Duration of signals for intertrial reinforcement and nonreinforcement in random control procedures.

In the random control procedure, responding to a conditioned stimulus (target CS) is prevented when the probability of unsignaled, unconditioned stimuli (UCS) in the intertrial interval (ITI) is equal to the probability of the UCS in the presence of the target CS. Three experiments used an autoshaping procedure with White Carneaux pigeons to examine the effects of the temporal duration of signals for the ITI UCS (cover CSs) and for concomitant periods of nonreinforcement. In Experiment 1, a short duration cover, but not a long duration cover, resulted in responding to the target CS. In Experiment 2, an explicit CS– cue during periods of nonreinforcement did not affect target acquisition. In Experiment 3, a long CS–, but not a short cover CS, was a sufficient condition for the acquisition of responding to the target CS. These results imply that the acquisition of responding to a target CS requires a discriminable period of nonreinforcement that is long relative to the target CS duration. (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)     

Context effects on choice

Four pigeons responded on a concurrent-chains schedule in four experiments that examined whether the effectiveness of a stimulus as a conditioned reinforcer is best described by a global approach, as measured by the average interreinforcement interval, or by a local contextual approach, as measured by the onset of the stimulus preceding the conditioned reinforcer. The interreinforcement interval was manipulated by the inclusion of an intertrial interval, which increased the overall time to reinforcement but did not change the local contingencies on a given trial A global analysis predicted choice for the richer alternative to decrease with the inclusion of an intertrial interval, whereas a local analysis predicted no change in preference. Experiment 1 examined sensitivity to intertrial intervals when each was signaled by the same houselight that operated throughout the session. In Experiment 2, the intertrial interval always was signaled by the stimulus correlated with the richer terminal link. In Experiment 3, the intertrial interval was signaled by the keylights correlated with the initial links and two novel houselights. Experiment 4 provided free food pseudorandomly during the intertrial interval. In all experiments, subjects' preferences were consistent with a local analysis of choice in concurrent chains. These results are discussed in terms of delay-reduction theory, which traditionally has failed to distinguish global and local contexts.     

Role of signals for unconditioned stimulus absence in the sensitivity of autoshaping to contingency.

Pigeons autoshape to a keylight conditioned stimulus (CS) that is poorly correlated with a food unconditioned stimulus (UCS) if UCSs occurring in the absence of the CS are signaled by some other cue. Three experiments examined if this is because signaling blocks context conditioning or because it converts the intertrial interval (ITI) into a predictor of UCS absence. Results indicated that cuing periods of UCS absence was not sufficient for acquisition. Signaling failed to produce acquisition if the signal also accompanied the CS, although this procedure converts the ITI into a predictor of UCS absence. The detrimental effect of compounding the signal with the CS occurred only if the signal was separately paired with the UCS, which suggests it was due to blocking of the CS by the signal. The results suggested that the signaling effect depends on blocking of the context by the signal, not on conversion of the ITI into a signal for UCS absence. (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)     

CS modality transfer of two-way avoidance in rats with central and basolateral amygdala lesions

Post-lesion acquisition of two-way avoidance and subsequent transfer to two warning signals (conditioned stimulus, CS) of different modality were investigated in 60 rats. In Experiment I the animals were originally trained with less salient (darkness) CS, then transferred to more salient compound (darkness and white noise), and finally to white noise CS. The opposite arrangement of the conditioned stimuli (CSi) during the subsequent stages was employed in Experiment II. In control animals, avoidance acquisition was faster and the intertrial responding (ITR) rate lower with the auditory than with the visual CS. Lesioned rats learned avoidance responses more slowly, independently of CS modality. The transfer to other CSi revealed dramatic between-group difference in the level and consistency of avoidance response, shuttle-box latencies and ITR rate. In control animals, transfer to more salient CSi enhanced avoidance performance, whereas change to less salient CS decreased it. Rather small changes in shuttle-box performance and consistency of avoidance response due to CS modality were seen in rats with the basolateral lesions. In contrast, central nucleus injury caused a strong deterioration in the avoidance transfer, especially when the visual CS followed the acoustic one. The results indicate differential involvement of the basolateral and central amygdala nuclei in stimulus-processing mechanisms of instrumental defensive behavior.     

Importance of trials versus accumulating time across trials in partially reinforced appetitive conditioning.

