FIGURE 5.2 Extinction and Spontaneous Recovery in Pavlov’s Laboratory This demonstration involved a dog that had already been conditioned to salivate (the CR) to just the sight of the meat powder (the CS). During the extinction phase, the CS was repeatedly presented at three-minute intervals and held just out of the dog’s reach. As you can see in the graph, over the course of six trials the amount of saliva secreted by the dog quickly decreased to zero. This indicates that extinction had occurred. After a two-hour rest period, the CS was presented again. At the sight of the meat powder, the dog secreted saliva once more, evidence for the spontaneous recovery of the conditioned response.

Source: Data from Pavlov (1927).