Spontaneous recovery is a medical phenomenon of learning and memory. This phenomenon was first coined and described by Ivan Pavlov in his studies of classical (Pavlovian) conditioning. In that context, it refers to the re-emergence of a previously extinguished conditioned response after a delay. The recovery of such lost behaviors can be observed in a variety of contexts, and the recovery of forgotten human memories is often of particular interest.
In classical conditioning
Spontaneous recovery is associated with classical conditioning, a learning process in which an organism learns to associate a neutral stimulus with a stimulus that produces an unconditioned response. As a result, the previously neutral stimulus comes to produce its own response, which is usually similar to that produced by the unconditioned stimulus. Although aspects of classical conditioning had been noted by previous scholars, the first experimental analysis of the process was conducted by Ivan Pavlov, a nineteenth-century physiologist who came across the associative effects of conditioning while researching canine digestion. To study digestion, Pavlov presented various types of food to dogs and measured their salivary response. He noticed that with repeated testing, the dogs began to salivate before the food was presented, such as when they heard the footsteps of an approaching experimenter. Pavlov named this anticipatory behavior the "conditioned" response. He and his associates discovered and published the basic facts about this process, which has come to be known as classical or Pavlovian conditioning. Among the phenomena that Pavlov observed was the partial recovery of a classically conditioned response after it had been extinguished by withholding the unconditioned stimulus. This recovery happened without any further unconditioned stimulation, and Pavlov referred to it as spontaneous recovery. Although the chance of spontaneous recovery increases with time following the extinction procedure, such conditioned responses generally do not return to full strength. Moreover, with repeated recovery/extinction cycles, the conditioned response tends to be less intense with each period of recovery. However, reconditioning by pairing the same conditioned and unconditioned stimuli usually occurs much faster than the original conditioning. A key conclusion is that conditioning leaves a lasting trace in the organism's memory, and that extinction does not erase the original conditioning but merely suppresses it. This insight has had profound implications for theories of classical conditioning and practical applications, particularly in behavioral therapy.
In human memory
Retroactive interference Spontaneous recovery as it pertains to human memory can be traced back to the work of George Edward Briggs, who was concerned with the concept of retroactive interference. Inhibition, or interference, is a function of competition among responses, whereby one memory has dominance over another. The inhibited responses are not lost from memory per se, but are kept from appearing by other responses. Retroactive interference is the psychological theory of memory whereby learning something new impedes retrieval of a previously learned memory. Briggs studied retroactive interference using a test of free recall. In his study, participants learned paired associate words (i.e. A1-B1, A2-B2,...Ai-Bi) over multiple trials, until the learning of the Ai-Bi associates was perfected. Following this, participants were given a new list of paired associates, where the second word of the pair was changed while the first word of the associate pair was kept the same (A1-C1, A2-C2,... Ai-Ci). After mastery of this second list, Briggs had participants perform a recall procedure. He presented a list A item and asked the participant to recall whichever pair (the -Bi or –Ci) that came to mind. Based on retroactive interference, learning of A-B paired associates declined due to the learning of the subsequent A-C associates, and as a result, there was a higher rate of responses from list C by the participants on the recall test. One day (24 hours) after learning both sets of associates, participants were tested again. A spontaneous recovery of Bi responses was observed, such that participants' responses of Bi items exceeded Ci items. After a rest period, participants could spontaneously remember the initial paired associates that they were not able to remember following the subsequent presentation of a second paired associate list the day prior. This A-B, A-C paradigm was replicated by researcher Bruce R. Ekstrand, thus increasing confirmation regarding the existence of spontaneous recovery.
Role of sleep In an experiment conducted to further the findings of Briggs and Ekstrand, it was discovered that sleep counteracts retroactive interference compared to wakefulness. Using the same A-B, A-C paradigm, results indicated that memory performance for the first list of word-pair associates (A-B) was superior when learning was followed by nocturnal sleep rather than wakefulness. Sleep differentially affected the memory consolidation of the two lists, enhancing the memory for the first list more significantly. It has been suggested that the degree of initial learning predicts whether spontaneous recovery shall occur, stating that the better the learning of the A-B associations, the more likely they are to recover after interference. This effect is further catalyzed by sleep, which appears to have an enhancing effect on memory consolidation.
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