Absence of overshadowing and blocking between landmarks and the geometric cues provided by the shape of a test arena

Orientation by environmental geometry and feature cues in the green and black poison frog (Dendrobates auratus)

The ability to use environmental geometry when orienting in space reflects an animal's ability to use a global, allocentric framework. Therefore, understanding when and how animal's use geometry relative to other types of cues in the environment has interested comparative cognition researchers for decades. Yet, only two amphibians have been tested to date. We trained the poison frog Dendrobates auratus to find goal shelters in a rectangular arena, in the presence and absence of a feature cue, and assessed the relative influence of the two types of cues using probe trials. We chose D. auratus because the species has complex interactions with their physical and social environments, including parental care that requires navigating to and from distant locations. We found that, like many vertebrates, D. auratus are capable of using geometric information to relocate goals. In addition, the frogs preferentially used the more reliable feature cue when the location of the feature conflicted with the geometry of the arena. The frogs were equally successful at using the feature cue when it was proximal or distal to the goal shelter, consistent with prior studies that found that D. auratus can use distal cues in a flexible manner. Our results provide further evidence that amphibians can use environmental geometry during orientation. Future studies that examine when and how amphibians use geometry relative to other types of cues will contribute to a more complete picture of spatial cognition in this important, yet understudied, group.

The effects of spatial stability and cue type on spatial learning: Implications for theories of parallel memory systems

Some theories of spatial learning predict that associative rules apply under only limited circumstances. For example, learning based on a boundary has been claimed to be immune to cue competition effects because boundary information is the basis for the formation of a cognitive map, whilst landmark learning does not involve cognitive mapping. This is referred to as the cue type hypothesis. However, it has also been claimed that cue stability is a prerequisite for the formation of a cognitive map, meaning that whichever cue type was perceived as stable would enter a cognitive map and thus be immune to cue competition, while unstable cues will be subject to cue competition, regardless of cue type. In experiments 1 and 2 we manipulated the stability of boundary and landmark cues when learning the location of two hidden goals. One goal location was constant with respect to the boundary, and the other constant with respect to the landmark cues. For both cue types, the presence of distal orientation cues provided directional information. For half the participants the landmark cues were unstable relative to the boundary and orientation cues, whereas for the remainder of the participants the boundary was unstable relative to landmarks and orientation cues. In a second stage of training, all cues remained stable so that both goal locations could be learned with respect to both landmark and boundary information. According to the cue type hypothesis, boundary information should block learning about landmarks regardless of cue stability. According to the cue stability hypothesis, however, landmarks should block learning about the boundary when the landmarks appear stable relative to the boundary. Regardless of cue type or stability the results showed reciprocal blocking, contrary to both formulations of incidental cognitive mapping. Experiment 3 established that the results of Experiments 1 and 2 could not be explained in terms of difficulty in learning certain locations with respect to different cue types. In a final experiment, following training in which both landmarks and boundary cues signalled two goal locations, a new goal location was established with respect to the landmark cues, before testing with the boundary, which had never been used to define the new goal location. The results of this novel test of the interaction between boundary and landmark cues indicated that new learning with respect to the landmark had a profound effect on navigation with respect to the boundary, counter to the predictions of incidental cognitive mapping of boundaries.

The Neurobiology of Mammalian Navigation

Mammals have evolved specialized brain systems to support efficient navigation within diverse habitats and over varied distances, but while navigational strategies and sensory mechanisms vary across species, core spatial components appear to be widely shared. This review presents common elements found in mammalian spatial mapping systems, focusing on the cells in the hippocampal formation representing orientational and locational spatial information, and 'core' mammalian hippocampal circuitry. Mammalian spatial mapping systems make use of both allothetic cues (space-defining cues in the external environment) and idiothetic cues (cues derived from self-motion). As examples of each cue type, we discuss: environmental boundaries, which control both orientational and locational neuronal activity and behaviour; and 'path integration', a process that allows the estimation of linear translation from velocity signals, thought to depend upon grid cells in the entorhinal cortex. Building cognitive maps entails sampling environments: we consider how the mapping system controls exploration to acquire spatial information, and how exploratory strategies may integrate idiothetic with allothetic information. We discuss how 'replay' may act to consolidate spatial maps, and simulate trajectories to aid navigational planning. Finally, we discuss grid cell models of vector navigation.

