Complete suppression to a compound CS does not block further conditioning to each element.

In 2 of 3 experiments studying conditioned suppression, 54 male hooded rats were initially given a small number of tone-shock and light-shock trials sufficient to produce complete suppression to the tone-light compound. According to a model proposed by R. A. Rescorla and A. R. Wagner in 1972, if a compound conditioned stimulus produces asymptotic suppression, no further conditioning will occur to either element when further reinforced trials are given with the compound. Although R. A. Rescorla has reported some evidence supporting this prediction, in both the present experiments Ss given further reinforced training with the tone-light compound showed significant increments in conditioning to each element. In the 3rd experiment 24 male hooded rats were given a larger number of noise-shock and light-shock trials, followed by reinforced noise-light compound trials. Additional reinforcement of the compound did not lead to a change in the associative strength of each element, although the model proposed by Rescorla and Wagner predicts that associative strength should decrease following such training. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Associative Change in the Representations Acquired During Conditional Discriminations: Further Analysis of the Nature of Conditional Learning.

Three experiments with rats investigated how the associative strengths of the representations that underlie conditional learning change when they are conditioned in compound. The results of each experiment suggest that the representation whose associative strength is most discrepant from the asymptote supported by the outcome of the trial undergoes the greatest change in associative strength. These results parallel those from simple Pavlovian conditioning (e.g., R. A. Rescorla, 2000). are inconsistent with unique-cue and configural accounts of conditional learning, and support a connectionist analysis of learning in which a "winner-takes-all" rule applies to the hidden units that can be activated and acquire associative strength at a given point in time. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Effect of classical conditioning on an internal clock.

Six experiments with 53 male Charles River rats used a psychophysical choice procedure to study the internal clock used to discriminate duration and to investigate whether this clock is sensitive to the signal value (associative strength) of a stimulus. The experiments involved 2 types of trials: On choice trials, a stimulus lasted a short (e.g., 3-sec) or long (e.g., 12-sec) duration; Ss then chose between 2 levers. The rewarded choice depended on the duration of the stimulus. On conditioning trials, the stimulus used on choice trials was presented, but it ended without food (extinction trials) or with food (pairing trials) regardless of what the S did. The main measure of performance was short bias, defined as accuracy with the short stimulus without a corresponding accuracy with the long stimulus. Exp I showed that extinction trials increased short bias relative to training without conditioning trials or to training with pairing trials. Exps II–VI tested explanations of these results. The same results were found when extinction trials were the same duration as the short stimulus (Exp II), when extinction trials were a random duration (Exp V), and when the signal value of the CS was changed in another way (Exp VI). The effect of conditioning trials was modality specific (Exps III and IV). It is concluded that, of the explanations considered, the most valid is that changing the signal value of a stimulus changes how the clock times the stimulus. Reducing signal value reduces the measured duration. (54 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Unblocking in Pavlovian fear conditioning.

Six experiments used rats to study blocking and unblocking of fear learning. An excitatory stimulus (A) blocked fear learning to a neutral stimulus (B). Unblocking of B occurred if the AB compound signaled an increase in unconditioned stimulus (US) intensity or number. Assessments of associative change during blocking showed that more was learned about B than A. Such assessments during unblocking revealed that more was learned about B than A following an increase in US intensity but not US number. These US manipulations had no differential effects on single-cue learning. The results show that variations in US intensity or number produce unblocking of fear learning, but for each there is a different profile of associative change and a potentially different mechanism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some factors that determine the influence of a stimulus that is irrelevant to a discrimination.

In 5 autoshaping experiments pigeons received 3 stimuli, A, B, and C, for a discrimination in which food was presented after the simultaneous compounds AC and BC, but not after the simultaneous compound ABC. The ease with which this discrimination was mastered was facilitated by presenting C continuously throughout each session (Experiment 1), by presenting C by itself for nonreinforced trials (Experiment 2), and by pairing C by itself consistently with food (Experiment 3). Presenting C by itself and pairing it with food according to a partial reinforcement schedule had no significant influence on the acquisition of the discrimination (Experiments 4 and 5). The results are consistent with a configural theory of associative learning that suggests that experience with a stimulus alters its salience. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioning of stimuli with nonzero initial value.

In five experiments, rats received conditioning of either moderately attractive or moderately aversive flavors using either a strongly negative lithium chloride (LiCl) or a strongly positive Polycose as the reinforcer. In each case, testing was done with a compound of the two moderately valued stimuli to determine the amount of associative change produced by the pairing. In both within-subject and between-subjects designs, the amount of associative change was greater for a signal whose moderate value was opposite in valence from that of the reinforcer. This suggests that, like learned stimulus value, inherent stimulus value can modulate further associative learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Blocking during serial feature-positive discriminations: Associative versus occasion-setting functions.

