Facilitative effect of a pretest exposure to the CS: Analysis and implications for the memory trace

Retention of a brightness discrimination avoidance task by rats is impaired (Kamin effect) following a 1-h training-to-test interval (TTI), is enhanced after a 3-day TTI (reminiscence, or long-term spontaneous improvement), and is disrupted following a 21-day TTI (long-term forgetting). An exposure to the conditioned stimulus (CS), delivered 5 mm before a 1-h delayed retention test, not only compensated for the performance deficit that corresponds to the Kamin effect, but induced a large improvement in performance similar to that normally obtained after a 3-day TTI. It can be proposed that such cuing may act either by accelerating a natural memory-trace maturation process or by improving the retrievability of the memory trace. Since these possibilities lead to opposite predictions concerning the length of the facilitation induced by cuing, the effect of a pretest exposure to the CS on performance obtained during a 1-h delayed retention test was studied after several cuing-to-test intervals (0, 5, 10, or 20 min). The results, which indicate that cuing transiently enhanced subsequent retention performance, more convincingly support the retrieval hypothesis. The effects of pretest exposure to the CS (which occurred 5 min before testing) were also examined 10 min, 1 h, or 24 h after initial training. The results indicate that the facilitative effect of cuing obtained when retention performance was disrupted shortly after training (1-h TTI) was also obtained after a 24-h retention interval, in the absence of performance disruption. An interpretation of the facilitative effect of a pretest exposure to the CS is proposed, and implications concerning the memory trace are further discussed in relation to the multidimensional hypothesis.     

Postresponse exposure to warning signal in avoidance extinction

Delayed termination of the warning signal following extinction responses has been shown to facilitate extinction of discriminative avoidance. In order to determine the relative roles in extinction of delayed termination per se and postresponse exposure to the warning signal, which is necessarily confounded with delayed termination treatment, seven groups of rats were first trained on a one-way avoidance task in which a buzzer served as part of the warning-signal complex. Then, on nonshock extinction trials, the buzzer (a) terminated immediately with a response and was not reinstated in the postresponse interval, (b) terminated immediately with a response and was reinstated for a 5- or 10-sec period 5 or 15 sec following the response, or (c) terminated 5 or 10 sec following a response (delayed termination). Results indicated that exposure to the buzzer at postresponse intervals greater than 5 sec following responses was critically involved in reducing resistance to extinction. This finding supports a conditioned relief interpretation of the delayed warning signal termination effect and is consistent with the effect of response prevention techniques on extinction.     

The effect of controllable and uncontrollable neonatal preshocks on adult escape/avoidance behavior in the guinea pig (Cavia porcellus)

Neonatal guinea pigs were given escapable, inescapable, or no shock and were later tested as adults on a signaled escape/avoidance task. During the neonatal period, the animals that could escape shock learned to do so quickly and steadily increased their overall level of activity, while those that could not, displayed a consistent decline in activity. Furthermore, during adult escape/avoidance sessions, guinea pigs, that could control neonatal shock were superior to those that lacked such control. These findings extend the generality of the interference effect to the guinea pig and highlight the influence of early control of aversive events on this phenomenon.     

Changes in the retrievability of associations to elements of the compound CS determine the expression of overshadowing

In two experiments, rats were presented with a taste conditioned stimulus (CS) alone, an odor CS alone, or an odor-taste compound followed by lithium chloride injection. When tested 1 day following conditioning, there was evidence that the odor cue overshadowed conditioning to the taste; however, there was no indication of overshadowing following a longer (21-day) retention interval, despite undiminished strength of the aversion in animals conditioned with only the single element (taste). The overshadowing observed at the 1-day retention interval was not reciprocal. Rats conditioned with the odor CS alone or with the compound CS expressed odor aversions of comparable strength—that is, no overshadowing. However, in contrast to the taste aversion, overshadowing of conditioning to the odor by taste was evident following a 21-day retention interval. Rather than reflecting a failure of the overshadowed stimulus to acquire associative strength, these data suggest that overshadowing may be expressed, or not expressed, as a result of changes in the relative retrievability of learned associations over time.     

Effects of proactive interference on rats’ continuous nonmatching-to-sample performance

Rats performed a new delayed matching-to-sample task—the continuous nonmatching-to-sample task. A variable number of trials with one stimulus alternated with trials with a second stimulus. A response on the trial following a stimulus change (nonmatch trial) was reinforced. Responses to repeated stimuli were never reinforced. Rats could maximize reinforcement by remembering across the intertriai interval which stimulus was presented on the previous trial. Sequential analysis indicated that interference from previous conflicting trials (proactive interference, PI) reduced response accuracy but did not affect retention: Accuracy was lower on trials following a nonmatch trial than on trials following repeated stimuli. Furthermore, accuracy increased as a function of the time between the to-be-remembered nonmatch trial and the previous interfering trial. However, neither time between trials nor the distance from a stimulus change affected the rate of decline in accuracy over the retention interval.     

