Mechanisms underlying retarded emergence of conditioned responding following inhibitory training: Evidence for the comparator hypothesis.

The comparator hypothesis posits that conditioned responding is determined by a comparison at the time of testing between the associative strengths of the conditioned stimulus/stimuli (CS) and stimuli proximal to the CS at the time of conditioning. The hypothesis treats all associations as being excitatory and treats conditioned inhibition as the behavioral consequence of a CS that is less excitatory than its comparator stimuli. Conditioned lick suppression by rats was used to differentiate 4 possible sources of retarded responding to an inhibitory CS. These include habituation to the unconditioned stimulus/stimuli (UCS), latent inhibition to the CS, blocking of the CS-UCS association by the conditioning context, and enhanced excitatory associations to the comparator stimuli. Prior research has demonstrated the 1st 3 phenomena. Therefore, we employed parameters expected to highlight the 4th one—the comparator process. In Exp I, our negative contingency training produced a conditioned inhibitor that passed inhibitory summation and retardation tests. In Exp II we found transfer of retardation from an inhibitory CS to a novel stimulus when the location where retardation-test training occurred was excitatory. In Exp III, extinction of the conditioning context attenuated retardation regardless of whether extinction occurred before or after the CS-UCS pairings of the retardation test. Exp IV demonstrated that habituation to the UCS did not contribute to retardation in the present case. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of contingency violations on the extinction of a conditioned fear inhibitor and a conditioned fear excitor.

In 4 experiments, 192 male Holtzman and Sprague-Dawley rats were used in a conditioned-suppression paradigm to assess the effects of contingency variations on responding to a conditioned stimulus (CS) inhibitor (CS–) and a conditioned stimulus excitor (CS+). In Exp I, various unconditioned stimulus/stimuli (UCS) frequencies were equated across the presence and absence of a CS– in the context of either background cues (continuous-trial procedure) or an explicit neutral event (discrete-trial procedure). With both procedures, a CS-alone treatment enhanced inhibition, whereas treatments involving 50 or 100% reinforcement for the CS– eliminated inhibition without conditioning excitation to that CS. The latter outcome also occurred in Exp II, with discrete-trial training equating considerably reduced UCS frequencies for the presence and absence of the CS–. In further evidence that inhibition was eliminated without conditioning excitation to the CS–, Exp III showed that a novel CS did not acquire excitation when 25, 50, or 100% reinforcement was equated across the presence and absence of that CS in the context of a discrete-trial event. Using the procedures of Exp I, Exp IV showed that a CS+ was extinguished by a CS-alone treatment but was substantially maintained by treatments involving 50 or 100% uncorrelated reinforcement. These effects for a CS+ and a CS– implicate CS–UCS contiguity, rather than contingency, as the factor determining the extinction of a CS. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analysis of the associative and occasion-setting properties of contexts participating in a Pavlovian discrimination.

In 3 conditioned suppression experiments with 64 male Wistar rats, contextual control of performance to a conditioned stimulus (CS) was generated by alternating CS–unconditioned stimulus (UCS) pairings in Context A with CS presentations alone in Context B. Suppression to the CS during discrimination training and during tests of the CS in a 3rd context suggested that Contexts A and B had both acquired an ability to modulate performance. Whether the contexts modulated behavior through their direct associations with the UCS or through their abilities to occasion-set the CS–UCS relation was explored. There was no evidence of direct context–UCS associations in either context. Repeated extinction exposures to Context A following discrimination training did not affect its ability to modulate CS performance. Excitatory conditioning of Context B, however, abolished its ability to modulate. It is suggested that demonstrable context–UCS associations are not necessary for the contextual control of CS performance and that although the parallel is not perfect, contexts share several critical properties with stimuli that occasion-set CS–UCS relations. The possible role of configural conditioning is discussed. (54 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Associative effects of US preexposure: Modulation of conditioned responding by an excitatory training context.

Conducted 2 experiments with 120 naive Sprague-Dawley rats to examine factors that contribute to retarded emergence of conditioned responding to a conditioned stimulus/stimuli (CS) trained in a context in which unsignaled unconditioned stimulus/stimuli (UCS) had previously been administered. In both experiments, water-deprived Ss were used in a conditioned lick suppression task to measure the conditioned response (CR) elicitation potential of the CS and the training context. From Exp I, it was determined that nonreinforced exposure to the excitatory context after UCS preexposure and prior to CS–UCS pairings in that context eliminated the CR deficit observed on a subsequent test of the CS. From Exp II, it was determined that the recovery induced by contextual deflation after CS training was specific to deflation of the context in which the CS was trained as opposed to another excitatory context. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Malleability of conditioned associations: Path dependence.

