Temporal Coding in Conditioned Inhibition: Analysis of Associative Structure of Inhibition.

Two experiments with rats as subjects were conducted to investigate the associative structure of temporal control of conditioned inhibition through posttraining manipulation of the training excitor-unconditioned stimulus (US) temporal relationship. Experiment 1 found that following simultaneous Pavlovian inhibition training (i.e., A → US/XA-no US) in which a conditioned stimulus (CS A) was established as a delay excitor, maximal inhibition was observed on a summation test when CS X was compounded with a delay transfer CS. Furthermore, posttraining shifts in the A-US temporal relationship from delay to trace resulted in maximal inhibition of a trace transfer CS. Experiment 2 found complementary results to Experiment 1 with an A-US posttraining shift from serial to simultaneous. These results suggest that temporal control of inhibition is mediated by the training excitor-US temporal relationship. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Posttraining shifts in the overshadowing stimulus–unconditioned stimulus interval alleviates the overshadowing deficit.

Two conditioned lick suppression experiments explored the effects on overshadowing of a posttraining change in the temporal relationship between the overshadowing conditioned stimulus (CS) and the unconditioned stimulus (US). Rats received either trace (Experiment 1) or delay (Experiment 2) overshadowing training. Then pairings of the overshadowing CS and US were given with either a trace or delay temporal relationship. Overshadowing was alleviated by shifting the overshadowing CS–US temporal relationship so that it no longer matched the overshadowed CS–US temporal relationship. These outcomes are explicable in terms of an integration of the comparator hypothesis, which states that cue competition effects (e.g., overshadowing) will be maximal when the information potentially conveyed by competing CSs is equivalent, and the temporal coding hypothesis, which states that CS–US intervals are part of the information encoded during conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Odor-guided fear conditioning in rats: 1. Acquisition, retention, and latent inhibition.

Three experiments examined the acquisition, retention, and latent inhibition of odor-guided fear conditioning in rats. The results of Experiment 1 indicate that forward conditioned stimulus (CS)–unconditioned stimulus (US) pairings resulted in robust freezing responses to subsequent presentation of the CS alone. In Experiment 2, rats in one group (PRE) received unreinforced preexposures to the odorant CS, and those in a second group (NON) were not preexposed to the odorant. All rats then received forward CS–US pairings. PRE rats exhibited a marked attenuation of freezing to subsequent exposure to the CS relative to NON rats. All rats were then retested at one of the following posttraining delays: 17, 24, or 31 days. Freezing behavior of the NON rats declined significantly across these delays, whereas rats in the PRE group froze no more at any delay than they had 24 hr after training. Experiment 3 examined the contextual specificity of latent inhibition. Only those rats that were preexposed and were trained in the same context exhibited latent inhibition. These results indicate that odor-guided fear conditioning is a robust and useful paradigm suitable for future studies of the neural bases of associative learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal specificity of fear conditioning: Effects of different conditioned stimulus--unconditioned stimulus intervals on the fear-potentiated startle effect.

Separate groups of rats were given 30 pairings of a light (conditioned stimulus, CS) and a 500-ms shock (unconditioned stimulus, US) at CS–US intervals of 0, 25, 50, 100, 200, 800, 3,200, 12,800, or 51,200 ms. Other groups had lights and shocks inconsistently paired. The startle reflex was elicited 2–4 days later with a noise burst alone or 25–51,200 ms after light onset. After CS–US pairings over a range of intervals (25–51,200 ms), startle was potentiated in testing, as rapidly as 50 ms after light onset. Magnitude of potentiation and resistance to extinction were generally greater with longer CS–US intervals. In several groups, potentiation was maximal at a test interval that matched the CS–US interval used in training. This temporal specificity sharpened with increasing numbers of training trials but even occurred with a single training trial in which a 51,200-ms CS–US interval was used. Data indicate that even during simple fear conditioning (FC), animals rapidly learn a temporal CS–US relationship. This has implications for understanding the neural mechanisms of FC. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Extending conditioned stimuli before versus after unconditioned stimuli: Implications for real-time models of conditioning.

In four experiments using the conditioned suppression procedure with rats, we compared the effects of extending conditioned stimuli (CSs) before versus after reinforcement (called B vs. A extensions). In Experiments 1 and 2, Group 0 (no extension) received 2-min noise CS trials (3 per day in Experiment 1, 1 per day in Experiment 2) that terminated with a 1-s grid shock unconditioned stimulus (US). For Group B, the CS began 12 min before the US; for Group A, the CS began 2 min before the US but persisted for 10 min past US termination. In Experiments 3 and 4, similar trials (3 per day in Experiment 3, 1 per day in Experiment 4) included a 2-min light CS that always terminated with the US; thus the noise CS became a systematically manipulated context cue in which light-shock pairings were embedded. In Experiments 1 and 2 we found asymmetrical effects of CS extensions: B extensions weakened conditioning more than did A extensions. In Experiments 3 and 4 we found symmetrical effects: A and B extensions weakened context conditioning equally. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learned irrelevance exceeds the sum of CS-preexposure and US-preexposure deficits.

