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)     

Effect of signaling intertrial unconditioned stimuli in autoshaping.

Context–UCS associations have been suggested as the mediator of the response decrement that occurs when extra UCSs are added to the intertrial intervals (ITIs) of a standard Pavlovian conditioning situation. The present autoshaping experiments were concerned with the effect of signaling those extra UCSs, since such signaling might be expected to lessen their ability to condition the context. In Exp I, 16 female Carneaux pigeons were trained in Skinner boxes before receiving pretraining with the CS to be used as the signal of the ITI UCSs. During the main training, Ss were given autoshaping with a keylight CS. Exp II used a tone CS with 31 Ss. Results show that signaling the ITI UCSs did reduce their detrimental effects in responding to the CS. To determine whether that reduction was due to an impact of signaling on the target-CS/UCS association or on performance to the target-CS, Exp III examined responding to differentially trained CSs in a common context, as well as responding to identically trained CSs in differentially trained contexts with 32 Ss. More responding occurred to the CS trained with signaled, as compared with unsignaled, ITI UCSs; further, there was more responding to that CS in the more highly valued context. Results suggest that contextual value does interact with CS–UCS learning and may also affect performance to the CS. (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simultaneous and backward fear conditioning in the rat.

Examined simultaneous and backward Pavlovian conditioning paradigms using a UCS event which was longer in duration than the CS. 3 experiments with male Sprague-Dawley rats (N = 96) paired a 4-sec electric shock with a 2-sec tone-light stimulus under conditions in which the onset of the stimulus occurred 0, .25, 1.0, 2.0, 4.0, or 4.5 sec. after the onset of the shock. Relative to nonpaired control procedures, response-contingent presentations of the CSs in these paradigms significantly suppressed a food-rewarded free operant, indicating that these temporal relationships can produce excitatory associative conditioning. It is suggested that the distinctions between "forward," "simultaneous," and "backward" procedures be modified to include a more molecular analysis of the UCS event. (21 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Potentiation and overshadowing in preweanling and adult rats.

Four experiments that compared the aversion acquired by 599 18- and 60-day-old Sprague-Dawley rats to a flavor that was either tasted alone or in combination (simultaneously or successively) with another flavor when paired with illness were conducted to study temporal variables and theoretical issues pertinent to potentiation and overshadowing while investigating ontogenetic differences in these phenomena. Results show that when either preweanlings or adults were presented with a simultaneous compound flavor (sucrose/coffee) followed by LiCl-induced illness, greater sucrose aversions were found than for Ss conditioned on sucrose alone. Preweanlings demonstrated greater potentiation than adults, whether the CS–UCS delay was 0 or 1 hr. This potentiation was eliminated by nonreinforced presentations of the alternative CS element. Potentiation was not observed when the 2 flavors were presented successively as the CS; instead, overshadowing occurred. Tests of configuring by extinction procedures indicated a tendency for these Ss to form a configured representation of the simultaneous compound solution. This disposition for configuring was more pronounced for preweanlings than for adults. Ontogenetic differences in response to configuration, CS saliency, and generalization decrement were consistent with the observed ontogenetic differences in potentiation. (33 ref) (PsycINFO Database Record (c) 2011 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)     

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)     

Effects of amygdala central nucleus lesions on blocking and unblocking.

The effects of lesions of the amygdala central nucleus (CN) on blocking and unblocking of appetitive Pavlovian conditioning were examined in 2 experiments with rats. In both lesioned and unlesioned rats, prior pairing of one CS with a food unconditioned stimulus/stimuli (UCS) blocked the acquisition of conditioning to a 2nd CS when a compound of both stimuli was paired with that same UCS. If the value of the UCS was increased or decreased when the 2nd CS was added, unlesioned rats acquired substantial conditioning to the 2nd cue (unblocking). Unblocking occurred in lesioned rats only when the UCS value was increased. In both lesioned and unlesioned rats, unblocking was prevented if the compound cue was paired with the original UCS prior to the change in UCS value. These data suggest that the CN is involved in increasing attention to signals for significant events but not in tuning out redundant cues. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transfer across unconditioned stimuli in serial feature discrimination training.

The transfer of conditioned modulation across CS and unconditioned stimulus/stimuli (UCS) was examined in 3 experiments that used Pavlovian appetitive training procedures with rats. In Exp 1, after training in a positive patterning discrimination (X→A+/X-/A-), X increased CR elicited by another trained-then-extinguished CS as long as that CS had been trained with the same UCS as was used in discrimination training. In Exp 2, after training with a feature-negative discrimination (X→A-/A+), X inhibited CR elicited by another trained-then-extinguished CS as long as that CS had been trained with the same UCS. Exps 1 and 2 used a between-groups design, and Exp 3 used a within-groups design. In Exp 3, rats were trained in a feature-positive discrimination (X→A+/A-). In transfer tests, X increased CR elicited by another CS trained then extinguished with the same UCS from training. This increase was greater than the X increased CR elicited by another CS trained then extinguished with a different UCS from training. Results supported the suggestion that features trained in serial discrimination tasks influence behavior indirectly by transiently raising or lowering the threshold for activation of the UCS representations by its target stimuli and by any other stimuli that may be associated with that UCS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evaluation of blocking and conditioned inhibition to a CS signaling a decrease in US intensity

