What–Where–When memory in magpies (Pica pica)

Some animals have been shown to be able to remember which type of food they hoarded or encountered in which location and how long ago (what–where–when memory). In this study, we test whether magpies (Pica pica) also show evidence of remembering these different aspects of a past episode. Magpies hid red- and blue-dyed pellets of scrambled eggs in a large tray containing wood shavings. They were allowed to make as many caches as they wanted. The birds were then returned either the same day or the next day to retrieve the pellets. If they returned the same day, one colour of pellets was replaced with wooden beads of similar size and colour, while if they returned the next day this would happen to the other colour. Over just a few trials, the birds learned to only search for the food pellets, and ignore the beads, of the appropriate colour for the given retention interval. A probe trial in which all items were removed showed that the birds persisted in searching for the pellets and not the beads. This shows that magpies can remember which food item they hoarded where, and when, even if the food items only differ from each other in their colour and are dispersed throughout a continuous caching substrate.     

Numerical and sensory categorization of serial information by animals

Rats were trained in a straight runway on a series consisting of 4 elements, each element being defined in terms of the number of .045-gm. Noyes pellets used as reward on 4 runway trials separated by about 20 sec. The series elements were 2, 6, 12, and 0 (2-6-12-0). The animals were trained each day on 3 such series, the series themselves being separated within a day by about 12 min. for 28 days before introducing a new transfer series to assess the relevance of the order of the series elements. In previous experiments with the simpler series, 2-12-0, alterations in order of elements eliminated the animals' tendencies to run much slower to the terminal nonreward element of the series, but transfer was clearly shown here when we shifted from 2-6-12-0 to 6-12-2-0. That is, the animals continued on the transfer test to approach the terminal element slowly, a result which we interpret as supporting the view that the rats either counted the rewarded trials and used that count to predict terminal nonreward, or they behaved on the basis of cues associated with the ordinal position of the trial.     

Trial order and retention interval in human predictive judgment

The influences of order of trial type and retention interval on human predictive judgments were assessed for a cue that was reinforced on half of its training presentations. Subjects observed 10 cue-outcome presentations (i.e., reinforced trials) and 10 cue-alone presentations (i.e., nonreinforced trials) in one of three different orders: all nonreinforced trials followed by all reinforced trials(latent inhibition), reinforced and nonreinforced trials interspersed (partial reinforcement), or al lreinforced trials followed by all nonreinforced trials (extinction). Ratings were based mainly on the most recent event type (i.e., a recency effect) when the test occurred immediately after training but were based mainly on initial event types (i.e., a primacy effect) when the test occurred after a 48-h delay. The subjects tested both immediately and with a long retention interval did not exhibit this shift to primacy (i.e., the recency effect persisted). These results demonstrate noncatastrophic forgetting and the flexible use of trial order information in predictive judgments.     

Between-list lag effects in recall depend on retention interval

Although the benefits of spaced retrieval for long-term retention are well established, the majority of this work has involved spacing over relatively short intervals (on the order of seconds or minutes). In the present experiments, we evaluated the effectiveness of spaced retrieval across relatively short intervals (within a single session), as compared to longer intervals (between sessions spaced a day apart), for long-term retention (i.e., one day or one week). Across a series of seven experiments, participants (N = 536) learned paired associates to a criterion of 70 % accuracy and then received one test–feedback trial for each item. The test–feedback trial occurred within 10 min of reaching criterion (short lag) or one day later (long lag). Then, a final test occurred one day (Exps. 1–3) or one week (Exps. 4 and 5) after the test–feedback trial. Across the different materials and methods in Experiments 1–3, we found little benefit for the long-lag relative to the short-lag schedule in final recall performance—that is, no lag effect—but large effects on the retention of information from the test–feedback to the final test phase. The results from the experiments with the one-week retention interval (Exps. 4 and 5) indicated a benefit of the long-lag schedule on final recall performance (a lag effect), as well as on retention. This research shows that even when the benefits of lag are eliminated at a (relatively long) one-day retention interval, the lag effect reemerges after a one-week retention interval. The results are interpreted within an extension of the bifurcation model to the spacing effect.     

