Landmark Stability: Further Studies Pointing to a Role in Spatial Learning

Two experiments were conducted to investigate the possible role of landmark stability in spatial learning. Rats were trained to search in a large arena for food hidden at a consistent distance and direction from either a single radially symmetric landmark or an array of two landmarks. We varied the relative degree to which the landmark array and/or the cues of the training context predicted the location of food, without varying the conditional probability of food being available given either cue. Experiment 1 used vestibular disorientation to ensure control of search location by experimenter-controlled cues. The results showed that making either a single landmark or a cluster of two adjacent landmarks the sole spatial predictor of reward location reduced the accuracy of search compared to a condition where both the landmark array and context cues were reliable spatial predictors. Varying global landmark stability had no effect when training was conducted using an array of two landmarks located some distance from each other. Context cues, when tested alone, triggered very little searching in appropriate locations, and the absolute magnitude of control over search was insufficient to account for the superiority of stable landmarks. The better learning with a stable landmark, and the dependence of this effect on the geometrical arrangement of landmarks, points to the conditions of spatial learning involving additional principles to those of simple associative conditioning. Experiment 2 examined landmark stability using a single landmark and fixed directional cues in the absence of vestibular disorientation. This also revealed a relative advantage of landmark stability, but animals with a landmark that moved from trial to trial did show some evidence of learning. Context cues when tested alone had minimal influence. Parametric manipulation of landmark stability offers a novel way of influencing spatial learning and thus understanding better the process through which egocentric representations of perceived space are transformed into allocentric representations of the real world. The purpose of this paper is to describe two experiments concerned with identifying the psychological processes of allocentric spatial learning. The results point to the idea that landmark stability is an important factor in spatial learning. Specifically, they reveal that whether or not a landmark will be used for the purpose of representing the location of another object (including hidden objects) is influenced by whether it is perceived as geometrically stable with respect to at least one other landmark and/or certain geometric features of the environment. This phenomenon is relevant to the application of associative learning principles to the spatial domain.     

Age and sex differences in children’s spatial search strategies

Male and female children, 3, 4, and 5 years old, searched for a sticker that was hidden in 1 of 15 linearly aligned boxes. Two identical bear-shaped landmarks cued the sticker location, which was always in the middle of 3 boxes that separated the two landmarks. The absolute locations of the landmarks and sticker varied across training trials, but the distance in relation to each other remained constant. Training continued until the child chose the correct box first for 3 consecutive trials or for a maximum of 20 trials. Striking age and sex differences emerged in acquisition: The percentage of children who reached criterion increased over age groups to 100% for the boys but stayed at approximately 20% for the girls. A landmark expansion test (with the landmarks moved farther apart) given to children who met criterion revealed that most of these children chose the middle location.     

Encoding of variability of landmark-based spatial information

Recent evidence suggests humans optimally weight visual and haptic information (i.e., in inverse proportion to their variances). A more recent proposal is that spatial information (i.e., distance and direction) may also adhere to Bayesian principles and be weighted in an optimal fashion. A fundamental assumption of this proposal is that participants encode the variability of spatial information. In a three-dimensional virtual-environment open-field search task, we provide evidence that participants encoded the variability of landmark-based spatial information. Specifically, participants searched for a hidden goal location in a 5 × 5 matrix of raised bins. Participants experienced five training phases in which they searched for a hidden goal that maintained a unique spatial relationship to each of four distinct landmarks. Each landmark was assigned an a priori value of locational uncertainty such that each varied in its ability to predict a goal (i.e., varied in number of potential goal locations). Following training, participants experienced conflict trials in which two distinct landmarks were presented simultaneously. Participants preferentially responded to the landmark with the lower uncertainty value (i.e., smaller number of potential goal locations). Results provide empirical evidence for the encoding of variability of landmark-based spatial information and have implications for theoretical accounts of spatial learning.     

Strategies in landmark use by children, adults, and marmoset monkeys

Common marmosets (Callithrix jacchus jacchus), human children, and human adults learned to find a goal that was located in the center of a square array of four identical landmarks. The location of the landmark array and corresponding goal varied across trials, so the task could not be solved without using the landmark array. In Experiment 1, a matrix of discrete goal locations was presented and the landmarks surrounded and were adjacent to the correct location during training. After training, an expansion test was given in which the distance between landmarks was increased. Marmosets, children (ages 5–9), and adults all readily learned to use the landmarks to search accurately during training. On the expansion test, adults uniformly searched in the center of the array. Monkeys and children concentrated their searching near the landmarks rather than in the center. The monkeys, but not the children, searched more often on the directionally appropriate side of the landmarks than on other sides of the landmarks. In Experiment 2, children (ages 3–5) were trained with a continuous search space and with the goal farther from the landmarks so that a beaconing strategy rule could not be used. Several of the children failed to acquire the training task. Of those who learned to find the goal, three searched in the middle on expansion tests but most searched nearer to the landmarks. The “middle rule” strategy that is uniformly used by adult humans does not appear to be a preferred strategy for children or non-human primates.     

