Covariation in conditioned response strength between stimuli trained in compound

Conditioned lick suppression by water-deprived rats was used to elaborate on recent evidence that the attenuated conditioned response elicited by an overshadowed stimulus may be enhanced by extinction of the overshadowing stimulus with which it had been trained in simultaneous compound. Using a modified serial stimulus arrangement in which a light coexisted with the last half of a tone that terminated with footshock, it was found in Experiment 1 that the tone overshadowed the light. Extinction of the tone-shock association resulted in a virtually complete recovery of the response to the overshadowed light. Using this serial overshadowing procedure, the possibility that the strength of a conditioned response to an element trained in compound covaries as a function of the strength of the response to the other element was tested in Experiment 2. Following overshadowing training similar to that of Experiment 1, independent reinforcement of the overshadowed light, that is, associative inflation, was found to have no deleterious effect on the response to the overshadowing tone. This suggests that the effects of postconditioning extinction and inflation of one element do not have symmetrical effects upon responding to the other element. The results of Experiment 2 were replicated in Experiment 3 using a simultaneous compound stimulus as opposed to the serial compound of the previous studies. These results are discussed in terms of various associative and cognitive models of learning and performance.     

Superlatent inhibition and spontaneous recovery: Differential effects of pre- and postconditioning CS-alone presentations after long delays in different contexts

In two pairs of three-stage conditioned taste aversion experiments, we examined the effects of delay interval (1 or 21 days) between the second and third stages, and of context in which the animals spent the delay (same as or different from the context of the other stages) on latent inhibition (LI) and spontaneous recovery following extinction. In the LI experiments (Experiments 1A and 1B), the first stage comprised nonreinforced presentations to saccharin or to water. In the second stage, rats were conditioned by saccharin paired with LiCl. In the extinction experiments (Experiments 2A and 2B), the order of the stages was reversed. For all experiments, Stage 3, the test stage, consisted of three presentations of saccharin alone. There was a super-LI effect in the saccharin-preexposed group that spent the 21- day delay in the different context (Experiment 1A). When the delay was spent in the same context, there was no difference in the amount of LI between the short- and long-delay groups (Experiment 1B). Conversely, there was a spontaneous recovery effect in the long-delay/same-context group (Experiment 2B), but not in the long-delay/different-context group (Experiment 2A). The pattern of results, incompatible with current explanations of delay-induced changes in memory performance, was interpreted in terms of an interaction between the delay conditions (same or different delay context), which modulate the extinction of previously acquired context-CS-nothing associations (during CS-alone presentations), and primacy effects.     

Taste avoidance and taste aversion: Evidence for two different processes

The terms conditioned taste avoidance and conditioned taste aversion are often used interchangeably in the literature; however, considerable evidence indicates that they may represent different processes. Conditioned taste avoidance is measured by the amount that a rat consumes in a consumption test that includes both appetitive phases and consummatory phases of responding. However, conditioned taste aversion is more directly assessed with the taste reactivity test, which includes only the consummatory phase of responding. Rats display a conditioned taste aversion as conditioned rejection reactions (gapes, chin rubs, and paw treads) during an intraoral infusion of a nausea-paired flavored solution. Treatments that produce nausea are not necessary for the establishment of taste avoidance, but they are necessary for the establishment of taste aversion. Furthermore, treatments that alleviate nausea modulate neither the establishment nor the expression of taste avoidance, but they interfere with both the establishment and the expression of taste aversion. Considerable evidence exists indicating that these two measures are independent of one another. Taste avoidance may be motivated by conditioned fear rather than conditioned nausea, but taste aversion (as reflected by rejection reactions) may be motivated by conditioned nausea.     

A contingency analysis of taste aversion conditioning

The acquisition of conditioned taste aversion was assessed relative to five control procedures. That is, forward conditioning using multiple-trial, brief-duration taste CSs and weak USs over a 30-min CS-US delay was compared to backward, CS alone, US alone, sham CS and sham US, and random control procedures. The outcome supported an associative conditioning interpretation of the learned aversion. While there were no differences between the various control procedures, all were different from the forward conditioning group. The argument was made that some of the distinctive associative and nonassociative phenomena attributed to taste aversion conditioning (but not seen in the present study) may in part be due to the duration and intensity of both the CS and US events.     

Chemosensory conditioning in molluscs: II. A critical review

We critically review chemosensory conditioning studies with molluscs and find that, in many studies, the influence of nonassociative processes complicates, obscures, and renders ambiguous the unique contribution of associative learning. These nonassociative processes include sensory adaptation, habituation, sensitization, and changes in feeding motivation. They arise from both the food extracts that have often been used as conditioned stimuli and the aversive stimuli that have been used as unconditioned stimuli.     

