spatial representation for described environments

Geoforum, Vol. 23, No. 2, pp. 165-174, 1992 OOM-7185/92 $5.00+0.00

Printed in Great Britain (CJ 1992 Pergamon Press Ltd

Spatial Representation for Described Environments

NANCY FRANKLIN,* Stony Brook, NY, U.S.A.

Abstract: Spatial characteristics are represented in mental models of environments learned exclusively through description, and the accuracy with which spatial relations are represented can be comparable to the accuracy of perceptually-derived representations. In addition, many of the effects of spatial features on construction, retrieval, updating, and inference are similar to those for perceptual and imaginal processes. Data relevant to these arguments are reviewed, and implications for the organization of mental models derived from text are discussed.

Introduction

We live and navigate in a highly detailed, three- dimensional world, and we construct and consult representations of space that are derived from different kinds of perceptual experience, including map- reading and navigation. We also seem to readily construct representations of environments even when the only source of information is description. We have no trouble following printed instructions for finding a location in an unfamiliar city, understanding the configuration of scattered landmarks described in a travel guide book, or understanding the layout of a fictitious town in a novel.

Mental models of space derived from description’ provide a particularly rich opportunity to investigate the relevance of learning and testing circumstances to construction of spatial representations and to investigate the versatility of constructive memory. To the extent that representations constructed from text contain detailed spatial information, and to the extent that operations on them lead to performance resembling performance from perceptually-derived representations, we have evidence that subjects con-

*Department of Psychology, State University of New York at Stony Brook, Stony Brook, NY 11794-2500, U.S.A.

struct and use models of spatial relations they never encountered.

There is a useful distinction to be made between the content and organization of memory. By simply asking people, one can demonstrate that knowledge about complex spatial relations is accurate. Subjects can draw fairly accurate maps of regions that they have experienced perceptually [e.g. CHASE and CHI, (1981)], and they are good at inferring novel paths that require knowledge of continuous distance (LEVINE et al., 1982; LYNCH, 1960). Under nor- mal circumstances, they are good at estimating areas of and distances between objects they are viewing (HABER, 1985) and making such estimates from memory (CADWALLADER, 1976; BAUM and JONIDES, 1979), at least for relatively short distances within large-scale environments.

Such accuracy is also found for mental models derived from description. Multidimensional scaling solutions from distance estimates produce almost identical configurations for subjects who are given only a description of an environment and for subjects who learn by studying a map (REGIAN et al., 1986). Estimates are accurate not only for distances described explicitly in the text but also for distances that must be inferred from it. In fact, subjects asked to

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draw maps of environments they had read about can be as accurate as those who learned by studying a map (TAYLOR and TVERSKY, 1991).

Organization of the Representation

Given that memory about space is generally fairly accurate regardless of the source of input, what can we say about its organization? Does the answer to this question depend on the source of learning? Regard- less of how one has learned information about space, most tasks that one can expect to perform on it involve drawing inferences about spatial relations. This is accomplished more easily by representing the spatial relations themselves than by representing a description about those relations. When memory is organized as a coherent, integrated model, all spatial relations, even those not explicitly described in the text, are represented explicitly. The act of constructing a mental model, then, requires already making many of the simple inferences about static spatial relations that one would need for subsequent spatial reasoning. Subjects could then retrieve stored relations rather than calculate them when they are needed. In addition, when features of the environment are dynamic or when one’s physical or mental position within it changes (FRANKLIN and TVERSKY, 1990; GLENBERG et al., 1987; MOR- ROW, 1985a; MORROW et al., 1987), spatial relations can be updated simultaneously and easily in a mental model of the situation itself.