Gender-Based Navigation Stereotype Improves Men’s Search for a Hidden Goal

While a general stereotype exists that men are better at navigating than women, experimental evidence indicates that men and women differ in their use of spatial strategies, and this preference determines gender-differences. When both environmental geometry and landmark cues are available, men appear to learn to navigate using both types of cues, while women show a preference for using landmarks. Using a computer-generated task, 80 undergraduate students from North-East England learned to navigate to a hidden goal. Activating the general navigation stereotype improved the performance of men, compared to the control condition, both when only geometric cues and only landmark cues were present (stereotype lift), suggesting that activating a general stereotype can affect tasks both with (geometry) and without (landmark) established gender-differences in preference. In addition, in the test trial (hidden goal removed) women who learned to navigate using only landmarks spent longer in the correct location of the hidden goal than those who learned to navigate using only geometry. In contrast, the opposite result was found for men, suggesting that when only one cue-type is available, gender-differences still occur, with women better able to navigate using landmarks than geometry, while men seemed to learn more about the location of the goal with reference to geometric than landmark cues.     

The role of landmarks and boundaries in the development of spatial memory

It has been suggested that learning an object's location relative to (1) intramaze landmarks and (2) local boundaries is supported by parallel striatal and hippocampal systems, both of which rely upon input from a third system for orientation. However, little is known about the developmental trajectories of these systems' contributions to spatial learning. The present study tested 5- and 7-year-old children and adults on a water maze-like task in which all three types of cue were available. Participants had to remember the location of an object hidden in a circular bounded environment containing a moveable intramaze landmark and surrounded by distal cues. Children performed less accurately than adults, and showed a different pattern of error. While adults relied most on the stable cue provided by the boundary, children relied on both landmark and boundary cues similarly, suggesting a developmental increase in the weighting given to boundary cues. Further, adults were most accurate in coding angular information (dependent on distal cues), whereas children were most accurate in coding distance, suggesting a developing ability to use distal cues to orient. These results indicate that children as young as 5 years use boundary, intramaze landmark, and distal visual cues in parallel, but that the basic accuracy and relative weighting of these cues changes during subsequent development.     

Geometric rule learning by Clark's nutcrackers (Nucifraga columbiana)

Clark's nutcrackers (Nucifraga columbiana) were trained to search in a location defined by its geometric relationship to 2 landmarks. Two groups were trained to search at different points along the line connecting the landmarks, and 2 groups were trained to find the 3rd point of a triangle, on the basis of either direction or distance from the landmarks. All groups learned and transferred to new interlandmark distances. However, the constant-distance group learned more slowly, searched less accurately, and showed less transfer than the other 3 groups. When tested with new orientations of the landmarks, the birds tended to follow small but not large rotations. When tested with a single landmark, birds in the half, quarter, and constant-bearing groups searched in the appropriate direction from the landmark, but birds in the distance group did not. These results demonstrate that nutcrackers can learn a variety of geometric principles, that directional information may be weighted more heavily than distance information, and that the birds can use both absolute and relative information about spatial relationships.     

Effect of absolute spatial proximity between a landmark and a goal

In two experiments rats were trained in a Morris pool to find a hidden platform in the presence of a single landmark. Circular black curtains surrounded the pool, with the single landmark inside this enclosure, so that no other room cues could provide additional information about the location of the platform. This landmark was hung from a false ceiling and rotated from trial to trial, and the position of the platform also changed on each trial, thus preserving a constant relation between the platform and the landmark. In Experiment 1, the position of the landmark was exactly above the hidden platform in Group Above and was relatively close to the hidden platform in Group Near. At the end of acquisition, test trials without the platform revealed a difference between the groups. Although a preference for searching in the correct quadrant of the pool, where the platform should have been, was found in both groups, this preference was significantly higher for Group Above. In Experiment 2, new rats in Group Near were compared to rats for which the position of the landmark was relatively far from the hidden platform in Group Far. Test trials revealed a preference for searching in the correct quadrant of the pool in both groups, but this preference was significantly higher for Group Near. The implication of these results is that the control acquired by a single landmark is different depending on its relative distance from a hidden platform: Closer landmarks acquire better control than distant ones. These results show a clear parallelism in comparison with the effect of absolute temporal proximity of the CS to the US in classical conditioning.     