Serial learning in rats: A test of three hypotheses

Findings obtained by providing rats with a single fixed series of events, A-B-C-…, often are equally compatible with three alternative serial learning interpretations: that the signal for items is (A) their position in the series (position view), (B) the prior item of the series (chaining view), and (C) one, two, or more prior items of the series (sequential view). By employing a novel procedure of supplying rats with two different series, rather than a single series, it was possible to choose between the three alternatives. Employing 10 and 0, 0.045 g, Noyes pellets as items, rats in both runway experiments reported here received a three trial series, either a 10-0-10 series or a 0-0-10 series. In Experiment 1, the other series was a single 0 pellet trial (along with 10-0-10) or a single 10 pellet trial (along with 0-0-10). In Experiment 2, the other series was either 0-0 (along with 10-0-10) or 10-0 (along with 0-0-10). Considering both experiments, findings were consistent with the sequential view but not with either the position view or the chaining view. The possibility was suggested that, under some other experimental conditions, particularly those not employing reward events as items, greater control over discriminative responding might be exercised by position cues than by item cues.     

Recognition memory retention interval and information load

Two experiments were conducted to study the effect of retention interval and information load on short-term recognition memory in retarded subjects. The task consisted of an input trial of 1–15 pictures followed by a test trial of one picture, with the subject having to press different levers to indicate whether the probe picture had been present on the input trial. Retention intervals between input trial and test trial were manipulated over a range of 1–24 sec. Both accuracy and latency of response were measured. Results showed that latency increased and accuracy decreased as a function of both retention interval and number of stimuli. In addition, number of stimuli interacted with retention interval such that accuracy was not affected by retention interval when information input was small, but decreased quite dramatically at longer retention intervals when input was larger. The results were discussed in terms of current memory search models for both normal and retarded subjects.     

Ordinal position learning and remote anticipation

Rats were runway trained on each of two 3-trial series of reward outcomes. The series are labeled XNY and ZNN, for which X represents a trial that was rewarded with Noyes pellets and N represents a trial that ended with no reward. Units of distinctively flavored breakfast cereals served as reward on trials labeled Y and Z. One group (Floor) had each series occur with a correlated runway floor, either smooth and black or rough and white. For a second group (Memory), the floor cue was uncorrelated with series. Animals in both groups learned to approach the goal rapidly on the 1st trials of the 2 series and slowly on the 2nd trials, but only Group Floor learned to differentiate the 3rd trials of the series. These results recommend a view of serial learning that emphasizes the role played by information about the ordinal position of series items.     

Ordinal Position Learning and Remote Anticipation

Rats were runway trained on each of two 3-trial series of reward outcomes. The series are labeled XNY and ZNN, for which X represents a trial that was rewarded with Noyes pellets and N represents a trial that ended with no reward. Units of distinctively flavored breakfast cereals served as reward on trials labeled Y and Z. One group (Floor) had each series occur with a correlated runway floor, either smooth and black or rough and white. For a second group (Memory), the floor cue was uncorrelated with series. Animals in both groups learned to approach the goal rapidly on the 1st trials of the 2 series and slowly on the 2nd trials, but only Group Floor learned to differentiate the 3rd trials of the series. These results recommend a view of serial learning that emphasizes the role played by information about the ordinal position of series items.     

Choice between food and heroin: effects of morphine, naloxone, and secobarbital.

Baboons responded on a choice task on which discrete trials involved choosing between an intravenous injection of heroin (.32 or 1.0 mg/kg) or the availability of food pellets. An intertrial interval of three hours followed the completion of each trial. Under baseline conditions baboons consistently completed the eight available trials each day. Typically, animals chose heroin on three or four trials a day and food on the remaining trials. Animals tended to space the selection of heroin rather than choosing heroin on consecutive trials. A series of single-day experimental manipulations was undertaken to characterize performance further. Manipulation of the heroin dose produced shifts in the relative frequency of choosing the drug option which were inversely related to dose. Manipulation of number of pellets per food trial produced little change in distribution of choices. Noncontingent administration of morphine produced dose-related decreases in relative frequency of heroin choices, and a higher dose decreased the number of trials completed. Noncontingent naloxone produced dose-related increases in the relative frequency of heroin choices. Noncontingent secobarbital had no effect on distribution of choices, and high doses reduced the number of trials completed per day. The results suggest that morphine and naloxone produce shifts in this choice behavior by selectively interacting with the reinforcing properties of the option involving heroin.     