Using conditioned suppression of barpressing to investigate the stability of a conditioned stimulus–unconditioned stimulus (CS–UCS) association, the present authors gave 151 water-deprived rats either a few pairings of the CS with a strong footshock UCS or many pairings with a weak footshock UCS so that barpress suppression in response to CS was equated. Exp I established training parameters that yielded this equivalence. Specifically, rapid acquisition to a preasymptotic level of responding with strong shock produced suppression comparable to the asymptotic level reached more slowly with weak shock. Exp II showed that although equivalent performance was obtained from extensive conditioning with a weak shock or limited conditioning with a strong shock, only extensive conditioning with weak shock resulted in retarded acquisition of an association between that same CS and a footshock level perceived as midway between the 2 initial training shock intensities as implied by asymptotic performance in Exp I. Exp III demonstrated that the observed retardation in Ss given many conditioning trials with weak shock was CS-specific. It is concluded that the malleability of learned behavior is not simply a function of initial associative strength but is dependent on the path during initial acquisition. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Element pretraining influences the content of appetitive serial compound conditioning in rats.

Examined the effects of prior pairings of conditioned stimulus/stimuli (CS)2 with the unconditioned stimulus/stimuli (UCS) on the nature of the associations formed in CS1?→?CS2?→?UCS serial compound conditioning, in 4 experiments with 72 male and 32 female albino rats. In Exps I and II, prior training of CS2 prevented the acquisition of stimulus–stimulus (S–S) associations between CS1 and stimulus features of CS2 but enhanced the acquisition of stimulus–response (S–R) associations between CS1 and the emotional conditioned response (CR) evoked by CS2. In Exps III and IV, the effects of CS2 pretraining were not due to CS2 training itself, but rather to its endowing CS2 with the ability to evoked a strong CR during the early stages of serial compound conditioning. In Exp III, suppression of the CR to a pretrained CS2 during serial compound conditioning permitted the establishment of S–S associations. In Exp IV, the induction of a CR in the presence of an untrained CS2 during serial compound conditioning prevented the acquisition of S–S associations. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pavlovian second-order conditioned analgesia.

Three experiments, with 118 Sprague-Dawley rats, assessed conditioned analgesia in a Pavlovian 2nd-order conditioning procedure by using inhibition of responding to thermal stimulation as an index of pain sensitivity. In Exp I, Ss receiving 2nd-order conditioning showed longer response latencies during a test of pain sensitivity in the presence of the 2nd-order conditioned stimulus (CS) than Ss receiving appropriate control procedures. Exp II found that extinction of the 1st-order CS had no effect on established 2nd-order conditioned analgesia. Exp III evaluated the effects of post 2nd-order conditioning pairings of subcutaneous morphine sulfate (10–20 mg/kg) and the shock unconditioned stimulus/stimuli (UCS). Ss receiving paired morphine–shock presentations showed significantly shorter response latencies during a hot-plate test of pain sensitivity in the presence of the 2nd-order CS than did Ss receiving various control procedures; 2nd-order analgesia was attenuated. Data extend the associative account of conditioned analgesia to 2nd-order conditioning situations and are discussed in terms of the mediation of both 1st- and 2nd-order analgesia by an association between the CS and a representation or expectancy of the UCS, which may directly activate endogenous pain inhibition systems. (52 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of the rat hippocampal system in several effects of context in extinction.

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 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 (UCS; 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–UCS associations, but not in other types of learning about the context. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rapid reacquisition in conditioning of the rabbit's nictitating membrane response.

Reacquisition after extinction often appears faster than original acquisition. However, data from conditioned suppression studies indicate that this effect may arise from spontaneous recovery and reinstatement of unextinguished contextual stimuli related to the unconditioned stimulus/stimuli (UCS). In the present experiments using the rabbit nictitating membrane preparation, spontaneous recovery was eradicated before reacquisition training. UCS contextual stimuli were controlled by retaining the UCS during extinction through explicit unpairings of the conditioned stimulus/stimuli (CS) and UCS. Attempts were also made to drive the associative strength of the CS into the inhibitory region by differential conditioning and conditioned inhibition procedures. In all cases, reacquisition was very rapid in comparison with a rest control. The results are discussed with respect to their implications for CS and UCS processing models of conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of context in autoshaping.

Three experiments used an autoshaping procedure in 64 female White Carneaux pigeons to investigate the conditioning of the context and of a discrete CS with a food UCS. CS–UCS associations were measured by directed pecking at the key light CS; context–UCS associations were assessed by general activity in the context. Exp I investigated the influence of context–UCS associations on performance to a previously trained CS. The same CS produced greater keypecking in a context of higher associative strength. Exp II examined the influence of context–UCS associations on learning of CS–UCS associations. When tested in a context of fixed associative strength, a CS that had been trained in a context of high associative strength elicited less responding than one trained in a context of low associative strength. Exp III found that signaling a UCS by a discrete CS interfered with the formation of context–UCS associations, as measured both in terms of general activity and ability to promote responding to another CS. Results suggest that the context and the CS compete for association with the UCS. They also suggest that context–UCS associations facilitate the exhibition of CS–UCS associations. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of context on performance to conditioned stimuli with mixed histories of reinforcement and nonreinforcement.

