Salient Landmarks Research Articles

The impact of landmark properties in shaping exploration and navigation

This study was aimed at uncovering physical and geometric properties that make a particular landmark a target of exploration and navigation. Rats were tested in a square open-field arena with additional portable corners featuring the same properties as the arena corners. It was found that the routes of progression converged upon the added corners, whether located at the arena wall or the arena center. Route convergence upon the added corners involved numerous visits to these corners. However, time spent at the added corners was relatively short compared with the arena corners, including that from which rats were introduced into the arena. There was no differential effect of testing rats in light or dark, or with a low versus a high portable corner. It is suggested that the added corners were distinct against the background of the arena enclosure, whereas the four arena corners and walls were encoded by the rats as one geometric module. This distinctness, together with the greater accessibility of the added corners, made them salient landmarks and a target of exploration. Thus, the impact of a landmark extended beyond its specific self-geometry to include accessibility and distinctness, which are contextual properties. In addition to the contextual impact on locomotor behavior there was also a temporal effect, with security initially dominating the rats' behavior but then declining along with an increased attraction to salient landmarks. These spatiotemporal patterns characterized behavior in both lit and dark arenas, indicating that distal cues were secondary to local proximal cues in shaping routes.

Hippocampal place cells: Parallel input streams, subregional processing, and implications for episodic memory

The hippocampus is thought to be involved in episodic memory in humans. Place cells of the rat hippocampus offer a potentially important model system to understand episodic memory. However, the difficulties in determining whether rats have episodic memory are profound. Progress can be made by considering the hippocampus as a computational device that presumably performs similar transformations on its inputs in both rats and in humans. Understanding the input/output transformations of rat place cells can thus inform research on the computational basis of human episodic memory. Two examples of different transformations in the CA3 and CA1 regions are presented. In one example, CA3 place fields are shown to maintain a greater degree of population coherence than CA1 place fields after a rearrangement of the salient landmarks in an environment, in agreement with computational models of CA3 as an autoassociative network. In the second example, CA3 place field appears to store information about the spatiotemporal sequences of place fields, starting with the first exposure to a cue-altered environment, whereas CA1 place fields store this information only on a temporary basis. Finally, recordings of hippocampal afferents from the lateral and medial entorhinal cortex (EC) suggest that these two regions convey fundamentally different representations to the hippocampus, with spatial information conveyed by the medial EC and nonspatial information conveyed by the lateral EC. The dentate gyrus and CA3 regions may create configural object+place (or item+context) representations that provide the spatiotemporal context of an episodic memory.

A framework for assessing the salience of landmarks for wayfinding tasks

BackgroundLandmarks play an important role for the understanding of and reasoning about physical large-scale space. Landmarks also play an important role in every day’s spatial tasks, such as wayfinding and navigation. The property of being a landmark has so far been attributed to distinct objects, which are either well known or otherwise unique, such as the Eiffel Tower or a lighthouse on the shore. We propose a framework for the assessment of the landmarkedness of potential landmarks for wayfinding tasks, which is based on the relationship between observer, physical environment, and potential landmark. We argue that landmarkedness is not an inherent property of some object, but rather the result of this tri-lateral configuration. The basic idea is to use this configuration to define the individual components that contribute to the total salience of the object and integrate them in a coherent framework.Main contributionThe framework considers two types of salience: (1) the perceptual salience, which describes the potential of a feature to capture a wayfinder’s attention (attentional capture), and (2) the cognitive salience, which explains how strong attention is guided by the wayfinder (attentional orienting). The assessment of the perceptual salience is based on the salience of the incoming stimuli, the perceived concepts, and the spatial layout of a scene, while the cognitive salience considers the subjective importance of the object with respect to the individual’s context and knowledge. The most general requirement of a landmark is that it must be salient in some sense. This requires that it contrast with the environment, either in terms of its attributes (i.e., color, texture, etc.), the status of the perceived concept (i.e., church or commercial building), or due to its spatial location with respect to the other objects in the scene (i.e., in the middle of town). Such contrast, however, is only perceivable if the potential landmark is visible from the observer’s current point of view. Therefore, for assessing an object’s landmarkedness, we consider attributes, objects, and relations to other visible objects only. In addition to the salience perceived from physical contrast, the cognitive abilities of the observer play an important role in selecting appropriate objects for reference. This subjective selection implies that the context, together with our knowledge, thoughts and preconceptions shape what we perceive and finally select as reference for making decisions, which directly influences the assessment of the relative importance or salience of potential landmarks. The assessment of the salience of potential landmarks, hence, needs to consider cognitive aspects, along with the perceptual stimuli.ImplicationsThe accurate assessment of the relative importance of geographic objects is a crucial aspect of many wayfinding-related tools and applications, such as route generation and description algorithms, navigation systems, or location-based services. The integration of appropriate landmarks in such applications decreases the cognitive load put on the wayfinder, and hence increases efficiency and reliability of the applications.