Differences in the memory-based searching of delayed and normally developing young children

The memory-based searching of developmentally delayed and normal 2-year-old children was compared. The results of the study confirmed the hypothesis that individual differences would be minimal in a relatively noneffortful memory task, but that substantial individual differences would occur when more cognitive effort was required. The performance of the delayed and normal children was very good and quite similar in the basic memory task, which simply involved remembering the location of a toy hidden in a distinctive, natural location in a room. Substantial individual differences were found, however, in the children's ability to draw inferences about plausible locations for a missing toy based on their memory for where it had been hidden. When they discovered that their toy was not where they remembered it had been hidden (it had been surreptitiously moved by the experimenter), a group of normal children searched for the toy in places that were nearby or otherwise related to the original location of the toy. They used their memory for where the toy had been hidden to generate plausible alternative locations to search. In contrast, delayed children, who discovered their toy to be unaccountably missing from a location, persevered in repeatedly searching that same place. Unlike the normal children, they did not try something new. An important aspect of the data reported is that they reveal an important difference-not just a delay-in the cognitive functioning of young delayed children.     

Tracking and inferring spatial rotation by children and great apes

Finding hidden objects in space is a fundamental ability that has received considerable research attention from both a developmental and a comparative perspective. Tracking the rotational displacements of containers and hidden objects is a particularly challenging task. This study investigated the ability of 3-, 5-, 7-, and 9-year-old children and great apes (chimpanzees, bonobos, gorillas, and orangutans) to (a) visually track rotational displacements of a baited container on a platform and (b) infer its displacements by using the changes of position or orientation of 3 landmarks: an object on a container, the color of the containers, and the color of the platform on which the containers rested. Great apes and 5-year-old and older children successfully tracked visible rotations, but only children were able to infer the location of a correct cup (with the help of landmarks) after invisible rotations. The ability to use landmarks changed with age so that younger children solved this task only with the most explicit marker on the baited container, whereas older children, particularly 9-year-olds, were able to use landmark orientation to infer correct locations.     

The effect of environmental cues on locomotor distance estimation by children and adults

Adults and 10-year-old children were tested for their abilities to view a target 12 m away, then walk to it unaided by vision. Environmental cues were manipulated by varying the number and locations of landmarks seen in the visual array surrounding the target. The inclusion of a single landmark 8 m from the viewer along the path to the target facilitated locomotor distance estimation by both children and adults. A 4 m landmark was of some help to children but not to adults. The presence of 2 landmarks improved adults performance, particularly when one was situated past the target creating the effect of framing the target between landmarks. Children did not respond positively to the two-landmark conditions, although detailed task orientation provided one group of children with sufficient preparation to make use of the greater information in the visual array. This is discussed in terms of the importance of cognitive processes in children's perceptual-motor performance.     

Clark's nutcrackers (Nucifraga columbiana) and the effects of goal--landmark distance on overshadowing

Three groups of Clark's nutcrackers (Nucifraga columbiana) were trained to find a goal location defined by an array of 4 landmarks that varied in goal--landmark distance. The arrays for each group differed in the distance of the closest landmark and contained goal--landmark distances that were common across groups, allowing for the examination of the effects of both relative and absolute goal--landmark distance on encoding of a landmark array. All 3 groups readily learned the task and were subsequently tested in probe tests with only single landmarks from the array available. Search error in tests with single landmarks was compared both within and across groups. Results demonstrated that both relative and absolute goal-landmark distances are important in spatial search.     

The effect of landmarks in human path integration

The effect of landmarks in human path integration was investigated using virtual hallway-mazes. Participants traveled along random 5-segment paths either with or without distinctive landmarks at some segment intersections. They were required to directly return to the origin or to one of the landmark locations from the end of the path. Results showed that knowledge of the return targets prior to the outbound trip significantly reduced RTs to both the origin and the landmarks. Moreover, RTs in the return-to-origin trials were longer with landmarks present than without landmarks. This effect was eliminated when the return target was given prior to the trip. These results suggest that processing of the origin and the landmarks interfere with each other. However this interference is not obligatory and can be eliminated or reduced by prior knowledge about the target. The influences of landmarks on path integration and spatial updating were discussed.     

Representation of object location in 6.5-month-old infants

Within a small bounded space, the location of a hidden object can be coded in terms of distance information, general area of hiding, or the boundary of the space. 6.5-month-old infants' use of these three coding strategies was examined using a visual search task. Infants watched as an object was hidden at one of four identical locations. After a short delay (10 s), the object either reappeared at the location where it was hidden (possible event), or reappeared at one of the other three locations (impossible event). Looking behavior was not systematically influenced by the amount of distance the object moved from the original location of hiding or by whether the object was hidden near a boundary. Infants did not appear to code the location of a hidden object in terms of distance information, general area of hiding, or whether it was hidden at a boundary. However, the location of reappearance (i.e., impossible event) did influence looking times. Infants were surprised when the object reappeared at a boundary position that was previously unoccupied. They were not surprised when the object reappeared at a central location. Thus, two factors influenced coding of location: boundary information (but in a different way than specified) and the nature of the change (absence vs. presence of an object). The influence of these two factors on coding of spatial information was discussed.     

