Foraging behaviour in domestic pigs (Sus scrofa): remembering and prioritizing food sites of different value

This experiment investigated whether domestic pigs can remember the locations of food sites of different relative value, and how a restricted retrieval choice affects their foraging behaviour. Nine juvenile female pigs were trained to relocate two food sites out of a possible eight in a spatial memory task. The two baited sites contained different amounts of food and an obstacle was added to the smaller amount to increase handling time. On each trial, a pig searched for the two baited sites (search visit). Once it had found and eaten the bait, it returned for a second (relocation) visit, in which the two same sites were baited. Baited sites were changed between trials. All subjects learnt the task. When allowed to retrieve both baits, the subjects showed no preference for retrieving a particular one first (experiment 1). When they were allowed to retrieve only one bait, a significant overall preference for retrieving the larger amount emerged across subjects (experiment 2). To test whether this preference reflected an avoidance of the obstacle with the smaller bait, 15 choice-restricted control trials were conducted. In control trials obstacles were present with both baits. Pigs continued to retrieve the larger bait, indicating they had discriminated between the two food sites on the basis of quantity or profitability and adjusted their behaviour accordingly when the relocation choice was restricted. This suggests for the first time that domestic pigs have the ability to discriminate between food sites of different relative value and to remember their respective locations.     

Validation of a rodent model of episodic memory

Episodic memory consists of representations of specific episodes that happened in the past. Modeling episodic memory in animals requires careful examination of alternative explanations of performance. Putative evidence of episodic-like memory may be based on encoding failure or expectations derived from well-learned semantic rules. In Experiment 1, rats were tested in a radial maze with study and test phases separated by a retention interval. The replenishment of chocolate (at its study-phase location) depended on two factors: time of day (morning vs. afternoon) and the presence or absence of chocolate pellets at the start of the test phase. Because replenishment could not be decoded until the test phase, rats were required to encode the study episode. Success in this task rules out encoding failure. In Experiment 2, two identical mazes in different rooms were used. Chocolate replenishment was trained in one room, and then they were asked to report about a recent event in a different room, where they had no expectation that the memory assessment would occur. Rats successfully answered the unexpected question, ruling out use of expectations derived from well-learned semantic rules. Our behavioral methods for modeling episodic memory may have broad application for assessments of genetic, neuroanatomical, neurochemical, and neurophysiological bases of both episodic memory and memory disorders such as those that occur in Alzheimer’s disease.     

Domestic dogs’ (Canis familiaris) choices in reference to agreement among human informants on location of food

When interacting with others, informants may offer conflicting information or information of varying accuracy. Recent research suggests that young children do not trust all informants equally and are selective in both whom they solicit for information and whose claims they support. We explored whether domestic dogs (Canis familiaris) are similarly sensitive to agreement among informants. To this end, we utilized a common human gesture, pointing, to which recent research suggests dogs are sensitive. We conducted two experiments in which an experimenter secretly hid food in one of two clear containers while the dog was distracted. Next, a small group moved to indicate the food's location using stationary points positioned above the containers. In Experiment 1, two experimenters moved to stand behind the non-baited container, while a third experimenter moved to stand behind the baited container. Then, all directed one static point at the container in front of them. Experiment 2 exactly resembled Experiment 1 with the exception that the single experimenter standing behind the baited container directed two static points at the container (one with each hand). Dogs chose the container indicated by the majority in Experiment 1 significantly more often than chance, but chose the container indicated by the minority in Experiment 2 significantly more often than chance. This suggests that the number of points, not the number of people, more strongly influenced dogs' choices.     

Development of reference and working spatial memory in preschool children

Three groups of preschool children (aged 18 to 28, 33 to 42, and 47 to 58 months) were given a radial search test similar to the radial arm maze used with nonhuman subjects. The children searched for chocolate sweets among 10 labeled locations in a room, 5 of which were baited with a sweet. Older children outperformed the intermediate group, who in turn outperformed the youngest group in requiring fewer choices to retrieve all of the sweets. Working memory and reference memory aspects of performance were then separated: Reference memory (restriction of choices to the baited subset) in older children was superior to that in the youngest group but not to that in the intermediate group. In terms of working memory (avoidance of repeat responses to already visited locations), the older group made fewer errors than the intermediate group, who, in turn, made fewer errors than the youngest group. We concluded that working and reference components of spatial memory in children may share common elements, perhaps the ability to recognize places as familiar, although reference memory may develop earlier than working memory.     

