Conditioned suppression, punishment, and aversion

Three experiments were conducted to assess the aversive properties of a visual stimulus in the presence of which one group of birds received response-contingent shock (discriminated punishment) while a yoked group of birds received non-contingent shocks (conditioned suppression). In Experiment 1, presentation of the visual stimulus contingent on key pecking reduced the response rate (conditioned punishment effect) for birds under the conditioned suppression procedure but did not reduce the response rate of birds under the discriminative punishment procedure. Non-contingent shocks also produced greater suppression of responding maintained by positive reinforcement in the presence of a visual stimulus than did response-contingent shocks. In Experiment 2, a greater shock intensity (2 mA) was used. All the differences between the two groups found in Experiment 1 were also found in Experiment 2. Experiment 3 demonstrated that response-contingent shock did not result in a conditioned punishment effect even when positive reinforcers were unavailable during the discriminative punishment schedule. The exteroceptive stimulus that was paired with shock in the conditioned suppression procedure acquired the ability to punish behavior. The exteroceptive stimulus in the discriminative punishment schedule did not acquire this ability.     

Some types of conditioned inhibitors carry collateral excitatory associations

Two experiments using summation tests in conditioned suppression with rats examined whether conditioned inhibitors generated by five different conditioning procedures have an associative structure which includes collateral excitatory associations. The existence of collateral conditioned excitation was inferred from an increase in the amount of manifest conditioned inhibition after a conditioned inhibitory stimulus (CS-) extinction treatment. The five CS-s evaluated were differential, explicitly unpaired, conditional, backward, and trace. With abbreviated conditioning (Experiment 1), the differential and explicitly unpaired CS-s exhibited conditioned inhibitory properties; the conditional, backward, and trace CS-s did not. Repeated extinction presentations of the CS- in the absence of the unconditioned stimulus unmasked conditioned inhibition to the conditional, backward, and trace CS-s revealing moderate degrees of conditioned inhibition for all five CS-s. After more extensive conditioning (Experiment 2), the explicitly unpaired and conditional CS-s were strongly inhibitory and the differential and trace CS-s were moderately inhibitory. The backward CS- was not inhibitory. Repeated presentations of the CS- in extinction unmasked conditioned inhibition to trace and backward CS-s. All five CS-s were now nearly equally inhibitory. That the measured inhibitory power of backward, trace, and conditional (after few trials) CS-s can be modulated by a CS- extinction treatment suggests that they have similar associative structures and carry, in addition to inhibitory associations, collateral excitatory associations that mask the expression of conditioned inhibition.     

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

Rats were used in a conditioned-suppression paradigm to assess the effects of contingency variations on responding to a conditioned inhibitor (CS-) and a conditioned excitor (CS+). In Experiment 1, various unconditioned stimulus (US) 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 Experiment 2, with discrete-trial training equating considerably reduced US frequencies for the presence and absence of the CS-. In further evidence that inhibition was eliminated without conditioning excitation to the CS-, Experiment 3 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 Experiment 1, Experiment 4 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-US contiguity, rather than contingency, as the factor determining the extinction of a CS.     

Role of the hippocampus in blocking and conditioned inhibition of the rabbit's nictitating membrane response.

Bilateral aspiration of the dorsal hippocampus produced a disrupttion of blocking of the rabbit's nictitating membrane response in Kamin's two-stage paradigm (Experiment 1) but had no effect on the formation of a Pavlovian conditioned inhibitor (Experiment 2). The results of Experiment 1 indicated that normal animals and those with cortical lesions given conditioning to a light-plus-tone conditioned stimulus (CS) gave conditioned responses (CRs) to both the light and the tone during nonreinforced presentations of each (test phase). If, however, compound conditioning was preceded by tone acquisition, only the tone elicited a CR during testing; that is, blocking was observed. In rabbits with hippocampal lesions, however, CRs were given to both the light and the tone during testing whether or not compound conditioning was preceded by tone acquisition. The data from Experiment 2 showed that rabbits with hippocampal lesions could discriminate as well as normal rabbits and those with cortical lesions between a light (CS+) and light plus tone (CS-). In addition, when the inhibitory tone was subsequently paired with the unconditioned stimulus in retardation testing, animals in all three lesion conditions acquired the CR at the same rate. Thus, it appears that hippocampal lesions do not disrupt conditioned inhibition. The results of these experiments were taken as support for the view that the hippocampus is responsible for "tuning out" stimuli that have no adaptive value to the organism.     