The influence of landmark salience in a navigation task: An additive effect between its components.

In 2 experiments, rats were trained in a Morris pool to find a hidden platform in the presence of 1 landmark. After acquisition, the rats were tested without the platform. Experiment 1 tested whether the size of a landmark and its relative distance from the platform are additive effects. On test, the rats' best performance was with a near and big landmark; intermediate performance was with either a near and small landmark or a far and big one; and the worst performance was with a far and small landmark. The results of Experiment 2 suggested that the different distances from the goal of the 2 landmarks might not be sufficient to explain the previous results.

Reorientation in a rhombic environment: No evidence for an encapsulated geometric module

Reorientation behavior of young children has been described as dependent upon a geometric module that is incapable of interacting with landmark information. Whereas previous studies typically used rectangular spaces that provided geometric information about distance, we used a rhombic space that allowed us to explore the way children use geometric information about angles. Reorientation was studied in manipulatory space (Experiment 1) and locomotor space (Experiment 2) in the presence and absence of a salient landmark. In the absence of salient landmarks, 4- to 6-year-olds used geometric features to reorient in both spaces. When a salient landmark was available in manipulatory space, 4-year-olds used the landmark and ignored the geometry. Five- and 6-year-olds used the geometry, but in combination with the landmark. In locomotor space, this combined use was already seen at age 4, and increased with age. Taken together, these results offer no support for the notion that reorientation behavior in young children depends on an informationally encapsulated geometric module.

Auditory In-Vehicle Routing and Navigation Systems and Facilitating Cognitive Map Development

Use of in-vehicle routing and navigational systems (IRANS) is on the rise. IRANS may place additional informational processing demands on drivers thus compromising safety. Driving requires extensive visual processing and therefore auditory route guidance (ARG) systems have important safety advantages. However, relative to visual guidance formats, little attention has been focused on the design components of ARG formats. The current investigation examined the relative impact of three different ARG formats (traditional, cardinal, and landmark) on drivers' ability to learn novel routes through unfamiliar areas in a driving simulator. Results indicated that the inclusion of salient landmark information in ARG instructions facilitated route learning ability for a majority of drivers, relative to traditional ARG information and the inclusion of cardinal directions. Application of these results has the potential to increase transportation safety by decreasing the attentional processing requirements and distraction cost of existing IRANS displays.

Egocentric and geocentric frames of reference in memory of large-scale space.

This experiment investigated the frames of reference used in memory to represent the spatial structure of a large-scale outdoor environment. Participants learned the locations of eight objects in an unfamiliar city park by walking through the park on one of two prescribed paths that encircled a large rectangular building. The aligned path was oriented with the building; the misaligned path was rotated by 45 degrees. Later, participants pointed to target objects from imagined vantage points using their memories. Pointing accuracy was higher in the aligned than in the misaligned path group, and the patterns of results differed: In the aligned condition, accuracy was higher for imagined headings parallel to legs of the path and for an imagined heading oriented toward a nearby lake, a salient landmark. In the misaligned condition, pointing accuracy was highest for the imagined heading oriented toward the lake, and decreased monotonically with angular distance. These results indicated that locations of objects were mentally represented in terms of frames of reference defined by the environment but selected on the basis of egocentric experience.