Solving small spaces: investigating the use of landmark cues in brown capuchins (Cebus apella)

Some researchers have recently argued that humans may be unusual among primates in preferring to use landmark information when reasoning about some kinds of spatial problems. Some have explained this phenomenon by positing that our species’ tendency to prefer landmarks stems from a human-unique trait: language. Here, we test this hypothesis—that preferring to use landmarks to solve such tasks is related to language ability—by exploring landmark use in a spatial task in one non-human primate, the brown capuchin monkey (Cebus apella). We presented our subjects with the rotational displacement task, in which subjects attempt to relocate a reward hidden within an array of hiding locations which are subsequently rotated to a new position. Over several experiments, we varied the availability and the salience of a landmark cue within the array. Specifically, we varied (1) visual access to the array during rotation, (2) the type of landmark, (3) the consistency of the landmark qualities, and (4) the amount of exposure to the landmark. Across Experiments 1 through 4, capuchins did not successfully use landmarks cues, suggesting that non-linguistic primates may not spontaneously use landmarks to solve some spatial problems, as in this case of a small-scale dynamic spatial task. Importantly, we also observed that capuchins demonstrated some capacity to learn to use landmarks in Experiment 4, suggesting that non-linguistic creatures may be able to use some landmarks cues in similar spatial tasks with extensive training.     

Developmental Changes in Young Children's Spatial Memory and Language in Relation to Landmarks

Two experiments investigated how young children and adults understand whether objects are by a landmark and remember their locations. Three- and 4-year-old children and adults were asked to judge whether several blocks were by a landmark. The blocks were arranged so that their absolute and relative distances from the landmark varied. Later, the blocks were removed, and participants were asked to place them in their original locations. All ages relied on relative distance between objects and a landmark when making by judgments; however, older children and adults showed systematic judgments. Relative distance also affected block placement, and systematicity increased across development. Children's understanding of the relative nature of by and their ability to remember locations precisely increased during the preschool years, indicating developmental changes in the adaptive combination of location cues for spatial language and memory.     

Strategies in landmark use by orangutans and human children

Landmark use has been demonstrated in a variety of organisms, yet the manner in which landmarks are encoded and subsequently used appears to vary between and sometimes within species, even when faced with identical landmark arrays. In the present experiments, orangutans and human children were shown a square array of identical landmarks and were trained to locate a hidden goal in the centre of the array. In Experiments 1 and 2, the search space appeared to be discrete, with white gridlines dividing up the space, and in Experiments 3a and 3b, the search space was uniformly coloured, making it appear continuous. In all experiments, following training, subjects were given a single expansion test, to determine their landmark strategy use, based on peak search activity. The orangutans appeared to use absolute directional vectors from individual landmarks, with peak search activities on the inner corners of the square array, and they used this strategy persistently. In contrast, human children showed two landmark-based strategies, absolute directional vectors and a relational or “middle” strategy, with the majority of children starting their search in the middle region. Although some children, especially young children, persistently used one strategy like the orangutans, many changed strategies when the original one failed to yield the hidden goal.     

Landmark-based search memory in the domestic dog (Canis familiaris)

Recent studies have suggested that any animal that relies on landmark-based search memory encodes and uses metric properties of space to navigate. So far, however, metric information provided by landmarks has been predominantly investigated in avian species. In the present study, I investigated whether the domestic dog (Canis familiaris), a mammalian species, encodes the distance and direction from landmarks. Dogs were trained to find a ball hidden next to an array of two distinct landmarks that remained at a constant location in a room from trial to trial. After training, the dogs were occasionally tested on unrewarded conditions where the array was either left in its usual position or shifted laterally, perpendicularly, or diagonally relative to the rear wall of the room. Although the dogs significantly shifted their search as a function of the displacement of the landmarks, they did not search at the predicted coordinates of the goal relative to the shift of the landmarks, suggesting that the global cues available in the testing room were also encoded and used by dogs to locate the position of the goal.     

Indirect landmark use at 6 months of age in a spatial orientation task

It was hypothesized that 6-month-old infants may be able to use indirect landmarks to locate a goal if (a) the landmarks are sufficiently distinctive and (b) the goal location is between landmarks, rather than on the opposite side of the space as was used in earlier research. Six-month-old infants were tested in a peekaboo paradigm in which they had to turn to a target location after displacement to a novel position. Infants looked to the goal location significantly more in a beacon and an indirect landmarks condition relative to a control and a single landmark condition. These results are discussed in terms of current theories of spatial development.