Long-term retention of a conditioned taste aversion in preweanling and adult rats

The retention and extinction of a conditioned taste aversion after either short (6-day) or long (60-day) intervals was investigated in preweanling (18-day-old) and adult rats. Taste-only and illness-only control conditions were employed, as were variations in the concentration of the US (holding LiCl amount constant). Results indicated that after the short retention interval, retention of the taste aversion was equivalent for both ages. After the long interval, however, the 18-day-old rats exhibited significantly weaker taste aversion than their adult counterparts— infantile amnesia. Manipulation of US concentration had no effect on the magnitude of the taste aversions for either age or retention interval. The results are discussed in terms of their implications for infantile amnesia and general laws of learning.     

Sexually dimorphic extinction of a conditioned taste aversion in rats

The existence of a sexual dimorphism in the extinction of conditioned taste aversions in both fluid-deprived and nondeprived rats was investigated. When nondeprived rats were poisoned with LiCl after consuming a sucrose solution, males extinguished the subsequent conditioned taste aversion more slowly than females. There was no difference in the rate of extinction of a LiCl-induced conditioned taste aversion in fluid-deprived rats. Using marihuana extract distillate as the toxin, it was shown that the dimorphism found in the nondeprived rats is not a toxin-specific effect, and does not appear to be due to the males being made more ill. Possible explanations for the appearance of the dimorphism and its relation to the deprivational state of the organism are discussed.     

The effect of nonreinforced stimulus exposure on the strength of a conditioned taste aversion as a function of retention interval: Do latent inhibition and extinction involve a shared process?

Two experiments examined the effects of nonreinforced flavor exposure on the strength of a conditioned taste aversion. Rats were conditioned by pairing maple flavor with LiC1. Prior to or subsequent to this pairing, some animals received nonreinforced exposure to either maple or saccharin. In separate subjects, preference for maple was tested 1 or 21 days after the last training episode. In the first experiment, the nonreinforced stimulus exposure occurred before conditioning (latent inhibition, or LI, procedure); in the second experiment, the nonreinforced exposure occurred after conditioning (extinction, or EXT, training). In both experiments, nonreinforced exposure to maple or saccharin reduced the magnitude of a conditioned maple aversion when testing occurred soon after conditioning. When testing was delayed, however, the attenuation due to nonreinforced saccharin exposure dissipated, both with the LI procedure and with EXT. In contrast, the nonreinforced exposure to maple was found to attenuate conditioned reactions at both short and long retention intervals. The release from generalized LI and spontaneous recovery following generalized EXT training are discussed in terms of retrieval processing. The possibility that the same mechanism may underlie LI and EXT is considered.     

Circadian-temporal context and latent inhibition of conditioned taste aversion: Effect of restriction in the intake of the conditioned taste stimulus

Latent inhibition of conditioned taste aversion (CTA) is sensitive to changes in the temporal context. A change in the time of day of conditioning with respect to the time of day of the preexposure can disrupt the latent inhibition. This contextual change in the time of day may reveal a temporal specificity of latent inhibition. The optimum procedure to induce this temporal specificity is not well established. For example, it has been shown that a long period of habituation to temporal contexts is one factor that can determine the effect. However, the experimental conditions on the conditioning day that facilitate this phenomenon are unknown. The aim of this study is to elucidate whether a restriction in the intake of the conditioned taste stimulus affects the temporal specificity of latent inhibition. Two main groups of Wistar rats were tested in a latent inhibition of CTA paradigm, in which the temporal specificity of this phenomenon was analyzed by a change in the time of day of conditioning. The intake of the taste stimulus was restricted in the conditioning day in one of the groups, but this restriction was not applied in the other group. The results indicated temporal specificity of latent inhibition only in the group without restriction, but not in the group with limitation in the intake of the taste stimulus during conditioning. These findings can help to elucidate the characteristics of the procedure to induce temporal specificity of latent inhibition.     