Barpress suppression by water-deprived rats was used to examine the retarded emergence of excitatory responding when a tone conditioned stimulus (CS) and a shock unconditioned stimulus (US) were paired following uncorrelated exposure to the CS and US. Experiment 1{a} established parameters whereby the retardation resulting from preconditioning CS-alone presentations (latent inhibition) was eliminated by presenting unpredictable, nontarget neutral stimuli (clicks) after each CS during the preconditioning phase, a treatment thought to maintain attention to the CS. Experiment 1{b} established parameters whereby the retardation resulting from preconditioning US-alone presentations was eliminated by preceding each US with a 2nd nontarget cue (a light) during the preconditioning phase, which presumably reduced acquisition of context–US associations. In Experiment 1{c}, the techniques to attenuate CS-preexposure and US-preexposure effects were imposed on a random schedule of CS and US presentations. Although this procedure reduced subsequent retardation, an appreciable response deficit remained. In Experiment 2 a context shift between CS-alone or US-alone presentations and subsequent CS–US pairings eliminated retardation, but retardation arising from uncorrelated exposures to the CS and US, albeit significantly reduced, transferred between contexts. These results suggest that the deficit resulting from preconditioning, uncorrelated exposures to the CS and US is composed of a CS preexposure effect, a US preexposure effect, and learned irrelevance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Counterconditioning of an overshadowed cue attenuates overshadowing.

In 3 Pavlovian conditioned lick-suppression experiments, rats received overshadowing treatment with a footshock unconditioned stimulus such that Conditioned Stimulus (CS) A overshadowed CS X. Subjects that subsequently received CS X paired with an established signal for saccharin (CS B) exhibited less overshadowing of the X–footshock association than subjects that did not receive the X–B pairings (Experiment 1). Experiment 2 replicated this effect and controlled for some additional alternative accounts of the phenomenon. In Experiment 3, this recovery from overshadowing produced by counterconditioning CS X was attenuated if CS B was massively extinguished prior to counterconditioning. These results are more compatible with models of cue competition that emphasize differences in the expression of associations than those that emphasize differences in associative acquisition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Backward conditioning: Mediation by the context.

The information acquired in backward conditioning (i.e., outcome→cue) was assessed in 3 Pavlovian lick-suppression experiments with water-deprived rats as subjects. Experiment 1 confirmed previous research that few outcome→cue pairings made the cue into a conditioned excitor and additionally showed that massive posttraining extinction of the training context attenuated a backward-trained cue's excitatory value. Experiment 2 found that many outcome→cue pairings made the cue into a conditioned inhibitor and that the same context manipulation attenuated this inhibitory value. Experiment 3 confirmed the observations of Experiments 1 and 2 and demonstrated that these effects of context extinction were specific to backward-trained cues conditioned in the extinguished context. These results are interpreted in terms of cue→context and context→outcome associations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms of second-order conditioning with a backward conditioned stimulus.

Five conditioned suppression experiments with rats examined the conditions under which backward pairings endow a first-order conditioned stimulus (CSI) with the ability to serve as a secondary reinforcer. Experiments 2-5B found evidence for excitatory second-order conditioning (SOC) if, during first-order pairings, the US-CS I interval was 0 s rather than 3 s. Levels of SOC were comparable after forward and backward pairings (Experiments 1-3), and were unaffected by extinction of CS I after SOC (Experiment 3). These results suggest that forward and backward CSIs support SOC for the same reason, and they call into question the need to invoke any special mechanism such as memory integration. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of stimulus ambiguity in conditional learning.

Three experiments using rats and the conditioned emotional response procedure examined the notion that when a conditioned stimulus (CS) is paired with a reinforcer (US), that CS must be ambiguous if the CS–US association is to become the target of conditional control. CS ambiguity was manipulated by varying whether the CS had been preexposed prior to conditioning. In Experiments 1 and 2, it was demonstrated that a cue that accompanied pairings of a CS and shock acquired conditional control over the CS–shock association when that CS had been preexposed, but not when it was novel. The measure of conditional control in Experiments 1 and 2 was the ability of the (conditional) cue to enhance responding to the target CS. Experiment 3 used a blocking procedure to show that this enhancement reflected an amplification of the target CS's effective associative strength. These findings extend existing knowledge of the conditions required for conditional cue formation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intertrial unconditioned stimuli preferentially interfere with delay conditioning.

