Blocking can occur without losses in attention in rats with selective removal of hippocampal cholinergic input.

Prior studies showed that 192 IgG-saporin lesions of cholinergic input to the hippocampus disrupted reductions in processing of uninformative stimuli. In 2 experiments in this study, the performance of rats with these lesions was examined in blocking procedures. In both lesioned and normal rats, previous pairing of one conditioned stimulus (CS) with food blocked conditioning of a 2nd CS when a compound of both CSs was paired with food. However, in subsequent savings tests, lesioned rats showed faster learning than did normal rats when the blocked CS was established as a signal for either reinforcement or nonreinforcement. Thus, the reduced attention to the blocked CS found in normal but not lesioned rats was not essential for the occurrence of blocking. Although rats with selective removal of hippocampal cholinergic input may be unable to reduce attention to redundant stimuli, other mechanisms of stimulus selection remain available to them. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential control by context in the inflation and reinstatement paradigms.

Examined, in 5 conditioned suppression experiments, the influence of summation between fear of the CS and the context in experimental paradigms in which the rat is exposed to UCSs following conditioning or extinction. Context-preference tests assessed contextual fear. In Exps I–III with 88 female Wistar rats, the inflation paradigm, in which fear of a CS paired with a weak UCS is enhanced by exposure to intense UCS alone, was investigated. Results show that the contextual fear that was present when the target CS was tested was reduced by presenting the intense UCSs in a different context, by exposing Ss to the context following their presentation, and by signaling the intense UCSs with a 2nd CS. In Exp IV with 32 female Wistar rats, UCS exposures following conditioning or extinction both produced contextual fear, but only fear of the extinguished CS was reinstated by that fear. In Exp V with 32 female Wistar rats, identical amounts of contextual fear reinstated fear of an extinguished CS, but not a nonextinguished CS, when the 2 types of CSs were arranged to evoke comparable amounts of fear prior to testing. It is suggested that contextual fear plays a role in the reinstatement paradigm but not in the inflation paradigm. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Slow reacquisition following extinction: Context, encoding, and retrieval mechanisms.

Investigated the slow reacquisition (RAQ) of responding in rats that occurs when the conditioned stimulus/stimuli (CS) and unconditioned stimulus/stimuli (UCS) are paired again after prolonged extinction training. In Exp 1, an extinguished CS acquired less suppression than a novel CS during a final conditioning phase, but more suppression than CSs that had received comparable nonreinforcement without initial conditioning. In Exp 2, CS–UCS pairings resumed in the context of extinction caused the least RAQ of suppression: Pairings in a neutral context produced better RAQ, while return of the CS to the conditioning context caused an immediate renewal of responding to the CS. In Exp 3, a return of the CS to the extinction context after RAQ training caused renewed extinction performance and interfered with performance appropriate to RAQ. This effect was not due to demonstrable inhibitory conditioning of the extinction context. Results suggest that representations of conditioning and extinction (or CS–UCS and CS–no UCS relations) are both retained through extinction and that performance appropriate to either phase can be cued by the corresponding context. RAQ may thus be slow when the context retrieves an extinction memory. Similar mechanisms may also play a role in other Pavlovian interference paradigms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Element pretraining influences the content of appetitive serial compound conditioning in rats.

Examined the effects of prior pairings of conditioned stimulus/stimuli (CS)2 with the unconditioned stimulus/stimuli (UCS) on the nature of the associations formed in CS1?→?CS2?→?UCS serial compound conditioning, in 4 experiments with 72 male and 32 female albino rats. In Exps I and II, prior training of CS2 prevented the acquisition of stimulus–stimulus (S–S) associations between CS1 and stimulus features of CS2 but enhanced the acquisition of stimulus–response (S–R) associations between CS1 and the emotional conditioned response (CR) evoked by CS2. In Exps III and IV, the effects of CS2 pretraining were not due to CS2 training itself, but rather to its endowing CS2 with the ability to evoked a strong CR during the early stages of serial compound conditioning. In Exp III, suppression of the CR to a pretrained CS2 during serial compound conditioning permitted the establishment of S–S associations. In Exp IV, the induction of a CR in the presence of an untrained CS2 during serial compound conditioning prevented the acquisition of S–S associations. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Unblocking in Pavlovian appetitive conditioning.

Two experiments, with 280 Sprague-Dawley rats, demonstrated unblocking in an appetitive conditioning preparation. One stimulus, A, was first paired with either a low-value reinforcer (1 food pellet) or a high-value reinforcer (1 food pellet followed by 2 more food pellets). A 2nd stimulus, X, was then added to A, and the compound was reinforced with either the high- or low-value reinforcer. Conditioning to X was blocked if the same reinforcer was used in both phases of the experiment, but there was substantial conditioning to X when the reinforcer value was shifted either up or down when X was introduced. Exp I demonstrated this unblocking phenomenon using a design that minimized the potential contribution of generalization decrement. Exp II examined the effects of a variety of posttraining manipulations on conditioned responding to the added X cue after unblocking procedures. Among Ss that received downshifts in reinforcer value when X was introduced, responding was affected by several posttraining manipulations, including changes in context value. Those manipulations had smaller effects on the responding of Ss that received upshifts in reinforcer value and no effects on responding in control conditions. Findings are considered in relation to the model of conditioning outlined by R. A. Rescorla and A. R. Wagner (1972). (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Representation-mediated overshadowing and potentiation of conditioned aversions.