Two experiments employing a conditioned emotional response procedure with rats evaluated the associative tendencies acquired by a target CS when a compound of that stimulus and another CS was reinforced by a low-intensity US whereas the latter CS alone was reinforced by a higher intensity US. Experiment 1 involved a blocking sequence in which the element and compound trials occurred in successive phases, followed by eventual testing of the responding to the target CS alone. Less evidence of excitatory conditioning was observed than in a comparison group which had the element and compound paired with the same low-intensity US. Experiment 2 included contemporaneous differential reinforcement of the element and compound CSs and periodic summation tests in which the target CS was compounded with another independently trained CS. Clear evidence was obtained of the development of inhibitory tendencies by the target CS. The results are consistent with the predictions of the Rescorla-Wagner model and are discussed in relation to the several determining assumptions of the model.     

Overshadowing and summation in compound stimulus conditioning of the rabbit's nictitating membrane response.

Examined acquisition of the rabbit's nictitating membrane response to a light?+?tone simultaneous compound stimulus and its components as a function of the intensity of the tone. In Exp I, the tone intensity was varied across the values of 85, 89, and 93 db, and the CS–UCS interval was 400 msec. In Exp II, the tone intensities were 73, 85, and 93 db, and the CS–UCS interval was 800 msec. Exps III and IV further examined the effects of the 73-db CS–UCS tone at CS–UCS intervals of 400 and 800 msec. All experiments included control groups, which were trained with either a light or a tone CS. Overall results show repeated instances of overshadowing: the impairment of CR acquisition to one or both of the components of a compound. Two types of summation were obtained: within-Ss summation, in which Ss trained with a compound showed a higher level of responding to the compound than to either of its component CSs; and between-groups summation, in which a group trained with a compound showed faster CR acquisition than either of its corresponding control groups trained with a single CS. Results are discussed in terms of perceptual and distributive processing models of compound stimulus conditioning. (37 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioned diminution of the unconditioned skin conductance response.

During Pavlovian conditioning the expression of a conditioned response typically serves as evidence that an association between a conditioned stimulus (CS) and an unconditioned stimulus (UCS) has been learned. However, learning-related changes in the unconditioned response (UCR) produced by a predictable UCS can also develop. In the present study, we investigated learning-related reductions in the magnitude of the unconditioned skin conductance response (SCR). Healthy volunteers participated in a differential conditioning study in which one tone (CS+) was paired with a loud white-noise UCS and a second tone (CS?) was presented alone. In addition, probe trials that consisted of UCS presentations paired with the CS+ (CS + UCS) and CS? (CS ? UCS), as well as presentations of the UCS alone were included to assess UCR diminution. SCR and participants' expectations of UCS presentation were monitored during conditioning. Greater diminution of the UCR was observed to the UCS when it followed the CS+ compared to when it followed the CS? or was presented alone. Further, UCR amplitude showed an inverse relationship with the participants' ratings of UCS expectancy. However, conditioned UCR diminution was also observed independent of differential UCS expectancies. Our findings demonstrate conditioned diminution of the unconditioned SCR. Further, these findings suggest that although UCR amplitude is modified by conscious expectations of the UCS, conditioned diminution of the UCR can be expressed independent of learning-related changes in these expectations. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Effects of US duration on classical conditioning of the rabbit's nictitating membrane response.

Attempted to distinguish the effects of UCS duration based on explicit pairings with the CS from the consequences of sheer exposure to the UCS in the rabbit nictitating membrane response. 228 albino rabbits received various proportions of CS (a 1,000-Hz tone) and UCS (a 60-Hz shock). Exp I revealed that there was an inverse relation between the overall level of CR acquisition and UCS durations of 50, l,500, and 6,000 msec. In addition, decrements in CR likelihood occurred within the daily sessions of 90 CS–UCS trials, and the magnitude of these within-session decrements was directly related to UCS duration. In Exp II, UCS duration of 50 and 6,000 msec were paired with the CS. When UCS exposure was equated, the UCS duration paired with the CS had a positive effect on CR likelihood. Conversely, in Exp III, the duration of interpolated UCSs had inverse effects on the rate of CR acquisition. In Exp IV, the opportunity for within-session decrements was eliminated by presenting only 1 CS–UCS trial per day, which resulted in a positive relation between CR likelihood and UCS duration. Results are discussed in terms of associative and performance hypotheses. (54 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

NMDA receptor antagonist MK-801 blocks learning of conditioned stimulus-unconditioned stimulus contiguity but not fear of conditioned stimulus in goldfish (Carassius auratus L.).