Working memory theory of hippocampal function needs qualification

To compare the predictive value of "cognitive map" and "working memory" theories of hippocampal function, the performance of rats with dorsal hippocampal lesions was compared to that of control rats in a series of experiments. In Experiment I, experimental rats learned a spatial alternation task with normal ease, but in Experiment II, they were significantly impaired on an elevated 8-arm radial maze. In Experiment III, the performance of the same experimental and control rats was compared on two versions of a 16-arm enclosed radial maze. In the first version, carpet inserts served as cues to mark eight unbaited arms and each of the remaining arms contained one food pellet. While both experimental and control rats successfully avoided the set of cued arms, experimental rats reentered uncued baited arms more frequently than did control rats. In the second version no intramaze cues were provided, but the spatial distribution of baited and unbaited arms remained the same as that used in the first version. In this uncued version, experimental rats both entered unbaited arms and reentered baited arms more frequently than did control rats, i.e., they were impaired in both "reference" and "working" memory. These findings are compatible with the hypothesis that hippocampal lesions result in an impaired capacity to form cognitive maps but they are not compatible with the working memory hypothesis. Furthermore, twelve separate evaluators classed experimental rats as using fewer mapping and more orientation strategies than control rats in the 8-arm maze.     

Episodic-like memory in pigeons

It has been proposed that memory for personal experiences (episodic memory, rather than semantic memory) relies on the conscious review of past experience and thus is unique to humans. In an attempt to demonstrate episodic-like memory in animals, we first trained pigeons to respond to the (nonverbal) question "Did you just peck or did you just refrain from pecking?" by training them on a symbolic matching task with differential responding required to the two line-orientation samples and reinforcing the choice of a red comparison if they had pecked and the choice of a green comparison if they had not pecked. Then, in Experiment 1, after providing the conditions for (but not requiring) the pigeons to peck at one new stimulus (a yellow hue) but not at another (a blue hue), we tested them with the new hue stimuli and the red and green comparisons. In Experiment 2, we tested the pigeons with novel stimuli (a circle, which they spontaneously pecked, and a dark response key, which they did not peck) and the red and green comparisons. In both experiments, pigeons chose the comparison appropriate to the response made to the test stimulus. Thus, the pigeons demonstrated that they could remember specific details about their past experiences, a result consistent with the notion that they have the capacity for forming episodic-like memories.     

Memory systems in the rat: effects of reward probability,context, and congruency between working and reference memory

The interaction of working and reference memory was studied in rats on an eight-arm radial maze. In two experiments, rats were trained to perform working memory and reference memory tasks. On working memory trials, they were allowed to enter four randomly chosen arms for reward in a study phase and then had to choose the unentered arms for reward in a test phase. On reference memory trials, they had to learn to visit the same four arms on the maze on every trial for reward. Retention was tested on working memory trials in which the interval between the study and test phase was 15 s, 15 min, or 30 min. At each retention interval, tests were performed in which the correct WM arms were either congruent or incongruent with the correct RM arms. Both experiments showed that congruency interacted with retention interval, yielding more forgetting at 30 min on incongruent trials than on congruent trials. The effect of reference memory strength on the congruency effect was examined in Experiment 1, and the effect of associating different contexts with working and reference memory on the congruency effect was studied in Experiment 2.     

The eye movement measure of memory and its relationship with explicit measures

This study examined whether the eye movement can be used to measure memory of past events and its relationship with the explicit measures. In Experiment 1, after studying a list of Chinese characters, the participants received a recognition memory test. For each trial the participants had to indicate, among one studied character and two nonstudied homonyms, which character they had studied. Participants’ eye movements were monitored while they viewed the three-character test display. Both the time-course and response-locked measures showed that participants viewed the studied character longer than the nonstudied character regardless of their explicit response. Experiment 2 used a wagering task to assess participants’ conscious awareness and found that wagering points predicted viewing time for the target better than the recognition accuracy did. These findings suggest that the effect of memory on viewing time occurs automatically and is weakly associated with subsequent conscious awareness of the studied event.     