Thinking outside of the box II: Disrupting the cognitive map

A number of influential spatial learning theories posit that organisms encode a viewpoint independent (i.e. allocentric) representation of the global boundary shape of their environment in order to support spatial reorientation and place learning. In contrast to the trial and error learning mechanisms that support domain-general processes, a representation of the global-shape of the environment is thought to be encoded automatically as part of a cognitive map, and without interference from other spatial cues. To date, however, this core theoretical assumption has not been appropriately examined. This is because previous attempts to address this question have failed to employ tasks that fully dissociate reorientation based on an allocentric representation of global-shape from egocentric reorientation strategies. Here, we address this issue in two experiments. Participants were trained to navigate to a hidden goal on one side of a virtual arena (e.g. the inside) before being required to find the same point on the alternative side (e.g. the outside). At test, performing the correct search behaviour requires an allocentric representation of the global boundary-shape. Using established associative learning procedures of overshadowing and blocking, we find that search behaviour at test is disrupted when participants were able to form landmark-goal associations during training. These results demonstrate that encoding of an allocentric representation of boundary information is susceptible to interference from landmark cues, and is not acquired through special means. Instead, the results suggest that allocentric representations of environmental boundaries are acquired through the same kind of error-correction mechanisms that support domain-general non-spatial learning.

The response strategy and the place strategy in a plus-maze have different sensitivities to devaluation of expected outcome

Previous studies have suggested that spatial navigation can be achieved with at least two distinct learning processes, involving either cognitive map‐like representations of the local environment, referred to as the “place strategy”, or simple stimulus‐response (S‐R) associations, the “response strategy”. A similar distinction between cognitive/behavioral processes has been made in the context of non‐spatial, instrumental conditioning, with the definition of two processes concerning the sensitivity of a given behavior to the expected value of its outcome as well as to the response‐outcome contingency (“goal‐directed action” and “S‐R habit”). Here we investigated whether these two versions of dichotomist definitions of learned behavior, one spatial and the other non‐spatial, correspond to each other in a formal way. Specifically, we assessed the goal‐directed nature of two navigational strategies, using a combination of an outcome devaluation procedure and a spatial probe trial frequently used to dissociate the two navigational strategies. In Experiment 1, rats trained in a dual‐solution T‐maze task were subjected to an extinction probe trial from the opposite start arm, with or without prefeeding‐induced devaluation of the expected outcome. We found that a non‐significant preference for the place strategy in the non‐devalued condition was completely reversed after devaluation, such that significantly more animals displayed the use of the response strategy. The result suggests that the place strategy is sensitive to the expected value of the outcome, while the response strategy is not. In Experiment 2, rats with hippocampal lesions showed significant reliance on the response strategy, regardless of whether the expected outcome was devalued or not. The result thus offers further evidence that the response strategy conforms to the definition of an outcome‐insensitive, habitual form of instrumental behavior. These results together attest a formal correspondence between two types of dual‐process accounts of animal learning and behavior.

The Occipital Place Area Is Causally Involved in Representing Environmental Boundaries during Navigation

Thirty years of research suggests that environmental boundaries-e.g., the walls of an experimental chamber or room-exert powerful influence on navigational behavior, often to the exclusion of other cues [1-9]. Consistent with this behavioral work, neurons in brain structures that instantiate spatial memory often exhibit firing fields that are strongly controlled by environmental boundaries [10-15]. Despite the clear importance of environmental boundaries for spatial coding, however, a brain region that mediates the perception of boundary information has not yet been identified. We hypothesized that the occipital place area (OPA), a scene-selective region located near the transverse occipital sulcus [16], might provide this perceptual source by extracting boundary information from visual scenes during navigation. To test this idea, we used transcranial magnetic stimulation (TMS) to interrupt processing in the OPA while subjects performed a virtual-reality memory task that required them to learn the spatial locations of test objects that were either fixed in place relative to the boundary of the environment or moved in tandem with a landmark object. Consistent with our prediction, we found that TMS to the right OPA impaired spatial memory for boundary-tethered, but not landmark-tethered, objects. Moreover, this effect was found when the boundary was defined by a wall, but not when it was defined by a marking on the ground. These results show that the OPA is causally involved in boundary-based spatial navigation and suggest that the OPA is the perceptual source of the boundary information that controls navigational behavior.