Previous work indicates that during serial feature-positive discriminations (i.e., feature–trace interval/common element/food presentations and separate nonreinforced common element presentations) the feature (A) acquires an association with food (unconditioned stimulus [UCS]) and also a capacity to modulate the common element (X)–UCS relation, which has been termed occasion setting (OS). In the present 2 experiments with 32 male Sprague-Dawley rats, a blocking design, serial feature-positive discrimination procedures, and a behavioral observation technique were used to assess the relation between associative and OS functions acquired by stimuli. In Exp I, prior conditioning of associative and OS functions to A blocked acquisition of both stimulus functions by a novel stimulus (B) trained in compound with A. In Exp II, prior acquisition of an A–UCS association blocked acquisition of a B–UCS association but had no effect on acquisition of B's OS function. These outcomes are discussed (a) as indicating that associative and OS functions are independent and may be based on separate learning processes, (b) as extending the known conditions for acquisitions of OS, and (c) with regard to the theoretical implications of assuming independence of associative OS functions acquired by stimuli. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Involvement of the retrosplenial cortex in processing multiple conditioned stimuli.

Lesions of retrosplenial cortex (RSP) disrupt spatial and contextual learning, suggesting that RSP may have a fundamental role in processing overlapping, or simultaneously presented stimuli. If so, then RSP lesions might also be expected to disrupt learning that requires the concurrent processing of phasic conditioned stimuli. In Experiment 1, rats were trained in a compound feature negative discrimination task in which a tone was presented and immediately followed by food on some trials, while on other trials a visual stimulus was simultaneously presented along with the tone and not reinforced. Normal rats learned to discriminate between the trials but RSP-lesioned rats exhibited low levels of conditioning on both types of trials. Experiment 2 demonstrated that this effect was not simply due to a general inability to form associations, since RSP-lesioned rats exhibited normal responding when the visual stimulus was presented alone and paired with food. These findings support the view that RSP has an important role in learning that involves the processing of simultaneously presented stimuli and have implications for understanding the functional relationship between the hippocampus and RSP. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

"Configural" conditioning in discrete-trial bar pressing.

Conducted 3 experiments with a total of 64 male Sprague-Dawley rats to compare responses to stimulus compounds and their elements. No loss was found when Ss responded to the elements of a repeatedly reinforced stimulus compound. When Ss were explicitly trained to discriminate between a compound and its elements, successful learning occurred regardless of whether the compound or the elements were reinforced. Addition of an explicit stimulus common to the compound and its elements retarded rather than facilitated the discrimination. Replacement of 1 element in a compound by another of similar intensity and associative strength disrupted performance. Findings rule out a number of interpretations of AB configural conditioning paradigms, but suggest that there is a unique stimulus element and limitations on the total associative strength of the compound. (16 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Averaging of temporal memories by rats.

Rats were trained on a mixed fixed-interval schedule in which stimulus A (tone or light) indicated food availability after 10 s and stimulus B (the other stimulus) indicated food availability after 20 s. Testing consisted of nonreinforced probe trials in which the stimulus was A, B, or the compound AB. On single-stimulus trials, rats responded with a peak of activity around the programmed reinforced time. On compound-stimulus trials, rats showed a single scalar peak of responding at a time midway between those for stimulus A and B. These results suggest that when provided with discrepant information regarding the temporal predictability of reinforcement, rats compute an average of the scheduled reinforcement times for the A and B stimuli and use this average to generate an expectation of reward for the compound stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transfer of configural learning between the components of a preexposed stimulus compound: Implications for elemental and configural models of learning.

In 2 experiments, rats received preexposure to 2 compound contexts: AB and CD for the congruent group and AC and BD for the incongruent group. Subsequently, all rats received a configural discrimination in which separate placement in contexts A or B indicated that presentations of stimulus X would be followed by food and presentations of Y would not, and separate placement in contexts C and D indicated that Y would be followed by food and X would not. In both experiments, rats in the congruent group acquired the conditional discrimination more rapidly than those in the incongruent group. These results are inconsistent with conventional associative accounts of either stimulus preexposure effects or configural learning and instead provide support for a connectionist account. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simultaneous backward conditioned inhibition and mediated conditioning.

Demonstrations of retrospective revaluation suggest that remembered stimuli undergo a reduction in association with the unconditioned stimulus (US) present during learning. Conversely, demonstrations of mediated conditioning in flavor-conditioning experiments with rats suggest that remembered stimuli undergo an increase in association with the US present during learning. In a food allergy prediction task with 23 undergraduates, we demonstrated simultaneous backward conditioned inhibition and mediated conditioning effects. These results are compatible with the hypothesis that the direction of change (decrease or increase) in associative strength depends on whether the remembered stimulus was of a different category (conditioned stimulus/antecedent) or the same category (US/outcome) as the presented US. (PsycINFO Database Record (c) 2011 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)     

Trial spacing is a determinant of cue interaction.

Four conditioned lick suppression experiments with rats examined the effect of trial spacing on cue interaction. Experiments 1 and 2 found overshadowing to be eliminated with massed compound stimulus- outcome pairings and the usual trial spacing effect to be reversed with compound acquisition trials. Experiment 3 found that whether acquisition compound- outcome pairings were massed or spaced determined the effect of posttraining extinction treatment. Extinction of the overshadowing cue reduced responding following massed training and increased responding following spaced training. Extinction of the context decreased responding following massed training. Experiment 4 found the conditioning and devaluation results to be associative and stimulus specific. These results are in accord with the extended comparator hypothesis (J. C. Denniston, H. I. Savastano, & R. R. Miller, 2001). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Associative changes in excitors and inhibitors differ when they are conditioned in compound.

