Overshadowing between landmarks on the touchscreen and in arena with pigeons.

The role of generalization decrement in spatial overshadowing was evaluated using a landmark-based spatial search task in both a touchscreen preparation (Experiment 1a) and in an Automated Remote Environmental Navigation Apparatus (ARENA, Experiment 1b). A landmark appeared as a colored circle among a row of eight (touchscreen) or six (ARENA) potential locations. On overshadowing trials, Landmark X was located two positions away from a hidden goal, while another landmark, A, was in the position between X and the goal. On control trials, Landmark Y was positioned two locations away from the goal but without a closer landmark. All subjects were then tested with separate trials of A, X, Y, and BY. Testing revealed poor spatial control by X relative to A and Y, thereby replicating the spatial overshadowing effect. Spatial control by Y was similar when tested in compound with novel landmark (BY) and on trials of Y alone. Thus, overshadowing in a small-scale environment does not appear to be due to a process of generalization decrement between training and testing. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Overshadowing and stimulus duration.

In 3 experiments, the authors investigated the effect of stimulus duration on overshadowing. Experiments 1 and 2 examined responding to a target conditioned stimulus (CS1) when it was conditioned in compound with a coterminating overshadowing stimulus (CS2) that was longer, shorter, or of the same duration (the long, short, and matched groups, respectively). Equal overshadowing of conditioning to CS1 was obtained in all 3 conditions relative to a control group conditioned to the light alone. There were, however, differences in responding to CS2 as a function of its absolute duration. Experiment 3 examined the contribution of the food-food interval/CS onset-food interval ratio to these findings. In Experiments 1 and 2, the ratio differed for the overshadowing CS but not for the target CS. In Experiment 3, this arrangement was reversed, but the pattern of results remained the same. The implications of these findings for trial-based and real-time models of conditioning are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Changes in cue associability across training in human causal learning.

A series of experiments studied the amount learned about two food cues (A and B) whose presentation in a meal was followed by an allergy (+) in a fictitious patient. Participants were trained with A+ and C+ in Phase 1 and then with AB+ or AB++ in Phase 2. Subsequent testing revealed that BC was more allergenic than AD, showing that more had been learned about B than A in Phase 2. Participants were also trained with A+, then with AB+, and finally with AB++. The results of interpolating AB+ between A+ and AB++ training were consistent with the hypothesis that pretraining with Cue A selectively suppressed attention to its associate across the AB+ trials and, thereby, reduced the amount subsequently learned about B on AB++ trials. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The influence of blocking on overt attention and associability in human learning.

Previous studies have demonstrated a retardation in the rate of novel learning about previously blocked cues as compared to appropriate control cues. We report an experiment investigating whether this retardation in novel learning about a blocked cue is accompanied by a reduction in attention to this cue, as anticipated by attentional theories of associative learning. Consistent with these theories, eye gaze measures revealed a reduction in overt attention to the blocked cue both during the compound training phase of the blocking procedure, and also during novel learning with respect to new outcomes. Moreover, the extent of the bias in overt attention away from blocked cues was positively correlated with the subsequent reduction in rate of novel learning about these cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differences in the associability of relevant and irrelevant stimuli.

Pigeons in two experiments were first trained with a set of simple discriminations of the form AX+ CX?, BY+ DY? where A, B, C, and D were relevant, and belonged to one dimension, and X and Y were irrelevant and belonged to a different dimension. They were then tested with a discrimination of the form AX+ AY? BX?. The experiments revealed that the discrimination between AX+ and BX? was acquired more readily than between AX+ and AY?, which indicates that the original training resulted in the associability of the relevant stimuli being greater than that of the irrelevant stimuli. Experiment 2 revealed that the status of other stimuli from the two dimensions influenced these changes in associability. The associability of X and Y was enhanced by making other stimuli from the same dimension relevant, and the associability of A and B was reduced by making other stimuli from the same dimension irrelevant. The associability of the stimuli is attributed to the attention they are paid. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Overexpectation and trial massing.

