Pigeons' withdrawal from an appetitive conditioned inhibitor under two training procedures

The approach-withdrawal behaviour of pigeons to a red keylight was measured under three conditions; a negative contingency (NC) between keylight and food reinforcement, a CI or conditioned inhibition procedure where the keylight was non-reinforced in compound with a tone which was reinforced when presented alone, and a random control procedure (RC). The keylight-food contingencies in CI and NC were identical, and keylight and food presentation frequency were the same in all conditions. Subsequently the effect of adding the red keylight to a novel CS+ during or after excitatory conditioning was examined (summation test of inhibition). The inhibitory procedures, CI and NC, generally yielded similar functions for the acquisition of withdrawal, and the results of the withdrawal and summation measures were positively correlated. The implications of the results for theories of the acquisition and behavioural action of conditioned inhibitors are discussed.     

UCS duration and conditioned suppression: Acquisition and extinction between-groups and terminal performance within-subjects

Two experiments demonstrated a positive monotonic relation between UCS duration and conditioned suppression ranging from no suppression at 0.05 sec to nearly complete suppression at 3.0 sec. In Exp 1, 5 acquisition groups were run at 0.5 mA. No suppression occurred at the shortest duration, approximately 50% suppression by Session 3 in two intermediate groups (0.2 and 0.5 sec) and nearly complete suppression by Session 3 at the two longest durations (1.0 and 3.0 sec). The relation between UCS duration and recovery of responding during extinction followed a parallel pattern. In Exp 2, terminal performance was studied within-subjects and the same relation was replicated.     

One-trial conditioned suppression: effects of instructions on extinction

Two experimental groups of undergraduate volunteers received a single Pavlovian conditioning trial consisting of a paired presentation of a tone conditioned stimulus (CS) and a shock unconditioned stimulus (UCS). Control groups received either the CS alone or the UCS alone. Subjects from one experimental group were subsequently instructed that they would not receive further shocks, while the other experimental group received no such instructions. The CS alone was then presented once to all four groups while subjects were engaged in a button-pressing task maintained by slide reinforcement. During the latter phase, rate of button-pressing was measured. Classically conditioned suppression of button-pressing was obtained in the noninstructed experimental group but not in the instructed group. The results demonstrate that suppression can be a sensitive index of Pavlovian conditioning in humans but question the use of conditioned suppression as an adequate experimental analog of clinically observed anxiety-motivated behavior.     

Generalization of conditioned suppression after differential training

In a modified conditioned suppression procedure, clicks at one frequency (danger signal) preceded shocks, while no shocks followed clicks at a different frequency (safe signal). During generalization tests, the maximal response rate was frequently shifted from the safe signal in the direction away from the danger signal, and the minimal response rate was frequently shifted in the opposite direction, away from the safe signal. There was considerable variability in the results from one animal to another. The generalization tests also suggested different generalization functions according to whether the danger signal was a lower or a higher frequency than the safe signal. The results also showed the development of systematic differences in response rate during and after the safe and danger signals, notably a relatively high rate at the beginning of the safe signal and after the danger signal.     

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.     

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.     

Stimulus factors in aversive controls: conditioned suppression after equal training to two stimuli

Pigeons trained to peck a key for food were periodically presented with tones ending with electrical shock until tone presentation consistently suppressed ongoing pecks. Shock was then discontinued and gradients of stimulus generalization were assessed by presenting tones with frequencies above, below, and at the frequencies of those used to develop conditioned suppression. When the training tones had frequencies at 670 and 1500 cps, resulting gradients were bi-modal with peak suppression at 670 and 1500 cps. Of the other test tones, 1000 cps produced the most suppression. When the training tones had frequencies at 450 and 2250 cps, bi-modal gradients were again obtained with peak suppression to the 450 and 2250 cps tones. Of the other test tones, 1000 cps produced the least suppression. These results support the hypothesis that generalized response tendencies summate.     

The effects of physical context changes and multiple extinction contexts on two forms of renewal in a conditioned suppression task with humans

Three experiments examined the effects of physical context changes and multiple extinction contexts on the renewal of conditioned suppression in humans. A conditioned suppression task used an undesirable event as the unconditional stimulus (US). One conditional stimulus (CS+) predicted the occurrence of the US and another (CS−) predicted US absence. In Experiment 1 (N = 32), conditioned suppression was acquired to the CS+ in one context and extinguished in a different context. An increase in suppression was found for the CS+ and not for the CS− when subsequent test trials were conducted in the acquisition context (ABA renewal). Experiment 2 (N = 32) tested for ABC Renewal and showed increased suppression to both the CS+ and CS− when test was conducted in a novel context. Experiment 3 (N = 80) showed that these two effects were abolished when extinction was conducted in multiple contexts. The experiments extend the ABA renewal of conditioned suppression found with non-human animal subjects and the reduction of renewal by extinction in multiple contexts. Context changes may also facilitate cue competition effects after training with elementary stimuli, as shown by the effects of US omission in the ABA and ABC renewal groups.     

