Table 1.

Glossary

Keyword	Definition
Fear learning	An adaptive function that allows an organism to predict potentially aversive events from environmental cues.
Unconditioned stimulus, US	A stimulus that reliably produces a natural, or unconditioned, response. In fear conditioning, this stimulus is aversive in nature (e.g., shock, aversive noise).
Conditioned stimulus, CS	A previously neutral stimulus that is paired with a US in classical conditioning (acquisition phase).
Fear extinction	The gradual process of fear reduction in classical conditioning that involves repeated exposure to the CS without the US.
Safety learning	The process of learning about safety in the environment. Tested using threat and safety discrimination.
Safety signal learning	The process through which a stimulus that is overly trained to signal the absence of threat (i.e., the safety cue) reduces fear in the presence of a threatening cue.
Conditioned inhibitor	A stimulus that inhibits a response as a result of learning (i.e., acquisition).
External inhibitor	A stimulus that inhibits a response without having undergone explicit training.
Safety behavior	An action or behavior that involves the use of a safety cue.
Preventative safety behavior	An action that employs a safety behavior prior to an anticipated threatening event to avoid harm or reduce the intensity of the event.
Restorative safety behavior	An action that employs a safety behavior following an aversive event with the goal of restoring safety.