Four experiments with rats examined partial reinforcement in appetitive conditioning. In Experiment 1, adding nonreinforced trials to a continuous reinforcement schedule slowed acquisition, whereas deleting reinforcers did not. Trial massing suppressed performance and learning. In Experiment 2, conditioning with a short conditioned stimulus (CS) was rapid, and partial reinforcement with a short CS was as effective as continuous reinforcement with equal accumulated time in the CS. In Experiment 3, conditioning was nevertheless influenced by the probability of reinforcement. In Experiments 3 and 4, conditioning was especially disrupted when nonreinforced trials preceded reinforced trials closely in time. The results underscore the importance of temporal variables in conditioning but are more consistent with trial-based accounts than time-accumulation accounts of conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus competition between a discrete cue and a training context: Cue competition does not result from the division of a limited resource.

Several associative learning theories explain cue competition as resulting from the division of a limited resource among competing cues. This leads to an assumption that behavioral control by 2 cues competing with each other should always reflect a tradeoff, resulting in apparent conservation of total reinforcer value across all competing cues. This assumption was tested in 3 conditioned lick suppression experiments with rats, investigating the effects of changing the conditioned stimulus (CS) duration (Experiment 1), administering pretraining exposures to the CS (Experiment 2), and presenting nonreinforced CSs during the intertrial interval (Experiment 3) on Pavlovian conditioned responding to both the CS and the conditioning context. Fear conditioned to the context and to the CS decreased when the CS was of longer duration, massively preexposed before being paired with the reinforcer, or presented alone during the intertrial interval. These observations are problematic for the theories that explain cue competition as the division of a limited resource and suggest that the total reinforcer value across competing cues is not always fixed for a given reinforcer. (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)     

Bridging temporal gaps between CS and US in autoshaping: Insertion of other stimuli before, during, and after CS.

In 4 experiments, female White Carneaux pigeons were exposed to key-light illuminations separated from food delivery by 12–60 sec. Approach to the key light did not develop on conventional trace-conditioning arrangements but occurred consistently whenever some auditory or visual stimulus filled the CS–UCS gap (serial conditioning) or was always present except during the gap. The CS approach was strong only when the stimulus present during the intertrial interval remained on until the termination of CS; if the stimulus ended at CS onset, conditioning did not occur. Although discriminability of CS–UCS gaps from intertrial periods seemed necessary for conditioning to occur in the absence of close CS–UCS contiguity, the outcome of the final experiment indicates that such discriminability was not sufficient for conditioning. Results are discussed in terms of possible 2nd-order conditioning effects and the changes in the associative strength of the "local context" existing when the CS appears, which may lead to superconditioning of CS. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Responses eliminated by noncontingent or negatively contingent reinforcement recover in extinction

Autoshaped key pecking in pigeons was eliminated by presenting reinforcers only during non-CS periods (negatively contingent reinforcement) or in both non-CS and CS periods (noncontingent reinforcement). In either case, when all reinforcers were subsequently removed (simple extinction), responding recovered strongly (Experiment 1). Recovery in extinction occurred only if the CS was in a conditioned state when non-CS reinforcers were introduced (Experiment 2). Recovery from noncontingent reinforcement was virtually complete, since total responding in extinction after response elimination was not less than in control groups extinguished without an intervening response-elimination phase (Experiment 3). Recovery also occurred for nonautoshapable, instrumentally reinforced key pecking (Experiment 4). The hypothesis that recovery is due to reinstatement of the non-CS stimulus conditions of acquisition (absence of food) was not supported (Experiments 5 and 6). Other accounts of recovery are considered.     

Double dissociation of effects on learning of medial versus lateral hyperstriatal lesions in pigeons.

Three experiments examined the effects of medial and lateral hyperstriatal lesions in two groups of pigeons. In Experiment 1, both hyperstriatal groups were impaired, relative to unoperated and operated control groups, in postoperative performance of preoperatively acquired serial reversal of both spatial and visual discriminations. The deficits of the two hyperstriatal groups appeared both quantitatively and qualitatively similar. Experiment 2 found that performance of spatial reversals was disrupted in the medial, but not in the lateral, hyperstriatal group by a long intertrial interval. Experiment 3 found that acquisition of simultaneous matching-to-sample was disrupted by lateral, but not by medial, hyperstriatal lesions; the lateral group also showed a lower rate of response to the sample stimulus than any of the other groups. Implications of these findings for current theories of hyperstriatal function are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The temporal dynamics of a visual discrimination: The role of stimulus comparison and opponent processes.

