Figure 4. Irreducible uncertainty predicts subjective stress.

(a) Example subjective stress trajectory for one participant (blue) and irreducible uncertainty estimates for that individual (red). (b) Comparison of regression models of subjective stress. All models shared two components: the value of the previous rating and the number of shocks delivered since the last rating. The surprise model summed the surprise (|δ₁|) for each outcome since the previous rating, while models σ_1–3 included the estimated uncertainty at each level of the Hierarchical Gaussian Filter at the time of rating. Irreducible uncertainty () provided the best fit to our participants (n=45). (c) Irreducible uncertainty predicts prediction response times. A curve describing the variance of a Bernoulli distribution representing beliefs about probabilities, corresponding to irreducible uncertainty, predicts average response times (Pearson r=0.99, P<0.001). (d) The winning regression model predicting subjective stress responses (mean r²=0.25). Shocks and irreducible uncertainty both predicted subjective stress ratings (single-sample t-tests, P<0.001; P=0.0024). Error bars represent s.e.m.