Perceptual representation of visible surfaces.

Two experiments are reported in which we examined the ability of observers to identify landmarks on surfaces from different vantage points. In Experiment 1, observers were asked to mark the local maxima and minima of surface depth, whereas in Experiment 2, they were asked to mark the ridges and valleys on a surface. In both experiments, the marked locations were consistent across different observers and remained reliably stable over different viewing directions. These findings indicate that randomly generated smooth surface patches contain perceptually salient landmarks that have a high degree of viewpoint invariance. Implications of these findings are considered for the recognition of smooth surface patches and for the depiction of such surfaces in line drawings.

Agnosia for scenes in topographagnosia

Topographagnosia is most commonly attributed to an agnosia for landmarks. In order to define the nature of this agnosia, we studied a patient with isolated topographic disorientation (TD) after a stroke in the right medial occipitotemporal region. The patient got lost in familiar environments but could readily read and draw maps, describe familiar routes, and provide correct directions. He had normal perceptual test performance and met criteria for topographagnosia rather than for other forms of topographic disorientation. Two ecologically valid route tests assessed the nature of his agnosia. On a familiar route, he could recognize major landmarks. He could not, however, recognize route configurations made up of combinations of visual features each lacking individual distinctiveness. On a test of route learning, he learned landmarks that differed in minor details and could use them to orient himself along a route. He had difficulty, however, recognizing and learning scenes lacking salient landmarks. This agnosia for scenes was worse for semantically-related environments, but improved with semantic knowledge such as street names. In addition, the patient lacked overt prosopagnosia but tended toward semantic errors in the recognition of famous faces. Together these findings suggest that this patient’s inability to recognize a route resulted from an inability of intact perceptual units for scenes, composed of specific visual configurations of individually indefinite features, from accessing stored representations.

Compression of space in visual memory

Human observers had to point to the location of a briefly presented target by means of a mouse after a brief delay following target offset. It was found that observers systematically mislocalized the target closer to the center of gaze, and to visually salient markers in the visual display. A perceptual judgment task revealed that these errors in localization were independent of whether or not eye movements were made, and even of planning for them, thereby demonstrating that the effect was a perceptual phenomenon, not a sensorimotor one. Further experiments demonstrated clearly that the magnitude of the time interval between target presentation and judgment regarding its spatial location was the critical parameter. A longer time interval between the event and its report enhanced significantly the amplitude of compression, thus establishing this phenomenon as a visual memory effect. We conclude that visual memory of spatial location is distorted over time in a systematic, monotonic fashion as a result of the sustained fixation of the observer on a fixed location during and shortly after target presentation, or by the continual presence of stable, salient landmarks in the environment.

Disorientation in Minimal Access Surgery: A Case Study

Navigating through minimal access surgical environments such as the human colon can be difficult, even for expert gastroenterologists. “Getting lost” is a common experience for endoscopists, especially within the tortuous sigmoid colon where salient landmarks are not generally available. This paper presents the concept of “getting lost” in endoscoppy as a loss of both global and local spatial orientation. For the endoscopist performing a colonoscopy, the consequence of local disorientation is an inability to continue the procedure, or possibly even injury to the patient, while consequences of global disorientation can be mistaking the location of a lesion, and/or incomplete examination, resulting in misdiagnosis. This study provides important insights into the physical and cognitive constraints of the task of navigating in colonoscopy, contributing to disorientation in the colon. The implications of our findings for the design of navigational aids and training tools are also discussed.

