Dissertations, Theses, and Capstone Projects

Date of Degree


Document Type


Degree Name



Cognitive Neuroscience


David Johnson

Subject Categories

Cognitive Neuroscience


fear, uncertainty, fear learning, threat discrimination, threat, intolerance of uncertainty


Learning to predict the arrival of threat is crucial to survival. Key to this learning process is the ability to discriminate between which stimuli signify safety and which signify threat. The extent to which a threat is uncertain impacts this ability, but which factors of uncertainty are primarily responsible remains unresolved. Uncertainty at the level of the stimulus can be examined in threat learning paradigms by adjusting threat reinforcement rate, referring to the frequency at which a cue is reinforced with an aversive stimulus. Previous research has shown that a continuous (more certain) threat reinforcement is associated with enhanced threat learning, but this could be a product of confounds in the experimental design in those studies. On the level of the individual, variability in sensitivity to uncertainty is measured using the Intolerance of Uncertainty scale (IU). Individual differences in IU scores have been shown to influence threat acquisition, generalization, and extinction processes in threat learning. This suggests the potential for interactive effects of individual and stimulus-level uncertainty on fear learning processes, but this has not been widely studied. This study tested the effects of uncertainty at the level of the stimulus (partial versus continuous reinforcement rate), at the individual level (differences in IU scores), and interactions of the two on threat/safety discrimination capacity. Johnson & Morriss (2023) showed tentative evidence against an effect of reinforcement rate on threat discrimination as well as support for distinct roles of IU’s subscales, Inhibitory and Prospective IU, in threat learning, as indexed by skin conductance response (SCR). Here, we attempted to replicate and extend their findings across additional operationalizations of threat responding. Using a within-participant design, participants (n=36) completed a task in which three different colors were paired with an electrical shock at three different reinforcement rates; 100% (CS+), 50% (CS+), or 0% (CS-). To test response coherence (or, the association of experiential and physiological response during threat acquisition) we collected measures of self-reported threat expectancy and evaluative ratings, an additional physiological fEMG of corrugator supercilii activity, and neurobiological measures of HPA (salivary cortisol) and noradrenergic activity 4 | P a g e (alpha amylase) in addition to SCR. While we found no evidence that reinforcement rate modulates threat discrimination, data showed that individuals scoring highly on IU total, Prospective-IU or Inhibitory IU independently, demonstrated poorer threat discrimination than those scoring low on those scales, as measured using SCR. However, no differential impact on threat discrimination was identified between the subscales. High total IU and high Prospective IU were associated with more negative evaluative ratings of the uncertain threat cue. These results contribute to the growing body of research exploring how uncertainty at the levels of the stimulus and individual affect threat learning, and provide further validity for the use of IU and its subscales as dispositional measures in threat conditioning studies.