinical interventions targeting anxiety and fear-related disorders.
Fear conditioning