Use of Landmarks in Three Species of Food‐storing Corvids

AbstractThe use of landmarks by Clark's nutcrackers (Nucifraga columbiana), pinyon jays (Gymnorbinus cyanocepbalus), and Western scrub jays (Apbelocoma coerulescens) was investigated in three experiments. In the first experiment, birds were trained to find a hidden food reward beneath wood chips near a plastic landmark located 20 cm from one edge of a stationary tray. During unrewarded test trials, all species displaced their searching in response to movement of the landmark in both parallel and perpendicular directions; however, searching was displaced significantly more in the parallel direction. In a second experiment, the landmark was removed with the tray stationary or shifted. When the tray was shifted, all species responded by searching relative to the shifted tray. This indicates that the global (room) cues were not being used as salient landmarks. In the third experiment, the tray was placed in different positions for each trial, making global cues unreliable. As in experiment 1, all species displaced their searching in response to parallel and perpendicular movement of the landmark, with movement being similar in both directions. These results indicate no species differences on this landmark‐use task.

Neural components of topographical representation.

Studies of patients with focal brain damage suggest that topographical representation is subserved by dissociable neural subcomponents. This article offers a condensed review of the literature of "topographical disorientation" and describes several functional MRI studies designed to test hypotheses generated by that review. Three hypotheses are considered: (i) The parahippocampal cortex is critically involved in the acquisition of exocentric spatial information in humans; (ii) separable, posterior, dorsal, and ventral cortical regions subserve the perception and long term representation of position and identity, respectively, of landmarks; and (iii) there is a distinct area of the ventral occipitotemporal cortex that responds maximally to building stimuli and may play a role in the perception of salient landmarks. We conclude with a discussion of the inferential limitations of neuroimaging and lesion studies. It is proposed that combining these two approaches allows for inferences regarding the computational involvement of a neuroanatomical substrate in a given cognitive process although neither method can strictly support this conclusion alone.

On the Metric Properties of Visual Images Generated from Verbal Descriptions: Evidence for the Robustness of the Mental Scanning Effect

When subjects mentally scan across visual images of spatial configurations, the “mental scanning effect” is said to occur when there is a linear relationship between distances scanned and scanning times. This effect has been documented in studies where configurations were learned perceptually, and also when mental images of spatial configurations were constructed from verbal descriptions. The scanning effect is generally taken to indicate that visual images incorporate the metric structure of represented objects or configurations in an analog fashion. This article reports three experiments designed to test whether the cognitive salience of landmarks in a configuration can alter the mental scanning effect. Three manipulations of landmark salience were used, but there was no evidence of such an alteration. The scanning times towards salient and non-salient landmarks were quite similar, and the experimental manipulations had no effect on the timedistance correlation coefficients. We conclude that the structural organisation of visual images constructed from verbal descriptions is robust, since semantic variations in the descriptions did not affect the mental scanning effect. The experiments showed that high visuo-spatial imagers (as classified on the basis of their scores on the Minnesota Paper Form Board) consistently had shorter scanning times than low imagers, and that only the responses of high imagers gave the time-distance correlation coefficients characteristic of the mental scanning effect. These findings suggest that the visual images constructed by high imagers include more accurate metric information than those constructed by low imagers.

Labeling a speech database with landmarks and features

A database of utterances has been labeled for acoustically salient landmarks and for phonetic features. The landmarks locate syllabic nuclei, glide midpoints, and acoustic discontinuities at the narrowing or releasing of consonantal constrictions. The consonantal landmarks are labeled with values of the articulator-free features (e.g., [continuant] and [sonorant]), and values of articulator-bound features are recorded at each landmark based on acoustic evidence near the landmark. These features specify, for example, the major articulator and its placement, as well as the activity of secondary articulators such as the glottis and the soft palate. Conventions have been developed for labeling reduced vowels, syllabic consonants, glottal stops, consonant sequences in which closures or releases are not acoustically marked, etc. The labeled database is being used for two purposes: (1) to provide a documentation of instances in which the acoustic/articulatory representation of an utterance deviates from the underlying feature-based lexical representation and (2) to train and to test signal-processing algorithms that are being developed to locate the landmarks and to identify the features attached to these landmarks. An advantage of this labeling method is that it gives a more fine-grained phonologically-relevant representation of an utterance than a conventional labeling in terms of phonetic symbols. [Supported in part by NIH Grant No. DC02978.]