Control of delayed matching-to-sample performance using directed forgetting techniques

Pigeons acquired a successive delayed matching-to-sample task at a delay interval of 4 sec. Instructional stimuli were interpolated in the delay interval signaling the occurrence (R-cue) or nonoccurrence (F-cue) of comparison stimuli, a procedure modeled after the directed forgetting techniques commonly used in human memory studies. Accuracy on probe trials (in which comparison stimuli were presented following F-cues) was reduced relative to performance on standard training trials in which R-cues signaling the occurrence of comparison stimuli appeared in the same temporal location. The extent of the reduction in accuracy depended on the temporal location of the F-cues, the reduction being greater when the cue was more remote from the comparison stimuli. Examination of retention interval keypecking revealed a strong correlation between matching performance and retention interval responding.     

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.     

Interaction between conflicting memories in the rat: Contextual pretest cuing reverses control of behavior by testing context

Two experiments were run in order to investigate the influence of external contextual cues on the interaction between two conflicting memories. Rats were trained, in the same apparatus, on a passive-avoidance task and, 10 min later, on an active-avoidance task, then submitted to a 24-h delayed test (without reinforcement). When contextual cues remained unchanged throughout these three phases, the animals exhibited proactive interference, as shown by longer response latencies than those of control animals that had learned only the active-avoidance task (Experiment 1). When training contexts were made slightly different from one task to the other (by the presence of a continuous tone during either the first or the second task), the animals behaved at subsequent testing in accordance with the response contingencies present in the context exactly similar to the test context; this control of behavior by testing context was demonstrated both when the tone was absent (Experiments 1 and 2) and present (Experiment 2) at testing. A cuing procedure—a 90-sec exposure to the tone in the experimental room 5 min prior to testing—led the animals to behave in accordance with the response previously acquired in the presence of the tone (Experiments 1 and 2), exactly in the same way as animals tested in the presence of the tone (Experiment 2). The same cuing treatment was ineffective when administered 1 h before testing (Experiment 2). These results are interpreted in terms of a dual function of contextual cues at the time of retrieval: the general contextual information present during testing or during pretest cuing is assumed to induce concurrent reactivation of both memories. Consequently, the experimentally manipulated contextual cue (the tone) would have a discriminative function, leading the animals to choose between the two equally available representations.     

Stimulus salience and asymmetric forgetting in the pigeon

Pigeons were trained using a symbolic delayed matching-to-sample procedure involving bright versus dim houselight samples. We hypothesized that when sample stimuli differ in salience, increasing the size of the retention interval will affect performance on trials initiated by the more salient sample only. In agreement with this prediction, accuracy following the dim sample did not decline as the retention interval increased, whereas accuracy following the bright sample declined to well below 50% correct. In a second experiment, the less salient (dim) sample from Experiment 1 was arranged as the more salient sample in a sample/no-sample procedure. Accuracy on dim sample trials then declined to well below 50% correct as the retention interval increased, whereas accuracy on no-sample trials remained constant. The results suggest that when sample stimuli differ in salience, pigeons may transform the nominal discrimination task into a detection task in which they respond on the basis of the presence or absence of the more salient sample.     

Comparing cognition by integrating concept learning,proactive interference,and list memory

This article describes an approach for training a variety of species to learn the abstract concept of same/different, which in turn forms the basis for testing proactive interference and list memory. The stimulus set for concept-learning training was progressively doubled from 8, 16, 32, 64, 128 . . . to 1,024 different pictures with novel-stimulus transfer following learning. All species fully learned the same/different abstract concept: capuchin and rhesus monkeys learned more readily than pigeons; nutcrackers and magpies were at least equivalent to monkeys and transferred somewhat better following initial training sets. A similar task using the 1,024-picture set plus delays was used to test proactive interference on occasional trials. Pigeons revealed greater interference with 10-s than with 1-s delays, whereas delay time had no effect on rhesus monkeys, suggesting that the monkeys’ interference was event based. This same single-item same/different task was expanded to a 4-item list memory task to test animal list memory. Humans were tested similarly with lists of kaleidoscope pictures. Delays between the list and test were manipulated, resulting in strong initial recency effects (i.e., strong 4th-item memory) at short delays and changing to a strong primacy effect (i.e., strong 1st-item memory) at long delays (pigeons 0-s to 10-s delays; monkeys 0-s to 30-s delays; humans 0-s to 100-s delays). Results and findings are discussed in terms of these species’ cognition and memory comparisons, evolutionary implications, and future directions for testing other species in these synergistically related tasks.     