Transfer of Spatial Behaviour Controlled by a Landmark Array with a Distinctive Shape

In two experiments, rats swam to a submerged platform in one corner of a rectangular or kite-shaped array created by four identical landmarks attached to the walls of a circular pool. After training in the rectangular array, rats expressed a preference for the corner in the kite-shaped array that was geometrically equivalent to where the platform was located previously. After training in either array, the removal of two landmarks from the rectangular array, or the landmark at the apex of the kite-shaped array, did not affect the control over searching exerted by the remaining landmarks. The results imply that rats use local rather than global spatial representations when searching for a hidden goal with reference to an array of landmarks.

Blocking spatial navigation across environments that have a different shape

According to the geometric module hypothesis, organisms encode a global representation of the space in which they navigate, and this representation is not prone to interference from other cues. A number of studies, however, have shown that both human and non-human animals can navigate on the basis of local geometric cues provided by the shape of an environment. According to the model of spatial learning proposed by Miller and Shettleworth (2007, 2008), geometric cues compete for associative strength in the same manner as non-geometric cues do. The experiments reported here were designed to test if humans learn about local geometric cues in a manner consistent with the Miller-Shettleworth model. Experiment 1 replicated previous findings that humans transfer navigational behavior, based on local geometric cues, from a rectangle-shaped environment to a kite-shaped environment, and vice versa. In Experiments 2 and 3, it was observed that learning about non-geometric cues blocked, and were blocked by, learning about local geometric cues. The reciprocal blocking observed is consistent with associative theories of spatial learning; however, it is difficult to explain the observed effects with theories of global-shape encoding in their current form.

Using Grid Cells for Navigation

Mammals are able to navigate to hidden goal locations by direct routes that may traverse previously unvisited terrain. Empirical evidence suggests that this “vector navigation” relies on an internal representation of space provided by the hippocampal formation. The periodic spatial firing patterns of grid cells in the hippocampal formation offer a compact combinatorial code for location within large-scale space. Here, we consider the computational problem of how to determine the vector between start and goal locations encoded by the firing of grid cells when this vector may be much longer than the largest grid scale. First, we present an algorithmic solution to the problem, inspired by the Fourier shift theorem. Second, we describe several potential neural network implementations of this solution that combine efficiency of search and biological plausibility. Finally, we discuss the empirical predictions of these implementations and their relationship to the anatomy and electrophysiology of the hippocampal formation.

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Grid cells (GCs) are believed to provide a path integration input to place cells

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However, GCs also provide a powerful context-independent metric for large-scale space

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Hence, we show how GCs can be used for vector navigation between arbitrary locations

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We simulate various neural implementations and make testable experimental predictions

Place recognition and heading retrieval are mediated by dissociable cognitive systems in mice

A lost navigator must identify its current location and recover its facing direction to restore its bearings. We tested the idea that these two tasks--place recognition and heading retrieval--might be mediated by distinct cognitive systems in mice. Previous work has shown that numerous species, including young children and rodents, use the geometric shape of local space to regain their sense of direction after disorientation, often ignoring nongeometric cues even when they are informative. Notably, these experiments have almost always been performed in single-chamber environments in which there is no ambiguity about place identity. We examined the navigational behavior of mice in a two-chamber paradigm in which animals had to both recognize the chamber in which they were located (place recognition) and recover their facing direction within that chamber (heading retrieval). In two experiments, we found that mice used nongeometric features for place recognition, but simultaneously failed to use these same features for heading retrieval, instead relying exclusively on spatial geometry. These results suggest the existence of separate systems for place recognition and heading retrieval in mice that are differentially sensitive to geometric and nongeometric cues. We speculate that a similar cognitive architecture may underlie human navigational behavior.