There thus seems to be a great potential advantage to creating a representation organized according to spatial characteristics, given an input organized primarily according to principles of coherent text. It is plausible that a sophisticated memory system such as ours would spontaneously perform this nontrivial conversion, and the current consensus is that text comprehension indeed involves ongoingly constructing multiple representations. In particular, it is generally agreed that readers retain propositions extracted from the text (at least, temporarily) and that they construct a mental model of the described situation based on both the text and default inferences (VAN DTJK and RINTSCH, 1983; JOHNSON-LAIRD, 1983). Once such a model of the environment is constructed, memory for it remains highly accurate,

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while memory for the wording of the text decays with time (BRANSFORD et al., 1972).

This greater retention of spatial than textual information is suggestive of a reorganization in memory to a pictorial or spatial representation, but it alone is not conclusive. To obtain evidence that organization for mental models differs from that for text, we need to look beyond recognition accuracy to processing itself. The underlying assumption is that the time required to construct, update, and inspect a memory representation depends on features that are used to organize it. Evidence comes from several measures of processing, including reading time for spatial information, time to retrieve or judge spatial relations, and recognition priming in spatial memory (where ‘priming’ refers to faster processing of a target immediately after processing information about another, associated item). Such measures have demonstrated that processing time can be affected by spatiaf features, indicating not only that representations include information about spatial features but that they are also organized according to some of them. We consider two such features next.