Five conditioned suppression experiments, with 160 Wistar rats, explored the role of the conditioning history of the conditioned stimulus (CS) in determining the effects of contextual fear on performance to the CS. Contextual fear was produced by postconditioning exposure to unconditioned stimulus/stimuli (UCS) alone in the context of conditioning; it was independently assessed with context-preference tests. When the number of reinforced and nonreinforced trials was equated across extinction, partial reinforcement, and latent inhibition procedures, only the extinction procedure produced a CS whose performance was subsequently affected (i.e., augmented) by contextual fear. Contextual fear's relatively unique augmenting effect on fear of an extinguished CS was abolished by extensive, but not by less extensive, reacquisition training. Results indicate that, depending on the CS's conditioning history, contextual fear either augments or has little effect on fear of the CS. It is suggested that augmentation by context should be viewed as the restoration of fear that is otherwise depressed by extinction. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal dynamics of the rabbit's nictitating membrane response in serial compound conditioned stimuli.

Two experiments, with 88 female albino rabbits, investigated conditioning of the nictitating membrane response to a reinforced serial compound stimulus. The serial compound was composed of a 400-msec CS (CSA), a trace interval of at least 2 sec, and a brief 2nd CS (CSB) prior to the UCS. The CSB duration was either 150, 250, or 400 msec in Exp I, and the CSB duration in Exp II was 400 msec. Exp I compared serial compound training to an "uncoupled" condition, which contained intermixed CSA–UCS trials and CSB–UCS trials. Exp II compared serial compound training with uncoupled training, 2nd-order conditioning (CSA–CSB/CSB–UCS), trace conditioning (CSA–UCS), and generalization testing that entailed CSB–UCS training and unreinforced tests with CSA. The serial compound, uncoupled, and 2nd-order conditioning procedures all produced high levels of responding during CSA, but only the reinforced serial compound procedure yielded an appreciable likelihood of CR initiation during the trace interval between CSA and CSB. The CRs during the trace interval were temporally distinct from the CRs during CSA and did not appear to be belated CRs to CSA itself. Results are discussed in connection with stimulus selection phenomena, for example, overshadowing and potentiation of toxicosis conditioning. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simultaneous conditioning in honeybees (Apis mellifera).

Honeybees were classically conditioned with odor as conditioned stimulus/stimuli (CS), sucrose as unconditioned stimulus/stimuli (UCS), and proboscis extension as response. The purpose of Exp 1 (Ns?=?26 and 27) was to look for facilitation of forward conditioning by CS–UCS overlap, but rapid conditioning without overlap left little room for improvement. In 2 further experiments, CS and UCS were simultaneous, and response to odor alone was measured in subsequent tests. In Exp 2, a simultaneous group (N?=?25) responded more to the training odor than did an unpaired control group (N?=?25). In Exp 3, a differentially conditioned simultaneous group (N?=?29) responded more to an odor paired with sucrose in training (S+) than to an odor presented alone (S–). The implications of the results for the problem of the role of amount of reward in honeybee learning are considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition of conditioned associations in Hermissenda: Additive effects of contiguity and the forward interstimulus interval.

Examined conditioned suppression of photokinesis (CSPK) by the marine mollusc in 3 experiments. In each experiment, groups of Ss received light (conditioned stimulus, CS) paired with high-speed orbital rotation (unconditioned stimulus, UCS), light and rotation explicitly unpaired, or no exposure to these stimuli. 24 hrs after training, all Ss were tested for CSPK in the presence of the light. 50 CS–UCS pairings resulted in a marginal CSPK, whereas 100 and 150 pairings produced strong CSPK. In Exp 2, delay between CS onset and UCS onset was varied between 1 and 10 s. The 10-s interstimulus interval (ISI) did not support conditioning, whereas 1-s and 2-s ISIs were effective. In Exp 3, CS–UCS pairings in which the CS preceded the onset of the UCS and ended with the offset of the UCS evoked stronger CSPK than either a CS that preceded the UCS and ended with its onset or a CS that was paired in simultaneous compound with the UCS. CS–UCS contiguity and the forward ISI act additively to establish the CS–UCS association. No differences were observed between groups that were untreated and that received the CS and UCS unpaired. Similarities are noted in the temporal characteristics of associative learning in these Ss and vertebrate species. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of signaling intertrial unconditioned stimuli in autoshaping.