A mixed design reveals that glucose moieties facilitate extinction of a conditioned taste aversion in rats

Separate groups of water-deprived rats had four trials with 15-min access to 0.0073 M saccharin, 0.3 M alanine, 0.3 M glucose, 0.1 M maltose, 0.3 M fructose, 0.06 M sucrose, or 0.03 M Polycose. Trials 1–3 were followed by injections of either 0.15 M LiCl (1.33 ml/100 g b.w., i.p.) or saline; Trial 4 (Test) was CS only. Extinction included either 48-h access to water alone or to the appropriate CS, both followed by a 24-h, two-bottle choice of CS and water. This 3-day cycle was repeated five to six times. All rats acquired comparable conditioned taste aversions (CTAs), but extinction rates varied with the test and the taste CS. No CTA extinguished during the two-bottle choices following 2 water days. During one-bottle CS exposure, all CTAs extinguished, but the aversion continued longer in the probe two-bottle tests. Intake of glucose moieties recovered rapidly, often in two cycles; the other CSs took four to six cycles. Thus, CTA extinction varies with the nature of the taste CS.     

Acquisition and retention of conditioned aversions to context and taste in laboratory mice

We compared the rate of acquisition and strength of retention of conditioned context aversion (CCA) with conditioned taste aversion (CTA) using pigmented, genetically heterogeneous mice (derived from Large and Small strains). Extending previous findings, in Experiment 1, mice accustomed to drinking from large glass bottles in the colony room learned to avoid graduated tubes after a single conditioning trial when drinking from these novel tubes was paired with injections of LiCl. The results also showed that CCA could be developed even when there was a 30-minute delay between conditioned stimulus and unconditioned stimulus. Retention of the aversion lasted for 4 weeks in both Immediate and Delay groups. Studies of conditioned saccharin aversion were conducted in Experiment 2. CTA acquisition was very similar to that observed in CCA and duration of aversion retention was similar in the CCA and CTA Delay groups, although at least 2 weeks longer in the Immediate group. Thus, CCA acquisition and retention characteristics are closer to those seen for CTA than has previously been reported. In Experiment 3, we examined whether albino mice (which are known to have weaker visual abilities compared to pigmented mice) would develop CCA comparable to those of pigmented mice. The development of conditioned aversion and its duration of retention was similar in albinos and pigmented mice. Nonspecific aversion emerged as an important contributor to strength of aversion during retention trials in both CCA and CTA paradigms with pigmented (but not albino) mice and deserves additional scrutiny in this field of inquiry.     

Differential effects of a retention interval on latent inhibition and the habituation of an orienting response

In Experiment 1, rats experienced presentations of a discrete visual stimulus (Stage 1) until habituation of the orienting response (OR) occurred. On a test session given after an interval of 16 days (Stage 2) the OR reappeared. For control subjects that received no Stage 1 training but presentations of the light in Stage 2, habituation persisted during the test. All subjects then received conditioning trials on which the light preceded the delivery of food. They showed latent inhibition, acquiring the conditioned response less readily than control subjects that had not previously experienced the light. Experiment 2 confirmed that the latent inhibition effect survived the retention interval for subjects that received no habituation test session. This pattern of results implies that habituation of the OR and latent inhibition are determined by different mechanisms.     

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.     

Impact of brief or extended extinction of a taste aversion on inhibitory associations: Evidence from summation,retardation, and preference tests

In five conditioned taste aversion experiments with rats, summation, retardation, and preference tests were used to assess the effects of extinguishing a conditioned saccharin aversion for three or nine trials. In Experiment 1, a summation test showed that saccharin aversion extinguished over nine trials reduced the aversion to a merely conditioned flavor (vinegar), whereas three saccharin extinction trials did not subsequently influence the vinegar aversion. Experiment 2 clarified that result, with unpaired controls equated on flavor exposure prior to testing; the results with those controls suggested that the flavor extinguished for nine trials produced generalization decrement during testing. In Experiment 3, the saccharin aversion reconditioned slowly after nine extinction trials, but not after three. Those results suggested the development of latent inhibition after more than three extinction trials. Preference tests comparing saccharin consumption with a concurrently available fluid (water in Experiment 4, saline in Experiment 5) showed that the preference for saccharin was greater after nine extinction trials than after three. However, saccharin preference after nine extinction trials was not greater, as compared with that for either latent inhibition controls (Experiments 4 and 5) or a control given equated exposures to saccharin and trained to drink saline at a high rate prior to testing (Experiment 5). Concerns about whether conditioned inhibition has been demonstrated in any flavor aversion procedure are discussed. Our findings help explain both successes and failures in demonstrating postextinction conditioned response recovery effects reported in the conditioned taste aversion literature, and they can be explained using a memory interference account.     

