Amygdala central nucleus lesions disrupt increments, but not decrements, in conditioned stimulus processing.

The effects of neurotoxic lesions of the amygdala central nucleus (CN) on changes in the associability of a CS in appetitive Pavlovian conditioning were examined in 2 experiments with rats. In Exp 1, CN lesions had no effect on the reduction in the associability of a CS produced by preexposure to that cue (latent inhibition). In Exp 2, CN lesions prevented the enhancement of the associability of a CS that is normally observed when an inconsistent predictive relation is arranged between that CS and another cue. Results support previous claims that the amygdala CN is involved in broad-based incremental, but not decremental, changes in the processing of CSs in Pavlovian conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective hippocampal lesions abolish the contextual specificity of latent inhibition and conditioning.

The contextual specificity of the CR and latent inhibition (LI) was examined in rats with selective hippocampal lesions. Acquisition of the CR to a novel CS was equally rapid in control and hippocampal rats (Exps 1 and 2), and CS preexposure disrupted acquisition (i.e., produced LI) to an equal extent in both groups (Exp 2). In control Ss, however, the CR established in one context transferred incompletely to a 2nd context (Exp 1), and LI was attenuated when CS preexposure and conditioning occurred in different contexts (Exp 3). This context specificity of the CR and LI was not apparent in hippocampal rats; the CR and LI transferred readily from one context to another. In addition, hippocampal rats were impaired in a spatial learning task (Exp 2) but were unimpaired in learning a Pavlovian contextual discrimination (Exp 3). Results suggest that a common contextual retrieval process underlies the contextual dependence of the CR and of LI and that this process is mediated by the hippocampus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Human blink startle during aversive and nonaversive Pavlovian conditioning.

Potentiation of blink startle during aversive and nonaversive Pavlovian single-cue conditioning was assessed in human Ss. In Exp 1 (N?=?89), the conditioning group received paired presentations of a visual CS and an unconditioned stimulus/stimuli (UCS), whereas the control group was presented with a random sequence. The UCS was an electric shock for half the Ss and a nonaversive reaction time (RT) task for the other half. Electrodermal conditioning was evident regardless of the nature of the UCS, but blink potentiation was found only in the conditioning group that had been trained with the aversive UCS. These results were replicated in Exp 2 (N?=?65), in which a nonaversive UCS of increased motivational significance was used. Thus, only aversive conditioning seems to affect the affective valence of the CS, at least as reflected by changes in a skeletal reflex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of long-term sensitization on long-term habituation of the acoustic startle response in rats: Central gray lesions, preexposure, and extinction.

The relation between long-term decrements of the acoustic startle response in rats and the development of freezing behavior during habituation training was examined. Freezing behavior developed over the initial trials of habituation training, and the rate of long-term response decrements was found to be inversely related to the development of freezing. Manipulations (neurological or behavioral) that either reduced the level of freezing or retarded its development promoted startle response decrements. In Experiment 1, rats receiving electrolytic lesions of the ventrolateral periaqueductal gray demonstrated both accelerated long-term startle response decrements and retarded development of freezing behavior. In Experiment 2, preexposure to the startle apparatus (i.e., latent inhibition) accelerated long-term startle decrements and inhibited development of freezing. In Experiment 3, exposure to the startle apparatus following initial habituation training (i.e., extinction) reduced both freezing behavior and startle response amplitudes. The results are discussed in terms of the influence of Pavlovian fear conditioning on long-term habituation of the acoustic startle response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Protection from latent inhibition provided by a conditioned inhibitor.

Two conditioned suppression experiments with rats investigated the influence on latent inhibition of compounding a Pavlovian conditioned inhibitor with the target cue during preexposure treatment. Results were compared with those of subjects that received conventional latent inhibition training, no preexposure, or preexposure to the target cue in compound with a neutral stimulus. In Experiment 1, greater attenuation of the latent inhibition effect was observed in subjects that received target preexposure in compound with a Pavlovian conditioned inhibitor relative to subjects that received preexposure with a neutral stimulus or to the target alone. In Experiment 2, this protection from latent inhibition was attenuated if the excitor that was used to train the conditioned inhibitor was extinguished between preexposure and target training. The results are consistent with an account offered by the extended comparator hypothesis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Latent inhibition experiments with goldfish (Carassius auratus).