The blockade of learning of Pavlovian fear conditioning by the N-methyl-D-aspartic acid (NMDA)-receptor antagonist MK-801 was examined in 166 goldfish. In previously untrained fish, MK-801 blocked learning of a light-off or a tone conditioned stimulus (CS) paired with an electrical shock unconditioned stimulus (UCS). Pretraining on the light-off CS did not affect the rate of learning of the tone CS but protected the tone learning from disruption by MK-801. Switching from the light-off to the tone CS changed the identity of the CS but not its temporal contiguity with the UCS. Pretraining consisting of pseudoconditioning of the light-off CS did not protect subsequent tone learning from blockade by MK-801. Thus, the NMDA receptor functions are necessary for learning related to the temporal contiguity of the CS and UCS but not to the identity of the CS as a cue to the occurrence of the fearful effects of the UCS. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of reinforcement of an inhibitory feature after serial and simultaneous feature negative discrimination training.

Two experiments using a conditioned suppression procedure with 64 Sprague-Dawley rats found that postconditioning reinforcement of an inhibitory feature stimulus (X) had substantially different effects depending on whether a serial or a simultaneous feature negative discrimination procedure was used to establish the inhibition. With the simultaneous procedure, acquisition of excitation to the previously inhibitory X was retarded when X was paired with shock. Subsequent summation tests showed no evidence of inhibition to X after reinforced X presentations. However, acquisition of excitation to X was unaffected by prior serial feature negative training, and X-shock pairings had relatively little effect on X's inhibitory power in summation tests. Data suggest that the nature of inhibition established in feature negative discriminations differs substantially depending on the temporal arrangement of stimuli. One possibility is that inhibitors established using simultaneous stimulus arrangements modulate behavior by acting on a representation of the UCS, but inhibitors established with serial procedures act on particular CS–UCS associations. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Impact of continuous versus intermittent CS-UCS pairing on human brain activation during Pavlovian fear conditioning.

During Pavlovian fear conditioning a conditioned stimulus (CS) is repeatedly paired with an aversive unconditioned stimulus (UCS). In many studies the CS and UCS are paired on every trial, whereas in others the CS and UCS are paired intermittently. To better understand the influence of the CS-UCS pairing rate on brain activity, the experimenters presented continuously, intermittently, and non-paired CSs during fear conditioning. Amygdala, anterior cingulate, and fusiform gyrus activity increased linearly with the CS-UCS pairing rate. In contrast, insula and left dorsolateral prefrontal cortex responses were larger during intermittently paired CS presentations relative to continuously and non-paired CSs. These results demonstrate two distinct patterns of activity in disparate brain regions. Amygdala, anterior cingulate, and fusiform gyrus activity paralleled the CS-UCS pairing rate, whereas the insula and dorsolateral prefrontal cortex appeared to respond to the uncertainty inherent in intermittent CS-UCS pairing procedures. These findings may further clarify the role of these brain regions in Pavlovian fear conditioning. (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)     

Involvement of retrosplenial cortex in forming associations between multiple sensory stimuli.

The retrosplenial cortex (RSP) is highly interconnected with medial temporal lobe structures, yet relatively little is known about its specific contributions to learning and memory. One possibility is that RSP is involved in forming associations between multiple sensory stimuli. Indeed, damage to RSP disrupts learning about spatial or contextual cues and also impairs learning about co-occurring conditioned stimuli (CSs). Two experiments were conducted to test this notion more rigorously. In Experiment 1, rats were trained in a serial feature negative discrimination task consisting of reinforced presentations of a tone alone and nonreinforced serial presentations of a light followed by the tone. Thus, in contrast to prior studies, this paradigm involved serial presentation of conditioned stimuli (CS), rather than simultaneous presentation. Rats with damage to RSP failed to acquire the discrimination, indicating that RSP is required for forming associations between sensory stimuli regardless of whether they occur serially or simultaneously. In Experiment 2, a sensory preconditioning task was used to determine if RSP was necessary for forming associations between stimuli even in the absence of reinforcement. During the first phase of this procedure, one auditory stimulus was paired with a light while a second auditory stimulus was presented alone. In the next phase of training, the same light was paired with food. During the final phase of the procedure both auditory stimuli were presented alone during a single session. Control, but not RSP-lesioned rats, exhibited more food cup behavior following presentation of the auditory cue that was previously paired with light compared with the unpaired auditory stimulus, indicating that a stimulus-stimulus association was formed during the first phase of training. These results support the idea that RSP has a fundamental role in forming associations between environmental stimuli. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Role of context in autoshaping.

Three experiments used an autoshaping procedure in 64 female White Carneaux pigeons to investigate the conditioning of the context and of a discrete CS with a food UCS. CS–UCS associations were measured by directed pecking at the key light CS; context–UCS associations were assessed by general activity in the context. Exp I investigated the influence of context–UCS associations on performance to a previously trained CS. The same CS produced greater keypecking in a context of higher associative strength. Exp II examined the influence of context–UCS associations on learning of CS–UCS associations. When tested in a context of fixed associative strength, a CS that had been trained in a context of high associative strength elicited less responding than one trained in a context of low associative strength. Exp III found that signaling a UCS by a discrete CS interfered with the formation of context–UCS associations, as measured both in terms of general activity and ability to promote responding to another CS. Results suggest that the context and the CS compete for association with the UCS. They also suggest that context–UCS associations facilitate the exhibition of CS–UCS associations. (17 ref) (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)