Final answer:
Spontaneous recovery provides evidence that an extinguished association still exists. It occurs when an extinct conditioned response reemerges after a rest period, as demonstrated by Pavlov's dogs beginning to salivate again to the bell (CS) or the cat Tiger getting excited by the sound of a can opener (CS) after a break.
Step-by-step explanation:
The piece of evidence that shows us an extinguished association is still intact, despite the fact that the conditioned stimulus (CS) may no longer immediately elicit the conditioned response (CR), is the phenomenon known as spontaneous recovery.
After a rest period following extinction, the conditioned response can suddenly reappear in the presence of the conditioned stimulus.
For example, Pavlov's dogs, after undergoing extinction where the bell (CS) was rung without presenting meat powder (unconditioned stimulus, UCS), stopped salivating (CR). However, after a rest period, the dogs began to salivate again when the bell was rung.
This indicates that the association between the CS and UCS wasn't completely eradicated during extinction.
In the context of daily life, if someone's cat, Tiger, used to get excited upon hearing the sound of an electric can opener (CS) because it signaled food (UCS), but then the can opener broke and wasn't used for a while, extinction might occur.
Yet, once the can opener is fixed and used again, Tiger is likely to display spontaneous recovery by getting excited once more, indicating that the association remained intact despite the period of non-reinforcement.