Examined evidence of latent inhibition in a series of experiments with goldfish. In Exp I, 12 Ss were given nonreinforced preexposure to a color that subsequently predicted shock in an activity conditioning situation; their performance did not differ from that of 12 control Ss preexposed to a markedly different color. In Exp II, 12 Ss given nonreinforced preexposure to a tone and an unstimulated control group of 12 Ss were trained in an appetitive situation, with the tone serving either as a conditioned excitor or as a conditioned inhibitor. Preexposure had significant effect in the conditioned excitation training, but it reduced the level of responding both to the positive stimulus and to the negative compound in the conditioned inhibition training. In Exps III and IV, classical aversive conditioning was studied in the shuttle box. In Exp III, excitatory conditioning to a color was found to be impaired (relative to the performance of nonpreexposed control Ss) as much by nonreinforced preexposure to the training color as by nonreinforced preexposure to a markedly different color; substantial variation in amount of preexposure was without significant effect. In the conditioned inhibition training of Exp IV, 12 Ss with nonreinforced preexposure responded less than did 12 unstimulated control Ss, both to the positive stimulus and to the negative compound. Results demonstrate that the effect of preexposure on goldfish is their reduction of general responsiveness or level of arousal. (47 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Latent inhibition in human adults without masking.

Latent inhibition refers to attenuated responding to Cue X observed when the X-outcome pairings are preceded by X-alone presentations. It has proven difficult to obtain in human adults unless the preexposure (X-alone) presentations are embedded within a masking (i.e., distracting) task. The authors hypothesized that the difficulty in obtaining latent inhibition with unmasked tasks is related to the usual training procedures, in which the preexposure and conditioning experiences are separated by a set of instructions. Experiment 1 reports latent inhibition without masking in a task in which preexposure and conditioning occur without interruption. Experiments 2 and 3 demonstrate that this attenuation in responding to target Cue X does not pass a summation test for conditioned inhibition and is context specific, thereby confirming that it is latent inhibition. Experiments 3 and 4 confirm that introducing instructions between preexposure and conditioning disrupts latent inhibition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Second-order conditioning with food unconditioned stimulus.

3 experiments investigating 2nd-order conditioning were conducted with a total of 72 male Sprague-Dawley rats. An appetitive Pavlovian conditioning situation was employed in which the response measure was the amount of general activity. Exp I provided a well-controlled demonstration of substantial 2nd-order conditioning. In Exp II extinction of the 1st-order conditioned stimulus (CS) had no effect upon the response to the 2nd-order CS. Exp III examined the relationship of the 2nd-order conditioning paradigm to that of conditioned inhibition. Both phenomena could be observed simultaneously in the same setting. Implications for 2nd-order conditioning and related conditioning phenomena are discussed. (16 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)     

Memory for the conditioned response: The proactive effect of preexposure to potential conditioning stimuli and context change.

Three experiments with 48 cats investigated memory for CR as a function of proactive inhibition. The proactive operation was the preexposure to quasi-random presentations of the potential CS and UCS. The possible CSs were light and tone, and the UCSs were brief mild shocks to either the right or left paw, which produced a brisk leg jerk. In Exp I, all possible combinations of CS and UCS components of the eventual CR were present in the preexposure period for one or another group as in the traditional interference paradigms of human paired-associate memory research. Exp II demonstrated that the decline cannot be attributed to a strategy type of interpretation that asserts that when the retention–extinction situation occurs, Ss "backward scan" and judge themselves to be once again in the preexposure period. Performance immediately after reaching the conditioning criterion did not differ between the controls that experienced no preexposure and the experimentals, but it did so after the 10-wk retention interval. Exp III investigated the role of context in the memory deficits by maintaining the same context in the preexposure, conditioning, and memory test situations or giving the preexposure experience in an environment different from the other 2 situations. Context change greatly reduced but did not eliminate the proactive inhibition. It is concluded that the CR is readily forgotten given appropriate interference and does not differ from other kinds of learning in this respect. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Psychopathy and autonomic conditioning.

