Perseveration of associative strength in rabbit nictitating membrane response conditioning

The present experiment used a transfer-of-training procedure in rabbit nictitating membrane response (NMR) conditioning to determine whether a retention interval and/or extinction could reduce associative strength. The experimental design required that groups receive 0, 3, 15, 45, 150, or 240 CS-US pairings in Stage 1. Next, the groups were given, in succession, a 10-day retention interval and 480 CS-alone trials. In Stage 2, all groups obtained 240 CS-US pairings for NMR conditioning. Another group was also employed and received only the 240 CS-US pairings in Stage 2. The results indicated that 15 to 240 CS-US pairings in Stage 1 substantially enhanced NM CR performance in Stage 2 despite the interpolation of the retention interval and CS-alone trials. When 3 CS-US pairings had been given in Stage 1, no augmentation in the NM CR performance rate occurred in Stage 2. However, the 3 CS-US pairings were effective in prohibiting the 480 CS-alone trials from retarding subsequent NM CR performance. Without any pairings in Stage 1, the 480 CS-alone trials produced strong latent inhibition of NMR conditioning in Stage 2. The data were used to support the theoretical view that associative strength resulting from CS-US pairings is relatively permanent. Moreover, the findings were relevant for an evaluation of Pearce and Hall’s (1980) recent statements concerning CS associability and the relationship between excitatory and inhibitory processes.     

Motivational vs. associative role of the US in classical conditioning of the rabbit’s nictitating membrane response

Two experiments tested the motivational role of the US in classical conditioning of the rabbit’s nictitating membrane (NM) response. In Experiment 1, subjects were trained to an intermediate performance level and then given a series of (1) CS-US trials, (2) “backwards” US-CS trials, (3) CS-alone trials, (4) US-alone trials, or (5) no-stimulus presentations. Interpolated presentations of the US, either alone or in a backwards contingency, tended to produce an impairment of subsequent acquisition. In Experiment 2, subjects were trained with strong or weak US intensity on paired or interpolated trials. US intensity on interpolated trials had only a very small effect, whereas the effect of US intensity on paired trials was quite large. Shifts in paired-trial US intensity produced corresponding shifts in performance, but shifts in the intensity of the interpolated US produced no apparent effect. We conclude that the arousal of motivation is not sufficient to maintain performance in classical NM conditioning.     

Effects of a backward conditioning procedure following acquisition on extinction of conditioned suppression

A one-trial-a-day procedure was used to investigate the effects of US-CS pairings on extinction of conditioned suppression of licking by rats. Following acquisition trials, response suppression was immediately eliminated when US preceded CS, but it reappeared during subsequent CS-alone presentations. Ss that received backward pairings reached a significant level of extinction one trial before Ss that received conventional extinction trials.     

The influence of shock during response prevention upon resistance to extinction of an avoidance response

A recent study found that avoidance extinction is equally facilitated by response prevention (blocking) whether the latter involves CS-alone or CS-shock presentations. An experiment was performed to determine whether this result was due to the use of a lengthy shock (5 sec) during response prevention. Five groups of rats were extinguished: (1) without prior blocking, (2) after blocking with CS only, (3) after blocking with a lengthy (5 sec) CS-contingent shock, (4) after blocking with a brief (.5 sec) CS-contingent shock, or (5) after blocking with a brief (.5 sec) shock only. The group blocked with the brief CS-contingent shock was substantially more resistant to extinction than the other four groups. The unblocked group and the group blocked with brief shock only required more trials to extinguish than the groups blocked with CS only or with lengthy CS-contingent shock, but did not differ from each other. The groups blocked with CS only or with lengthy CS-contingent shock also failed to differ from one another. The data support a significant role for Pavlovian conditioning processes in the effect of response prevention upon avoidance extinction.     