Effects of preexposure and retention interval placement on latent inhibition and perceptual learning in a choice-maze discrimination task

In two experiments, we examined how preexposure to discriminative stimuli and introduction of a 21-day retention interval affected the latent inhibition (LI) and perceptual learning (PL) of rats in a choice-maze discrimination task. Experimental groups were preexposed to three wall patterns, one in each of three arms of a maze. Control groups were preexposed only to white arms. PL groups were trained to discriminate A versus B, and LI groups, to discriminate A or B versus C. The A and B patterns shared many elements not shared with the C pattern. In Experiment 1, both at the end of training and after the subsequent retention interval, the PL groups performed better than controls, whereas the LI groups performed worse. In Experiment 2, inserting the 21-day retention interval between preexposure and discrimination training disrupted final measures of LI but not PL performance. Implications for current concepts of PL and LI are discussed.     

Compound-component differentiation as a function of CS-US interval and CS duration in the rabbit’s conditioned nictitating membrane response

The acquisition of the rabbit’s nictitating membrane response to a tone + light compound and its components was examined as a function of the CS-US interval (Experiment 1) and CS duration (Experiment 2). In Experiment 1, responding to the compound attained high levels in all groups, but responding on component test trials declined to low levels as the CS-US interval increased across values of 300, 800, and 1,300 msec. Further disparities between the compound and components appeared when the animals were shifted to a positive patterning schedule. In Experiment 2, disparities between the compound and components increased as the duration of the CS was increased across values of 50, 200, and 800 msec within a fixed CS-US interval of 800 msec. The results are discussed with respect to distributive processes, configuration, and speed-accuracy tradeoffs.     

Conditioned taste aversion in Philippine rice rats (R. r. mindanensis): Comparisons among drugs,dosages, modes of administration,and sexes

The effects of select drugs, dosages, and modes of administration upon learned taste aversions were compared among groups of wild-caught male and female Philippine rice rats (R. r. mindanensis). Experiment 1 compared two-choice saccharin aversions for 28 days among groups intubated with copper sulfate, cyclophosphamide, lithium chloride, red squill, sodium chloride (control), or deionized water (control). Main results were that 375 mg/kg lithium chloride produced the greatest sustained aversions, whereas 198 mg/kg cyclophosphamide and 210 mg/kg red squill produced moderate aversions, with males showing more resistance to extinction than females. Experiment 2 compared saccharin aversion among matched groups of male and female rats that received low (36 mg/kg), moderate (105 mg/kg), or high (368 mg/kg) dosages of lithium by gavage, ip injection, or ingestion. Sex differences in rates of extinction were found for the ingestion and injection-dosed rats, but no sex difference was again found for rats dosed by gavage. A significant mode × day interaction indicated that extinction progressed more rapidly for rats dosed by gavage. For all modes of administration, high dosages yielded intense 28-day aversion, moderate dosages produced intermediate 3–5 day aversion, and low dosages caused no aversion.     

Deactivation and reactivation of the inhibitory power of a conditioned inhibitor: Testing the predictions of an attentional-associative model

An attentional-associative model (Schmajuk, Lam, & Gray Journal of Experimental Psychology: Animal Behavior Processes, 22, 321–349, 1996) assumes that nonreinforced presentations of an inhibitory conditioned stimulus (CS) do not decrease its inhibitory associations. However, the model predicts that extended presentations will decrease attention to the inhibitor, thereby decreasing both (1) the expression of its inhibitory power in a summation test and (2) the rate of acquisition in a retardation test. The model also predicts that subsequent presentations of the inhibitory CS with a novel CS will increase both (1) and (2). Using a predictive learning design in humans, Experiment 1 examined the predictions involving the summation tests, whereas Experiments 2 and 3 examined the predictions involving the retardation tests. Experimental results were in agreement with the predictions of the model.     

