An extended comparator hypothesis account of superconditioning

Three conditioned taste aversion experiments with rats investigated superconditioning. In each experiment, alternate exposures of 2 flavor compounds with a common element (i.e., AB/AS) were administered to establish an inhibitory relationship between the 2 unique elements, B and S, and prior to testing, S was paired with lithium chloride (LiCl). In Experiment 1, pairings of a neutral cue (X) with S in compound with B after the AB/AS exposures resulted in superconditioning between X and S. Extinction of the common element (A) just before the S-LiCl pairing attenuated both the inhibitory relationship between B and S (Experiment 2) and superconditioning between X and S (Experiment 3). These observations suggest that superconditioning consists of enhanced performance rather than enhanced associative acquisition.     

Taste avoidance caused by spontaneous wheel running: effects of duration and delay of wheel confinement

Confinement of a rat in a running wheel results in the rat's subsequent avoidance of the taste consumed before the confinement. This phenomenon has been ascribed to taste aversion conditioned by spontaneous wheel running. As a first step toward clarification of the underlying mechanism of this phenomenon, we manipulated two parameters of the taste-confinement procedure: duration of wheel confinement (Experiments 1A and 1B) and temporal intervals between the taste consumption and the wheel confinement (Experiments 2A and 2B). In general, longer confinement and shorter inter-event interval caused stronger taste avoidance. However, the results also suggested that it is possible to establish taste avoidance when wheel confinement was delayed 1-h after the taste consumption. These results correspond to those of conventional taste aversion caused by illness-inducing agents, suggesting similar mechanisms in the both preparations. Experiment 3 revealed that running in a wheel rather than wheel confinement itself is the effective factor for establishing taste avoidance.     

Renewal of Extinguished Lever-Press Responses upon Return to the Training Context

Two experiments with rats explored renewal effects in operant conditioning preparations. When pressing a lever was trained in one context and then extinguished in a second context, the responding was renewed by returning to the original context (ABA renewal) in Experiment 1. This finding was replicated in Experiment 2 with discriminative operant performance signaled by a localized light cue. In spite of the successful demonstration of ABA renewal effect in these experiments, AAB renewal was detected in neither experiment: When the responses had been extinguished in the context of acquisition, testing the rats in a second context did not renew the responses. The demonstration of ABA renewal but no AAB renewal suggests that extinction in another context and/or a return to the original context are critical for renewal of extinguished operant performance.     

Overshadowing and the outcome-alone exposure effect counteract each other

Three conditioned lever-press suppression experiments with rats investigated the interaction between overshadowing and outcome-alone exposure effects. Experiment 1 found in first-order conditioning that combined overshadowing and outcome-preexposure treatments attenuate the response deficit produced by either treatment alone. Experiments 2 and 3 investigated the interaction between overshadowing and outcome pre- and postexposure effects in sensory preconditioning, varying retention intervals to engage recency and primacy effects with respect to treatment order. Contrary to when a solitary cue is conditioned, responding to a cue conditioned in compound appeared positively correlated with the context's associative status. These findings suggested that some of the basic laws of learning applicable to cues conditioned alone do not similarly apply to a component of a compound cue.     

Reasoning rats: forward blocking in Pavlovian animal conditioning is sensitive to constraints of causal inference

Forward blocking is one of the best-documented phenomena in Pavlovian animal conditioning. According to contemporary associative learning theories, forward blocking arises directly from the hardwired basic learning rules that govern the acquisition or expression of associations. Contrary to this view, here the authors demonstrate that blocking in rats is flexible and sensitive to constraints of causal inference, such as violation of additivity and ceiling considerations. This suggests that complex cognitive processes akin to causal inferential reasoning are involved in a well-established Pavlovian animal conditioning phenomenon commonly attributed to the operation of basic associative processes.     

Renewal of operant performance formerly eliminated by omission or noncontingency training upon return to the acquisition context

Renewal of operant performance formerly eliminated by omission or noncontingency training was explored in two experiments with rats. When pressing a lever was trained with food reinforcement in one context (A) and then eliminated in a second context (B), responding was renewed by returning the rats to the original context (A). This ABA renewal effect was demonstrated in Experiment 1 when the elimination training was an omission procedure (delivery of food for withholding responding) and in Experiment 2 when it was a noncontingency procedure (delivery of food irrespective of responding). Because omission training (differential reinforcement of other behavior) and noncontingency training have been used in applied settings as effective procedures to reduce undesired human behaviors, the clinical implications of our findings for the relapse of undesirable behavior were discussed.     

The basic laws of conditioning differ for elemental cues and cues trained in compound

The cue-duration effect (i.e., longer cues result in less conditioned responding than shorter cues) was examined as a function of whether cues were trained alone or in compound. Compound (AX) or elemental (X) cues of either long or short duration were paired with the unconditioned stimulus. In testing with X alone, the cue-duration effect was observed with elementally trained cues, but not with compound cues. Instead, stronger responding resulted from training with long compound cues relative to short compound cues (i.e., a reversed cue-duration effect). Moreover, an overshadowing effect (i.e., decreased responding due to compound conditioning) was observed when conditioning was conducted with a short cue, but compound conditioning resulted in enhanced responding when it was conducted with a long cue (i.e., reversed overshadowing). These findings are consistent with other recent demonstrations that some laws of learning that apply to elementally trained cues do not similarly apply to cues trained in compound.     

Spontaneous recovery from forward and backward blocking

This article demonstrates and analyzes spontaneous recovery of stimulus control following both forward and backward blocking in a conditioned suppression preparation with rats. Experiment 1 found, in first-order conditioning, robust forward blocking and an attenuation of it following a retention interval. Experiment 2 showed, in sensory preconditioning, recovery of responding following both forward and backward blocking. Also, the results of this experiment indicated that response recovery to the blocked stimulus cannot be explained by an impaired status of the blocking stimulus after a retention interval. Experiment 3, also in sensory preconditioning, suggested that spontaneous recovery following both forward and backward blocking in Experiment 2 was due to impaired associative activation of the blocking stimulus' representation during testing with the blocked stimulus. Although no contemporary model of associative learning can explain these results, a modification of R. R. Miller and L. D. Matzel's (1988) comparator hypothesis is proposed to do so.     

Outcome pre- and postexposure effects: retention interval interacts with primacy and recency

Effects of outcome-alone pretraining and posttraining exposure were investigated in conditioned suppression experiments conducted within a sensory preconditioning preparation with rats. Experiment 1 found that interference by outcome postexposure was stronger than that by outcome preexposure, suggesting a recency effect. Experiment 2 found that after a long retention interval, outcome preexposure produced more interference than outcome postexposure, suggesting a shift from recency to primacy with increasing retention interval. Experiment 3 showed that presentation of a priming stimulus that had been embedded within the earlier phase of treatment also caused a shift from recency to primacy. These results suggest that, at least in a sensory preconditioning paradigm, retrievability of outcome-alone exposure memory is an important determinant of any outcome-alone exposure effect.