Dominance,the bidirectional hypothesis,and Pavlovian backward conditioning in the US-US paradigm

Based upon considerations raised by Soviet research, the role of relative stimulus intensity, or dominance, in the unconditioned stimulus-unconditioned stimulus (US-US) paradigm was investigated under circumstances presumed favorable to the backward conditioned response (CR). Using the classically conditioned forelimb response of the cat, a brief shock (USD delivered to one forepaw preceded a shock (US2) to the opposite forepaw in paired conditioning fashion; subjects in the control group received explicitly unpaired presentations of the stimuli. Conditioning in both the forward and backward directions was evaluated by the appearance of contralateral CRs on test trials to each of the USs. In Experiment 1, a ratio of the intensities between US1 and US2 of 100:80 was used to create a relative dominance in favor of the backward CR. In addition, to evaluate the suggestion that the appearance of the backward CR is retarded in the Pavlovian paradigm, overtraining was provided to a forward conditioning criterion of 200%. In Experiment 2, the cats were exposed to successive reductions in the intensity of US2 to verify manipulations of dominance reportedly involved in the reactivation of a latent backward CR. Although forward conditioning was readily established to USl, there was no evidence of back-ward conditioning to US2 under any of the conditions.     

Cue-induced transfer of CS preexposure effects across contexts

These experiments confirmed previous reports that latent inhibition effects can be abolished if rats receive CS preexposures and CS-US pairings in different contexts. However, latent inhibition effects were restored if animals were given a cuing treatment in the conditioning context prior to the conditioning trials. This restoration of latent inhibition occurred only when the cuing treatment could have served to remind the animals of CS-alone presentations in the specific context used for conditioning. These findings are discussed in relation to various accounts of latent inhibition effects.     

Slow reacquisition of a conditioned taste aversion

Rats were used to examine the extent to which extinction of an acquired conditioned taste aversion retards subsequent reacquisition. A saccharin-flavored solution (sac) was paired with LiCl and then followed by CS-alone extinction trials with this flavor. A control group received a different flavor, decaffeinated-coffee (coff), during initial conditioning and extinction. Sac was then paired with LiCl for all rats during a second conditioning phase. Reacquisition of the aversion to sac was retarded relative to the acquisition of an aversion to sac by the control group. A similar experiment with fewer extinction trials, but still with complete loss of the initial aversion, did not obtain slow reacquisition. The results are discussed with respect to an interference view of extinction and the slow-reacquisition effect.     

Classically conditioned heart rate in rats following preconditioning exposure to the CS

The influence of preexposure to the CS on classically conditioned heart rate was examined in three groups of rats receiving either 0, 10, or 50 CS-alone trials prior to the beginning of acquisition training. The conditioned response was a deceleration in heart rate for all groups. Compared to the 50 group, the 0 and 10 groups both showed a lower overall level of conditioning performance and a slower rate of development of the conditioned response. It was suggested that the presence of the nonhabituated orienting response may have interfered with the conditioning process.     

Stimulus-reinforcer interactions in Pavlovian conditioning of pigeons: Implications for selective associations

In a Pavlovian procedure, groups of pigeons were presented with a compound auditory-visual stimulus that terminated with either response-independent electric shock or food. In a subsequent test, the tone CS was dominant in aversive conditioning, reliably eliciting conditioned head raising and prancing. The red light CS was dominant in appetitive conditioning, reliably eliciting pecking. This result was replicated in a second experiment, in which trials were widely spaced. Pour additional groups of pigeons received pairings of the separate element CSs with the USs. Red light, but not tone, was an effective CS in appetitive conditioning, whereas tone, but not red light, was effective in aversive conditioning. There was no discriminative responding in zero-contingency control groups. Several theoretical accounts of these data are discussed.     

Second-order conditioning of the rabbit’s nictitating membrane response as a function of the CS2-CS1 and CS1-US intervals

Three experiments investigated conditioning of the rabbit’s nictitating membrane response (NMR) in a second-order conditioning procedure which intermixed first-order trials (CS1-US) and second-order trials (CS2-CS1) from the outset of training. Experiment 1 provided a controlled demonstration that substantial levels of second-order conditioning can be obtained with the NMR preparation. Experiment 2 showed that the level of CR acquisition to CS2 was an inverse function of the CS2-CS1 interval over the values of 400, 800, and 2,400 msec. Experiment 3 found that CR acquisition to CS2 and CS1 in second-order conditioning varied in a parallel fashion across CS1-US intervals. Similarly, Experiment 3A found that the level of CR acquisition to the two components of a serial compound (CSA-CSB-US) varied in a parallel fashion as a function of the CSB-US interval. The results of the CS2-CS1 and CS1-US interval manipulations were all predictable from the known CS-US interval effects in NMR conditioning with a single CS. The present results are discussed with regard to their implications for accounts of serial compound conditioning and second-order conditioning.     