Correlation between head direction cell activity and spatial behavior on a radial arm maze.

This study assessed the activity of head direction (HD) cells during performance of a spatial reference memory task on a radial arm maze. Rats were trained to select a maze arm located in a constant position in relation to a salient extramaze visual landmark. HD cell discharge properties remained relatively stable across task acquisition in most rats. Following acquisition, rotation of the landmark by 90 degrees or 180 degrees usually led to a corresponding shift in the maze arm selected and the HD cell's preferred firing direction. When the cell's preferred direction did not shift, rats usually selected the wrong arm. HD cell activity was not influenced by the rat's approach to the goal, reward consumption, or exit from the reward area. This demonstration of landmark control over behavior and the cell's preferred direction supports the hypothesis that HD cells contribute to an absolute representation of the environment that can be used to guide spatial behavior.

Spatial Representation for Navigation in Animats

This article considers the problem of spatial representation for animat navigation systems. It is proposed that the global navigation task, or "wayfinding, " is best supported by multiple interacting subsystems, each of which builds its own partial representation of relevant world knowledge. Evidence from the study of animal navigation is reviewed to demonstrate that similar principles underlie the wayfinding behavior of animals, including humans. A simulated wayfinding system is described that embodies and illustrates several of the themes identified with animat navigation. This system constructs a network of partial models of the quantitative spatial relations between groups of salient landmarks. Navigation tasks are solved by propagating egocentric view information through this network, using a simple but effective heuristic to arbitrate between multiple solutions.

Subjective landmarks in perception and memory for spatial location.

Four experiments investigated the use of cognitive strategies for encoding spatial location in visual figures. Subjects reproduced the position of a dot in a square figure that had distance markers placed along two sides. Subjects' responses were biased toward imaginary points of intersection formed by the distance markers when subjects responded from memory (Experiment 1) or while viewing the figures (Experiment 2). Dots located at an intersection point were reproduced more accurately than those located off an intersection. These findings demonstrate that empty regions of a figure can serve as subjective landmarks for spatial localization. In Experiment 3, dot relocation was found to be similarly distorted toward physical cross marks placed at the intersections of distance markers, supporting the landmark hypothesis. The attraction of dots to intersection points depends on the viewer employing a strategy of mentally projecting from distance markers to form imaginary intersections, which makes intersection points salient landmarks for coding location of nearby stimulus dots. In Experiment 4, attraction toward intersection points was observed only when subjects employed the projection strategy and not when instructed to use a different encoding strategy.

Age and exposure differences in acquisition of route information.

Age and exposure differences were studied in the acquisition of sequentially ordered spatial information and in memory for critical route events. Ss in 4 age groups (older adults, middle-aged adults, college students, and adolescents) viewed slides depicting 2 overlapping neighborhood routes either 1 or 3 times. Older adults were less likely to recall landmarks sequentially and were more likely to recall nonspatial associations to the routes and to regard salient landmarks (rather than turns) as critical route-maintaining events. Exposure was related to number of landmarks recalled, route scene assignment, and reason for selecting critical scenes and was marginally related to critical scene selection. The results suggest that landmark saliency may relate to route learning for older adults, influencing both encoding organization and evaluation of environmental events. The role of decline in cognitive capacity, and the tendency to encode general vs. specific aspects of complex episodic experiences, are discussed.

The use of maps by 4–6‐year‐old children in a large‐scale maze

Previous research has demonstrated that even very young children can use simple maps to find a location. The aim of our study was to find out if young children (aged 4–6 years) could also use a map to follow a route. A large‐scale maze (25 metres long) was designed in a school playground and 120 children, divided into five age groups, were given maps of the maze. The children were asked to walk through the maze, and to do this successfully they had to make correct route choices at different T‐junctions in the maze. For half the children, salient landmarks were placed at the junctions in the maze (and on the maps). In both conditions all but the youngest age group performed much better than chance expectations and were able to use the maps successfully.