Examined the ability of CS-evoked representations of flavored substances to modulate the conditioning of LiCl-based aversions to simultaneously presented flavors or odors. In Exps I–III, 156 thirsty Sprague-Dawley rats first received pairings of an auditory CS with a flavored-water UCS; they then received pairings of a compound stimulus with a toxin. Exp IV examined the potentiation of aversion conditioning to a novel odor using 32 Ss. In Exp I, conditioning of a flavor was partially overshadowed when it was presented in compound with a tone that had been previously paired with another flavor. Exp II replicated that result and also found that conditioning to a flavor was not overshadowed when the flavor was presented in compound with a tone that had been paired with that same flavored substance. In Exps III and IV, conditioning to an odor stimulus was potentiated when it was presented in compound with either a tone or another odor that had been previously paired with a flavor stimulus. Results suggest that evoked representations of stimuli may substitute for those events themselves in a variety of associative functions. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal encoding as a determinant of blocking.

A blocking paradigm with rats was used to evaluate whether different temporal information is encoded in simultaneous rather than forward associations. During Phase 1, the blocking CS was simultaneously or forward paired with a unconditioned stimulus/stimuli (UCS). During Phase 2, the pretrained CS occurred in compound with a novel target CS that was paired in a simultaneous or forward manner with the UCS. Forward pretraining resulted in more blocking of a forward than a simultaneously trained target CS, and simultaneous pretraining resulted in more blocking of a simultaneously than a forward trained target CS. Thus, greater blocking occurred when the blocking and blocked CSs had the same temporal relation to the UCS. The results support the temporal coding hypothesis and question the necessity of predictive information in blocking. (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)     

Cerebellar stimulation as an unconditioned stimulus in classical conditioning.

Implanted rabbits with chronic stimulating electrodes in white matter underlying lobule HVI of the cerebellar cortex. Stimulation elicited movements of the face or neck and, when paired with a tone CS, produced learning comparable to that seen with peripheral unconditioned stimulus/stimuli (UCS). CS-alone trials produced extinction. Reinstatement of paired trials produced reacquisition with savings. Additional groups received either explicitly or randomly unpaired CS–UCS trials before paired conditioning. Low-frequency responding during these sessions indicated that the paired training results were associative and not due to pseudoconditioning or sensitization. Explicitly unpaired sessions retarded learning on subsequent paired trials compared with groups that received either randomly unpaired or no CS–UCS preexposure. These results are interpreted in terms of the role of the cerebellum and associated pathways in classical conditioning of motor responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal dynamics of the rabbit's nictitating membrane response in serial compound conditioned stimuli.

Two experiments, with 88 female albino rabbits, investigated conditioning of the nictitating membrane response to a reinforced serial compound stimulus. The serial compound was composed of a 400-msec CS (CSA), a trace interval of at least 2 sec, and a brief 2nd CS (CSB) prior to the UCS. The CSB duration was either 150, 250, or 400 msec in Exp I, and the CSB duration in Exp II was 400 msec. Exp I compared serial compound training to an "uncoupled" condition, which contained intermixed CSA–UCS trials and CSB–UCS trials. Exp II compared serial compound training with uncoupled training, 2nd-order conditioning (CSA–CSB/CSB–UCS), trace conditioning (CSA–UCS), and generalization testing that entailed CSB–UCS training and unreinforced tests with CSA. The serial compound, uncoupled, and 2nd-order conditioning procedures all produced high levels of responding during CSA, but only the reinforced serial compound procedure yielded an appreciable likelihood of CR initiation during the trace interval between CSA and CSB. The CRs during the trace interval were temporally distinct from the CRs during CSA and did not appear to be belated CRs to CSA itself. Results are discussed in connection with stimulus selection phenomena, for example, overshadowing and potentiation of toxicosis conditioning. (46 ref) (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)     

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)     

Stimulation at a site of auditory-somatosensory convergence in the medial geniculate nucleus is an effective unconditioned stimulus for fear conditioning.

The medial division of the medial geniculate nucleus (MGm) and the posterior intralaminar nucleus (PIN) are necessary for conditioning to an auditory conditioned stimulus/stimuli (CS), receive both auditory and somatosensory input, and project to the amygdala, which is involved in production of fear conditioned responses (CRs). If CS–unconditioned stimulus (UCS) convergence in the MGm-PIN is critical for fear conditioning, then microstimulation of this area should serve as an effective UCS during classical conditioning, in place of standard footshock. Guinea pigs underwent conditioning (40–60 trials) using a tone as the CS and medial geniculate complex microstimulation as the UCS. Conditioning bradycardia developed when the UCS electrodes were in the PIN. However, microstimulation was not an effective UCS for conditioning in other parts of the medial geniculate or for sensitization training in the PIN or elsewhere. Learning curves were similar to those found previously for footshock UCS. Thus, the PIN can be a locus of functional CS–UCS convergence for fear conditioning to acoustic stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential contribution of amygdala and hippocampus to cued and contextual fear conditioning.