Discriminative conditioning alters food preferences in the leech, Haemopis marmorata

The feeding behavior of the carnivorous leech, Haemopis marmorata, was aversively trained in a discriminative classical conditioning task. Two conditioned stimuli were used: One consisted of a food (chicken or liver) paired with an unconditioned stimulus of quinidine (bitter chemical); the other consisted of the alternate food presented in an unpaired relationship with the quinidine. Training consisted of alternating exposures to the two conditioned stimuli. Testing consisted of the simultaneous presentation of a conditioned stimulus food and a neutral food, beef. The percentages of responding to the conditioned stimuli were tabulated. Haemopis could discriminate between the conditioned stimuli. As a result of pairing a food with quinidine, the leeches selectively reduced their preference for that paired food, while they did not alter their preference for the unpaired food.     

Emotional conditioning to masked stimuli and modulation of visuospatial attention

Two studies investigated the effects of conditioning to masked stimuli on visuospatial attention. During the conditioning phase, masked snakes and spiders were paired with a burst of white noise, or paired with an innocuous tone, in the conditioned stimulus (CS)+ and CS- conditions, respectively. Attentional allocation to the CSs was then assessed with a visual probe task, in which the CSs were presented unmasked (Experiment 1) or both unmasked and masked (Experiment 2), together with fear-irrelevant control stimuli (flowers and mushrooms). In Experiment 1, participants preferentially allocated attention to CS+ relative to control stimuli. Experiment 2 suggested that this attentional bias depended on the perceived aversiveness of the unconditioned stimulus and did not require conscious recognition of the CSs during both acquisition and expression.     

Duration of signals for intertrial reinforcement and nonreinforcement in random control procedures

In the random control procedure, responding to a conditioned stimulus (target CS) is prevented when the probability of unsignaled, unconditioned stimuli (USs) in the intertrial interval (ITI) is equal to the probability of the US in the presence of the target CS. Three experiments used an autoshaping procedure with White Carneaux pigeons to examine the effects of the temporal duration of signals for the ITI USs (cover CSs) and for concomitant periods of nonreinforcement. In Experiment 1, a short duration cover, but not a long duration cover, resulted in responding to the target CS. In Experiment 2, an explicit CS- cue during periods of nonreinforcement did not affect target acquisition. In Experiment 3, a long CS-, but not a short cover CS, was a sufficient condition for the acquisition of responding to the target CS. These results imply that the acquisition of responding to a target CS requires a discriminable period of nonreinforcement that is long relative to the target CS duration.     

Differential acquisition, extinction, and reinstatement of conditioned suppression in mice

In animals, the reappearance of conditioned fear responses after extinction has been primarily investigated using single-cue conditioning paradigms. However, a differential paradigm can overcome several of the disadvantages associated with a single-cue procedure. In the present study, the reinstatement phenomenon was assessed in mice using a differential conditioned suppression paradigm. In a first phase, one conditioned stimulus (CS + ) was consistently paired with an unconditioned stimulus (US; footshock) while another CS (CS-) was not, resulting in selective suppression of previously trained instrumental behaviour during the CS + . After the extinction phase, half of the animals (reinstatement group) were presented with unsignalled USs, while the other half were not (control group). A differential return of conditioned responding was observed in the reinstatement group, but not in the control group. The implications of these findings for future conditioning research are discussed.     