Conditioned inhibition in taste aversion learning: Testing methodology and empirical status

Learning & Behavior - Several assays were used in assessing conditioned inhibition within a taste aversion procedure. Following Pavlovian conditioned inhibition training, in which one taste was...     

Mechanisms of inhibitory discriminative control

Rats were trained to discriminate between trials signaled by a tone, during which leverpressing was reinforced with food, and trials signaled by the tone in compound with a light stimulus, during which no reinforcers were delivered. A subsequent transfer test suggested that the light had acquired the ability to suppress operant responding; there was no evidence that this suppression could be attributed to Pavlovian inhibitory conditioning. It is argued that these data cannot be accommodated by current accounts of discriminative control.     

Spontaneous recovery varies inversely with the training-extinction interval

Four experiments found the magnitude of spontaneous recovery after extinction to be greater with a shorter interval between initial conditioning and extinction. Experiments 1 and 2 used a Pavlovian magazine approach procedure with rat subjects, Experiment 3 used an instrumental training procedure with rats, and Experiment 4 used a sign-tracking procedure with pigeons. These results are not anticipated by many accounts of spontaneous recovery that attribute it to the fading of learning that occurred during extinction.     

Effect of odor preexposure on acquisition of an odor discrimination in dogs

In two experiments, we investigated the impact of odor preexposure treatments on the acquisition of an olfactory discrimination in dogs. In the first experiment, four groups of dogs were each given five days’ odor-exposure treatment prior to discrimination training. Dogs in the exposure group were exposed to anise extract (S+) for 30 min daily. Dogs in the Pavlovian-relevant pairing group received six daily delayed-conditioning trials to the same S+. The Pavlovian-irrelevant pairing group received conditioning trials to almond extract (S'). Dogs in the control group received no pretreatment. All of the dogs were then trained to detect S+ from a background pine odor (an AX-vs.-X discrimination). The Pavlovian-relevant pairing group acquired the odor discrimination significantly faster than all of the other exposure and control groups, and the remaining groups acquired the discrimination at the same rate as the no-exposure control group. In a second experiment, we extended these results to a within-subjects design using an AX-versus-BX discrimination. Six dogs were simultaneously trained on two different odor discriminations, one discrimination in which the S+ was previously Pavlovian conditioned, and one discrimination in which the S+ was novel. All of the dogs learned the odor discrimination with the previously conditioned S+ faster than they learned the novel odor discrimination, replicating the results of Experiment 1, and demonstrating that familiarity in the form of Pavlovian conditioning enhances odor-discrimination training. The potential mechanisms of the facilitated transfer of a Pavlovian conditioned stimulus to discrimination training are discussed.     

Differential response gradients to a Pavlovian safety signal following active avoidance training in young and adult rats

Following 300 training trials in two-way shuttle avoidance signaled by a tone (CS+), two groups each of weanling and adult rats were given Pavlovian discrimination training in which the CS+ was followed by inescapable shock, and a more intense tone (CS—) signaled no shock. An additional group at each age level received both tones paired randomly with shock or no shock. Subsequent generalization tests along the frequency dimension indicated that both pups and adults tested at the CS+ intensity showed similar gradients of frequency control. Gradients for the adults tested at the CS — intensity tended to be inverted, with least responding at CS—, a result not found in the young subjects. The results were considered in light of Pavlovian extradimensional influences on the control of avoidance behavior.     

CS preexposure: Latent inhibition and Pavlovian conditioning of heart rate and eyeblink responses as a function of sex and CS intensity in rabbits

Male and female rabbits received Pavlovian conditioning in which a 1, 216-Hz tone served as the CS and a 3-mA paraorbital electric shock train served as the US. Eyeblink (EB) and heart rate (HR) CRs were assessed. Half of the animals received prior exposure to the CS, while half were restrained in the chamber for a similar length of time but did not receive prior CS exposure. Different groups of each sex received three different CS intensities including 60, 75, and 90 dB (SPL) during both preexposure and conditioning. The results revealed that latent inhibition of the EB CR occurred only at the intermediate CS intensity, as indicated by a significant impairment of EB conditioning in this group. However, the magnitude of the decelerative HR CR was attenuated by prior CS exposure at all three CS intensities. Females showed faster EB conditioning than males, but latent inhibition occurred in both sexes. These results suggest that somatomotor and autonomic systems are affected differently by prior CS exposure.     