When an AB stimulus compound is reinforced or nonreinforced, there are associative changes in both A and B elements. In many contemporary theories those changes are viewed as governed by a common error term, computed as the discrepancy between the total associative strength of the AB compound and that supported by the trial consequence. This implies that if A and B are equally salient, then the magnitude of their associative change should be the same, whatever their strengths prior to the AB trial. This implication was explored for a compound consisting of an excitatory A and an inhibitory B. A novel assessment procedure avoided the difficulty of making comparisons at different locations on the performance scale. Three experiments using a magazine approach preparation in rats and 3 using autoshaping in pigeons found evidence contradicting this implication. The excitatory A changed less than the inhibitory B when the compound was reinforced but more than B when the compound was nonreinforced. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Supernormal conditioning.

In Experiment 1, rats received an A+AX° discrimination in which food was presented after Stimulus A by itself but not after a simultaneous compound of A with Stimulus X. AX was then paired with food in a 2nd stage, followed by test trials with A alone. Responding on the test trials with A was more vigorous than during a control stimulus that had been consistently paired with food. The remaining experiments were of similar design to Experiment 1, except that the 2nd stage also contained conditioning trials with X. The results from the test trials were essentially the same as for Experiment 1. The high level of responding during the test trials with Stimulus A is regarded as evidence of supernormal conditioning. Overall, the results are more consistent with a configural than an elemental theory of conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence for "unique stimulus" account of configural conditioning.

Conducted 4 experiments with male Sprague-Dawley rats (N = 80) testing the proposition that a compound stimulus, AB, may be conceptualized as composed of the individual A and B elements as well as a separate stimulus unique to their combination. Together with an assumption about limitations on the total associative strength of the compound, this conceptualization can account for the learning of various configural conditioning paradigms. Each experiment examined whether the hypothesized unique stimulus has properties like those of a separable element. Results indicate that, like the separate elements, the unique stimulus can acquire associative strength which is either excitatory or inhibitory, which summates with other associative strengths, which influences the effectiveness of reinforcement and nonreinforcement, and which is attenuated when the unique stimulus becomes irrelevant to reinforcement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simultaneous temporal processing.

Seven studies assessed the ability of 36 male albino Norway rats to process temporal information from 2 internal clocks simultaneously and independently. In the 1st 6 experiments, a light stimulus signaled an overall interval (OI) between the beginning of a trial and the availability of food reinforcement; a sound stimulus was used to signal shorter intervals that divided the OIs into equal segments. When there was a fixed temporal relation between the final segment signal and the availability of reinforcement, there was a double-scallop pattern of responding throughout the segmented OI; the function relating response rate (FRRR) to time during the segment intervals was similar to the FRRR to time in unsegmented OIs; a change in response rate occurred at the time that a normally presented segment signal was omitted. Results show that Ss timed the OI and the segment intervals simultaneously and independently without interference. In Exp VII, a light stimulus was used on some trials and a sound stimulus was used on others to signal a discrete-trial 50-sec peak procedure. When these 2 signals were presented in compound, there was a leftward shift of the response function that suggested that Ss timed both signals simultaneously. (81 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of context on responding during a compound stimulus.

In 4 experiments, the authors used rats to examine the strength of responding during a clicker-tone compound in the presence of a light, after the auditory stimuli had individually been paired with food in the presence of the same light. Experiment 1 demonstrated a higher rate of responding during the compound when the duration of the light was short rather than long. In Experiments 2, 3, and 4, the long duration light was used as a signal for food in a conditional discrimination involving the tone and the clicker. Responding on test trials with the clicker-tone compound during the light was enhanced by this treatment and resulted in a level of performance that was no different from that observed when the duration of the light was short. The results are more compatible with a configural than an elemental theory of associative learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned inhibition in the spatial domain.

Using a variation on the standard procedure of conditioned inhibition (Trials A+ and AX?), rats (Rattus norvegicus) in a circular pool were trained to find a hidden platform that was located in a specific spatial position in relation to 2 individual landmarks (Trials A → platform and B → platform; Experiments 1a and 1b) and to 2 configurations of landmarks (Trials ABC → platform and FGH → platform; Experiment 2a). The rats also underwent inhibitory trials (Experiment 1: Trials AZ → no platform; Experiment 2a: Trials CDE → no platform) interspersed with these excitatory trials. In both experiments, subsequent test trials without the platform showed both a summation effect and retardation of excitatory conditioning, and in Experiment 2a rats learned to avoid the CDE quadrant over the course of the experiment. Two further experiments established that these results could not be attributed to any difference in salience between the conditioned inhibitors and the control stimuli. All these results contribute to the growing body of evidence consistent with the idea that there is a general mechanism of learning that is associative in nature. (PsycINFO Database Record (c) 2010 APA, all rights reserved)