Flavor preexposures in a conditioned taste aversion situation: a dissociation of behavioral and endocrine effects in rats

A series of experiments examined the effects of flavor preexposures on pituitary-adrenal/behavior relations in a conditioned taste aversion paradigm. It was found that reexposure to a novel milk solution paired earlier with lithium chloride (LiCl) elicited conditioned activation of the pituitary-adrenal system (Experiment 1). The unconditioned response to LiCl (measured by changes in plasma levels of corticosterone) did not vary as a function of prior (2 and 5 vs. 10) exposures to the milk solution (Experiment 2). Increased familiarity with the substance (resulting from 10 prior exposures) rendered the conditioning of a taste aversion to this substance less effective. Further, reexposure to this familiar substance after its pairing with LiCl was not accompanied by the characteristic conditioned pituitary-adrenal activation (Experiment 3). By titrating the number of conditioned stimulus (CS) preexposures (Experiment 4) it was found that within the range of preexposures manipulated (5-10), subjects exhibited (a) a coupling of behavioral and pituitary-adrenocortical responses when the conditioned taste aversion to the milk solution was paralleled by elevated plasma corticosterone (5-6 preexposures), (b) a coupling of these two response systems when flavor consumption was accompanied by suppressed plasma titers of corticoids (9-10 preexposures), or (c) a dissociation of the two system when the conditioned taste aversion was not accompanied by conditioned adrenocortical activity (7-8 preexposures). These data are discussed in terms of a dissociation in the effects of CS preexposures on conditioned adrenocortical and behavioral response systems.     

Potentiation of the acoustic startle response by a conditioned stimulus paired with acoustic startle stimulus in rats

The hypothesis that the standard acoustic startle habituation paradigm contains the elements of Pavlovian fear conditioning was tested. In a potentiated startle response paradigm, a startle stimulus and a light conditioned stimulus (CS) were paired. A startle stimulus then was tested alone or following the CS. Freezing behavior was measured to index conditioned fear. The startle response was potentiated on CS trials, and rats froze more in CS than in non-CS periods. In Experiment 1, response to a previously habituated, weak startle stimulus was potentiated. In Experiment 2, response to the same stimulus used as the unconditioned stimulus (US) in training was potentiated. This CS-potentiated response retarded the course of response decrements over training sessions as compared with an explictly unpaired control group. Conditioned fear is a standard feature of this habituation paradigm, serves to potentiate the startle response, and provides an associative dimension lacking in the habituation process per se.     

Changes in pain reactivity induced by unconditioned and conditioned excitatory and inhibitory stimuli

In three experiments we investigated the effects of aversive-conditioning components on the reactivity of rats to pain. After training in Experiment 1 with a discrete conditioned stimulus (CS) for a shock unconditioned stimulus (US), different groups were exposed to the CS, US, CS/Us compound, just the training context, or none of those immediately prior to a hot-plate test assessing the latency of a paw-lick response. Relative to no exposure and context alone, the CS produced a shorter latency--that is, an apparent sensitization effect--whereas the US produced a longer latency--that is, a hypoalgesic effect--that was actually augmented by the CS/US compound. Furthermore, whereas the US-induced hypoalgesia was unaffected by the opiate antagonist, naloxone, hypoalgesia produced by the CS/US compound was appreciably decremented by the drug. Experiment 2 showed the same effects with parameters more typical of conditioning research. Experiment 3 compared signals for the presence (CS+) and absence (CS-) of the US. The CS- did not itself affect pain reactivity, but in inhibited the effects of the CS+, US, and CS+/US compound. Collectively, the results suggest that a CS+sensitizes the animal to imminent events and also potentiates an opioid reaction that supplants the less effective nonopioid hypoalgesia induced by the US. In contrast, a CS- functions as a general moderator of excitation, inhibiting both sensitization and hypoalgesic effects, whether opioid or nonopioid.     