An olfactory discrimination procedure for mice

This paper describes an olfactory discrimination procedure for mice that is inexpensively implemented and leads to rapid discrimination learning. Mice were first trained to dig in small containers of sand to retrieve bits of buried chocolate. For discrimination training, two containers were presented simultaneously for eight trials per session. One container held sand mixed with cinnamon, and the other held sand mixed with nutmeg. Both containers were baited with chocolate buried in the sand. One odor was designated S+, and mice were allowed to dig and retrieve the chocolate from this container. The other odor was S-, and both containers were removed immediately if subjects began to dig in an S- container. After meeting a two-session acquisition criterion, subjects were given a series of discrimination reversals. In Experiment 1, 12 Swiss-Webster mice (6 male and 6 female) acquired the olfactory discrimination in three to five sessions and completed 3 to 10 successive discrimination reversals within a 50-session testing limit. In Experiment 2, subjects were 14 Pah(enu2) mice, the mouse mutant for phenylketonuria; 7 were homozygotes in which the disorder was expressed (PKU), and 7 were heterozygotes with normal metabolism (non-PKU). Thirteen mice completed pretraining in four to seven sessions, acquisition required 3 to 12 sessions, and all mice completed at least three reversals. Learning rates were similar in PKU and non-PKU mice. We discuss issues related to implementation and several potentially useful procedural variations.     

The role of response and reward in spatial memory

Two experiments were conducted to determine the role of the response and of reward in spatial working memory. Rats were initially trained on a four-arm maze to run to the end of each arm for a single pellet of food. On subsequent tests, rats were first placed at the end of one, two, or three arms. In Experiment 1, the arms on which the rat was placed (“placed arms”) had food which the rat was allowed to eat, whereas in Experiment 2 these placed arms did not have food. Following the placements the rat was allowed to choose among the four arms; only unplaced arms contained food. Two measures indicated that the response made a slight but reliable contribution to spatial memory. (a) When a rewarded arm was still available, choice accuracy after placements was less than choice accuracy on tests in which no placements had occurred; this difference diminished over test days. (b) When all four arms had been chosen once, the rats were more likely to go back to a placed arm rather than an unplaced arm. No influence of the presence or absence of food on the placed arms was found. These data demonstrate that the response of running down an arm, but not the reward outcome at the end, had a small influence on the memorability of a visit. Overall, above chance performance in the spatial working memory task was maintained without either running to the arm or obtaining food on it.     

How intention to retrieve a memory and expectation that a memory will come to mind influence the retrieval of autobiographical memories

While involuntary memories are retrieved with no intention and are usually unexpected (when one is not waiting for a memory to arise), voluntary memories are intended and expected (when one is searching and waiting for a memory to arise). The present study aimed to investigate the effects of retrieval intentionality (i.e. wanting to retrieve a memory) and monitoring processes (i.e. waiting for a memory to appear) during autobiographical memory retrieval. In addition, we introduced two novel laboratory conditions that have not been used in previous research on voluntary memories: in the first, participants were asked to report anything they could think of in response to each cue word; in the second, they could skip a word if nothing came to mind. These novel manipulations allowed us to differentiate between voluntary memories retrieved in response to experimenter-generated cues (when participants were forced to provide a memory or a thought for each cue) and self-selected cues (when participants were free to not answer a cue if they found it too difficult). We found that highly accessible memories were mostly experienced when retrieval was involuntary and unexpected, while memories with low accessibility were accessed through intentional retrieval and monitoring processes. Response times for memories recalled in the experimenter-generated cue conditions were longer compared to the self-selected cue conditions. This novel finding shows that experimenter-generated recall favours memories with low accessibility; it further supports the idea that, in a substantial number of trials, voluntary memories are directly rather than effortfully retrieved. The idea that the driving force behind differences between involuntary and voluntary memories is not the intention per se is further discussed.     