Spontaneous recovery and ABC renewal from retroactive cue interference

Two conditioned suppression experiments with rats were conducted to determine whether the spontaneous recovery and renewal that are commonly observed in retroactive outcome interference (e.g., extinction) also occur in retroactive cue interference. Experiment 1 showed that a long delay between Phase 2 (the interfering phase) and testing produces a recovery from the cue interference (i.e., the delay enhanced responding to the target cue trained in Phase 1), which is analogous to the spontaneous recovery effect observed in extinction and other retroactive outcome interference procedures. Experiment 2 showed that, when target and interfering cues are trained in separate contexts and testing occurs in a different but familiar context, a recovery from the cue interference is also observed (i.e., the context shift enhanced responding to the target), which is analogous to ABC renewal from extinction. The results are discussed in terms of the possibility that similar associative mechanisms underlie cue and outcome interference.     

Conditioned inhibition of rotation-induced taste aversion

In three experiments, we investigated the existence of conditioned inhibition of body rotation-induced taste aversion. Rats were given conditioned inhibition training in which the taste of saccharin was always followed by rotations, but the taste of vanilla was not. Flavor-preference tests, retardation-of-acquisition tests, and summation tests of inhibition indicated that the vanilla stimulus had acquired conditioned inhibitory properties. These findings could not be interpreted as functions of either initial solution preferences or simple nonassociative effects of flavor preexposure. They lend support to a theory that views learning mechanisms as being central to the phenomenon of motion sickness, and suggest that inhibitors might be effectively employed to ameliorate its symptoms.     

The role of injection cues in the production of the morphine preexposure effect in taste aversion learning

The attenuation of an LiCl-induced conditioned taste aversion (CTA) by LiCl preexposure is mediated primarily by associative blocking via injection-related cues. Given that preexposure to morphine attenuates morphine-induced CTAs, it was of interest to determine whether injection cues also mediate this effect. Certain morphine-induced behaviors such as analgesic tolerance are controlled associatively, via injection-related cues. Accordingly, animals in the present experiments were preexposed to morphine (or vehicle) every other day for five total exposures, followed by an extinction phase, in which the subjects were given saline injections (or no treatment) for 8 (Experiment 1) or 16 (Experiment 2) consecutive days. All of the animals then received five CTA trials with morphine (or vehicle). The morphine-preexposed animals in Experiment 1 displayed an attenuation of the morphine CTA that was unaffected by extinction saline injections, suggesting that blocking by injection cues during morphine preexposure does not mediate this effect. All of the morphine-preexposed subjects in Experiment 2 displayed a weakened preexposure effect, an effect inconsistent with a selective extinction of drug-associated stimuli. The attenuating effects of morphine preexposure in aversion learning are most likely controlled by nonassociative mechanisms, like drug tolerance.     

The effect of morphine preexposure on the acquisition of morphine-induced taste aversions: A nonassociative effect

In Experiment 1, the amount of time rats spent engaged in a range of behaviors was recorded immediately prior to and following the intraperitoneal administration of morphine sulfate (6 mg/kg) or distilled water. No behavioral differences were observed between these groups. In Experiment 2, preexposure to this low dose of morphine attenuated the subsequent acquisition of a morphine-induced taste aversion independent of the similarity of the preexposure and conditioning environments. These results with a dose of morphine that does not produce any behavioral effects, which in turn could potentially mask associative conditioning during preexposure, confirm that the attenuating effects of morphine preexposure on taste aversion learning are nonassociative.     

Interaction of retention interval with CS-preexposure and extinction treatments: Symmetry with respect to primacy

Imposition of a retention interval between cue-outcome pairings and testing can alleviate the retardation of conditioned responding induced by pretraining exposure to the cue (i.e., the CS-preexposure effect). However, recent studies have reported an enhanced effect of CS-preexposure treatment with longer retention intervals (De la Casa & Lubow, 2000, 2002; Lubow & De la Casa, 2002). In a series of conditioned barpress suppression studies with rats, we examined the effects of imposing a retention interval just prior to testing following either CS-preexposure (cue alone before cue-outcome pairings) or extinction (cue alone after cue-outcome pairings) treatments. Experiment 1 replicated in a different preparation recent reports of CS-preexposure treatment effects increasing with longer retention intervals. Experiment 2 showed that spontaneous recovery of stimulus control of behavior after extinction can be obtained with the same parameters as those used to observe the augmented effect of CS-preexposure treatment. In Experiment 3, both the augmented effect of CS-preexposure treatment and spontaneous recovery from extinction were found when we used, in place of a retention interval, an associative priming manipulation.     