Three experiments were conducted to examine the interaction of overexpectation treatment and trial massing using a Pavlovian fear conditioning procedure with rats. In first-order conditioning, Experiment 1 found the overexpectation effect (i.e., decreased conditioned responding to a cue after compound training when the elements were previously reinforced), the trial spacing effect (i.e., decreased responding to a cue when reinforced trials are massed), and a counteraction between overexpectation treatment and trial massing (i.e., an alleviation of the decrement in responding seen with overexpectation treatment or trial massing alone when the two treatments are conjointly administered). Experiment 2 replicated Experiment 1 with the critical treatments embedded within a sensory preconditioning preparation. The overexpectation effect, the trial spacing effect, and the mutual counteraction of overexpectation treatment and trial massing all proved significant. In Experiment 3, either the nontarget conditioned stimulus of overexpectation treatment or the excitatory context resulting from trial massing was extinguished. Results are best explained by the extended comparator hypothesis (J. C. Denniston, H. I. Savastano, & R. R. Miller, 2001). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recency-to-primacy shift in cue competition.

Three experiments were conducted using a lick-suppression preparation with rats to determine whether temporal and physical context shifts modulate the effectiveness of 2 sequentially trained blocking stimuli. Experiment 1 ascertained that it is possible to obtain blocking by conditioning rats to react to a target cue using 2 different blocking cues, each trained with a single-phase blocking paradigm. Experiment 2 showed that the more recently trained blocking stimulus was more effective (i.e., showed a recency effect) when testing was conducted immediately after training, but a long retention interval attenuated blocking by the most recently trained blocking stimulus and increased blocking by the initially trained blocking stimulus (i.e., a recency-to-primacy shift). This shift from recency to primacy affected in Experiment 2 by varying the retention interval was replicated in Experiment 3 by changing the physical context between training and testing. Taken together, the results indicate that the effectiveness of sequentially trained competing stimuli follows the same recency-to-primacy shift rule that is seen in traditional interference phenomena. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Potentiation of latent inhibition.

Rats were given exposure either to an odor (almond) or a compound of odor plus taste (almond plus saline), prior to training in which the odor served as the conditioned stimulus. It was found, for both appetitive and aversive procedures, that conditioning was retarded by preexposure (a latent inhibition effect), and the extent of the retardation was greater in rats preexposed to the compound (i.e., latent inhibition to the odor was potentiated by the presence of the taste). In contrast, the presence of the taste during conditioning itself overshadowed learning about the odor. We argue that the presence of the salient taste in compound with the odor enhances the rate of associative learning, producing a rapid loss in the associability of the odor. This loss of associability will generate both overshadowing and the potentiation of latent inhibition that is observed after preexposure to the compound. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The loss of latent inhibition across compound conditioning.

Six experiments used a magazine approach paradigm with rats to investigate latent inhibition (LI). Experiment 1 found that compound conditioning did not increase evidence for LI, in contrast to predictions from acquisition-deficit models that are based on a common error term (e.g., J. M. Pearce & G. Hall, 1980; A. R. Wagner, 1981). Instead, it appeared that preexposed and non-preexposed stimuli conditioned to the same asymptote following compound conditioning, as is the case when these stimuli are conditioned separately. This was confirmed in three further experiments that used probe trials to measure conditioning to each conditioned stimulus across the course of compound training. In these experiments, LI was observed during initial but not extended compound training, consistent with predictions derived from M. E. Bouton (1997) and the SLG model (N. A. Schmajuk, Y. Lam, & J. A. Gray, 1996). However, 2 further experiments did not support these models. Instead, these findings are most consistent with models that use separate error terms to compute the associative strength of conditioned stimuli conditioned in compound (S. E. Brandon, E. H. Vogel, & A. R. Wagner, 2003; M. E. Le Pelley, 2004; N. J. Mackintosh, 1975). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of hippocampal lesions in overshadowing and blocking procedures.

The effects of ibotenic acid lesions of the hippocampus on overshadowing and blocking were examined in a Pavlovian appetitive conditioning experiment with rats. In a standard test of performance to the overshadowed or blocked target stimulus, sham-lesioned rats displayed both of these stimulus-selection phenomena. Rats with hippocampal lesions showed normal blocking, but no overshadowing. Subsequent inhibitory learning about the target stimulus was slower after overshadowing or blocking procedures than after a control procedure in sham-lesioned rats, but not in lesioned rats. These results suggest that exposure to these procedures can induce hippocampally mediated losses in conditioned stimulus associability (learning rate parameter), even when those losses are not a major determinant of the stimulus-selection effects themselves. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Two kinds of attention in Pavlovian conditioning: Evidence for a hybrid model of learning.