Rats acquire win-stay more readily than win-shift in a water escape situation

Independent groups of Sprague-Dawley rats were found to acquire a win-stay, but not a win-shift, escape resporse in a circular water maze in each of three experiments that varied with respect to swim time and distance prior to escape following an incorrect first choice. The subjects were given pairs of trials: an information trial and a test trial, separated by 10 min. On the information trial the camouflaged escape platform was randomly placed in one of two positions. On the test trial the platform was placed in the same position for the win-stay task and in the opposite position for the win-shift task. Animals that did not acquire either the stay or the shift response perseverated in their responses, consistently going to the same escape location first on both information and test trials. In the fourth experiment, in which win-shift, win-stay, and perseveration all led to escape, all rats perseverated in their responses. It was concluded that response perseveration and win-stay are more natural responses than win-shift for rats in a water escape situation. This finding contrasts with the spontaneous alternation and readily acquired win-shift behavior previously demonstrated in rodents in exploratory and appetitive situations.     

Pigeons’ short-term memory for temporal and visual stimuli in delayed matching-to-sample

In the present experiment, we compared directly pigeons’ short-term memory of temporal and visual stimuli in a delayed matching-to-sample task. The sample stimuli consisted of red and green lights presented for 5 and 30 sec, followed by a retention interval and blue and yellow comparisons. For subjects in the visual group, duration was irrelevant and the color of the sample was the conditional cue. For animals in the temporal group, color was irrelevant and duration of the sample was the conditional stimulus. The results showed that acquisition of the matching task was faster and accuracy was higher in the visual than in the temporal group. More importantly, memory of either sample generally declined at a similar rate when the duration of the retention interval was increased and when the intertrial interval was reduced. Taken together, the results indicate that with 1–8-sec retention intervals, short-term memory for temporal stimuli is similar to that found with color-visual samples. The findings are discussed in terms of retrospective and prospective processing.     

The role of US novelty in retention interval effects in single-element taste-aversion learning

Retention interval effects are seen in taste-aversion learning when single-element aversions are significantly weaker 24 h after conditioning compared with tests at later intervals. This report contains three experiments which suggest that the source of the increased drinking at the 1-day interval is nonassociative interference produced by the novel conditioning episode. In Experiment 1, a parametric analysis demonstrated that aversion strength increased monotonically over a 30-h period following conditioning, and that by 48 h after conditioning it was stabilized. In Experiment 2, a single US preexposure was used to reduce the novelty of the US prior to conditioning. As a result, animals preexposed to the US had stronger taste aversions than did non-preexposed controls at a 1-day retention interval; however, no differences were seen at a 5-day interval. Experiment 3 investigated whether the counterintuitive outcome of Experiment 2 was due to the summation of environment-illness and taste-illness associations at the 1-day test. The results ruled out the summation argument; the US preexposure did not need to be presented in the conditioning context to strengthen the aversion at the 1-day interval. Collectively, these results suggest that the presentation of a surprising US can interfere with the retrieval of the taste-illness association for a short period after conditioning, and that this contributes to the retention interval effect.     

Directed forgetting effects in pigeons: Remember cues initiate rehearsal

Pigeons were trained in a two-choice delayed matching-to-sample task with red and green hues. A brief postsample cue (a vertical or horizontal line) signaled whether the comparison stimuli would be presented or omitted on each trial. Comparison stimuli were always presented following the remember-cue (R-cue) trial, but never following the forget-cue (F-cue) and no-cue trials. In Experiment 1, matching accuracy on F-cue and no-cue trials was equivalent and was considerably inferior to accuracy on R-cue trials. In Experiment 2, the placement of the postsample cue was manipulated. Matching accuracy decreased as the R cue was delayed in the retention interval, but performance in the F-cue condition was not affected. These data indicate that the no-cue condition can function as an implicit F cue and that the R cue can function to initiate and maintain rehearsal.     

Delayed matching in the pigeon: Interference produced by the prior delayed matching trial

Pigeons’ delayed matching performance on Trial n was examined as a function of whether the correct and incorrect comparison stimuli from Trial n?1 were maintained in the same role on Trial n (positive transitions), were reversed in role on Trial n (negative transitions), or were absent on Trial n (neutral transitions). Relative to neutral transitions, positive transitions did not significantly facilitate performance. Negative transitions, however, produced significant proactive interference on Trial n, and the magnitude of proactive interference was greater when the Trial n retention interval was 1 sec than when it was 0 sec. As the intertriai interval increased from 2 to 10 sec, the amount of interference dissipated. The results suggest that a prior delayed matching trial can serve as a significant source of forgetting but not a significant source of facilitation on an immediately following delayed matching trial.     