Septal area lesions impair spatial working memory in homing pigeons (Columba livia)

The septo-hippocampal system in birds resembles that of mammals, motivating research into the function of the avian hippocampus while surprisingly little attention has been given to the septum. To investigate a possible role of the avian septum in memory, the effects of septal area lesions on a spatial working memory (SpWM) task was tested in homing pigeons. After preoperative training on an analogue eight-arm (feeders) radial maze, now sham-operated control and septal lesioned pigeons were then trained again on the same task of locating the four feeders on the test phase of a trial that were not baited during the sample phase of a trial. During the test phase of a working memory trial, septal lesioned pigeons, compared to both their own preoperative performance and the performance of the controls, required significantly more choices to locate the four baited feeders not baited during the sample phase of a trial, and they made significantly fewer correct responses to the now baited feeders on their first four choices. The results demonstrate that, like its mammalian counterpart, the avian septum plays an important role in SpWM, suggesting that at least some functional properties of the septum are evolutionarily conserved in birds and mammals.     

Prospective memory for future intentions: Some comparisons with memory for past events

Abstract

Memory for future intentions was compared with memory for past activities by asking members of a film society to retrieve names of films they intended to see later on in a Season and films they had seen earlier. Memory for films that had been seen showed the usual recency effect, while retrieval of films to be seen showed an analogous proximity effect in that films to be seen sooner were more accessible. It was also found that recall of past films was inversely related to the total number of such films, but was unrelated to the average time interval since they were seen. In a similar fashion, retrievability of future films was inversely related to the total number of such films and was unrelated to when they were to be seen. There was a small but significant correlation between an individual's ability to retrieve the names of past and future films. Taken together, these correspondences suggest that similar empirical laws may govern the retrieval of stored information about past events and future intentions. Possible interpretations of the proximity effect and its theoretical implications are discussed.     

Spatial memory in rats under restricted viewing conditions

In a procedure devised by J. A. Walker and D. S. Olton (Learning and Motivation, 1979, 10, 73–84), rats were placed on two arms of a four-arm radial maze and then were placed in the center of the maze to test how accurately they could choose the alleys on which they had not been placed. In three experiments, the conditions under which animals viewed the environment from the arms were varied. In Experiment 1, both the extent of spatial view and the exposure time were varied factorially in a within-subjects design; animals viewed the environment down a tunnel or had a 180° or 360° view, and subjects were allowed to view the environment for either 2 or 20 sec. In Experiment 2, a between-subjects design was used, in which different groups of subjects were tested repeatedly under either the tunnel, 180°, or 360° conditions. Both experiments showed that animals could avoid the arms previously visited at no better than a chance level of accuracy in the tunnel viewing condition but could perform with progressively better accuracy at the 180 and 360° viewing conditions. Animals also were more accurate in Experiment 1 after viewing for 20 sec than after viewing for 2 sec. Experiment 3 involved a procedure in which restricted viewing conditions were used both during arm placements and testing. Animals tested under tunnel viewing eventually achieved above-chance performance with this procedure, but did not exceed chance as rapidly as groups tested with 45 and 90° views of the environment. These results suggest that animals can learn about their position in a spatial environment through observation and that an animal's ability to locate its position is directly related to the extent of the surrounding environment it can see and the length of time it is allowed to look. The implications of these findings for list and map hypotheses of spatial memory representation are discussed.     

Endogenous versus exogenous attentional cuing effects on memory

Three experiments were conducted to investigate the influence of early attentional cuing effects on subsequent memory. In an incidental study phase, a cue preceded two simultaneously displayed words. An endogenous cue (row of arrows pointing toward one word) or an exogenous cue (row of stars at the location of one word) indicated which word to read aloud. In a subsequent test phase, memory for these cued and uncued words was measured. In Experiment 1, these attentional manipulations had almost no effect on subsequent implicit memory measured using a speeded reading (naming) test. Experiments 2 and 3 demonstrated that, on an explicit memory test, words were reliably better recognized in the endogenous condition than in the exogenous condition. These results suggest that endogenous attentional cues promote more active processing and hence elaboration of words, assisting their subsequent conscious retrieval.     