Learned predictiveness training modulates biases towards using boundary or landmark cues during navigation

A number of navigational theories state that learning about landmark information should not interfere with learning about shape information provided by the boundary walls of an environment. A common test of such theories has been to assess whether landmark information will overshadow, or restrict, learning about shape information. Whilst a number of studies have shown that landmarks are not able to overshadow learning about shape information, some have shown that landmarks can, in fact, overshadow learning about shape information. Given the continued importance of theories that grant the shape information that is provided by the boundary of an environment a special status during learning, the experiments presented here were designed to assess whether the relative salience of shape and landmark information could account for the discrepant results of overshadowing studies. In Experiment 1, participants were first trained that either the landmarks within an arena (landmark-relevant), or the shape information provided by the boundary walls of an arena (shape-relevant), were relevant to finding a hidden goal. In a subsequent stage, when novel landmark and shape information were made relevant to finding the hidden goal, landmarks dominated behaviour for those given landmark-relevant training, whereas shape information dominated behaviour for those given shape-relevant training. Experiment 2, which was conducted without prior relevance training, revealed that the landmark cues, unconditionally, dominated behaviour in our task. The results of the present experiments, and the conflicting results from previous overshadowing experiments, are explained in terms of associative models that incorporate an attention variant.

Shape shifting: Local landmarks interfere with navigation by, and recognition of, global shape

An influential theory of spatial navigation states that the boundary shape of an environment is preferentially encoded over and above other spatial cues, such that it is impervious to interference from alternative sources of information. We explored this claim with 3 intradimensional-extradimensional shift experiments, designed to examine the interaction of landmark and geometric features of the environment in a virtual navigation task. In Experiments 1 and 2, participants were first required to find a hidden goal using information provided by the shape of the arena or landmarks integrated into the arena boundary (Experiment 1) or within the arena itself (Experiment 2). Participants were then transferred to a different-shaped arena that contained novel landmarks and were again required to find a hidden goal. In both experiments, participants who were navigating on the basis of cues that were from the same dimension that was previously relevant (intradimensional shift) learned to find the goal significantly faster than participants who were navigating on the basis of cues that were from a dimension that was previously irrelevant (extradimensional shift). This suggests that shape information does not hold special status when learning about an environment. Experiment 3 replicated Experiment 2 and also assessed participants' recognition of the global shape of the navigated arenas. Recognition was attenuated when landmarks were relevant to navigation throughout the experiment. The results of these experiments are discussed in terms of associative and non-associative theories of spatial learning.

Overshadowing and blocking between landmark learning and shape learning: the importance of sex differences

Rats were trained in a triangular-shaped pool to find a hidden platform that maintained a constant relationship with two sources of information, an individual landmark and one part of the pool with a distinctive shape. In Experiment 1, shape learning overshadowed landmark learning but landmark learning did not overshadow shape learning in males, while landmark learning overshadowed shape learning but shape learning did not overshadow landmark learning in females. In Experiment 2, rats were pretrained either with the single landmark relevant or with the shape relevant, in the absence of the alternative cue. Final test trials, without the platform, revealed reciprocal blocking only in females; in males, shape learning blocked landmark learning, but not viceversa (Experiment 2a). In Experiment 2b, male rats received a longer pretraining with the single landmark relevant, and now landmark learning blocked shape learning. The results thus confirm the claim that males and females partially use different types of spatial information when solving spatial tasks. These results also agree with the suggestion that shape learning interacts with landmark learning in much the same way as does learning about any pair of stimuli in a Pavlovian conditioning experiment.

