Testing response generation rules.

Preconditioning experience with the unconditional stimulus (UCS) retards subsequent excitatory conditioning. Three experiments demonstrated that this UCS retardation effect is attenuated by associative manipulations of contextual stimuli of the UCS preexposure environment. The UCS retardation effect was reduced by (a) altering contextual stimuli between preexposure and conditioning (Experiment 1), (b) latently inhibiting contextual stimuli prior to UCS preexposure (Experiment 2), and (c) extinguishing contextual stimuli subsequent to UCS preexposure (Experiment 3). Although UCS preexposure retarded excitatory conditioning, the results of Experiment 4 demonstrated that UCS preexposure facilitated inhibitory conditioning. These results indicate that an association between contextual stimuli and the preexposed UCS contributes to the effects of preconditioning UCS experience on subsequent learning.

Acquisition to a target conditioned stimulus (CS) is prevented when extra, unsignaled unconditioned stimuli (USs) are presented with sufficient frequency to remove contingency between target CS and US. Acquisition occurs, however, when the extra USs are signaled by another CS. According to the Rescorla-Wagner theory, signaling reduces contextual conditioning, which otherwise prevents acquisition. Results of Experiment 1 led to the rejection of a rival explanation derived from scalar expectancy theory by showing that acquisition does not occur when only half of the extra USs are signaled. The results of Experiment 2 were, however, contrary to the Rescorla-Wagner theory because they showed equivalent acquisition when the stimulus used to signal the extra USs was also present concurrently with the target CS. Signaling may exert its effect by converting the intertriai interval to CS−.

Three experiments demonstrated that repeated exposure to an electric-shock unconditioned stimulus (US) resulted in a decrement in retention of conditioned suppression evoked by a previously established excitatory conditioned stimulus (CS) and retarded subsequent acquisition of conditioned suppression to a novel CS paired with shock. Experiment 1 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. Experiment 2 demonstrated that the magnitude of both the decrement in retention of conditioned suppression and the retardation in the acquisition of conditioned suppression produced by exposure to shock alone was directly related to the intensity of those shocks. Experiment 3 demonstrated that 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. These findings are discussed in terms of associative and nonassociative accounts of the effects of US-alone procedures.

MK-801 is a noncompetitive antagonist to N-methyl-d-aspartate (NMDA) receptors. MK-801 was given (0.05 or 0.10 mg/kg i.v.) to rabbits during extinction of a well-established conditioned response (CR) in the nictitating membrane preparation. The drug administration produced an immediate deficit in CR performance during extinction. However, when MK-801 administration was suspended, CRs reappeared immediately and showed no evidence of the previous extinction treatment. In addition, we confirmed previous findings that MK-801 impairs both the acquisition and the expression of CRs during CS—US training. A reduction in CS processing caused by MK-801 is the most parsimonious explanation of the data. There are also two-factor alternatives, which contend that MK-801 directly hinders associative formation and either directly blocks CR output or produces a state-dependent generalization decrement.

Using conditioned suppression to investigate compulsive drug seeking in rats

Signaling the unconditioned stimulus and backward conditioned inhibition: Prior conditioning of the signal and context

Three experiments are described investigating whether olfactory repellents DEET and butyric acid can support the classical conditioning of proboscis extension in the honeybee, Apis mellifera caucasica (Hymenoptera: Apidae). In the first experiment DEET and butyric acid readily led to standard acquisition and extinction effects, which are comparable to the use of cinnamon as a conditioned stimulus. These results demonstrate that the odor of DEET or butyric acid is not intrinsically repellent to honey bees. In a second experiment, with DEET and butyric acid mixed with sucrose as an unconditioned stimulus, proboscis conditioning was not established. After several trials, few animals responded to the unconditioned stimulus. These results demonstrate that these chemicals are gustatory repellents when in direct contact. In the last experiment a conditioned suppression paradigm was used. Exposing animals to butyric acid or DEET when the proboscis was extended by direct sucrose stimulation or by learning revealed that retraction of the proboscis was similar to another novel odor, lavender, and in all cases greatest when the animal was not permitted to feed. These results again demonstrate that DEET or butyric acid are not olfactory repellents, and in addition, conditioned suppression is influenced by feeding state of the bee.