Two apparent orgunizutionul features: distance and direction

In both two- and three-dimensional configurations, regardless of scale or complexity, we can expect all pairs of objects to be related’by some distance and direction, and we can expect that even a crude representation of the layout will include information about both. Not surprisingly, then, they are the most thoroughly investigated visuo-spatial features of mental models, and they have produced the most evidence for spatial organization in mental models.

~~~ta~ce. The more discriminable two objects are on some dimension of comparison, the easier it is to identify the difference along that dimension (MOYER and BAYER, 1976). For example, subjects will make a size comparison between two objects more quickly as the difference between their sizes increases from barely different to very different. Similarly, if items in memory for an environment are organized according to spatial extent, distance comparison times should be an inverse function of dis-

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tance. As differences in distances between pairs of locations increase, subjects should identify the pair separated by the longer distance more quickly. Such effects have indeed been found for perceptually available space (BAUM and JONIDES, 1979), for spatial relations that were once but are not currently perceptually available (BAUM and JONIDES, 1979; EVANS and PEZDEK, 1980), and for environments that have been learned through description only (DENIS and ZIMMER, 1991). It may not be so surprising that representations derived from perception would incorporate spatial extent or that inspection of them would be influenced by a feature that affects visual discriminability. But it appears that perceptual input is irrelevant to this finding; spatial representations can apparently incorporate a distance feature that affects discriminability similarly, regardless of the mode of input.

When a task requires physically or mentally scanning over distances rather than comparing them, processing time tends to increase with distance. This phenomenon has been demonstrated extensively for images of objects once viewed. Where greater trans- formations of the observer’s gaze would be required over real grids and maps (ATINEAVE and CUR- LEE, 1983; KOSSLYN et al., 1978), for example, corresponding imaginal operations obey similar (typically linear) functions. Distance effects have also been shown for described environments. During initial learning about both room-sized (SHARP and McNAMARA, 1991) and city-sized (FRANKLIN, 1992) environments, reading time is longer for far than for near distances. It is as if subjects are mentally traversing or mentally drawing a path, and it takes longer to do so when a far rather than a near relation- ship is described. After the environment has been learned, reading times for sentences describing objects that are near a story’s current focus are read faster than those describing far objects (GLEN- BERG et al., 1987). For example, reading time is faster when a sweatshirt is mentioned that subjects know John has put on and taken with him on his jog than a sweatshirt they know he has left behind. It is as if the time to identify the referent of a phrase depends on a search that begins at John’s position within the mental model and leads outward from it. This effect occurs even when descriptions are constructed so that near objects are functionally no more important than far objects and recency of mention in the text is

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controlled, so the effect appears to genuinely depend on spatial distance.

When distance is divided into more categories (e.g. here, near, far, and very far), time to retrieve objects in the environment still depends on their distance from a protagonist’s current location. In stories describing a protagonist’s movement over a large build- ing for which subjects had viewed a map (MORROW et al., 1987)) objects at the current focus of attention (‘here’) were responded to in a judgment task most rapidly. Further, the linear trend among the distance values was significant, suggesting the possibility of a perception-like search. Even more impressive linear functions have been produced when subjects are explicitly instructed to imagine scanning mental models (DENIS and COCUDE, 1989).

Priming provides another means for studying the effects of distance. In a typical experiment, subjects are first presented with the name of a location in a known environment (the ‘prime’). Immediately afterwards (typically within 100 or 200 msec), they are presented with a ‘target’ name, which they must respond to by identifying as a place in the environment or categorizing according to location. Response times for target locations learned either from direct experience or from a map are affected by the targets’ Euclidean distance from primes [e.g. McNAMARA (1986)]. This effect implies use of a representation in which distance is a determinant of association between the locations named by target probes.

Some cases of spatial priming have been reported for mental models as well. WENDER et al. (1990) produced a priming effect for a one-dimensional array of words, each designating a concrete noun. Items near each other more effectively primed one another than did items farther apart in the array, even though the array itself was not present at test. There is a potential confound to this study, however. Without experimental control of the order in which items are studied, we can expect subjects to read from left to right, so the effect could be the result of temporal rather than spatial association (CLAYTON and HABIBI, 1991; SHERMAN and LIM, 1991). DENIS and ZIMMER (1991) partially controlled for this by using a large-scale configuration that was two-dimensional and described in a fixed linear order. The times taken to judge whether words designated objects that had

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been in the scene showed a spatial priming effect for the text-learners independent of textual (and thus temporal) distance.

Considering the different literatures on distance together, it appears that both distance effects and inverse distance effects similar to those for perceptually available stimuli also occur for representations derived from text. Response times that are monotonic, even linear, functions of distance suggest the possibility that ~ntinuous space can be represented when it has actually been viewed and when it has not.