Updating the hippocampal representation of space: place cell firing fields are controlled by a novel spatial stimulus

To ask if the properties of spatial learning supported by the hippocampus are distinct from the properties of conditioning, we conducted a blocking-like experiment in which the measured variable was not a conditioned response but rather the ability of a novel visual stimulus to control the location of place cell firing fields after being briefly combined with a familiar, salient stimulus to form a compound stimulus. For most rats, we found that rotations of the novel stimulus on the wall of a cylindrical recording chamber produced equal rotations of firing fields, whether exposure to the compound stimulus lasted 10 min or 60 min. Thus, there was little indication that the blocking phenomenon (Kamin, 1969) acted to prevent the rapid inclusion of a new stimulus into a previously experienced cue constellation. This result is in agreement with the finding of Doeller and Burgess (2008) that blocking is seen for landmark stimuli inside an arena but not for boundary stimuli that circumscribe the arena. We conclude that the rules governing incidental spatial learning are different for the hippocampal representation of a rat's environment than for conditioning.

Framing spatial cognition: neural representations of proximal and distal frames of reference and their roles in navigation

The most common behavioral test of hippocampus-dependent, spatial learning and memory is the Morris water task, and the most commonly studied behavioral correlate of hippocampal neurons is the spatial specificity of place cells. Despite decades of intensive research, it is not completely understood how animals solve the water task and how place cells generate their spatially specific firing fields. Based on early work, it has become the accepted wisdom in the general neuroscience community that distal spatial cues are the primary sources of information used by animals to solve the water task (and similar spatial tasks) and by place cells to generate their spatial specificity. More recent research, along with earlier studies that were overshadowed by the emphasis on distal cues, put this common view into question by demonstrating primary influences of local cues and local boundaries on spatial behavior and place-cell firing. This paper first reviews the historical underpinnings of the "standard" view from a behavioral perspective, and then reviews newer results demonstrating that an animal's behavior in such spatial tasks is more strongly controlled by a local-apparatus frame of reference than by distal landmarks. The paper then reviews similar findings from the literature on the neurophysiological correlates of place cells and other spatially correlated cells from related brain areas. A model is proposed by which distal cues primarily set the orientation of the animal's internal spatial coordinate system, via the head direction cell system, whereas local cues and apparatus boundaries primarily set the translation and scale of that coordinate system.

Potentiation and overshadowing between landmarks and environmental geometric cues

Rats were required in three experiments to find one of two submerged platforms that were situated in the same pair of diagonally opposite corners of a rectangular grey swimming pool. The experimental groups were trained with landmarks, comprising A4 cards attached to the walls, located in the corners containing the platforms. For the control groups, the landmarks were situated in the corners containing the platforms for half of the trials, and in the other corners for the remaining trials. Learning about the positions of the platforms with reference to the shape of the pool was overshadowed in the experimental groups when the landmarks were white, and enhanced when the landmarks were black. A fourth experiment assessed whether geometric cues influenced the control acquired by the landmarks. As in the previous experiments, the presence of the geometric cues overshadowed learning about the landmarks when they were white, but enhanced learning when the landmarks were black.

Theoretical accounts of spatial learning: a neurobiological view (commentary on Pearce, 2009)

Theories of learning have historically taken, as their starting point, the assumption that learning processes have universal applicability. This position has been argued on grounds of parsimony, but has received two significant challenges: first, from the observation that some kinds of learning, such as spatial learning, seem to obey different rules from others, and second, that some kinds of learning take place in processing modules that are separate from each other. These challenges arose in the behavioural literature but have since received considerable support from neurobiological studies, particularly single neuron studies of spatial learning, confirming that there are indeed separable (albeit highly intercommunicating) processing modules in the brain, which may not always interact (within or between themselves) according to classic associative principles. On the basis of these neurobiological data, reviewed here, it is argued that rather than assuming universality of associative rules, it is more parsimonious to assume sets of locally operating rules, each specialized for a particular domain. By this view, although almost all learning is associative in one way or another, the behavioural-level characterization of the rules governing learning may vary depending on which neural modules are involved in a given behaviour. Neurobiological studies, in tandem with behavioural studies, can help reveal the nature of these modules and the local rules by which they interact.