Intratrial proactive interference in rats’ serial alternation performance in the radial maze

Rats acquired a serial alternation task in an eight-arm radial maze that was partitioned into four pairs of arms. Each pair was associated with a different distal stimulus. Rats were initially forced to the left or right arm in each pair (the study segment) before being exposed to both arms in each pair (the free-choice or test segment). Only the previously blocked arm of each pair remained baited. Following initial training, proactive interference (PI) was induced by presenting rats with a forced-choice (prestudy) segment containing arm positions opposite those in the subsequent study segment. Such trials generated poorer free-choice accuracy than did trials without a prestudy segment. Forcing rats to both arms in the pair in a prestudy segment produced only transient PI. A slight improvement in rats’ free-choice performance was obtained by forcing them to the same arm position, but only when the test segment was delayed by 30 min. Increasing the interval between the prestudy and study segments from 2 to 30 min eliminated PI, but only when free-choice testing was delayed by 2 min rather than by 30 min. These results suggest that intratrial PI in this preparation was primarily due to confusion about which arm position in each pair had been visited during the last forced-choice segment.     

Variables affecting alternation behavior in the cockroach,Blatta orientalis

To investigate alternation behavior in the cockroach as an invertebrate, three T-maze experiments were conducted assessing the effects of (a) intratrial (exposure) and intertrial (exposure to test) interval, (b) brightness similarity of the alternatives and response-direction factors, and (c) an initial free-choice vs. a varying number of forced-choice exposures. Alternation was enhanced with a long exposure on Trial 1, a short interval between Trial 1 and Trial 2 (test), greater dissimilarity (or discriminability) of the arm brightnesses and more frequent forced-choice exposures to an arm prior to test. These results highlight the role of intramaze brightness cues as controlling alternation in the cockroach and accord well with a response-to-change interpretation of the phenomenon. In addition, they suggest that the alternation paradigm can be used effectively to assay short-term memory storage in neurologically simple organisms.     

Differential effects of several retrieval cues over time: Evidence for time-dependent reorganization of memory

The retention performance following partial training (15 trials) of a brightness-discrimination avoidance task has been shown to fluctuate over time, with a drop in performance 1 h after training (Kamin effect), a long-term spontaneous improvement (LTSI) after 3 days, and long-term spontaneous forgetting after 21 days. The purpose of this paper was to determine if these time-dependent modulations of retention performance reflect time-dependent modifications in the organization of the attributes that constitute the memory trace. We studied the relative effectiveness of several pretest cuings on retention performance when they were delivered just before a retention test occurring 1 h, 3 days, or 21 days following initial training. Some cuing treatments were related to a particular training event (conditioned or unconditioned stimulus, experimental context). Compound cuings, composed of two or more training events, were also studied to test a possible additive effect between retrieval cues. To demonstrate time-dependent modifications in the memory trace, a differential effectiveness over time was expected for at least some retrieval cues. The results show that cuing may compensate for performance deficits (1 h or 21 days), but does not further enhance performance when spontaneously improved (3 days). No detectable additive effects of retrieval cues were obtained. However, these results provide information that suggests a time-dependent effectiveness for some cuing treatments. In the last experiment, we investigated this possibility by studying the effects of each of these treatments when delivered after either a 1-h or a 21-day retention interval. The results confirm a time-dependent decrease in effectiveness of a pretest exposure to the CS and an increase in effectiveness over time of a pretest exposure to the experimental context or to a well-ordered sequence of events. Such differential retrievability of a partially learned episode according to both the nature of the cues and the length of the retention interval suggests a time-dependent reorganization of memory attributes.     

The relationship between reading level and retention in average and supra readers

Research which indicates a relationship between reading level and memory has generally focused on the performance of average and delayed readers, leaving open the question of performance by above average (supra) readers. The present study considered the performance of average and supra readers on a partial report task with a variable interstimulus interval. The results demonstrated that the two groups do not differ when the interval is less than 200 ms, but the supra readers perform better when the interval extends beyond that point. The results are interpreted as supporting the concept of a continuous relationship between memory and reading level.     

Spatial memory in rats: Resistance to retroactive interference

Treatments that interfere with animals’ short-term retention (e.g., in delayed matching-to-sample) were studied using a spatial memory task. Rats performed in an eight-arm radial maze in which choosing each arm without repetition was the optimal behavior. Performances were interrupted between fourth and fifth choices for a delay of 15 sec to 2 min. A variety of events occurring during the delay interval did not disrupt memories for prior choices (as assessed by the accuracy of postdelay choices). The ineffective treatments included variations in visual and auditory environments, removal from the maze, food consumed during the delay, a distinctive odor added to the maze, or combinations of these manipulations. Additionally, performance on another spatial task (a four-arm maze) during the delay between Choices 4 and 5 did not interfere with performance in the eight-arm maze. These findings suggest that rats’ memories for spatial locations are immune to retroactive interference, at least within the range of conditions reported, and that the rat can successfully segregate memories for spatial locations established in different contexts.