Attenuation of the CS-preexposure effect after a retention interval in preweanling rats

The effects of flavor preexposure and retention interval were assessed in 6- and 12-day-old rats. Conditioned aversions to a flavor appeared at both ages. The conditioning of the younger pups was unaffected by conditioned stimulus (CS) preexposure and was not evident after a 10-day retention interval. For the 12-day-old rats, preexposure to either the flavor CS or a different flavor attenuated aversion strength when the rats were tested soon after conditioning. Other 12-day-old rats that were tested 10 days after conditioning also expressed substantial aversions, but with a retention interval of this length, the aversions were equivalent for animals preexposed to the CS and those not preexposed before conditioning. This loss of the CS-preexposure effect over a long interval, which has also been observed in adult rats, identifies the locus of this effect as postacquisition and perhaps at the stage of memory retrieval.     

A consideration of direct and indirect teaching styles with respect to achievement and retention of learning in science classes

Students taught by teachers of science with a higher I/D ratio, according to Flanders scale, will achieve more and retain more information than will students of teachers with a lower I/D ratio. This study tested students in high school chemistry and junior high school general science at the end of a year of study in their respective classes. They were then retested four months later. The teachers were scaled according to their I/D ratio. It was found that the I/D ratio of a teacher could be a guide toward determining the success of students so taught in a particular class.     

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.     

Observational extinction: Observation of nonreinforced responding reduces resistance to extinction in rats

Rats trained to push a joystick to the left or right for food reward were given two successive tests in which neither response was reinforced. Prior to Test 1, subjects were either confined in the apparatus with a passive conspecific (Group None), or allowed to observe a conspecific demonstrator making 50 nonreinforced responses in the direction that had beeirrewarded during observer training (Group Same) or in the opposite direction (Group Different). In Test 1, Group Same made fewer previously reinforced responses than did Group Different, which made fewer than Group None, and Groups Same and Different each made fewer previously nonreinforced responses than did Group None. In Test 2, Group Same made fewer previously reinforced responses than did Group None. These results indicate that observation of nonreinforced responding can reduce resistance to extinction (Test 1) and spontaneous recovery (Test 2) in rats.     

One-trial backward excitatory fear conditioning in rats: Acquisition,retention, extinction,and spontaneous recovery

Water-deprived male albino rats received a single presentation of a 4-sec electric-grid-shock unconditioned stimulus followed by a 4-sec white-noise conditioned stimulus (a single backward conditioning trial.) Excitation conditioned to the noise was indexed in terms of the noise’s subsequent ability to suppress ongoing licking of a water tube. The main findings were: (1) Excitation was acquired and was retained over a 30-day retention interval; (2) although excitation was retained, it did not grow significantly stronger during the interval (there was no incubation effect); (3) excitation was extinguished by noise-alone trials; and (4) excitation showed more spontaneous recovery when extinction trials were separated by 29 days than when separated by only 1 day. Because these results are similar to those in the forward conditioning literature, they seem consistent with, but do not demand, the view that forward and backward excitatory conditioning involve similar learning processes. A current theory that embraces this view is opponent-process theory (Solomon & Corbit, 1974). We suggest that opponent-process theory can (1) account for existing backward conditioning data, (2) explain the phenomenon of incubation that has previously been described in the literature while simultaneously explaining its absence in the present study, and (3) integrate certain nonmonotonic acquisition phenomena that have appeared in both the forward and backward conditioning literatures.     

Resistance to extinction: contingency termination and generalization decrement

We present an algebraic model of resistance to extinction that is consistent with research on resistance to change. The model assumes that response strength is a power function of reinforcer rate and that extinction involves two additive, decremental processes: (1) the termination of the reinforcement contingency and (2) generalization decrement resulting from reinforcer omission. The model was supported by three experiments. In Experiment 1, 4 pigeons were trained on two-component multiple variable-interval (VI) 60-sec, VI 240-sec schedules. In two conditions, resistance to change was tested by terminating the response-reinforcer contingency and presenting response-independent reinforcers at the same rate as in training. In two further conditions, resistance to change was tested by prefeeding and by extinction. In Experiment 2, 6 pigeons were trained on two-component multiple VI 150-sec schedules with 8-sec or 2-sec reinforcers, and resistance to change was tested by terminating the response-reinforcer contingency in three conditions. In two of those conditions, brief delays were interposed between responses and response-independent reinforcers. In both Experiments 1 and 2, response rate was more resistant to change in the richer component, except for extinction in Experiment 1. In Experiment 3, 8 pigeons were trained on multiple VI 30-sec, VI 120-sec schedules. During extinction, half of the presentations of each component were accompanied by a novel stimulus to produce generalization decrement. The extinction data of Experiments 1 and 3 were well described by our model. The value of the exponent relating response strength and reinforcement was similar in all three experiments.     