Reinforcement magnitude effects in first- and second-order conditioning of directed action

Three experiments investigated the effects of reinforcement magnitude on conditioned key pecking in pigeons. Experiment 1, which included between-groups and within-subject designs, yielded significant effects of unconditioned stimulus (US) magnitude on the within-conditioned stimulus (CS) distribution of key pecks and on choice behavior, but no effect on the overall rate of key pecking. Experiment 2 employed a larger US-magnitude difference in a within-subject design. This manipulation resulted in differential rates of key pecking as well as a significant choice effect and differential within-CS key-peck distributions. A second-order conditioning procedure was used in Experiment 3, in which diffuse, visual stimuli (S1's) served as Pavlovian reinforcers for two key-light S2's. The S1 previously paired with a large US was more effective in conditioning second-order key-peck behavior to an S2 than was the S1 paired with a small US. The results of these experiments demonstrate that the associative effects of US magnitude can be expressed in the strength of CS-directed motor responding. The distinctive within-CS key-peck distributions in first-order conditioning suggests an interaction between CS- and US-directed responses.     

An animal model of fetishism

An animal model of sexual fetishism was developed with male Japanese quail based on persistence of conditioned sexual responding during extinction to an inanimate object made of terrycloth (Experiments 1 and 3). This persistent responding occurred only in subjects that came to copulate with the terrycloth object, suggesting that the copulatory behavior served to maintain the fetishistic behavior. Sexual conditioning was carried out by pairing a conditioned stimulus (CS) with the opportunity to copulate with a female (the unconditioned stimulus or US). Copulation with the CS object and persistent responding did not develop if the CS was a light (Experiment 1) or if conditioning was carried out with a food US (Experiment 2). In addition, subjects that showed persistence in responding to the terrycloth CS did not persist in their responding to a light CS (Experiment 3). The results are consistent with the hypothesis that conditioned copulatory behavior creates a form of self-maintenance that leads to persistent responding to an inanimate object. The development of an animal model of such fetishistic behavior should facilitate experimental analysis of the phenomenon.     

Sub-Optimal Choice by Pigeons: Failure to Support The Allais Paradox

Pigeons show a preference for an alternative that provides them with discriminative stimuli (sometimes a stimulus that predicts reinforcement and at other times a stimulus that predicts the absence of reinforcement) over an alternative that provides them with nondiscriminative stimuli, even if the nondiscriminative stimulus alternative is associated with 2.5 times as much reinforcement (Stagner & Zentall, 2010). In Experiment 1 we found that the delay to reinforcement associated with the nondiscriminative stimuli could be reduced by almost one half before the pigeons were indifferent between the two alternatives. In Experiment 2 we tested the hypothesis that the preference for the discriminative stimulus alternative resulted from the fact that, like humans, the pigeons were attracted by the stimulus that consistently predicted reinforcement (the Allais paradox). When the probability of reinforcement associated with the discriminative stimulus that predicted reinforcement was reduced from 100% to 80% the pigeons still showed a strong preference for the discriminative stimulus alternative. Thus, under these conditions, the Allais paradox cannot account for the sub-optimal choice behavior shown by pigeons. Instead we propose that sub-optimal choice results from positive contrast between the low expectation of reinforcement associated with the discriminative stimulus alternative and the much higher obtained reinforcement when the stimulus associated with reinforcement appears. We propose that similar processes can account for sub-optimal gambling behavior by humans.     

Reinstatement of fear in humans: autonomic and experiential responses in a differential conditioning paradigm

The present study investigated reinstatement of fear in humans using an aversive differential conditioning paradigm. Two neutral human face pictures were presented during habituation, acquisition, extinction, and postreinstatement phases. One picture served as a conditioned stimulus (CS) reinforced by an unconditioned stimulus (US) in the form of electrical stimulation (CS+) and the second picture as a control stimulus that was never reinforced (CS-). The prediction that in a reinstatement manipulation a previously extinguished fear response in humans can be reinstated in a reinstatement group by the mere presentation of three unpredicted electrical stimulations (USs) was tested. Participants in the control group were not exposed to unpredicted USs and no reinstatement effect was expected. Outcome measures included subjective US expectancy ratings and skin conductance responses. Results showed non-selective return of the fear response due to fear recovery associated with both CSs (CS+/CS-) in the reinstatement group. Unexpected fear recovery was observed for both CSs (CS+/CS-) in control participants. Results are discussed with respect to context conditioning, fear generalisation, and anxiety-related cognitive mechanisms underlying fear recovery after extinction.     