Cognitive maps and attention

Cognitive map theory suggested that exploring an environment and attending to a stimulus should lead to its integration into an allocentric environmental representation. We here report that directed attention in the form of exploration serves to gather information needed to determine an optimal spatial strategy, given task demands and characteristics of the environment. Attended environmental features may integrate into spatial representations if they meet the requirements of the optimal spatial strategy: when learning involves a cognitive mapping strategy, cues with high codability (e.g., concrete objects) will be incorporated into a map, but cues with low codability (e.g., abstract paintings) will not. However, instructions encouraging map learning can lead to the incorporation of cues with low codability. On the other hand, if spatial learning is not map-based, abstract cues can and will be used to encode locations. Since exploration appears to determine what strategy to apply and whether or not to encode a cue, recognition memory for environmental features is independent of whether or not a cue is part of a spatial representation. In fact, when abstract cues were used in a way that was not map-based, or when they were not used for spatial navigation at all, they were nevertheless recognized as familiar. Thus, the relation between exploratory activity on the one hand and spatial strategy and memory on the other appears more complex than initially suggested by cognitive map theory.

The 36th Sir Frederick Bartlett Lecture: An associative analysis of spatial learning

The ability of animals to find important goals in their environment has been said to require a form of learning that is qualitatively different from that normally studied in the conditioning laboratory. Such spatial learning has been said to depend upon the construction of a global representation of the environment, and the acquisition of knowledge about the position of goals with reference to this representation is said to be unaffected by the presence of other cues or landmarks. To evaluate the first of these claims, experiments are described that investigated the extent to which the effects of training in one environment transfer to another. To evaluate the second claim, experiments are described that investigated whether cue competition effects normally found in conditioning studies can be found in spatial tasks. Overall, the results indicate that most of the phenomena of spatial learning can be explained by the principles of associative learning. The implications of the reported results for an understanding of the neural mechanisms of spatial learning are considered.

A landmark blocks searching for a hidden platform in an environment with a distinctive shape after extended pretraining

In the blocking phase of three experiments, rats had to find a submerged platform beneath a spherical landmark in one corner of a triangular pool. Prior to this treatment, they were required to find the platform relative to either a sphere above it (blocking groups) or a rod attached to it (control groups). The position of the platform changed from trial to trial for the initial training. The sphere did not restrict learning about the geometric cues provided by the triangular arena in the blocking phase when 12 sessions of initial training took place in either the triangular (Experiment 1) or a circular (Experiment 3) pool. Blocking was observed, however, after 24 sessions of initial training in either the triangular (Experiment 2) or the circular (Experiment 3) pool. Thus, blocking of geometric cues by a landmark is possible after extended initial training with the blocking cue.

Distinct error-correcting and incidental learning of location relative to landmarks and boundaries

Associative reinforcement provides a powerful explanation of learned behavior. However, an unproven but long-held conjecture holds that spatial learning can occur incidentally rather than by reinforcement. Using a carefully controlled virtual-reality object-location memory task, we formally demonstrate that locations are concurrently learned relative to both local landmarks and local boundaries but that landmark-learning obeys associative reinforcement (showing "overshadowing" and "blocking" or "learned irrelevance"), whereas boundary-learning is incidental, showing neither overshadowing nor blocking nor learned irrelevance. Crucially, both types of learning occur at similar rates and do not reflect differences in levels of performance, cue salience, or instructions. These distinct types of learning likely reflect the distinct neural systems implicated in processing of landmarks and boundaries: the striatum and hippocampus, respectively [Doeller CF, King JA, Burgess N (2008) Proc Natl Acad Sci USA 105:5915-5920]. In turn, our results suggest the use of fundamentally different learning rules by these two systems, potentially explaining their differential roles in procedural and declarative memory more generally. Our results suggest a privileged role for surface geometry in determining spatial context and support the idea of a "geometric module," albeit for location rather than orientation. Finally, the demonstration that reinforcement learning applies selectively to formally equivalent aspects of task-performance supports broader consideration of two-system models in analyses of learning and decision making.