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.     

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.     

Increase in retention of a taste aversion by weanling rats after a long interval

Weanling rats were tested for retention of an aversion to a novel flavor (chocolate milk) that had been conditioned as a single-element conditioned stimulus (CS) or in compound with a novel ambient odor (banana). The presence of the ambient odor during conditioning had no effect on flavor aversion shortly thereafter, confirming previous results. The flavor aversion observed 21 days after conditioning, however, was significantly stronger for pups conditioned with the single-element CS than for those given the flavor-odor compound as the CS. This retention effect was due to a surprisingincrease in the conditioned aversion observed 21 days after conditioning with the single-element CS. A second experiment confirmed this paradoxical increase in retention of the aversion to chocolate milk. This experiment also verified that no such increase occurred in retention of the conditioned aversion to a different flavor (saccharin), whether the initial aversion was strong or weak. The results may be explained in terms of generalized latent inhibition from consumption of mother’s milk.     

Expression of a taste aversion conditioned with an odor-taste compound: Overshadowing is relatively weak in weanlings and decreases over a retention interval in adults

Adult rats were injected with lithium chloride (LiCl) after consumption of a novel flavor (chocolate milk) that either was or was not presented together with a novel ambient odor (banana) as a compound conditioned stimulus (CS). In Experiment 1, the adults’ consumption of the flavor 24 h after conditioning was compared with that of weanling rats given the same conditioning treatment on Postnatal Day 21. The results confirmed previous indications that the reduction in aversion observed for adults conditioned with the compound CS (overshadowing) was weak or nonexistent in weanlings. After a longer retention interval (21 days), there was no evidence of overshadowing in adults despite maintained retention of the basic conditioned aversion. In Experiment 2 this decrease in overshadowing after a long retention interval was replicated with adult animals and extended to a different method of testing. The form of the effect was the same as in Experiment 1: The decrease in overshadowing occurred over the retention interval without loss in retention of the basic taste aversion; the decrease in overshadowing was a consequence of anincrease in the flavor aversion displayed by animals conditioned with the compound CS. The impaired flavor aversion (i.e., the overshadowing) observed shortly after conditioning apparently was due to factors associated with memory retrieval, rather than to reduced attentional or associative strength.     

Policy making processes with respect to teacher education in Finland and Norway

This article examines policy making processes in the area of teacher education (TE) in Finland and Norway. Particular attention is given to the roles different actors play in these processes and the potential effects of their involvement on the TE programs in the two countries. Contemporary policy processes are analyzed through a set of interviews with profiled and experienced policy makers in the area in question. The analyses show that TE policy processes in Norway rely heavily on political actors and changes in political conditions, while Finnish TE policy processes rely more on academic expertise in the development of TE policies.     

A comparison of resistance to satiation and resistance to extinction

In two experiments, resistance to satiation was compared with resistance to extinction. In Experiment 1, rats given initial trials in a straight-alley runway while satiated failed to show increased resistance to satiation in a later test phase. This negative finding contrasts with the increased resistance to extinction usually found following initial nonrewarded trials in a straight alley. In Experiment 2, rats were extinguished or were run while satiated following deprived acquisition, and then were either shifted to the other condition or maintained under the same condition. A greater response decrement was produced by extinction than by satiation, both when current performance was examined and when the persistent effect of satiation or extinction on later performance was examined. These results show that there are important dissimilarities in the effects of satiation and extinction, dissimilarities that suggest that extinction is more nonrewarding or aversive than satiation. It seems likely that extinction involves processes (such as frustration, arousal of aversive motivation, and conditioned inhibition) not involved in satiation, which account for the greater response decrement in extinction as compared with satiation.     

Rats do show primacy and recency effects in memory for lists of spatial locations: A reply to Gaffan

It has been demonstrated that rats display both primacy and recency effects in list-learning experiments for both item- and order-recognition memory for spatial location information. Contrary to a suggestion made by Gaffan (1992) that previous demonstrations of primacy effects in rats are not valid due to statistical and methodological problems, we show that (1) it is not likely that our results are due to experimenter bias and/or nonindependence of trials, (2) primacy and recency effects are obtained whether or not one uses a training criterion, and (3) when many of the published reports from our laboratory are combined, the number of subjects and trials are sufficient to evaluate the validity of primacy and recency effects in list-learning experiments.     

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.