Three types of Pavlovian conditioning procedures for modeling of fear:

• Delay conditioning. Conditioned responses, including fear, begin to occur during the CS presentation before the US is presented.
• Long-delay conditioning. Conditioned fear responses move forward in time during long CS presentations and, with continued training, reach maximal levels during the interval just preceding the presentation of the aversive US.
• Trace conditioning. Conditioned fear can be observed during the interval when only the trace, or memory, of the CS is present.
  

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