The curve of acquisition, extinction, and spontaneous recovery

The rising curve in the graph on the slide represents the conditioned response becoming stronger through repeated association of the conditioned stimulus and the unconditioned stimulus, after which the strength weakens during the extinction phase when only the conditioned stimulus is presented.¹ The spontaneous recovery describes how, after a pain in time, the conditioned response may reappear.¹

Reference:

1. Spielman RM, Jenkins WJ, Lovett MD. Psychology 2e, 6.2: Classical conditioning. OpenStax. Available at: https://openstax.org/books/psychology-2e/pages/6-2-classical-conditioning. Accessed July 2025.
2. Duits P, Cath DC, Lissek S, et al. Updated meta-analysis of classical fear conditioning in the anxiety disorders. Depress Anxiety 2015; 32 (4): 239–253.