Figure 1. Description of a trial.

Each trial lasted 2000 milliseconds, during which either an air puff alone (US only), a tone alone (CS only) or a paired CS and US stimulus could be presented. The 520 millisecond tone (CS) would start at 500 milliseconds after trial onset, the 20 millisecond air puff (US) would start at 1000 milliseconds after trial onset and both stimuli would end at 1020 milliseconds in the trial. During each trial, the eyelid movement (trace) is recorded, and blinks are shown as peaks in the recording. Traces of an unconditioned response (UR trace) and a conditioned response (CR trace) are shown. An eyelid response with an onset latency between 650 and 1025 milliseconds with respect to the start of a CS-only or paired trial was considered a conditioned response.