The contribution of the amygdala and hippocampus to the acquisition of conditioned fear responses to a cue (a tone paired with footshock) and to context (background stimuli continuously present in the apparatus in which tone–shock pairings occurred) was examined in rats. In unoperated controls, responses to the cue conditioned faster and were more resistant to extinction than were responses to contextual stimuli. Lesions of the amygdala interfered with the conditioning of fear responses to both the cue and the context, whereas lesions of the hippocampus interfered with conditioning to the context but not to the cue. The amygdala is thus involved in the conditioning of fear responses to simple, modality-specific conditioned stimuli (CS) as well as to complex, polymodal stimuli, whereas the hippocampus is only involved in fear conditioning situations involving complex, polymodal events. Findings suggest an associative role for the amygdala and a sensory relay role for the hippocampus in fear conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Classical conditioning of autonomic fear responses is independent of contingency awareness.

The role of contingency awareness in classical conditioning experiments using human subjects is currently under debate. This study took a novel approach to manipulating contingency awareness in a differential Pavlovian conditioning paradigm. Complex sine wave gratings were used as visual conditional stimuli (CS). By manipulating the fundamental spatial frequency of the displays, we were able to construct pairs of stimuli that varied in discriminability. One group of subjects was given an “easy” discrimination, and another was exposed to a “difficult” CS+ and CS–. A 3rd group was exposed to a stimulus that was paired with the unconditional stimulus (UCS) 50% of the time and served as a control. Skin conductance response (SCR) and continuous UCS expectancy data were measured concurrently throughout the experiment. Differential UCS expectancy was found only in the easy discrimination group. Differential SCRs were found in the easy discrimination group as well as in the difficult discrimination group, but not in the 50% contingency control. The difficult discrimination group did not exhibit differential UCS expectancy but did show clear differential SCR. These observations support a dual process interpretation of classical conditioning whereby conditioning on an implicit level can occur without explicit knowledge about the contingencies. The role of contingency awareness in classical conditioning experiments using human subjects is currently under debate. This study took a novel approach to manipulating contingency awareness in a differential Pavlovian conditioning paradigm. Complex sine wave gratings were used as visual conditional stimuli (CS). By manipulating the fundamental spatial frequency of the displays, we were able to construct pairs of stimuli that varied in discriminability. One group of subjects was given an “easy” discrimination, and another was exposed to a “difficult” CS+ and CS–. A 3rd group was exposed to a stimulus that was paired with the unconditional stimulus (UCS) 50% of the time and served as a control. Skin conductance response (SCR) and continuous UCS expectancy data were measured concurrently throughout the experiment. Differential UCS expectancy was found only in the easy discrimination group. Differential SCRs were found in the easy discrimination group as well as in the difficult discrimination group, but not in the 50% contingency control. The difficult discrimination group did not exhibit differential UCS expectancy but did show clear differential SCR. These observations support a dual process interpretation of classical conditioning whereby conditioning on an implicit level can occur without explicit knowledge about the contingencies. (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)     

Flavor-illness aversions: Potentiation of odor by taste with toxin but not shock in rats.

Paired almond odor or saccharin taste as a single CS or as a compound CS for both a footshock UCS and a toxin UCS (LiCl) to test the generality of potentiation in male Sprague-Dawley rats. Extinction tests with the almond and saccharin components were then given. In single CS–toxin experiments, taste was more effective than odor, and after compound conditioning, the taste component potentiated the odor component. Conversely, in single CS–shock experiments, odor was more effective than taste, and after compound conditioning, no potentiation was observed. Instead, interference effects were observed. In Exps I and II, the addition of taste disrupted odor CS–shock conditioning, and in Exp III, odor interfered with taste CS–shock conditioning. Visceral feedback was apparently a necessary UCS for the potentiation of odor by taste. Data support the neural convergence and gating hypothesis of flavor aversion conditioning. (33 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)     

An analysis of blocking in odorant mixtures: An increase but not a decrease in intensity of reinforcement produces unblocking.

Studies of blocking between elements from the same stimulus modality elucidate how animals analyze such mixtures. Proboscis-extension conditioning of honey bees was used to examine the role of unconditioned stimulus (UCS) intensity in blocking in odorant mixtures. Several predictions from theoretical accounts of blocking were tested. One-trial blocking was found when Ss were pretrained with a high but not a low UCS concentration. Increases in UCS intensity produced unblocking, but decreases did not. Furthermore, an equivalent level of unblocking was observed when the increase occurred on the 1st or 2nd mixture-phase trials. These results are consistent with studies of vertebrates in which UCS intensity is altered to produce unblocking. Extension of these studies to include variation in other UCS parameters and to intramodal blocking in vertebrates will be necessary to determine whether this correspondence to vertebrate blocking is robust. (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)