Fig. 1.

Experiment 1 Study Design – Contingency Degradation Task. (a) Contingency degradation task design. In each block, subjects were presented with a white triangle, signalling that they had the opportunity to press or to not press the space bar, in a free-operant, self-paced procedure (Vaghi et al., 2018). The triangle turned yellow (here pictured in grey) when a response was recorded. Rewards (a 25 pence image) were delivered according to a probability of outcome given action, P(O|A), on trials when a response was made, and a probability of outcome given no action, P(O|−A), when a response was not made. (b) Physiological response to anxiety induction. Subjects' heart rate was elevated significantly during the gas condition, p < 0.001. Error bars represent s.e.. (c) Programmed contingencies. Each participant completed eight blocks where contingency was systematically varied through changes to P(O|−A). The first two blocks were considered training blocks and appeared in a fixed order as denoted in the table. The six remaining test blocks were presented in a counterbalanced order across subjects. (d) Psychological response to anxiety induction. Anxiety scores measures using a visual analogue scale (VAS) were also significantly elevated during the inhalation of gas compared with air, p < 0.001. Error bars represent s.e. ***, p < 0.001.