It is important to note, though, that not all distance functions, for either perceptual or imagined space, are linear or even monotonic. It is not always necessary or expedient to perform a continuous transformation over the world, an image, or a mental model to accomplish a task. Travelling from one to another location within a described environment can be imagined by mentally skipping from one directly to the other, or between important locations along the route, a process resembling the ‘blink transform’ over images (KOSSLYN, 1980). Similarly, readers prob- ably do not represent John’s plane moving over all intervening states when they read the sentence, ‘John flew from New York to California.’ When smooth search or transformation over continuous space is not necessary, then distance may influence processing time only according to gross categories of distance (e.g. near and far) or not at all.

When subjects read about a character having moved within a small environment, their reading times for short and long movements do not differ (SHARP and McNAMARA, 1991). When they retrieve information from a mental model about a city route that has been designated by its endpoints, response time is not a monotonic function of the route’s length (FRANKLIN, 1992). Although the relevant factors are not yet clear, it appears that distance and priming effects for mental models are likeliest and strongest when subjects have viewed the referent environment before reading a story involving operations on it (MORROW et al., 1987), during the initial reading about an environment (SHARP and McNAMARA, 1991), when subjects are explicitly instructed to imagine scanning (DENIS and ZIMMER, 1991), or when described movement in a learned environment involves crossing boundaries into new regions

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(GLENBERG et al., 1987; SHARP and McNA- MARA, 1991).

Direction. Direction, too, is represented in and affects processing of both perceptually and textually derived representations. As was discussed for distance, organization based on direction does not imply that search is continuous. With respect to direction, space seems to be organized in memory not homo- geneously but with respect to axes (nosh-south, east-west, up-down, front-back, left-right, etc.), and time to retrieve information about directions in space appears to depend on characteristics of the axes. It is useful for the following discussion and for the discussion about perspective to classify these into two categories: egocentrically- and canonically- defined. Egocentric directions are determined by the front-back, left-right, and head-feet axes of one’s body, and assignment of objects to these directions depends on one’s current orientation in the environment. For example, what is in front of you after you turn 180” is different from what used to be in front of you. Canonical directions (north, south, east, and west) are defined independently of one’s perspective (although in map comprehension subjects apparently come to associate the north-south axis of maps with their own front-back and the east-west with their left-right).

For local space, retrieval appears to be a function of the relative importance of the three egocentric axes, where importance is a function of the perceptual and behavioral asymmetries associated with each. For the upright observer, head-feet is the only body axis associated with a universally defined environmental axis, gravity. Gravity is associated with highly salient behavioral and perceptual asymmetries; objects (including oneself) move unidirectionally and with high acceleration on the gravitational axis. Further, objects above and below tend to remain in their respective directions with reorientations in the environment, while horizontal relations of objects to oneself change much more frequently. The front- back is not consistently associated with any asymmet- ric axis of the world, but it is characterized by important navigational, behavioral, and perceptual asymmetries. All are oriented primarily toward the front rather than the back. Finally, the right-left axis has weak if any asymmetries, and its physical symmetry leads to interference and confusion. For upright ob-

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servers, then, head-feet is argued to be most salient, and thus most quickly retrieved, followed by front- back, followed by right-left (CLARK, 1973; FRANKLIN and TVERSKY, 1990; SHEPARD and HURWITZ, 1984). Within the front-back axis, the front plays the more important perceptual, functional, and navigational role, making it the more accessible (BRYANT et al., 1992; SHOLL, 1987).

This spatial framework analysis has been partially tested for perceptually available environments, and the times taken to locate objects in the environment support the analysis. For example, SHOLL (1987) studied time to localize objects in a familiar large- scale environment in which subjects had extensive navigational experience. Subjects were faster to localize objects in front of themselves than objects to the back or sides, regardless of their own orientation or whether any of the objects was in view. The special status in memory of the frontward region, at least for environments with which one interacts, was sup- ported. In addition, when subjects identify locations on a visual map with which they have just become familiar, they are faster to front-back, slower to right-left, and slowest of all to oblique directions (HINTZMAN et al., 1981). This finding demon- strates both a framework-like organization and the differential salience of the body axes composing it.

The results for physically present space have been shown for memory of physically surrounding space as well. For example, HINTZMAN et al. (1981) had subjects view objects surrounding themselves on the horizontal plane, move to a new environment, and then identify objects’ previous directions with respect to themselves. Again, subjects were faster for objects that had been toward the front or back than those to the right or left, and were slowest for objects in oblique directions.

Examining retrieval for all six egocentrically defined directions, FRANKLIN and TVERSKY (1990) found that the spatial framework organization holds for mental models of surrounding environments that are learned solely through description. After reading about an environment in which an upright observer was surrounded by objects, subjects identified the objects on the head-feet axis fastest, followed by the front-back axis, followed by the right-left. These results imply that readers organized a spatial rep-