Differential inflation with short and long CS-US intervals: Evidence of a nonassociative process in long-delay taste avoidance

Three experiments were performed to investigate the learning process underlying the phenomenon of long-delay taste conditioning. An associative model views taste avoidance as due to a conditioned stimulus-unconditioned stimulus (CS-US) associative structure, despite the long interval interposed between the flavor and illness. A nonassociative account of this avoidance behavior posits that avoidance stems from the interaction of two nonassociative processes: habituation of neophobic avoidance to a novel taste, and the poison-induced dishabituation of this process. A postconditioning inflation manipulation was used to discriminate between these two views. It has been demonstrated that enhanced responding with a US inflation manipulation depends, in part, on a previously conditioned association. Therefore, if long-delay taste avoidance arises from nonassociative processes, an inflation manipulation should not affect conditional responding. Experiment 1 demonstrated a delay of reinforcement effect, enhanced avoidance of saccharin in the immediate/inflation group, and no effect of inflation in the delay group and sham controls. Experiment 2 revealed that this differential effect of inflation is not due to absolute differences in the strength of the avoidance response. In Experiment 3, we investigated a potential associative learning mechanism that could account for the differential inflation effect. Together, the present results support the various predictions of a nonassociative account of long-delay taste avoidance.     

Comparison of retention and extinction of a visual discrimination as an index of forgetting in mice

The retention and extinction of a visual discrimination was examined in BALB/c mice. The mice were trained to perform a go/no-go discrimination task in parallel runways. Initial training resulted in an intermediate level of performance. Testing consisted of an additional session using either retention (Experiment 1) or extinction (Experiment 2) at one of five time intervals between 1 and 30 days. It was found in Experiment 1 that forgetting progressively increased over intervals of between 14 and 30 days. In Experiment 2, extinction testing induced more impairment of performance, so that forgetting occurred earlier relative to retention testing in Experiment 1. However, in both experiments, the measure of performance by a discrimination ratio revealed the same amount of forgetting when the training-test interval was 30 days. These results define the forgetting curve for such a discrimination by mice. They are discussed in terms of possible factors involved in forgetting.     

Blocking in eyelid conditioning: Effect of changing the CS-US interval and introducing an intertriai stimulus

Kamin’s three-stage blocking paradigm was investigated in rabbit eyelid conditioning, Two manipulations were examined. A change in the CS-US interval from Stage 1 to Stage 2 did not attenuate blocking. The introduction of a salient stimulus during the intertriai interval in Stage 2 also failed to attenuate blocking. The first result is not consistent with Kamin’s interpretation of the blocking effect in terms of US surprisingness. The second resuit is inconsistent with a prediction based on the Rescorla-Wagner model.     

Place conditioning with d-amphetamine: The effect of the CS-UCS interval and evidence of a place avoidance

In Experiment 1, a dose-response study of place conditioning with amphetamine was conducted. Male Sprague-Dawley rats receiving 0.0, 0.05, 0.1, 0.5, 2.0, 5.0, 7.5, or 10.0 mg/kg of d-amphetamine underwent 104-day cycles of place conditioning. On alternate days, each rat was injected with its designated dose of amphetamine while confined to its originally nonpreferred end of a three-compartment, straight alley box. On intervening days, each rat was injected with saline while confined to its originally preferred compartment. Following each 4-day cycle, a choice test was administered in which each rat was allowed 20 min of access to the entire alley box. Doses of amphetamine (≥0.5 mg/kg) induced a significant avoidance of the compartment in which amphetamine had been administered. In Experiment 2, animals received 0.0, 0.5, 2.0, or 5.0 mg/kg of amphetamine and underwent place conditioning procedures identical to those for the animals in Experiment 1. Unlike in Experiment 1, the animals were given a single choice test following 104-day place conditioning cycles. All groups that received amphetamine exbibited-a-eonditioned place avoidance. In Experiment 3, the effect of various CS-UCS intervals on place conditioning with 2.0 mg/kg of amphetamine was examined. Animals that received amphetamine immediately following their removal from the chamber exhibited a conditioned place avoidance.     

Language development in deaf children's interactions with deaf and hearing adults: a Dutch longitudinal study

The language development of two deaf girls and four deaf boys in Sign Language of the Netherlands (SLN) and spoken Dutch was investigated longitudinally. At the start, the mean age of the children was 3;5. All data were collected in video-recorded semistructured conversations between individual children and deaf and hearing adults. We investigated the lexical richness and syntactic complexity of the children's utterances in SLN and spoken Dutch, as well as language dominance and interactional participation. Richness and complexity increase over time, as well as children's participation. An important outcome is that syntactic complexity is higher in utterances with both sign and speech. SLN does not have higher outcomes on richness or complexity, but is dominant in terms of frequency of use.