Figure 4.2 | Acquisition, Extinction, and Spontaneous Recovery | Panel (a) depicts the acquisition of the CR. Note that during acquisition, the UCS follows the CS on each trial. Acquisition of the CR is reflected in the increase in its strength across conditioning trials. Extinction is depicted in panel (b). On extinction trials, the UCS never follows the CS. This process is reflected in the decrease of the strength of the CR across extinction trials. Note, however, that when a break is taken during extinction training, there is a temporary partial recovery in strength of the CR following the break, depicted in panel (c). This partial recovery is called spontaneous recovery. The amount of recovery lessens as extinction training continues.