Anticipation can be more terrifying than the event itself. This idea, expressed by filmmaker and “master of suspense” Alfred Hitchcock, has been scientifically explored by researchers at the University of California, Davis. Their recent study, published in the journal Computational psychiatryreveals that the hazard rate (the increasing probability that a negative event will occur over time) intensifies anxiety more than the actual probability of the event itself.
The motivation behind this study arose from a fundamental need to understand the mechanisms of anxiety, a condition that affects a significant portion of the world’s population. Anxiety disorders are among the most common mental health problems, often leading to significant distress and impairment in daily functioning.
Despite their prevalence, the underlying mechanisms, including how uncertainty exacerbates anxiety, remain poorly understood. This lack of knowledge prompted researchers at the University of California, Davis, to study how different aspects of uncertainty contribute to the intensity of anticipatory fear.
The researchers were particularly interested in the concept of hazard ratio, or the perceived likelihood of an adverse event occurring over time. Traditional studies of anxiety have often focused on the likelihood of an event, but the UC Davis researchers hypothesized that the timing of uncertainty might play a crucial role in how intense the anxiety is.
The study involved 42 volunteers who participated in a virtual environment. In this environment, they could receive mild electric shocks at unpredictable times. Participants were incentivized to stay in the environment with a small cash reward, earning a cent per second, but they had the option to leave at any time to avoid the shock.
To isolate the effect of the hazard rate, the researchers created two separate scenarios. In the first scenario, the shock could occur at any time within a ten-second interval, making the hazard rate high because the probability of the shock increases over time.
“If you know something is going to happen, the hazard rate increases over time because you know it didn’t happen sooner,” said lead author Andrew S. Fox, an associate professor of psychology at UC Davis. “The hazard rate is always going to be higher if you don’t know when it’s going to happen.”
In the second scenario, a countdown was scheduled before the shock, so participants knew exactly when the shock was going to occur, making the hazard rate low until the countdown ended. Both scenarios had the same overall probability of receiving a shock, but the perceived timing of the threat was different.
Participants’ behavior and self-reported anxiety levels were monitored throughout the experiment. The researchers measured how often participants chose to leave the environment to avoid the shock and collected subjective anxiety ratings at different points during the experiment. This allowed the researchers to compare the impact of high and low risk ratings on the decision to avoid the shock and on the level of anxiety experienced.
The researchers found that participants’ anxiety levels were influenced more by the risk rating than by the actual probability of receiving an electric shock. In the scenario where the shock could occur at any time (high risk rating), participants reported significantly higher levels of anxiety than in the countdown scenario (low risk rating). This was evident both in their self-reported anxiety ratings and in their behavior.
Participants were more likely to withdraw from the high-risk scenario to avoid the shock, even though the overall probability of receiving a shock was the same in both scenarios. This behavior indicated that the anticipation of a potential threat, when its timing was uncertain, was more anxiety-provoking than the certainty of an imminent threat. The data showed that as the perceived probability of the shock increased over time, participants’ anxiety also increased, leading them to forgo the potential monetary reward to avoid the anticipated shock.
“At each time point in the experiment, the threat risk rating matched our participants’ behavior almost perfectly, whereas momentary threat probabilities had no predictive value,” says co-author Dan Holley, a graduate student. “Volunteers also reported feeling significantly more anxious in an environment where the threat rating was higher.”
These findings suggest that our brains are wired to track risk rates as a survival mechanism. This tracking likely evolved to help us anticipate and avoid threats in our environment, even if those threats are not immediate.
“Imagine a gazelle in the Serengeti,” Holley says. “To survive, it might keep its head down and graze a little longer, but the tradeoff is that it’s a little more likely to be attacked by a lion.”
The longer the gazelle grazes, the greater the risk. “Something in its mind has to track the risk and guide its behavior accordingly,” Holley said.
The study’s findings provide insight into how uncertainty and the perception of increasing threat contribute to anxiety. By focusing on risk ratings, the researchers were able to identify a specific aspect of uncertainty that drives anxiety, providing new insights that could inform more effective treatments for anxiety disorders.
“Our model echoes Hitchcock’s theory: prolonged anticipation of a negative event can lead to increasing anxiety as the risk rating increases,” the researchers conclude. “Anxious psychopathology is often characterized by emotional distress in supposedly safe contexts, leading to avoidance and missed opportunities. Our model suggests that risk rating estimates may increase disproportionately in response to imagined or exceptionally rare threats.”
“This paves the way for identifying the precise mechanisms that lead to the maladaptive avoidance and emotional distress characteristic of pathological anxiety by dissociating threat probability, risk-rate calculations, and uncertainty per se. This computational reimagining of uncertainty—a transdiagnostic marker of anxiety—provides an actionable framework for basic and clinical research aimed at understanding, preventing, and treating these conditions.”
The study, “Temporal Dynamics of Uncertainty Cause Anxiety and Avoidance,” was authored by Dan Holley, Erica A. Varga, Erie D. Boorman, and Andrew S. Fox.