Real-time factors in the rabbit’s nictitating membrane response to pulsed and serial conditioned stimuli

Conditioning theories and recent real-time models commonly postulate that a reinforcer is signaled by a series of stimuli. In both Pavlovian and operant procedures, serial stimuli have been shown to control the likelihood and timing of responses over intervals of seconds and minutes. The present experiments were conducted to determine whether serial stimuli exercise similar effects over stimulus-reinforcer intervals in the order of hundreds of milliseconds. Such intervals typify those used in conditioning of the rabbit nictitating membrane response. A sequence of four tone pulses (50–100 msec) was used as the CS to assess the effectiveness of serial stimuli. After training with this CS, tests were conducted in which one or more of the pulses were removed. These perturbations of the sequence of stimuli over a 400-msec interval produced large deficits in CR likelihood and smaller alterations in CR timing. The results are discussed with respect to their implications for current real-time models of conditioning, and particularly with respect to their assumptions about the source of internal stimuli, rules for learning, and rules for generating CRs.     

Effects of trial duration on overall and momentary rates of maintained autoshaped keypecking: Choice and single-stimulus trials

Pigeons were exposed to differentially cued autoshaping trials in which conditioned stimuli were followed by food after 6 or 14 sec. Average and momentary rates of keypecking were examined on two types of unreinforced test trials: single-stimulus probe trials and simultaneous choice trials, each 40 sec in duration. Rates averaged over the 40-sec test trials did not favor the cue associated with the shorter delay to food (the short-delay cue) on either type of test trial; however, average rates prior to the scheduled time of food delivery were reliably higher for the short-delay cue on choice trials. Momentary rates of keypecking during choice trials varied as a function of both cue and elapsed time from trial onset. At short elapsed trial times, rate of pecking was higher for the short-delay cue, with this difference reversing at longer times. A reversal of the programmed relation between key color and delay to food presentation for 5 birds confirmed the generality of these findings. Implications of these data for models of Pavlovian conditioning and for methods of assessing conditioned response strength are discussed.     

Outcome-specific conditioned inhibition in Pavlovian backward conditioning

In the present experiments, the outcome specificity of learning was explored in an appetitive Pavlovian backward conditioning procedure with rats. The rats initially were administered Pavlovian backward training with two qualitatively different unconditioned stimulus conditioned-stimulus (US-CS) pairs of stimuli (e.g., pellet --> noise or sucrose --> light), and then the effects of this training were assessed in Pavlovian-to-instrumental transfer (Experiment 1) and retardation-of-learning (Experiment 2) tests. In the transfer test, it was shown that during the last 10-sec interval, the CSs selectively reduced the rate of the instrumental responses with which they shared a US, relative to the instrumental responses with which they did not share a US. The opposite result was obtained when the USs (in the absence of the CSs) were presented noncontingently. In the retardation test, conditioned magazine approach, responding to the CSs was acquired more slowly when the stimulus-outcome combinations in the backward and the forward conditioning phases were the same, as compared with when they were reversed. These results are collectively in accord with the view that Pavlovian backward conditioning can result in the formation of outcome-specific inhibitory associations. Alternative views of backward conditioning are also examined.     

Response variability in pigeons in a pavlovian task

Instrumental response variation is inversely related to reward probability. Gharib, Derby, and Roberts (2001) theorized that individuals behave more variably when their expectation of reward is low. They postulate that this behavioral rule assists the discovery of alternative actions when a target response is unlikely to be reinforced. This suggests that response variability may be unaffected in a situation in which an animal’s behavior is inconsequential to outcome delivery. We trained 6 pigeons in a within-subjects Pavlovian autoshaping procedure. On any given trial, the pigeons were presented with one of six colored discs on a touchscreen; each stimulus was associated with a particular probability of food, ranging from 100% to 0.6%. Pecking was more variable with low probabilities of food delivery, thus extending the rule relating variability and expectation to a Pavlovian situation.