Four experiments with rats in an appetitive conditioned magazine entry preparation examined spontaneous recovery after extinction. Spontaneous recovery was obtained 6 days but not 5 hr following extinction; recovery depended on the passage of time but not on the removal of a cue that was featured in extinction or on the reintroduction of early-session cues. A cue featured in extinction attenuated recovery when presented on the test. The attenuation effect depended on the cue's correlation with extinction; a cue featured in conditioning did not attenuate recovery. The extinction cue did not evoke responding on its own, suggesting that it was not a conditioned excitor. Retardation tests and a summation test did not reveal that it was a conditioned inhibitor. The cue might work by retrieving a memory of extinction. Spontaneous recovery thus occurs because the subject fails to retrieve an extinction memory. Other accounts of spontaneous recovery are discussed.

The effect of fornix lesions on some effects of manipulating the context on performance in extinction were studied. In renewal, subjects' responding to an extinguished conditioned stimulus (CS) recovered when the CS was presented in the context in which it had been conditioned after extinction in a different context. In reinstatement, it recovered when the CS was tested after independent presentation of the unconditioned stimulus (US; an effect mediated by contextual conditioning.) In spontaneous recovery, it recovered after the passage of time, that is, when the CS was tested in a new temporal context. In the conditioned suppression method, fornix lesions had no effect on conditioning, extinction, renewal, or spontaneous recovery; however, they abolished the reinstatement effect. The results suggest that the hippocampal system may be important in the formation of context-US associations, but not in other types of learning about the context.

Five conditioned suppression experiments with rats explored retention interval and context effects in discrimination reversal learning. In the discrimination phase, a tone (T) was paired with shock, and a houselight-off stimulus (L) was presented alone; in the reversal phase, T was extinguished and L was paired with shock. Discrimination training made L a latent inhibitor but not a conditioned inhibitor. A 28-day delay after the reversal caused spontaneous recovery to T but had no effect on L. A context switch before the reversal caused more rapid conditioning to L but did not affect extinction to T. A return to the original context after the reversal had occurred in a different context renewed suppression to T and latent inhibition to L; contextual control was still strong 21 days later. Tests in a neutral context indicated that each training context controlled performance to T and L. A memory retrieval framework may begin to integrate the effects of context and time.

No abstract

Reinstatement after counterconditioning was examined in three experiments with rats. The rats received CS-shock pairings in Phase 1and then CS-food pairings in Phase 2. When unsignaled shock was presented after appetitive conditioning, fear performance to the CS replaced food performance. This reinstatement effect depended on initial pairings of the CS and shock in Phase 1. It also depended on shock exposure occurring in the test context. The results parallel previous data obtained after extinction. Counterconditioning and extinction yield several parallel effects (spontaneous recovery, renewal, and now reinstatement) which suggest that Phase 2 does not destroy the learning acquired in Phase 1.Performance to a conditioned stimulus (CS) can recover following extinction. Recovery of performance after extinction suggests that extinction does not result in unlearning; that is, information acquired during conditioning is not destroyed by a procedure in which the CS is repeatedly presented without the unconditioned stimulus (US; Bouton, 1991Bouton, , 1993. One recovery effect is spontaneous recovery, the return of the conditioned response (CR) that occurs when time passes following extinction (e.g., Pavlov, 1927;Rescorla & Cunningham, 1978;Robbins, 1990;Thomas & Sherman, 1986). Another is the renewal effect, the return of the CR that occurs when the background context is switched following extinction (e.g., Archer, Sjoden, Nilsson, & Carter, 1979;Bouton & Bolles, 1979;Bouton & King, 1983;Bouton & Peck, 1989;Bouton & Ricker, 1994;Bouton & Swartzentruber, 1989;Brooks & Bouton, 1994). A third example is reinstatement, in which the extinguished CR returns when the CS is tested after exposures to the US alone (e.g., Bouton, 1984;Bouton & Bolles, 1979;Bouton & King, 1983;Bouton & Peck, 1989;Rescorla & Cunningham, 1978;Rescorla & Heth, 1975; cf. Baker, Steinwald, & Bouton, 1991). Bouton (1993) has recently noted parallels between extinction and counterconditioning, another procedure in which the CS is associated with a different event after conditioning with a particular US. In counterconditioning, the CS is paired with a second, qualitatively different US in the second phase. For example, aversive-appetitive transfer involves pairing the CS with an aversive US (e.g., shock) in Phase 1 and an appetitive US (e.g., food or water) in Phase 2. The second phase establishes a CR (e.g., magazine entry) different from that conditioned in Phase I (freezing).