The personalisation method applied to a working memory task: Evidence of long-term working memory effects

Ericsson and Kintsch (1995) proposed that, in situations of expertise, individuals can overcome working memory limitations by using long-term working memory. It allows a greater capacity than working memory thanks to long-term memory encoding and retrieving. To test this characteristic, an adaptation of Daneman and Carpenter's (1980) reading span was used. To operationalise expertise, the personalisation method (Guida & Tardieu, 2005) was employed. In Experiment 1, a personalised group, which read reading span sentences that mentioned familiar locations, was compared to a nonpersonalised group, which read sentences with unfamiliar locations. In Experiment 2, a personalised group, which read reading span sentences with neutral locations, was encouraged to mentally personalise these locations by thinking about known locations. This group was compared to a nonpersonalised group, which was encouraged to think about unknown locations. The personalised groups were expected to store and retrieve information in long-term memory via long-term working memory more easily than the nonpersonalised groups, which had to count massively on working memory. The results showed that personalisation enhanced reading span and confirmed one implication of the long-term working memory theory: high- and low-reading-span differences could also be due to long-term memory retrieval. Finally, these results are interpreted in terms of interaction between working memory size and long-term memory knowledge, showing that participants with a lower reading span benefited more from high domain knowledge than participants with a higher reading span.     

Spatial memory of domestic dogs (Canis familiaris) for hidden objects in a detour task

Spatial memory of domestic dogs (Canis familiaris) for hidden objects was investigated via a visible displacement problem of object permanence with a detour paradigm. Experiment 1 showed that dogs were able to spontaneously locate a disappearing object in a detour situation. In Experiments 2 and 3, dead reckoning and allocentric spatial information were put in conflict. Results revealed that dogs simultaneously encoded both sources of information when they had to bypass an obstacle to locate a hidden object. Experiment 3 also revealed that, over the course of testing, dogs gradually learned to rely predominantly on allocentric cues when the detour involved several reorientations. The current study reveals that spatial memory of dogs for hidden objects in a detour task was guided by flexibility in processing spatial information. Dogs could simultaneously encode dead reckoning and allocentric information to locate a disappearing object and used them hierarchically according to the complexity of the detour they encountered in the environment.     

Single-item memory, associative memory, and the human hippocampus

We tested recognition memory for items and associations in memory-impaired patients with bilateral lesions thought to be limited to the hippocampal region. In Experiment 1 (Combined memory test), participants studied words and then took a memory test in which studied words, new words, studied word pairs, and recombined word pairs were presented in a mixed order. In Experiment 2 (Separated memory test), participants studied single words and then took a memory test involving studied word and new words. In a separate test, they studied word pairs and then took a memory test involving studied word pairs and recombined word pairs. In both experiments, patients were impaired at memory for single items as well as memory for associations, suggesting that the hippocampus is important for both of these memory functions. In Experiment 1, patients appeared to be more impaired at associative memory than item memory. In Experiment 2, patients were similarly impaired at associative memory and item memory. These different findings are considered, including the fact that in Experiment 1 the results depended on the fact that controls produced unexpectedly low false-alarm rates to recombined pairs. We discuss single-item and associative memory from the perspective that the hippocampus and adjacent cortex work cooperatively to signal recognition and that simple dichotomies do not adequately describe the division of labor within the medial temporal lobe.     

Investigating the output monitoring component of event-based prospective memory performance

The goal of this study was to augment the standard event-based prospective memory paradigm with an output monitoring component. That component involves memory for past actions and, in the context of prospective memory, is largely responsible for repetition and omission errors. The modified paradigm also provides an index of what people believe to be true concerning their past prospective memory performance. More elaborate prospective responses decreased forgetting that an intention had been fulfilled, whereas contextual change increased forgetting. In Experiments 1-3, people often reported that they had fulfilled an intention on a previous occasion when they actually had not, but distinctive responses reduced that error in Experiment 4. Therefore, people's beliefs about their past performance can influence the incidence of repetition and omission errors in event-based prospective memory tasks.