Effects of postconditioning inflation on odor + taste compound conditioning

The within-compound association approach has been proposed as an account of synergistic conditioning in flavor aversion learning. One prediction from the within-compound association approach is that following taste + odor compound conditioning, postconditioning inflation of one element of the compound should increase responding to the second element. In four experiments with rats, the AX+/A+ design was used to determine whether postconditioning inflation of A would increase responding to X. In Experiments 1 and 3, responding to X was significantly stronger after AX+/A+ conditioning, as compared with AX+ conditioning. In Experiments 2 and 4, the specificity of the inflation effect was demonstrated, because AX+/A+ conditioning produced a stronger aversion to X than did AX+/B+ conditioning. Furthermore, it appears that the taste + odor association is symmetrical because inflation of the taste aversion increased responding to the odor (Experiments 1 and 2) and inflation of the odor aversion increased responding to the taste (Experiments 3 and 4).     

Latent inhibition of conditioned disgust reactions in rats

The present experiments, using the latent inhibition (LI) paradigm, evaluated the effect of nonreinforced exposure to saccharin on the acquisition of an LiCl-induced saccharin aversion as measured by conditioned disgust reactions in the taste reactivity test and conditioned taste avoidance in a consumption test. When rats were preexposed to saccharin by bottle exposure (Experiments 1 and 3), LI was evidenced only by conditioned taste avoidance (bottle testing), but not by conditioned disgust reactions (intraoral [IO] testing). On the other hand, when rats were preexposed to saccharin by IO infusion (Experiments 2 and 3), LI was evidenced only by conditioned disgust reactions, but not by conditioned taste avoidance. Experiment 4 showed that LI of conditioned disgust reactions does not appear to be affected by a context shift from preexposure to testing phases. These results show that the expression of LI of both conditioned taste avoidance and conditioned disgust reactions depends critically on a common method of flavor exposure during preexposure and testing.     

Simple delayed discrimination of tastes in the rat

Although taste memory has been extensively studied within the context of long-delay taste aversion learning, little attention has been devoted to taste memory within more traditional memory designs, for example, simple delayed discriminations. This was examined in the present experiment. Specifically, following taste discrimination training during which responding was reinforced following exposure to only one of two tastes, delays were imposed between sampling of the initial taste and the opportunity to respond. On the average, subjects were able to perform the simple delayed taste discrimination with an accuracy of 80% or better at a delay of 45 sec. Discrimination performance returned to chance at an average delay of 58 sec. Taste memory within the simple delayed discrimination paradigm is discussed and compared with other assessments of short-term memory in the rat and other species.     

Reinstatement of postresponse stimuli prior to reward in delayed-reward discrimination learning by pigeons

Delayed-reward learning in pigeons was examined using a simultaneous red-green visual discrimination task in which the conditions during the delay interval were varied between groups. The nondifferential group received training in which the stimulus present during the 1-min delay was the same following a peck on the correct and incorrect colors. The other three groups received 1-min delay training in which different stimuli occurred in the delay interval following correct and incorrect choices. The differential group received continuous, differential stimuli during the delay. The reinstatement group received the differential stimuli in the 10 sec immediately following the choice and during the last 10 sec of the delay. The reversedcue group was treated in the same way, except that the 10-sec delay stimulus immediately following an incorrect response was also presented for 10 sec prior to reward on correct choices, and the stimulus following a correct response also occurred 10 sec before nonreward on incorrect choices. Nondifferential birds failed to learn the discrimination, while differential and reinstatement birds learned it readily. The reversed-cue birds learned to choose the incorrect stimulus. Differential and reinstatement birds showed no decrement in performance when the delay was increased to 2 min. These findings suggest that similarity of prereward and postresponse delay stimuli controls choice responding in long-delay learning, a finding compatible with both memorial and conditioned reinforcement interpretations.     

Extinction and blocking of conditioned inhibition in human causal learning

Two experiments investigated extinction and blocking of a conditioned inhibitor in a human contingency learning task. Lotz and Lachnit (2009) and Melchers, Wolff, and Lachnit (2006) reported extinction of inhibition only when participants experienced outcome levels lower than those used in training. In Experiment 1, which used more neutral instructions than the previously mentioned studies, we found that extinction of inhibition occurred, whether or not participants experienced lower outcome levels. In Experiment 2, we applied this outcome manipulation to blocking of a conditioned inhibitor. We found blocking of inhibition both when participants had experience with lower outcomes and when they did not. The results of our two experiments are consistent with Rescorla and Wagner’s (1972) associative model, and inconsistent with an inferential account of causal learning (De Houwer, Beckers, & Vandorpe, 2005).     