Context–UCS associations have been suggested as the mediator of the response decrement that occurs when extra UCSs are added to the intertrial intervals (ITIs) of a standard Pavlovian conditioning situation. The present autoshaping experiments were concerned with the effect of signaling those extra UCSs, since such signaling might be expected to lessen their ability to condition the context. In Exp I, 16 female Carneaux pigeons were trained in Skinner boxes before receiving pretraining with the CS to be used as the signal of the ITI UCSs. During the main training, Ss were given autoshaping with a keylight CS. Exp II used a tone CS with 31 Ss. Results show that signaling the ITI UCSs did reduce their detrimental effects in responding to the CS. To determine whether that reduction was due to an impact of signaling on the target-CS/UCS association or on performance to the target-CS, Exp III examined responding to differentially trained CSs in a common context, as well as responding to identically trained CSs in differentially trained contexts with 32 Ss. More responding occurred to the CS trained with signaled, as compared with unsignaled, ITI UCSs; further, there was more responding to that CS in the more highly valued context. Results suggest that contextual value does interact with CS–UCS learning and may also affect performance to the CS. (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Associative regulation of Pavlovian fear conditioning: Unconditioned stimulus intensity, incentive shifts, and latent inhibition.

Conditional stimuli (CS) associated with painful unconditional stimuli (UCS) produce a naloxone-reversible analgesia. The analgesia serves as a negative-feedback regulation of fear conditioning that can account for the impact of UCS intensity and CS predictiveness on Pavlovian fear conditioning. In Exp 1, training under naloxone produced learning curves that approached the same high asymptote despite UCS intensity. Shifting drug treatment during acquisition had effects that paralleled UCS intensity shifts. In Exp 3, naloxone reversed Hall-Pearce (1979) negative transfer using a contextual CS, indicating that conditional analgesia acquired during the CS–weak-footshock phase retards acquisition in the CS–strong-footshock phase. Exp 5 used a tone CS in both a latent-inhibition and a negative-transfer procedure. Only negative transfer was blocked by naloxone. Therefore, negative transfer but not latent inhibition is mediated by a reduction of UCS processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Responding to a conditioned stimulus depends on the current associative status of other cues present during training of that specific stimulus.

The comparator hypothesis is a response rule stating that responding to a Pavlovian conditioned stimulus/stimuli (CS) reflects the associative strength of the CS relative to that of other cues (comparator stimuli) that were present during CS training. Thus, modulation of the associative strength of a CS's comparator stimulus should alter responding to that CS. These studies examined the stimulus specificity of this effect using within-Ss designs. Rats were trained on 2 CSs, each with a unique comparator stimulus, to determine the degree to which posttraining extinction of the comparator stimulus for one CS influences responding to the other CS. Using negative contingency (Exps 1 and 2), overshadowing (Exp 3), and local context (Exp 4) preparations, stimulus specificity was observed. In each case, posttraining extinction of the comparator stimulus for one CS had greater impact on responding to that CS than on responding to the alternate CS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cerebellar stimulation as an unconditioned stimulus in classical conditioning.

Implanted rabbits with chronic stimulating electrodes in white matter underlying lobule HVI of the cerebellar cortex. Stimulation elicited movements of the face or neck and, when paired with a tone CS, produced learning comparable to that seen with peripheral unconditioned stimulus/stimuli (UCS). CS-alone trials produced extinction. Reinstatement of paired trials produced reacquisition with savings. Additional groups received either explicitly or randomly unpaired CS–UCS trials before paired conditioning. Low-frequency responding during these sessions indicated that the paired training results were associative and not due to pseudoconditioning or sensitization. Explicitly unpaired sessions retarded learning on subsequent paired trials compared with groups that received either randomly unpaired or no CS–UCS preexposure. These results are interpreted in terms of the role of the cerebellum and associated pathways in classical conditioning of motor responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Excitatory conditioning of individual Drosophila melanogaster..

Demonstrated, in 5 studies, conditioning of the proboscis extension reflex in D. melanogaster. The presentation of paired (conditioning) stimuli produced (a) an increase in the average number of conditioned responses (CRs) over trials, (b) measured differences in performance levels among individual Ss, and (c) greater conditioning among males than females. The presentation of unpaired (control) stimuli produced significantly lower average levels of acquisition responding and a change in the distribution of individual response patterns. Neither central excitatory state nor sensitization induced by the conditioned stimulus/stimuli (CS) or the unconditioned stimulus/stimuli (UCS) directly affected the CR, whereas UCS preexposure adversely affected performance levels. Presenting the unpaired (extinction) stimuli after conditioning produced less of a decline in responding than did an extinction procedure with removal of the UCS. With the ability to identify individual differences in acquisition and extinction patterns, and given the relatively large samples that can be tested simultaneously on the automated stimulation apparatus, it is suggested that it is now possible to make precise behavioral measurements for the behavior-genetic analysis of D. melanogaster with conditioning as the phenotype. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)