Utilized a delayed, differential paradigm to investigate electrodermal, cardiac, and vasomotor conditioning in 18 psychopathic, 18 nonpsychopathic, and 18 "mixed" inmates. 3 tones, each 10 sec. long, were presented 16 times each in random order, alone, or followed by a shock or slide of a nude female. The psychopaths gave very little evidence of differential electrodermal conditioning. However, they acquired differential cardiac and digital vasomotor responses just as readily as did the nonpsychopaths to the CS followed by shock or by slides. Neither group gave any evidence of differential cephalic vasomotor conditioning. The psychopaths exhibited a lower level of tonic electrodermal activity and were less electrodermally responsive than were the other Ss. There were no differences between groups in tonic heart rate or in cardiac or digital vasomotor responsivity. However, the psychopaths responded to shock with cephalic vasodilation while the nonpsychopaths responded with vasoconstriction. (34 ref.) (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)     

Associative regulation of Pavlovian fear conditioning: Unconditioned stimulus intensity, incentive shifts, and latent inhibition.

Conditional stimuli (CS) associated with painful unconditional stimuli (UCS) produce a naloxone-reversible analgesia. The analgesia serves as a negative-feedback regulation of fear conditioning that can account for the impact of UCS intensity and CS predictiveness on Pavlovian fear conditioning. In Exp 1, training under naloxone produced learning curves that approached the same high asymptote despite UCS intensity. Shifting drug treatment during acquisition had effects that paralleled UCS intensity shifts. In Exp 3, naloxone reversed Hall-Pearce (1979) negative transfer using a contextual CS, indicating that conditional analgesia acquired during the CS–weak-footshock phase retards acquisition in the CS–strong-footshock phase. Exp 5 used a tone CS in both a latent-inhibition and a negative-transfer procedure. Only negative transfer was blocked by naloxone. Therefore, negative transfer but not latent inhibition is mediated by a reduction of UCS processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Potentiation of latent inhibition.

Rats were given exposure either to an odor (almond) or a compound of odor plus taste (almond plus saline), prior to training in which the odor served as the conditioned stimulus. It was found, for both appetitive and aversive procedures, that conditioning was retarded by preexposure (a latent inhibition effect), and the extent of the retardation was greater in rats preexposed to the compound (i.e., latent inhibition to the odor was potentiated by the presence of the taste). In contrast, the presence of the taste during conditioning itself overshadowed learning about the odor. We argue that the presence of the salient taste in compound with the odor enhances the rate of associative learning, producing a rapid loss in the associability of the odor. This loss of associability will generate both overshadowing and the potentiation of latent inhibition that is observed after preexposure to the compound. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Context specificity of conditioning, extinction, and latent inhibition.

Three experiments, using a conditioned suppression procedure with 112 male hooded Lister rats, examined the mechanisms of context specificity of conditioning, extinction, and latent inhibition. Exp I replicated previous demonstrations of context specificity of conditioning and extinction. Conditioning in one context did not necessarily transfer perfectly to another, and if extinction was carried out in a context different from that of conditioning, Ss showed a recovery of suppression when tested in the conditioning context. But both of these results disappeared when the familiarity and associative values of the 2 contexts were equated. Exp II replicated this failure to obtain context specificity of conditioning and extinction, but it did obtain context specificity of latent inhibition. Ss preexposed and conditioned to stimuli in the same context showed more profound latent inhibition than those preexposed and conditioned in different contexts. In Exp III, this effect was replicated. It is concluded that context specificity of conditioning or extinction may arise from the failure to control the associative status of the contexts used, whereas that of latent inhibition can best be explained by A. R. Wagner's (1976, 1981) theory of associative learning. Results offer no support for the view that, under conditions such as these, contexts serve as conditional cues, signaling the relationships between events occurring in their presence. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Latent inhibition.

Reviews the latent inhibition literature concerning the decremental effects of nonreinforced preexposure to the to-be-conditional stimulus on subsequent learning. Latent inhibition is found to be a broadly based phenomenon appearing across a variety of species (goldfish, goat, sheep, rat, rabbit, dog, human child, and, under special conditions, the human adult) and across a variety of tasks (classical conditioning, avoidance conditioning, Ivanov-Smolensky conditioning, conditioned emotional response, go/no-go discrimination, reaction time, and conditioned taste aversion paradigms). The stability of latent inhibition as well as its stimulus specificity and the effects of number of nonreinforced preexposures are examined. Current explanations of latent inhibition which include the habituation of the orienting response, selective filtering, specific antagonistic and complementary responses, and conditioned inhibition are discussed. The need for a combined learning and attention theory is suggested. (64 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pavlovian second-order conditioned analgesia.