Rats’ anticipation of current and future trial outcomes in the ordered RNR/RNN serial pattern task

In the ordered RNR/RNN serial pattern task, rats often reduce their running speeds on trial 2 less within the RNR than within the RNN series. Initially, investigators (Capaldi, 1985; Capaldi et al., 1983) considered this trial 2 differential speed effect evidence for rats’ anticipation of inter-trial outcomes within each series. Later findings, however, suggest that this effect reflects some generalization of the ordinal position of trial 3 (Burns et al., 1986) or its similar runway cues during trial 2 (Capaldi et al., 1999). To test these generalization hypotheses, we made trial 2 more distinct from trial 3 in each series by forcing rats to alternate runways in a T-maze only on the last trial rather than on trial 2 in each series in Experiment 1, or by forcing rats to alternate runways between trials rather than to run down the same runway on all trials within each series in Experiment 2. Although enhancing the distinctiveness between these trials reduced the trial 2 differential speed effect, extensive training failed to eliminate it. Therefore, this residual difference between trial 2 speeds could reflect rats’ anticipation of trial 3 outcomes during trial 2 as originally proposed by Capaldi (1985) Experiment 3 was designed to determine whether we could enhance rats’ final trial outcome expectancies during trial 2 by making different trial 2 choices distinctive cues for each trial 3 outcome. The trial 2 speed effect was greater when rats were forced to alternate over all trials only within one of the series than when they were sometimes forced to do so in either series. Post-training probe tests revealed that both series position and the relevant within-series runway events contributed to this enhanced anticipation of trial 3 outcomes.     

Intertrial interval effects on internal stimulus control of behavior in brightness differential conditioning

In Experiment 1, groups were given a trial sequence in differential conditioning in which all S+ trials preceded all S? trials (+? schedule) or one in which some S+ trials followed S? trials (+?+ schedule) and either a 1- or a 30-min intertrial interval (ITI). ITI affected discrimination learning only in the +? schedule condition; schedule affected discrimination only at massed trials. In Experiment.2, all groups received a +?+ schedule. In two groups, given a 1- or 15-min ITI between all trials, discrimination learning was independent of ITI. Discrimination learning was facilitated in two other groups given a 1-min ITI between all trials except between S? and the subsequent S+ trial, when the ITI was either 15 or 60 min. The results were discussed in terms of their implications for internal reward-related stimulus control of behavior in differential conditioning.     

Memory for lists of spatial events in the rat

Three experiments are reported in which rats were presented with lists of spatial events or responses in distinct visual contexts, and retention subsequently was measured for the events occuring at each serial position. In Experiments 1 and 2, lists contained different numbers of forced choices on successively presented T-mazes, and memory for each serial position was tested on each trial. In Experiment 3, lists were made up of different numbers of forced entries into randomly ordered arms on the eight-arm radial maze, and memory for one serial position was probed on each trial. All three experiments yielded serial position curves which demonstrated recency effects but no primacy effects. Comparisons of retention for different list lengths within each experiment indicated that retention of shorter lists was equivalent to retention of the final items of longer lists and superior to retention of the initial items on longer lists. This pattern of results indicated that there was no evidence of proactive inhibition in the serial position curves. Analysis of input and output interference effects and the results of control tests suggested that both retroactive inhibition and time-based forgetting processes were responsible for recency effects.     