ACTH and ACTH4-10 modification of neophobia and taste aversion responses in the rat.

A series of experiments assessed the effects of ACTH and the ACTH analogue ACTH4-10 on drinking in conditioned taste aversion and neophobic situations. Both substances delayed the extinction of a conditioned taste aversion established by a single pairing of lithium chloride with milk (Experiment 1). However, in this situation, the ACTH parent peptide was more potent behaviorally. Administration of ACTH suppressed milk consumption in animals with no toxicosis experience (Experiment 2). This effect was apparently not due to the conditioning of a taste aversion (Experiment 3) with ACTH serving as a weak aversive unconditioned stimulus. Administration of exogenous ACTH (Experiment 4) or ACTH4-10 (Experiment 5) did not enhance neophobia; however, repeated injections of ACTH suppressed drinking. This ACTH suppression was related to the familiarity/novelty of the subtance being consumed. The neophobic response to milk eas no accompanied by pituitary-adrenal activation (Experiment 6). Both neophobic and conditioned taste aversion situation appear to be useful for assessing peptide effects on consummatory behavior.     

Operant conditioning of autogrooming in vervet monkeys: Cercopithecus aethiops

Vervet monkeys received food reinforcement contingent on autogrooming. Experiment 1 reinforced grooming on a schedule of increasing intermittency and grooming increased in frequency and duration; with only pauses reinforced, grooming decreased in frequency and duration. Experiment 2 demonstrated differentiation of operant autogrooming; in each session a different single form of grooming was reinforced (for example, grooming the tail only), and that form increased in frequency while other forms became less frequent. In Experiment 3 scratching was succesfully conditioned with a method that selectively reinforced variety in behavior; reinforcement was contingent on a shift in scratching form. In Experiment 4, with no contingencies on grooming, a prefood stimulus did not increase autogrooming whether or not grooming had previously resulted in contingent reinforcement. The form of conditioned autogrooming resembled the form of unconditioned autogrooming. The discussion suggests how reinforcement principles can account for changes in the topography of operant behavior.     

Goal-tracking behavior in the pond snail, Lymnaea stagnalis

The occurrence of goal-tracking, an unconditioned stimulus (US)-directed autoshaping behavior, was studied in open-field tests with control and classically conditioned pond snails, Lymnaea stagnalis. In an appetitive classical conditioning paradigm with a tactile stimulus as conditioned stimulus (CS) and a localized food stimulus as US a conditioned feeding response built up in the experimental but not in the control animals. In the post-training open-field tests the experimental group alone showed an enhanced attraction toward the source of water current in the environment which previously signalled the arrival of the US but did not act as CS in the classical conditioning procedure. We suggest that this stimulus-directed goal-tracking behavior in Lymnaea is the result of a classical-operant interaction, described so far only in vertebrate animals, and that neurophysiological analysis of this behavior is possible in this snail.     

Classical discrimination conditioning of the rabbit's eyelid response using pontine stimulation as a conditioned stimulus

Classical discrimination conditioning of the nictitating membrane/eyelid response was performed on seven rabbits using stimulation of the pontine nuclei or middle cerebellar peduncle as the conditioned stimulus (CS) and an air puff as the unconditioned stimulus (US). The rabbits learned to discriminate between a CS paired with a US and delivered to one pontine nucleus (the CS+) and a CS presented alone and delivered to the contralateral pontine nucleus (the CS-). Subsequent reversal of the discrimination was also achieved when the CS+ and CS- stimulation sites were interchanged. The results are interpreted as support for the idea that essential plasticity for classical eyelid conditioning occurs efferent to the pontine nuclei, possibly in regions of the cerebellum.