Asymmetrical participation of the left and right hippocampus for representing environmental geometry in homing pigeons

Control, right and left HF lesioned homing pigeons (Columba livia) were trained to locate a goal in one corner of a rectangular enclosure with a distinctive feature cue. Probe tests revealed that all groups were able to encode in parallel geometric (enclosure shape) and feature information, and in the absence of one of them, they could us the other to locate the goal. However, left HF lesioned pigeons learned the task at a faster rate, and when the geometric and feature information were set in conflict, they relied more on the feature cue compared to control and right HF lesioned pigeons. It was also found that pigeons, independent of group, trained to a goal adjacent to the feature cue learned the task in fewer sessions and relied more on feature information compared to pigeons trained to a goal opposite the feature cue. The latter group relied more on geometric information. The results support the hypothesis that the left HF plays a more important role in the representation of a goal location with respect to environmental shape/geometry. We further propose that the observed functional asymmetry can be explained by the lateralized properties of the pigeon tectofugal visual system.

Spatial learning based on the shape of the environment is influenced by properties of the objects forming the shape

In 3 experiments rats had to find a submerged platform that was located in a corner of a kite-shaped pool. The color of the walls creating this corner provided an additional cue for finding the platform in the shape + color condition but not the shape-only condition. During tests in a pool with walls of a uniform color but no platform, more time was spent in the corner where the platform was originally located after training in the shape + color than in the shape-only condition. The results challenge theories that assume either that learning about the shape of the environment takes place in a dedicated module or that cues compete for the control they acquire over behavior.

Is there a geometric module for spatial orientation? Squaring theory and evidence

There is evidence, beginning with Cheng (1986), that mobile animals may use the geometry of surrounding areas to reorient following disorientation. Gallistel (1990) proposed that geometry is used to compute the major or minor axes of space and suggested that such information might form an encapsulated cognitive module. Research reviewed here, conducted on a wide variety of species since the initial discovery of the use of geometry and the formulation of the modularity claim, has supported some aspects of the approach, while casting doubt on others. Three possible processing models are presented that vary in the way in which (and the extent to which) they instantiate the modularity claim. The extant data do not permit us to discriminate among them. We propose a modified concept of modularity for which an empirical program of research is more tractable.

The geometric module in the rat: independence of shape and feature learning in a food finding task

Rats found food in a rectangular enclosure in three experiments testing how learning about a distinctive feature near a goal interacts with learning based on the geometry of an enclosure. Rats trained to follow a feature in square and triangular enclosures and to use geometry in the rectangle followed the feature when it was in the rectangle (Experiment 1). Rats trained with the feature in a geometrically consistent corner of the rectangle learned about both geometry and the feature (Experiment 2). Training with the feature in the square did not block learning of geometry when both predicted the location of food in the rectangle (Experiment 3). The "geometric module" (Cheng, 1986) may have a special status in spatial learning.

Sensory Preconditioning in Spatial Learning Using a Touch Screen Task in Pigeons

The authors used a touch screen-based visual-search task to investigate spatial integration in pigeons. First, pigeons were presented with a consistent spatial relationship between compound visual landmarks (LMs) A-X and B-Y, separately. Next, pigeons learned to find a hidden goal on the monitor in the presence of LMs A and B. The goal bore a consistent spatial relationship to LM A, but not to LM B. On nonreinforced probe tests, the peak and distribution of responses to LM X suggest that pigeons computed a novel X-goal spatial relationship on the basis of X-A and A-goal spatial vectors. Responses to LM Y, however, revealed no evidence of spatial integration. These results replicate and extend those of A. P. Blaisdell and R. G. Cook (2005) using an open-field task.

