Safety signals reinforce instrumental avoidance in humans

Safety signals reinforce instrumental avoidance behavior in nonhuman animals. However, there are no conclusive demonstrations of this phenomenon in humans. Using human participants in an avoidance task, Experiments 1-3 and 5 were conducted online to assess the reinforcing properties of safety signals, and Experiment 4 was conducted in the laboratory. Participants were trained with CSs+ and CSs-, and they could avoid an aversive outcome during presentations of the CSs+ by pressing their space bar at a specific time. If successful, the aversive outcome was not presented but instead a safety signal was. Participants were then tested-whilst on extinction-with two new ambiguous test CSs. If participants made an avoidance response, one of the test CSs produced the trained safety signal and the other was a control. In Experiments 1 and 4, the control was followed by no signal. In Experiment 2, the control was followed by a signal that differed in one dimension (color) with the trained safety signal, and in Experiment 3, the control differed in two dimensions (shape and color) from the trained safety signal. Experiment 5 tested the reinforcing properties of the safety signal using a choice procedure and a new response during test. We observed that participants made more avoidance responses to the ambiguous test CSs when followed by the trained signal in Experiments 1, 3, 4, and 5 (but not in Experiment 2). Overall, these results suggest that trained safety signals can reinforce avoidance behavior in humans.