US inflation with trace and simultaneous fear conditioning

Two experiments with rat subjects in a conditioned punishment paradigm are reported. These experiments attempted to determine if the events entering into association with the CS following conditioning with informative (forward) and noninformative (simultaneous) CSs were comparable. In Experiment 1, exposure to intense shock alone following trace (ISI = 10 sec) conditioning with moderate shock enhanced the suppressive effects of a 2-sec CS. A similar manipulation following explicitly unpaired CS-US presentations (ISI = 2 min) had no effect. These data were taken as evidence that the CS and US were associated during trace conditioning. Experiment 2 showed that exposure to intense shock following simultaneous conditioning also enhanced suppression to the CS. These results suggested that simultaneous and forward conditioning procedures yield similar forms of associative learning.     

Ontogeny of long-term,nonassociative memory in the rat

The primary purpose of the present study was to assess the ontogeny of nonassociative learning and memory in 16-, 30-, and 75-day-old rats. In each of three experiments, habituation of the orienting response to a novel auditory stimulus was measured. The orienting response is an unconditioned reaction elicited by innocuous environmental stimulation that habituates with repeated stimulus presentations. Both an autonomic component (heart-rate deceleration) and a behavioral index (head jerk) of the orienting response were recorded in this study. Although no age differences in rate of habituation (i.e., rate of nonassociative learning) were found (see Experiment 1), a marked effect of age on retention of habituation was observed. Preweanling rats retained habituation of the orienting response to an auditory stimulus for less than 4 h (Experiment 2), whereas adult animals exhibited no forgetting even after a 1-week interval (Experiment 3). These results are discussed in terms of (1) demonstrations of age-related differences in associative memory, (2) the persistence of nonassociative memories in adults, and (3) the significance of the orienting response as a measure of retention of nonassociative learning.     

Cross-modality contrast: Exteroceptive context habituation enhances taste neophobia and conditioned taste aversions

The relationship between absolute and relative stimulus novelty was examined within the context of the conditioned taste aversion paradigm in which the relative novelty of the conditioned interoceptive stimulus was manipulated by differential exteroceptive context habituation. Rats received similar isolation histories but either 5 or 30 days of habituation to the test environment prior to treatment. One group was administered lithium chloride following saccharin consumption, a second group was administered isotonic saline following saccharin consumption, and a third group was administered saline after water consumption. The animals habituated for 30 days exhibited greater conditioned avoidance and greater neophobic avoidance of saccharin than did animals habituated for only 5 days. The results are interpreted in terms of a cross-modality stimulus contrast effect which implicates context habituation as an important parameter of both taste neophobia and taste aversion learning.     

Variations in the retention of taste aversions: Evidence for retrieval competition

In six experiments, we examined taste and compound taste/taste aversions at different retention intervals. In Experiment 1, saccharin aversions were significantly weaker 1 day after conditioning than 21 days after conditioning. This effect was determined not to be caused by the aftereffects of illness or differential hydration. With the use of a saccharin/denatonium compound, Experiment 2 demonstrated overshadowing of a denatonium aversion at 21- and 1-day retention intervals, Experiment 4 showed a potentiated saccharin aversion only at the 21-day retention interval, and both Experiments 2 and 4 revealed that the aversion of the taste-only controls was stronger at the later retention interval. Experiments 3 and 5 demonstrated that the differences at the two retention intervals were not caused by unconditioned changes in taste preference. Finally, Experiment 6 showed that extinction of the conditioning environment prior to testing results in stronger saccharin aversions than occur in nonextinguished controls. Collectively, these experiments suggest that testing within a 24-h period after conditioning will result in significantly weaker taste aversions. Also, these results support a retrieval-competition explanation that may account for the weakened aversions at the 1-day testing interval of both groups conditioned to single elements and those conditioned to compounds.     

Contribution of conditioned opioid analgesia to the shock-induced associative US-preexposure deficit

The modulatory effect of conditioned opioid analgesia on learning in the US-preexposure paradigm was examined in three experiments using water-deprived rats. In Experiment 1, it was found that tailflick latencies increased immediately after the rats were exposed to a context in which footshock had previously been administered. Prolonged nonreinforced exposure to the context attenuated this analgesia. Experiment 2 tested the possibility that the effectiveness of CS-US pairings in an excitatory context might be reduced by a conditioned analgesic response that lessens the perceived intensity of the US. Administration of the opiate antagonist naloxone prior to CS-US pairings in the excitatory context reduced the US-preexposure deficit—that is, the retarded response to the CS—but did not eliminate it, suggesting that part of the observed deficit resulted from conditioned activation of the endogenous opioid system. In Experiment 3, it was found that exposure to the excitatory context immediately prior to a CS-US pairing in an associatively neutral context resulted in a conditioned response deficit, indicating that the analgesia elicited by the excitatory context was sufficient to reduce US effectiveness. In combination with other recent reports, these results suggest that the associative deficit resulting from preexposure to a shock US may, in certain instances, represent the sum of several different associative processes.