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)     

Slow reacquisition following extinction: Context, encoding, and retrieval mechanisms.

Investigated the slow reacquisition (RAQ) of responding in rats that occurs when the conditioned stimulus/stimuli (CS) and unconditioned stimulus/stimuli (UCS) are paired again after prolonged extinction training. In Exp 1, an extinguished CS acquired less suppression than a novel CS during a final conditioning phase, but more suppression than CSs that had received comparable nonreinforcement without initial conditioning. In Exp 2, CS–UCS pairings resumed in the context of extinction caused the least RAQ of suppression: Pairings in a neutral context produced better RAQ, while return of the CS to the conditioning context caused an immediate renewal of responding to the CS. In Exp 3, a return of the CS to the extinction context after RAQ training caused renewed extinction performance and interfered with performance appropriate to RAQ. This effect was not due to demonstrable inhibitory conditioning of the extinction context. Results suggest that representations of conditioning and extinction (or CS–UCS and CS–no UCS relations) are both retained through extinction and that performance appropriate to either phase can be cued by the corresponding context. RAQ may thus be slow when the context retrieves an extinction memory. Similar mechanisms may also play a role in other Pavlovian interference paradigms. (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)     

The comparator hypothesis of conditioned response generation: Manifest conditioned excitation and inhibition as a function of relative excitatory strengths of CS and conditioning context at the time of testing.

Water-deprived rats were used in a conditioned lick suppression paradigm to test and further develop Rescorla's (1968) contingency theory, which posits that excitatory associations are formed when a conditioned stimulus (CS) signals an increase in unconditioned stimulus (US) likelihood and that inhibitory associations develop when the CS signals a decrease in US likelihood. In Exp I we found that responding to a CS varied inversely with the associative status of the context in which the CS was trained and that this response was unaltered when testing occurred in distinctively dissimilar context with a different conditioning history, provided associative summation with the test context was minimized. Results suggest that manifest excitatory and inhibitory conditioned responding is modulated by the associative value of the training context rather than that of the test context. Exp II demonstrated that postconditioning decreases in the associative value of the CS training context reduced the effective inhibitory value of the CS even when testing occurred outside of the training context. This contextual deflation effect was specific to the CS training context. These studies support the comparator hypothesis, which states that conditioned responding is determined by a comparison of the associative strengths of the CS and its training context that occurs at the time of testing rather than at the time of conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exposure to the unconditioned stimulus alone: Effects on retention and acquisition of conditioned suppression.

In 3 experiments with 104 male Sprague-Dawley rats, repeated exposure to an electric-shock UCS resulted in a decrement in retention of conditioned suppression evoked by a previously established excitatory CS and retarded subsequent acquisition of conditioned suppression to a novel CS paired with shock. Exp I showed that 10 sessions of exposure to shock alone were required to produce a decrement in retention of conditioned suppression, whereas retardation in the acquisition of conditioned suppression was obtained following either 5 or 10 sessions of exposure to shock alone. Exp II demonstrated that both of these effects were directly related to the intensity of the shocks. In Exp III, the decrement in retention of conditioned suppression produced by 10 sessions of exposure to shock alone was inversely related to the interval between the last exposure to shock and the test of the target CS. Findings are discussed in terms of associative and nonassociative accounts of the effects of UCS-alone procedures. (29 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)     

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)     

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)     

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)     

Pavlovian and instrumental determinants of response suppression in the pigeon.

Exp I demonstrated the formation of a discriminated punishment effect in the absence of a conditioned emotional response. Electric shocks were delivered at random intervals to 3 naive male White Carneaux pigeons pecking for food on a variable-interval schedule. During a 1-min visual conditioned stimulus (CS), scheduled shocks were delayed until a response occurred (punishment). Differential suppression to the CS was observed in addition to overall suppression. Suppression was related to shock intensity. In Exp II with the same Ss, CS suppression was related to the CS and was not an artifact of response pattern or discrimination of shock patterns. The punishment contingency without the CS did not suppress behavior, and the CS without the punishment contingency did not relieve suppression. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Second-order conditioning and Pavlovian conditioned inhibition: Operational similarities and differences.