Four appetitive Pavlovian conditioning experiments with rats examined the rate at which the discrimination between compounds AY and AX was solved relative to the discrimination between compounds AY and BY. In Experiments 1 and 2, these discriminations were preceded by training in which A and B were continuously reinforced and X and Y were partially reinforced. Consistent with the Pearce and Hall (1980) model, the results showed that the AY/AX discrimination was solved more readily than the AY/BY discrimination. In Experiments 3 and 4, the discriminations were preceded by feature-positive training in which trials with AX and BY signaled food but trials with X and Y did not. Consistent with the Mackintosh (1975) model, the results showed that the AY/BY discrimination was solved more readily than the AY/AX discrimination. These results are discussed with respect to a hybrid model of conditioning and attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Latent inhibition and compound conditioning: A reply to Holmes and Harris (2009).

Schmajuk, Lam, and Gray (SLG, 1996) presented a neural network model of classical conditioning that addresses the multiple properties of latent inhibition (LI). According to the model, LI is the result of the decreased attention to the target stimulus during preexposure and testing. Recently, Holmes and Harris (2009) suggested that, although the model was able to describe their experimental results showing that LI to a preexposed stimulus disappears with extended compound conditioning, it could not describe the fact that LI is not affected by a delay following compound conditioning. However, computer simulations demonstrate that the SLG model describes and explains both results. Because the model also explains both the deleterious and the facilitating effects on LI of a delay following simple conditioning, the SLG model seems unique in explaining the complete range of reported effects of temporal delays on LI as well as most of the properties of LI. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Potentiation and overshadowing in Pavlovian fear conditioning.

The present experiments addressed a fundamental discrepancy in the Pavlovian conditioning literature concerning responding to a target cue following compound reinforced training with another cue of higher salience. Experiment 1 identified one determinant of whether the target cue will be overshadowed or potentiated by the more salient cue, namely contiguity between compound CS termination and US presentation. Overshadowing and potentiation were observed with delay and trace procedures, respectively. Experiments 2 and 3 contrasted elemental and configural explanations of potentiation. Both experiments supported a configural account. Experiments 3 and 4, by manipulating prior learning experiences to bias subjects to encode the same compound elementally or configurally, demonstrated decreased potentiation and overshadowing, respectively. Overall, these experiments demonstrate potentiation with nontaste stimuli and identify one variable that determines whether overshadowing or potentiation will occur. Moreover, they show that prior experiences can determine how a compound is encoded and are compatible with the idea of flexible encoding as a principle of information processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Elemental associability changes in human discrimination learning.

Participants initially completed a discrimination task (D1) involving categorization of patterns with multiple common features, each feature being partly predictive of the correct response. In a subsequent target discrimination task (D2), these features were redistributed across new discriminative stimuli. The relative predictiveness of the features in D1 was either maintained in D2 (i.e., features were equally informative in D1 and D2) or switched (i.e., more informative features in D1 were made less informative in D2, and vice versa). Differential performance on D2 suggested that features most predictive of the correct D1 responses became more highly associable than features that were less predictive in D1. This finding suggests that the associability of individual stimulus elements changes as a consequence of their role in discrimination learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Counteraction between overshadowing and degraded contingency treatments: Support for the extended comparator hypothesis.

Four experiments using rats in a Pavlovian lick-suppression preparation investigated the effects of combining 2 treatments known for their response-decrementing effects, namely, overshadowing and degraded contingency. Contrary to most contemporary learning theories, the extended comparator hypothesis predicts that these 2 treatments will counteract each other, and therefore, less of a decrement in conditioned responding should be observed than with either treatment alone. Experiments 1 and 2 confirmed this prediction in first-order conditioning and sensory preconditioning preparations, respectively. Experiment 3 demonstrated that posttraining extinction of the training context resulted in a recovery from degraded contingency and reversed the counteractive effect on overshadowing. Finally, Experiment 4 demonstrated that posttraining extinction of the overshadowing stimulus resulted in recovery from simple overshadowing and also reversed the counteractive effect on degraded contingency. These results are consistent with the extended comparator hypothesis but not traditional or recent acquisition-focused models. (PsycINFO Database Record (c) 2011 APA, all rights reserved)