Sequential control of navigation by locale and taxon cues in the Morris water task

The neurobehavioral dissociation between place navigation and cued navigation has been central to contemporary thinking regarding the psychological processes involved in spatial behavior. In cases where locale (place) cues and taxon cues (e.g., beacons) are present it has been suggested that navigation may be controlled by either stimulus type in isolation, or, alternatively, by both simultaneously. In this report we provide evidence that place cues and beacons sequentially control navigation during a single trip to a visible goal. Rats were trained to navigate to a visible escape platform in a circular swimming pool surrounded by numerous visual cues and the kinematics and accuracy of the trajectories to the platform were analyzed. Shortly after initiating a trajectory to the visible platform, animals routinely engaged in stimulus sampling behaviors (e.g., horizontal head scans) which were consistently associated with changes in accuracy (heading error) and swim velocity. Subsequently, animals swam quickly and accurately to the visible platform suggesting that the sampling behaviors correspond to a shift in exteroceptive stimulus control. Consistent with this idea, removal or relocation of the platform disrupted navigation following the stimulus sampling behaviors, whereas the initial trajectory was unaffected. In contrast, changes in the distal cue constellation selectively disrupted the initial trajectory. The results showing that navigation to a visible goal is controlled sequentially by locale and taxon cues are discussed in relation to contemporary theories of navigation.

Hippocampal Lesions Disrupt Navigation Based on the Shape of the Environment

Geometric information provided by the walls of an environment has a strong influence over hippocampal unit activity. This suggests that the hippocampus forms part of a cognitive mapping system that encodes geometric relationships between environmental cues and the animal's location. Here, the authors show for the first time that excitotoxic lesions of the hippocampus disrupt the ability of rats to navigate to a goal using shape information provided by a solid-walled arena and an array of identical landmarks. These results are consistent with cognitive mapping theories of hippocampal function and extend previous research by showing that hippocampal cell loss impairs navigation with respect to shape information provided by both physical barriers and an array of landmarks.

Transfer of spatial behavior between different environments: implications for theories of spatial learning and for the role of the hippocampus in spatial learning

In 3 experiments, rats were required to find a submerged platform located in 1 corner of an arena that had 2 long and 2 short sides; they were then trained to find the platform in a new arena that also had 2 long and 2 short sides but a different overall shape. The platform in the new arena was easier to find if it was in a corner that was geometrically equivalent, rather than the mirror image, of the corner where it had previously been located. The final experiment revealed that hippocampal lesions impaired rats' ability to find the platform in these arenas. The results suggest that rats did not use the overall shape of the arena to locate the platform but relied on more local cues and that the hippocampus plays a role in navigation based on these cues.

Absence of an Interaction Between Navigational Strategies Based on Local and Distal Landmarks

In 3 experiments, rats were required to escape from a Morris pool by swimming to a submerged platform that was located at the apex of a notional, equilateral triangle with 2 different landmarks occupying the corners at the base. Training for 1 group was always conducted in view of the landmarks surrounding the pool and with the triangular array in a fixed orientation. Subjects could therefore identify the direction of the platform from a single landmark within the pool by reference to cues outside the pool or to the other landmark within the pool. Both strategies were used, and the results from additional groups revealed that the first of these strategies did not affect the acquisition of the second one.

Reorientation in a Two-Dimensional Environment: I. Do Adults Encode the Featural and Geometric Properties of a Two-Dimensional Schematic of a Room?

Adults searched for a goal in images of a rectangular environment. The goal's position was constant relative to featural and geometric cues, but the absolute position changed across trials. Participants easily learned to use the featural cues to find the target, but learning to use only geometric information was difficult. Transformation tests revealed that participants used the color and shape of distinct features to encode the goal's position. When the features at the correct and geometrically equivalent corners were removed, participants could use distant features to locate the goal. Accuracy remained above chance when a single distant feature was present, but the feature farthest from the goal yielded lower accuracy than one closer. Participants trained with features spontaneously encoded the geometric information. However, this representation did not withstand orientation transformations.

Acquisition of knowledge about spatial location: assessing the generality of the mechanism of learning

A selection of studies in the last 20 years is reviewed. These studies show basic Pavlovian phenomena in the spatial domain (like blocking, overshadowing, latent inhibition, and perceptual learning) with nonhuman subjects, specifically with rats, both in the radial maze and in the circular pool. The generality of these phenomena with respect to other species and to other spatial preparations is also discussed. The conclusion is that the mechanism responsible for the acquisition of knowledge about spatial location seems to be associative in nature.