One way to minimize excitation acquired by the conditioned stimulus (CS) is to introduce intertrial presentations of the unconditioned stimulus (US). However, even in the presence of frequent intertrial USs, Experiments 1a and 1b found that rats anticipated the customary arrival time of a food pellet US when it occurred before (embedded)—versus coincident with (delay)—the termination of a white noise CS. Delay conditioning emerged in Experiment 2 in the absence of intertrial USs; hence, the detrimental effects of intertrial USs depended on the CS-US relationship, delay versus embedded, and not the duration of CS-US interval. Experiments 3a, 3b, and 4 found that random USs located in the early portion of the intertrial interval increased the control acquired by contextual stimuli at the expense of temporal stimuli occasioned near CS termination. Our results suggest that delay relationships leave the CS especially vulnerable to the deleterious effects of intertrial USs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus and temporal cues in classical conditioning.

In 2 experiments, separate groups of rats were given stimulus conditioning, temporal conditioning, untreated control and (in Experiment 2) learned irrelevance control procedures followed by a compound with both stimulus and temporal cues. Stimulus conditioning consisted of a random 15-s duration conditioned stimulus (CS) followed by food; temporal conditioning consisted of food–food intervals of fixed 90 s (Experiment 1) or fixed 75?+?random 15 s (Experiment 2). The stimulus group abruptly increased responding after CS onset, and the temporal group gradually increased responding over the food–food interval. When the food–food interval was fixed 90 s, the temporal cue exerted stronger control in the compound, whereas when the food–food interval was fixed 75?+?random 15 s, the stimulus cue exerted stronger control. The strength of conditioning, temporal gradients of responding, and cue competition effects appear to reflect simultaneous timing of multiple intervals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms of Pavlovian conditioning: Role of protection from habituation in spinal conditioning.

Conditioned antinociception can be established in spinal rats by pairing stimulation to one hind leg (the conditioned stimulus [CS]) with an intense tailshock (the unconditioned stimulus [US]). After this training, the paired CS (CS+) elicits greater antinociception on the tail-flick test than a CS that was explicitly unpaired (CS–). Five experiments are reported that suggest that this effect reflects protection from habituation. Experiment 1 showed that the CS (legshock) induces antinociception before training. Presenting the CS alone weakened (habituated) its antinociceptive impact (Experiment 2). Less habituation was observed when the CS was paired with the US (Experiment 3). Decreasing habituation to the CS– (by increasing the interval between trials) and facilitating habituation to the CS+ (by increasing the number of trials) effectively eliminated the CS+/CS– difference (Experiments 4 and 5). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of contingency in classical conditioning.

The assumption that classical conditioning depends on a contingent relation between the conditioned stimulus (CS) and the unconditioned stimulus (US), which was proposed some decades ago as an alternative to the traditional contiguity assumption, still is widely accepted as an empirical generalization, if no longer as a theoretical postulate. The first support for the contingency assumption was provided by experiments in which occasional CS–US pairings produced no response to the CS in random training—i.e., training in which the probability of the US was the same in the presence and absence of the CS. Those early experiments, the results of which too often are taken at face value, are reconsidered along with various later experiments that show conditioning, both of the CS and its context, in random training. The evidence suggests that CS–US contingency is neither necessary nor sufficient for conditioning and that the concept has long outlived any usefulness it may once have had in the analysis of conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contextual control over conditioned responding in a latent inhibition paradigm.

We used 1-, 2-, and 3-context designs to study the control exerted by contexts over freezing in rats exposed to a conditioned stimulus (CS) in advance of its pairing with a shock unconditioned stimulus. The latent inhibition observed when preexposure, conditioning, and testing occurred in the same context was attenuated if preexposure occurred in a different context to conditioning and testing. Latent inhibition (i.e., attenuated performance) was restored in a CS-specific manner if preexposure and testing occurred in the same context and conditioning in a different one. Latent inhibition was also reduced by a long retention interval but remained specific for a particular context–CS relation. Finally, CS preexposure resulted in contextual control over the expression of excitatory conditioned performance. The results are discussed in terms of memory, associative, and associative-performance models of CS-preexposure effects. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contrasting reduced overshadowing and blocking.