Three experiments, with 118 Sprague-Dawley rats, assessed conditioned analgesia in a Pavlovian 2nd-order conditioning procedure by using inhibition of responding to thermal stimulation as an index of pain sensitivity. In Exp I, Ss receiving 2nd-order conditioning showed longer response latencies during a test of pain sensitivity in the presence of the 2nd-order conditioned stimulus (CS) than Ss receiving appropriate control procedures. Exp II found that extinction of the 1st-order CS had no effect on established 2nd-order conditioned analgesia. Exp III evaluated the effects of post 2nd-order conditioning pairings of subcutaneous morphine sulfate (10–20 mg/kg) and the shock unconditioned stimulus/stimuli (UCS). Ss receiving paired morphine–shock presentations showed significantly shorter response latencies during a hot-plate test of pain sensitivity in the presence of the 2nd-order CS than did Ss receiving various control procedures; 2nd-order analgesia was attenuated. Data extend the associative account of conditioned analgesia to 2nd-order conditioning situations and are discussed in terms of the mediation of both 1st- and 2nd-order analgesia by an association between the CS and a representation or expectancy of the UCS, which may directly activate endogenous pain inhibition systems. (52 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Second-order excitation mediated by a backward conditioned inhibitor.

Conditioned suppression studies with rats explored the informational content of a backward conditioned inhibitor. Pairings of an unconditioned stimulus/stimuli (UCS) and Stimulus 1 (US > S1) established S1 as an inhibitor in Exp 1. Pairing the inhibitor S1 with a novel S2 (S2→S1) promoted excitatory second-order conditioning (SOC) to S2, which suggested S1 was well associated with the UCS. Degrading presumed S1-US associations in Exp 2 by S1- (extinction) treatment eliminated S2's excitation while preserving Sl's inhibition. Exp 3 and 4 converged in showing that S2 was not an excitor when Pavlovian conditioned inhibition (CI) was the inhibitory treatment prior to the SOC phase, but instead acted as a second-order inhibitor. Results are discussed in relation to the temporal coding hypothesis, the SOP ("sometimes opponent process") and Rescorla-Wagner models of conditioning, and the associative structure of SOC. Also, the data suggest that backward inhibition is special and that not all forms of CI are equal. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A cohort mortality study of foundry workers

The present study aimed to demonstrate conditioned inhibition of Pavlovian conditioning of autonomic responses in humans. Subjects (N = 21) were presented initially with four geometric shapes (A, B, C and D). An electric shock served as the unconditioned stimulus (US) during acquisition. Conditional stimuli lasted for 8 s and US onset coincided with CS offset. Subjects were trained with A-US, C-US, and AC-US pairings and AB alone and B alone presentations. The subsequent summation test consisted of C-US pairings and CB alone and CD alone presentations. Conditioning was evident in self-reported US expectancy and first and second interval electrodermal responses. Evidence for conditioned inhibition during the summation test was found in US expectancy and second interval electrodermal responses.     

Latent inhibition and stimulus generalization of the classically conditioned nictitating membrane response in rabbits (Oryctolagus cuniculus) following hippocampal ablation.

30 male and female New Zealand albino rabbits received 0 to 450 exposures of a tone CS prior to classical defensive conditioning of the nictitating membrane response based on an infraorbital eye shock UCS. Tone preexposure resulted in retarded conditioning in normal Ss, but was not present in Ss with bilateral dorsal hippocampectomy produced by aspiration. Controls with bilateral neocortical and callosal aspiration lesions demonstrated a latent inhibition effect similar to that shown by normal nonoperated Ss. The failure of CS preexposure to retard conditioning in hippocampal Ss was not due to differences in threshold of the conditioned response to the CS or to differences in response mechanisms as determined by tests of habituation and dishabituation of the UCR. A subsequent experiment with 24 Ss used combined-cue summation tests to confirm the fact that preexposure did not endow the tone with conditioned as well as latent inhibitory properties. Finally, tests of stimulus generalization along the auditory frequency dimension indicated flatter relative gradients for hippocampals than for nonoperated controls, with cortical controls in between. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)