Procedures for establishing 2nd-order excitation (CS1-unconditioned stimulus [UCS] trials followed by CS2-CS1 trials) are highly similar to those for Pavlovian conditioned inhibition (CS1-UCS trials interspersed with CS2-CS1 trials). Conditioned suppression in rats was used to identify the critical operational differences that result in 2nd-order excitation as opposed to Pavlovian inhibition. No, few, or many CS2-CS1 trials were either interspersed with or given after CS1-UCS trials. CS2 proved excitatory only after few CS2-CS1 trials, either interspersed or sequential (Exp 1). In contrast, CS2 proved inhibitory on both summation (Exp 2) and retardation (Exp 3) tests only after many CS2-CS1 trials, and then only when the excitatory status of CS1 was preserved. Apparently, the critical difference for establishing 2nd-order excitation or Pavlovian inhibition is the number of CS2-CS1 pairings. (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)     

Within-compound associations modulate the relative effectiveness of differential and Pavlovian conditioned inhibition procedures.

Four conditioned suppression experiments with 98 male albino rats compared the inhibitory strength of a Pavlovian conditioned inhibitory stimulus (CS–) and a differential CS– and identified some postconditioning manipulations that modulate the measured effectiveness of the CS–. In Exp I, more inhibition was detected to a differential inhibitor than to a Pavlovian inhibitor in summation and retardation tests. Exps II–IV provided evidence that some inhibition conditioned to the Pavlovian CS–, but not to the differential CS–, was masked by a within-compound association. In Exp II, postconditioning extinction presentations of the Pavlovian conditioned excitatory stimulus (CS+) increased the inhibition observed to its CS–. In Exp III, postconditioning pairings of the Pavlovian CS+ with a more powerful UCS than that used for conditioning reduced the inhibition observed to its CS–. In Exp IV, nonreinforced postconditioning presentations of the Pavlovian CS– increased the inhibition observed to that CS–. The unmasking and masking of inhibition conditioned to the Pavlovian CS– by operations that modulate the strength of the within-compound association also changed the relative effectiveness of the Pavlovian and differential procedures. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of inflation of the unconditioned stimulus value following conditioning.

Conducted 3 experiments using a conditioned suppression procedure in male Sprague-Dawley rats. Exp I and II (N = 56) found that exposure to a more severe shock either before or after conditioning elevated the CR established by a moderate shock. Exp III (n = 32) found 2nd-order conditioning immune to such modification. These findings parallel earlier results with habituation of the UCS in the absence of the CS. They encourage the view that organisms form memories of the UCS independently of associative connections with the CS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Inhibition as a "slave" process: Deactivation of conditioned inhibition through extinction of conditioned excitation.

In 4 experiments with 176 male albino Sprague-Dawley rats, a conditioned-suppression paradigm was used to investigate why a conditioned inhibition (CS–) does not extinguish when presented alone. Exp I assessed the role of blocking by excitatory contextual cues and/or an evoked representation of the conditioned excitor (CS+), which had been nonreinforced in conjunction with the CS–. When the CS+ and context were extinguished prior to presentations of the CS– alone, the CS– showed a retardation effect, reflecting latent inhibition, because no inhibition was detected in controls for which presentation of the CS– alone had been omitted. Exp II showed that the loss of conditioned inhibition (CI) was due to excitatory extinction and not to time since conditioning. When excitation was reconditioned to the extinguished CS+ (Exp I) or to a novel CS in the same context (Exp II), CI was restored. Exps III and IV evaluated whether the maintenance of CI depended on excitation that was generic in form or associatively tied to the training context. Results indicate no loss of CI when groups received CS+ extinction in that context, with concomitant presentations in a different context of the UCS by itself, for a novel CS, or correlated either positively or negatively with the original CS+. Overall findings suggest that CI is dependent on excitation: When excitation is extinguished, CI is deactivated; when excitation is reconditioned to the original or a new CS+ in the same or a different context, CI is restored. (41 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Stimulus competition between a discrete cue and a training context: Cue competition does not result from the division of a limited resource.

Several associative learning theories explain cue competition as resulting from the division of a limited resource among competing cues. This leads to an assumption that behavioral control by 2 cues competing with each other should always reflect a tradeoff, resulting in apparent conservation of total reinforcer value across all competing cues. This assumption was tested in 3 conditioned lick suppression experiments with rats, investigating the effects of changing the conditioned stimulus (CS) duration (Experiment 1), administering pretraining exposures to the CS (Experiment 2), and presenting nonreinforced CSs during the intertrial interval (Experiment 3) on Pavlovian conditioned responding to both the CS and the conditioning context. Fear conditioned to the context and to the CS decreased when the CS was of longer duration, massively preexposed before being paired with the reinforcer, or presented alone during the intertrial interval. These observations are problematic for the theories that explain cue competition as the division of a limited resource and suggest that the total reinforcer value across competing cues is not always fixed for a given reinforcer. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transfer across unconditioned stimuli in serial feature discrimination training.

