Individual Differences in Fear Conditioning: Influence of Compound Presentation of Stimuli and Reinforcement Rate

Trait anxiety has been strongly linked to fear learning and we sought to examine how it can modulate the differences in how people learn fear towards compound stimuli and partially reinforced stimuli. Highly anxious people have been shown to generalize fear stronger than their non-anxious counterparts and to exhibit higher levels of fear towards ambiguous stimuli. A recent study examined the effect of anxiety levels in associating fear towards partially conditioned stimuli by comparing control mice with mice missing a gene responsible for anxiety suppression. After exposing both groups of mice to a light and tone compound that was paired with an aversive stimulus and just the tone itself unreinforced, the researchers noted increased fear levels in the highly anxious mice when exposed to just a tone. This is attributed to anxiety playing a role in causing elevated fear towards partially predictive stimuli. However, studies on the transfer of fear in compound stimuli indicate that they may be processed differently than single-part stimuli and that anxiety may play a role in modulating this. We believe that fear may transfer from the compound stimulus to its individual parts for highly anxious individuals and that this could also explain the results seen in the experiment described above. To our knowledge, no one has yet tested this possibility. In 2 order to decipher this, we designed five different fear conditioning paradigms. By measuring pupillary responses from participants before and after each type of conditioning in order to measure fear, we were able to measure the effects of conditioning partial predictors of fear and compound stimuli. Additionally, we were able to replicate the described experiment as one of our conditions. Our results from all five conditions revealed no anxiety effect, but we observed prolonged fear retention towards compound stimuli and a configural association of compounds.