The strength of the orienting response (OR) to a light and its associability was studied in three experiments. In Experiment 1, three groups of rats received serial conditioning in which the light served as the first element of a serial compound. For Group Diff the light was followed by a conditioned stimulus (CS) of 10-s duration on some trials and by a different CS of 30-s duration on others. For the other groups, the light was also followed by different stimuli, but these had equivalent durations. This procedure resulted in a stronger OR toward the light in Group Diff than in either of the other groups. In Experiments 2 and 3 the OR was stronger to a light that was followed by a 10-s CS on some trials and by a 30-s CS on others than to one that was followed by different CSs that were both randomly either 10 s or 30 s. Following this training, both excitatory and inhibitory conditioning with the light was faster in those groups for which the light elicited a strong rather than a weak OR. These results are most readily explained by the proposal that the strength of the OR toward a CS is determined by the accuracy with which the value of its immediate consequences can be predicted and that this OR can be used as an index of the associability of the CS.

Rats were trained to run up and down an alleyway for sucrose reinforcement a variable interval schedule. Differential aversive classical conditioning with auditory CSs was then conducted in a separate apparatus (off the baseline) prior to those CSS being presented while the subjects were responding for sucrose in the alleyway. Once the effects of the CSs had extinguished, shock was reintroduced following one CS but not the other (on the differential aversive classical conditioning). Both off the and on the conditioning resulted in conditioned suppression to the CS followed by shock, but little effect of the CS followed by no shock was found. In the on the phase, total suppression of baseline responding occurred at moderate US intensities, and this appeared to result from the subject avoiding the location at which he was last shocked. At lower values, both baseline response rate and relative suppression ratio were functions of US intensity. The results are discussed in relation to the effects found in similar experiments using avoidance baselines. Estes and Skinner (1941) found that food reinforced 1everpressing was suppressed by a conditioned stimulus (CS) that was followed by an unconditioned stimulus (US) of an electric shock. Such conditioned suppression of operant behavior by a preaversive CS has also been found using avoidance baselines (Bryant, 1972). However, Rescorla and Solomon (1967) were able to find support for their motivational account of operant classical interactions from a number of studies carried out in the Pennsylvanian laboratories (e.g., Rescorla & Lolordo, 1965; Rescorla, 1967). In general, these in­ volved training dogs to jump over a hurdle a Sidman

Associative learning and latent inhibition in a conditioned suppression paradigm in humans

We have used the pairing of camphor odor conditioned stimulus (CS) and injection of poly I:C unconditioned stimulus (US) in a short 3 day single trial conditioning paradigm. Conditioning was done by exposing mice to the CS/US combination on day 0 and reexposing the conditioned animals to the CS on day 2. This results in a conditioned augmentation of the natural killer (NK) cell response. Indomethacin treatment and/or handling stress induced by simply measuring rectal temperature was found to dramatically alter the direction of the conditioned NK cell response. Conditioning of indomethacin treated mice produced a conditioned suppression of the NK cell response mimicking a conditioned tolerance response. If handling stress was superimposed on day 2 the conditioned suppression response was replaced by a conditioned augmentation of the NK cell response. Even with one trial conditioning, drugs and handling stress can serve as additional cues to alter the direction of the conditioned response. The studies also show that the conditioning of the fever response is independent of conditioning of the NK cell response.

Effect of amount of context extinction on revaluation of a target CS.

Three experiments were conducted to examine the effect of assessment procedure, either conditioned punishment extinction or conditioned suppression reacquisition, on the associative outcome of backward conditioning in the rat. Each experiment consisted of three phases: (a) magazine and barpress training; (b) Pavlovian training in which groups received one of backward, explicitly unpaired, or no presentation of a conditioned stimulus (CS) and unconditioned stimulus (US); and (c) either conditioned punishment or conditioned suppression transfer of training tests. In Experiment 1, backward conditioning resulted in excitatory associative effects during the conditioned punishment test. In Experiment 2, backward conditioning produced excitatory conditioning when assessed by a conditioned suppression reacquisition test. In Experiment 3, a number of backward conditioning parameters were manipulated, and backward pairings yielded facilitative reacquisition relative to the unpaired group, but did not differ from the no-treatment control group. The pattern of results suggests that backward conditioning produces qualitatively similar outcomes when assessed by a conditioned punishment extinction or conditioned suppression reacquisition test.

Periodicity in the hoffmann reflex recovery curve

The use of a drug state as a conditioned stimulus (CS) in a classical conditioning paradigm was investigated. Suppression of a single-lever food-reinforced response (variable-interval 60 s) served as an index of a classically conditioned response (conditioned suppression). d-Amphetamine (0.8 mg/kg) injections were paired with a series of inescapable shocks. Following drug-shock pairing, the effects of d-amphetamine on operant response totals was compared to effects obtained in control subjects which had received unpaired d-amphetamine and shock exposures. d-Amphetamine administered during daily operant sessions unaccompanied by shock was an effective CS for conditioned suppression of the operant response. Administration of cocaine hydrochloride (7.5 mg/kg) also produced a decrease in total responses, suggesting stimulus generalization from the shock-paired drug to a novel drug.