The influence of trial spacing on simple conditioning is well established: When successive reinforced conditioned stimulus, CS+, trials are separated by a short interval (massed training), conditioned responding emerges less rapidly than when such trials are separated by longer intervals (spaced training). This study examined the influence of trial spacing on the acquisition of an appetitive visual discrimination in rats. Experiments 1 and 2 established that massed training facilitates the acquisition of such discriminations. The results of subsequent experiments demonstrated that this trial-spacing effect reflects the proximity of nonreinforced, CS-, trials to preceding (Experiment 3) and signaled (Experiment 4) presentations of the reinforcer. Experiment 5 showed that the facilitation of discrimination learning with massed training reflected an effect on learning rather than performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Overshadowing and stimulus duration.

In 3 experiments, the authors investigated the effect of stimulus duration on overshadowing. Experiments 1 and 2 examined responding to a target conditioned stimulus (CS1) when it was conditioned in compound with a coterminating overshadowing stimulus (CS2) that was longer, shorter, or of the same duration (the long, short, and matched groups, respectively). Equal overshadowing of conditioning to CS1 was obtained in all 3 conditions relative to a control group conditioned to the light alone. There were, however, differences in responding to CS2 as a function of its absolute duration. Experiment 3 examined the contribution of the food-food interval/CS onset-food interval ratio to these findings. In Experiments 1 and 2, the ratio differed for the overshadowing CS but not for the target CS. In Experiment 3, this arrangement was reversed, but the pattern of results remained the same. The implications of these findings for trial-based and real-time models of conditioning are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Intertrial interval as a contextual stimulus: Further analysis of a novel asymmetry in temporal discrimination learning.

Four experiments investigated discrimination learning when the duration of the intertrial interval (ITI) signaled whether or not the next conditional stimulus (CS) would be paired with food pellets. Rats received presentations of a 10-s CS separated half the time by long ITIs and half the time by short ITIs. When the long ITI signaled that the CS would be reinforced and the short interval signaled that it would not be (Long+/Short?), rats learned the discrimination readily. However, when the short ITI signaled that the CS would be reinforced and the long interval signaled that it would not (Short+/Long?), discrimination learning was much slower. Experiment 1 compared Long+/Short? and Short+/Long? discrimination learning with 16-min/4-min or 4-min/1-min ITI combinations. Experiment 2 found no evidence that Short+/Long? learning is inferior because the temporal cue corresponding to the short interval is ambiguous. Experiment 3 found no evidence that Short+/Long? learning is poor because the end of a long ITI signals a substantial reduction in delay to the next reinforcer. Long+/Short? learning may be faster than Short+/Long?because elapsing time involves exposure to a sequence of hypothetical stimulus elements (e.g., A then B), and feature-positive discriminations (AB+/A?) are learned quicker than feature-negative discriminations (A+/AB?). Consistent with this view, Experiment 4 found a robust feature-positive effect when sequentially presented CSs played the role of elements A and B. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Timed excitatory conditioning under zero and negative contingencies.

Rats (rattus norvegicus) anticipated the arrival of a food pellet unconditioned stimulus (US) even when the conditioned stimulus (CS) signaled no overall change or a substantial decrease in the overall rate of US occurrence. Pellet USs were scheduled probabilistically in the intertrial interval at either an equivalent rate (Experiment 1) or a four times higher rate (Experiments 2 and 3) than in the CS, which included one fixed-time target US. Conditioning has been said to involve learning "whether" (contingency) the CS signals a change in the US, and if so, "when" (contiguity) the US is scheduled to arrive. Our results suggest that "when" trumps "whether," challenging the received view that a positive CS-US contingency is necessary for successful conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal Learning in Random Control Procedures.

Experiments 1 and 2 delivered conditioned stimuli (CSs) at random times and unconditioned stimuli (USs) at either fixed (Experiment 1) or random (Experiment 2) intervals. In Experiment 3, CS duration was manipulated, and US deliveries occurred at random during the background. In all 3 experiments, the mean rate of responding (head entries into the food cup) in the background was determined by the mean US-US interval, and the mean rate during the CS was a linear combination of responding controlled by the mean US-US and mean CS onset-US intervals; the pattern of responding in time was determined by the interval distribution form (fixed or random). An event-based timing account, Packet theory, provided an explanation of the results. (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)     

Pavlovian contingencies and temporal information.

The effects of altering the contingency between the conditioned stimulus (CS) and the unconditioned stimulus (US) on the acquisition of autoshaped responding was investigated by changing the frequency of unsignaled USs during the intertrial interval. The addition of the unsignaled USs had an effect on acquisition speed comparable with that of massing trials. The effects of these manipulations can be understood in terms of their effect on the amount of information (number of bits) that the average CS conveys to the subject about the timing of the next US. The number of reinforced CSs prior to acquisition is inversely related to the information content of the CS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)