Preexposure of a cue without an outcome (X-) prior to compound pairings with the outcome (XZ→O) can reduce overshadowing of a target cue (Z). Moreover, pairing a cue with an outcome (X→O) before compound training can enhance its ability to compete with another cue (i.e., blocking). Four experiments were conducted in a conditioned bar-press suppression preparation with rats to determine whether spacing of the X- or X→O trials would differentially affect reduced overshadowing and blocking. Experiment 1a showed that reduced overshadowing was larger with massed trials than with spaced trials. Experiment 1b found that blocking was larger with spaced trials than with massed trials. Experiments 2a and 2b indicated that these effects of trial spacing were both mediated by the associative status of the context at test. The results are interpreted in the framework of contemporary learning theories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pairings of a drug or place conditioned stimulus with lithium chloride produce conditioned sickness, not antisickness.

In different experiments, pairings of a drug (pentobarbital or morphine) or place as the conditioned stimulus (CS) with lithium-induced sickness as the unconditioned stimulus (UCS) were given to rats to produce Pavlovian conditioning. Control rats received unpaired exposures. In the test, each rat was exposed to the CS, injected with lithium, and then offered food. If such pairings produce conditioning of antisickness (i.e., a compensatory response that opposes lithium sickness), then the experimental rats should eat more than the controls. The reverse occurred. Thus, pairings of a drug or place CS with a lithium UCS resulted in conditioned sickness rather than antisickness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Excitation and inhibition in unblocking.

In four experiments the nature of learning established with unblocking procedures in the appetitive conditioning of rats was examined. Measures of learning included response topography, effects of selective satiation, and summation and retardation tests of conditioned inhibition. One cue (A) was first paired with either a single unconditioned stimulus event, US1, or a sequence of two events, US1→US2. US2 was either qualitatively similar to (US2-Same) or different from (US2-Diff) US1. Then, a compound of A and a novel cue (X) was reinforced with US1 or US1→US2. Conditioning to X was blocked if either the single US1 or the US1→US2 sequence was used in both phases. If X accompanied an upshift in the reinforcer, from US1 to US1→US2, it acquired conditioned responding, especially when US2-Diff was used. Responding in the latter case was the consequence of both X-US1 and X-US2 associations. In Experiments 1–3, if X accompanied a downshift from US1→US2-Same to US1, it acquired conditioned responding that was based on X–US1 associations, but if it accompanied a downshift from US1→US2-Diff to US1, it acquired conditioned inhibition based on X-US2 associations. In Experiment 4, X acquired net inhibition at short US1→US2 intervals and net excitation at longer intervals, with downshifts from either US1→US2-Same or US1→US2-Diff to US1. However, the interval gradient was broader with downshifts from US1→US2-Diff. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioning across the duration of a backward conditioned stimulus.

Five conditioned suppression experiments examined the extent to which an appetitively motivated lever-press response can be punished by different components of a backward conditioned stimulus (CS). Using a 0-s unconditioned stimulus UCS–CS interval, Experiments 1 and 2 showed that the initial 3 s of a normally 30-s backward CS served as a more effective punisher than the CS as a whole, Experiment 3 found no such effect if the UCS–CS interval were 3 s rather than 0 s. Experiments 4A and 4B found that if the UCS–CS interval were 0 s, the initial part of the backward CS acquired excitatory properties although the CS as a whole passed a summation test for conditioned inhibition. By contrast, the 3-s UCS–CS interval supported inhibitory conditioning across the whole duration of the backward CS. Taken together, these findings support a modified version of Wagner's sometimes opponent process model, which suggests that different components of a backward CS become either excitatory or inhibitory depending on the components' temporal proximity to the UCS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition of conditioned associations in Hermissenda: Additive effects of contiguity and the forward interstimulus interval.

Examined conditioned suppression of photokinesis (CSPK) by the marine mollusc in 3 experiments. In each experiment, groups of Ss received light (conditioned stimulus, CS) paired with high-speed orbital rotation (unconditioned stimulus, UCS), light and rotation explicitly unpaired, or no exposure to these stimuli. 24 hrs after training, all Ss were tested for CSPK in the presence of the light. 50 CS–UCS pairings resulted in a marginal CSPK, whereas 100 and 150 pairings produced strong CSPK. In Exp 2, delay between CS onset and UCS onset was varied between 1 and 10 s. The 10-s interstimulus interval (ISI) did not support conditioning, whereas 1-s and 2-s ISIs were effective. In Exp 3, CS–UCS pairings in which the CS preceded the onset of the UCS and ended with the offset of the UCS evoked stronger CSPK than either a CS that preceded the UCS and ended with its onset or a CS that was paired in simultaneous compound with the UCS. CS–UCS contiguity and the forward ISI act additively to establish the CS–UCS association. No differences were observed between groups that were untreated and that received the CS and UCS unpaired. Similarities are noted in the temporal characteristics of associative learning in these Ss and vertebrate species. (PsycINFO Database Record (c) 2010 APA, all rights reserved)