The transfer of conditioned modulation across CS and unconditioned stimulus/stimuli (UCS) was examined in 3 experiments that used Pavlovian appetitive training procedures with rats. In Exp 1, after training in a positive patterning discrimination (X→A+/X-/A-), X increased CR elicited by another trained-then-extinguished CS as long as that CS had been trained with the same UCS as was used in discrimination training. In Exp 2, after training with a feature-negative discrimination (X→A-/A+), X inhibited CR elicited by another trained-then-extinguished CS as long as that CS had been trained with the same UCS. Exps 1 and 2 used a between-groups design, and Exp 3 used a within-groups design. In Exp 3, rats were trained in a feature-positive discrimination (X→A+/A-). In transfer tests, X increased CR elicited by another CS trained then extinguished with the same UCS from training. This increase was greater than the X increased CR elicited by another CS trained then extinguished with a different UCS from training. Results supported the suggestion that features trained in serial discrimination tasks influence behavior indirectly by transiently raising or lowering the threshold for activation of the UCS representations by its target stimuli and by any other stimuli that may be associated with that UCS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age-dependent improvement in passive avoidance learning of the young chick: Cholinergic mediation?

Studied cholinergic mediation of the age-dependent improvement in response suppression of the young chick by determining the performance of 144 Vantress?×?Arbor Acre 4-day-old chicks, pretreated with scopolamine (SCO), during passive avoidance (PA) and extinction testing. In Exp I, Ss were trained to keypeck for heat reward (prepunishment training), and then tested for PA learning under immediate, 2-sec-delayed, or no shock condition. Half of the Ss in each condition received saline injections before prepunishment training and .5 mg/kg SCO injections after training. The rest received .5 mg/kg SCO injections both before and after training. For Ss in both SCO groups, delaying shock onset resulted in significantly less response suppression than immediate response-contingent shock. In Exp II, 4-day-old Ss injected with saline or SCO were trained to keypeck for heat reward and then tested for resistance to extinction under response-contingent shock or nonshock conditions. Punishment decreased the number of extinction responses for both saline and SCO groups. Results indicte that the age-dependent improvement in response suppression of the young chick cannot be explained solely by a significant increase in central cholinergic functioning. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An auditory conditioned stimulus modulates unconditioned stimulus-elicited neuronal activity in the cerebellar anterior interpositus and dentate nuclei during nictitating membrane response conditioning in rabbits.

Investigated the effects of the presentation of an auditory conditioned stimulus (CS) on unconditioned stimulus (UCS)-elicited neuronal activity in the anterior interpositus (AIPN) and dentate (DN) nuclei of the cerebellum during the initial stages of classical conditioning of the nictitating membrane (NM) response in rabbits. In Exp 1, a 500-msec CS (but not a 30-msec CS) facilitated UCS-elicited single-unit activity in the AIPN and depressed UCS-elicited activity in the DN during training. In Exp 2, lesions of the AIPN but not of the DN prevented acquisition of conditioned NM responses. The results are interpreted within the framework of a model of classical conditioning that proposes that conditioned neuronal activity that underlies behavioral plasticity develops from the modulation of UCS-elicited neuronal activity by the CS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquired equivalence between cues trained with a common antecedent.

In Exp 1, rats experienced 2 stimuli (A and N) each preceded by the same event (food) or by different events (food preceded 1 but not the other). N was then paired with shock, and the generalization of conditioned suppression to A was assessed. Generalization was more marked when A and N had been experienced along with a common antecedent. In Exp 2, 3 stimuli (A, B, and N) were presented in initial training. For 1 group, A and N were preceded by food and B was not; for a 2nd group A alone was preceded by food. In each group, suppression generalized more readily from N to the stimulus that had received the same initial training as had been given to N. Exp 3 found that generalization was not enhanced between stimuli when 1 had preceded food in initial training and 1 had followed it. These results demonstrate that stimuli that have shared a common antecedent will come to be treated as equivalent. (PsycINFO Database Record (c) 2010 APA, all rights reserved)