Serial position curves in spatial memory of rats: Primacy and recency effects

Memory for lists of items was tested in rats (N = 18) in an 8-arm radial maze. In Experiment 1 trials consisted of a study phase, in which the rat could freely choose five arms to obtain a food reward, and a test phase in which the animal was presented with a choice between a novel and a previously visited arm. The rat received additional food reinforcement only when visiting the novel arm. The two phases of a trial were separated by a retention interval of 30 sec or of 4, 16 or 60 min. It was found that recall of the five free arm choices was related to the serial position of the previously visited arm. There was a significant recency effect at the 30-sec delay. With longer retention intervals this disappeared, and a significant primacy effect could be observed. In Experiment 2 the same animals were given forced arm entries during the study phase and delays of 30 sec or 4 or 16 min before the test phase. Again, there was a trend towards a recency effect after the shorter delays and a significant primacy effect after the 16-min interval. These results show that, in the recall of lists of spatial items, rats have serial position curves with primacy and recency effects, depending on the length of the retention interval.     

Effects of associatively significant posttrial stimuli on learning and memory

Pigeons were trained on a delayed conditional discrimination in which the choice between two simultaneously presented stimuli depended on how the trial started. Choice of one of the stimuli was reinforced if the trial had been initiated by presentation of a food sample and choice of the other was reinforced if no sample had been presented. Subsequently, test trials were administered on which an associatively significant stimulus was presented during the retention interval. This manipulation was intended to modulate the short-term retention of information about the food sample. It was found that performance on food sample test trials was enhanced by presentation of an excitor for food, disrupted by presentation of an inhibitor for food and unaffected by presentation of an associatively neutral stimulus. The impact of these posttrial stimuli was also assessed on the ability of the food sample to serve as a reinforcer. This was done by recording the development of responding to a keylight that signalled the food sample on these test trials. Compared to the associatively neutral stimulus, both the excitor and the inhibitor interfered with the development of keypecking. These results are discussed with regard to the issue of how posttrial events modulate associative learning.     

Grouping, chunking, memory, and learning

An example of grouping is dividing a long series of digits into two or more smaller units by, for example, pausing for a short time between items within groups but for a longer time between groups. Grouping, virtually neglected in animal learning, was examined in each of five rat investigations reported here in which a series of two or more runway trials was either grouped together with or apart from a terminal large reward trial. It was found that running speed on early small reward trials in the series was greater when prior trials were grouped together with rather than apart from the terminal large reward trial and this when the intertrial interval was short, 20 sec, or long, 20 to 40 min. Three possible explanations of the present findings were examined: a reward schedule view, a rule-learning view, and an anticipation view based on memory. The most feasible of these explanations, it was suggested, was the anticipation view. According to this view, when prior trials are grouped together with a terminal large reward, there is a tendency for the rat to anticipate the terminal large reward well before its scheduled occurrence, elevating running speed on earlier small reward trials. Such anticipation occurs, it was suggested, because when trials are grouped together the memory of each reward event in the series is retrieved on each subsequent trial, including the remote terminal large reward trial, where it becomes a signal for large reward. Thus the present results implicate not merely adjacent associations—associations between adjacent events—but also the highly controversial remote associations—associations between two events separated not only in time but by one or more intervening events as well.     

Attentional resources in timing: Interference effects in concurrent temporal and nontemporal working memory tasks

Three experiments examined interference effects in concurrent temporal and nontemporal tasks. The timing task in each experiment required subjects to generate a series of 2- or 5-sec temporal productions. The nontemporal tasks were pursuit rotor tracking (Experiment 1), visual search (Experiment 2), and mental arithmetic (Experiment 3). Each nontemporal task had two levels of difficulty. All tasks were performed under both single- and dual-task conditions. A simple attentional allocation model predicts bidirectional interference between concurrent tasks. The main results showed the classic interference effect in timing. That is, the concurrent nontemporal tasks caused temporal productions to become longer (longer productions represent a shortening of perceived time) and/or more variable than did timing-only conditions. In general, the difficult version of each nontemporal task disrupted timing more than the easier version. The timing data also exhibited a serial lengthening effect, in which temporal productions became longer across trials. Nontemporal task performance showed a mixed pattern. Tracking and visual search were essentially unaffected by the addition of a timing task, whereas mental arithmetic was disrupted by concurrent timing. These results call for a modification of the attentional allocation model to incorporate the idea of specialized processing resources. Two major theoretical frameworks—multiple resource theory and the working memory model—are critically evaluated with respect to the resource demands of timing and temporal/ nontemporal dual-task performance.     