Explicit disassociation of a conditioned stimulus and unconditioned stimulus during extinction training reduces both time to asymptotic extinction and spontaneous recovery of a conditioned taste aversion

Conditioned taste aversions (CTAs) may be acquired when an animal consumes a novel taste (CS) and then experiences the symptoms of poisoning (US). This aversion may be extinguished by repeated exposure to the CS alone. However, following a latency period in which the CS is not presented, the CTA will spontaneously recover (SR). In the current study we employed an explicitly unpaired extinction procedure (EU-EXT) to determine if it could thwart SR of a CTA. Sprague-Dawley rats acquired a strong CTA after three pairings of saccharin (SAC the CS) and Lithium Chloride (LiCl the US). CTA acquisition was followed by extinction (EXT) training consisting of either (a) CS-only exposure (CSO) or (b) exposure to saccharin and Lithium Chloride on alternate days (i.e., explicitly unpaired: EU). Both extinction procedures resulted in ?90% reacceptance of SAC, although the EU extinction procedure (EU-EXT) significantly decreased the time necessary for rats to reach this criterion (compared to CSO controls). Rats were subsequently tested for SR of the CTA upon re-exposure to SAC following a 30-day latency period of water drinking. Rats that acquired a CTA and then underwent the CSO extinction procedure exhibited a significant suppression of SAC drinking during the SR test (as compared to their SAC drinking at the end of extinction). However, animals in the EU-EXT group did not show such suppression in drinking compared to CSO controls. These data suggest that the EU-EXT procedure may be useful in reducing both time to extinction and the spontaneous recovery of fears.     

Counteraction between two kinds of conditioned inhibition training

In a Pavlovian fear-conditioning preparation, we investigated the effects of combining Pavlovian and explicitly unpaired inhibition treatments. A summation test for inhibition suggested a strong tendency toward unpaired inhibition when that treatment was administered alone and found robust Pavlovian inhibition when that treatment was administered alone, but detected little behavior indicative of inhibition in subjects that experienced both treatments during training. The retardation test showed reliable unpaired and Pavlovian inhibition when these treatments were administered alone but no indication of inhibition in subjects that experienced both treatments. These counterintuitive results suggest that in some circumstances the effects of two inhibitory treatments are not additive but rather counteractive. The present results provide some information about the nature of conditioned inhibition and, more generally, cue interaction.     

Acquisition of a conditioned taste aversion becomes context dependent when it is learned after extinction

A conditioned taste aversion experiment tested context-switch effects on retrieval of conditioned stimulus (CS)-unconditioned stimulus (US) acquisition performance in rats. A context switch impaired performance when the target flavour was trained in a context where a different flavour underwent extinction. Conditioned taste aversion in the absence of previous extinction of the alternate flavour was not context dependent. It is suggested that the ambiguity in the meaning of the extinguished cue leads animals to pay attention to the context, so that the information learned in that context becomes context dependent.     

Acquisition of a conditioned taste aversion becomes context dependent when it is learned after extinction

A conditioned taste aversion experiment tested context-switch effects on retrieval of conditioned stimulus (CS)–unconditioned stimulus (US) acquisition performance in rats. A context switch impaired performance when the target flavour was trained in a context where a different flavour underwent extinction. Conditioned taste aversion in the absence of previous extinction of the alternate flavour was not context dependent. It is suggested that the ambiguity in the meaning of the extinguished cue leads animals to pay attention to the context, so that the information learned in that context becomes context dependent.     

Effects of hippocampal stimulation on acquisition, extinction and generalization of conditioned suppression in the rat.

Rats implanted with electrodes in the dorsal or ventral hippocampus received posttrial stimulation in training sessions with footshock reinforcement. Afterdischarges without overt seizures were consistently without effect on the rate of acquisition of suppression of licking during an auditory conditioned stimulus (CS), although conditioning was retarded by the delivery of distracting stimuli following footshock. The rate of conditioning remained insensitive to elicitation of dorsal hippocampal afterdischarges (DHAD) despite subsequent alterations of session length, intertrial interval and preexposure to the CS. However, faster extinction of suppression occurred following DHAD, suggesting a limited but essential role of the hippocampus in addressing stored information.