The CS-US interval function in rabbit nictitating membrane response conditioning: Single vs multiple trials per conditioning session

The effect of varying trials per day conditions on the CS-US interval or interstimulus interval (ISI) function in rabbit nictitating membrane response conditioning was studied in two experiments. Experiment 1 showed that a 1250-msec ISI was more effective than a 250-msec ISI when there was 1 trial/day. Experiment 2 showed that as the number of trials per day decreased from 20 to 1, the superiority of the 250-msec ISI group over the 1250-msec ISI group declined, with a reversal at 1 trial/day. Results are interpreted in terms of the role of a hypothesized CS-elicited short-duration orienting response in CR performance.     

Dynamics of time discrimination

Pigeons tracked sinusoidal sequences of interfood intervals (IFIs) by pausing in each interval for a time proportional to the preceding interval. Schedules with either long (30-90 s) or short (5-15 s) values, with variable numbers of cycles and starting phase each day, were tracked about equally well. Tracking was apparently immediate and did not improve across sessions. Experiment 2, in which long and short series were presented on alternate days, showed that tracking on long was more impaired than on short. Experiment 3 showed that occasional presentation of a short IFI in a series of fixed, longer IFIs caused a reduction in waiting time in the next IFI. These effects are evidence for a fast-acting timing mechanism in which waiting time in the IFI N + 1 is strongly determined by the preceding IFI, N. Earlier IFIs have some cumulative effect, but the details remain to be elucidated.     

Time and order effects on causal learning

Five experiments were conducted to explore trial order and retention interval effects upon causal predictive judgments. Experiment 1 found that participants show a strong effect of trial order when a stimulus was sequentially paired with two different outcomes compared to a condition where both outcomes were presented intermixed. Experiment 2 found that a 48-h retention interval eliminates the trial order effect, so that participants gave a global judgment about the relationship between the stimulus and the two outcomes equivalent to the one given by participants that received the two phases intermixed. This result was replicated in Experiment 3 in a situation in which the probability of the outcome in the presence of the cue was changed from .5 for both outcomes (Experiments 1, 2, 4, and 5) to .75 and .25 for outcomes 1 and 2, respectively. Experiment 4 found that retention intervals ranging from 45 min to 48 h eliminated the trial order effect similarly. Experiment 5 found that a 10-min retention interval replicated the effect of time upon sequential training found in precedent experiments, regardless of whether participants remained within the laboratory during the retention interval or spent it outside. The combined results of this experimental series suggest that retention intervals reduce retroactive interference in causal learning by allowing participants to use all the information presented across phases, rather than differentially increasing or decreasing retrieval of information about each of them.     

Chronic propranolol induces deficits in retention but not acquisition performance in the water maze in mice

Agents that alter adrenergic receptors, such as "beta-blockers," also alter memory storage. However, reports suggest that beta-adrenergic receptor antagonists, such as propranolol, have conflicting behavioral effects with acute vs chronic dosing. This study was designed to evaluate the effects of chronic propranolol on retention for a spatial learning task. Adult male ICR mice were given daily injections of propranolol (2, 4, 8, or 12 mg/kg ip) or 0. 9% NaCl for 15 days prior to, and during, trials in a Morris water maze. Mice received five massed acquisition (escape) trials in each of three daily sessions, followed by a single 60-s probe trial on the fourth day. The location of the submerged platform was constant for each animal over acquisition trials, but varied across animals; starting position varied across trials. A 5 (dose) x 3 (trial blocks) mixed factorial ANOVA for escape time yielded a significant trial blocks effect only (p <.001), showing performance improving over sessions. Time spent in the target quadrant on the probe trial was shorter under all doses of propranolol when compared to vehicle group (all p <.001), indicating poorer retention of prior platform location. This effect, however, was not dose-related. Swim speed was not significantly affected by propranolol. These data demonstrate that chronic dosing with propranolol can impair retention of spatial learning, which cannot be attributed to reduced arousal or motor function.