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resentation according to principles that depend on interaction with physical space, even in the absence of physical experience with the particular referent situation. Further, in order for asymmetries associated with the various axes to be relevant and to affect processing, subjects must adopt the perspective according to which the axes are defined. Thus, when subjects read about ‘you’ at the center of an environment, surrounded by objects beyond ‘your’ head, feet, front, back, right, and left, they adopt ‘your’ embedded perspective, at the origin of these egocen- t&ally defined axes. Similarly, retrieval times for subjects who read descriptions of objects surrounding a central third person or inanimate figure are consistent with the spatial framework, suggesting that subjects adopt the perspective of the central figure and define space according to their own body axes (BRYANT et al., 1992; FRANKLIN et al., 1992).

So from the current literature on processing of direc- tional information around oneself, we see that surrounding space is treated similarly for perceptually present environments, those that once were but are not now viewed, and those that are learned only through descriptions. Further, when free to adopt the embedded perspective that allows them to organize an environment according to a single spatial framework, they appear to do so. As we found for distance, it appears that inspection of various directions in space does not necessarily require smooth transformation of one’s mental gaze for any of the different sources of learning. In fact, in the case of direction, discontinuity appears to be the rule and not the exception. Regardless of the original source of information, perceptual or textual, surrounding space appears to be spontaneously organized according to functional and perceptual asymmetries that arise from one’s interaction with the local world.

Perspective and foregrounding

I have been discussing simple physical features that affect processing. I can now introduce a more complex feature upon which both distance and direction can depend: perspective. Perspective becomes important to processing because of limitations on working memory. Like real visual fields, imagined objects and environments are spatially bounded and ‘over- flow’ as they are mentally approached (KOSSLYN,

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1978). And like perceptually present objects, imagined objects have limited resolution (ATT- NEAVE and CURLEE, 1983; FINKE and KURTZ- MAN, 1981). Particularly for a large or complex configuration, not all of its parts are maximally available for inspection at any moment. (This principle underlies the distance effects discussed earlier.)

If mental models are like views of pictures or images, they have some perspective associated with them that then affects differential accessibility of locations. The earlier discussion of spatial frameworks illustrates this point. Use of the spatial framework requires adopting the central figure’s perspective. On the other hand, mental models may represent spatial relations directly but in a more abstract, perspective- free manner. If the latter holds, then, as the task calls for it, the representation may be instantiated as different images with associated perspectives. Evi- dence exists for perspective-biased and perspective- free mental models, as we will see. Most of the evidence implies that, when they are being used, they are instantiated according to some perspective, which might be switched as needed.

Foregrounding. Just as we could distinguish between content of a memory and the effects of its organization, we can attempt to both identify the reader’s perspective at any moment and study how it affects processing. One way in which it affects relative accessibility is by affecting what is foregrounded. Fore- grounding can be thought of as mental focusing, typically resulting from mentally looking at a portion of the environment (although several other factors can also affect it). Generally what is foregrounded from a survey perspective is whatever is near the current focus of attention or near the main protagonist . Generally what is foregrounded from an embedded perspective is whatever is in the main protagonist’s field of view. Foregrounding of areas within an environment can lead to increased free recall for objects at that location (ABELSON, 1975) and faster recognition for them (BLY, 1989; DENIS and LE NY, 1986). When presented with deictic terms and ambiguous pronouns in text, subjects are biased to interpret them to be most consistent with what is currently foregrounded (MORROW, 1985b).

Bias toward perspective. Clearly, one’s perceptual interaction with a physical configuration is associated

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at any time with some perspective, and relative avail- ability depends in part on that perspective. Similarly, perspective can be represented in memory for a previously perceived configuration and affect processing. This is most apparent when memory for a previously viewed environment is heavily biased toward some particular perspective, which generally results when perceptual experience is limited to few exposures and restricted to a single orientation. A fixed perspective on a cognitive map can facilitate spatial inference if its orientation is appropriate to the task, but conflicts in orientation may slow spatial inference and lead to errors (LEVINE et al., 1982; SHOLL, 1987). You-are-here maps that are posted so that they are misaligned with the environment lead people who are new to the environment to walk away from their goal (LEVINE, 1982; LEVINE et al., 1984).

Another common example of fixed orientation in memory for previous perception is the standard map (and associated cognitive map) of the United States. Judgment times for relative positions among U.S. cities depend on the degree of rotation from the standard map orientation (EVANS and PEZDEK, 1980), as if subjects must perform a mental rotation until the experimental configuration coincides with their image of the U.S. map. Similarly, when pointing toward distant cities, subjects’ performance is best if they themselves face north (SHOLL, 1987).

Fortunately, such problems of misalignment between the environment and cognitive maps of fixed orientation rarely arise. Particularly when observers have had extensive navigational experience with an environment, they appear to develop representations that allow them more freedom to use various perspectives (EVANS and PEZDEK, 1980; PRESSON et al., 1987; SHOLL, 1987). Global relations among objects and relations of objects to a canonical frame of reference generally become more apparent with exposure, such that Euclidean distances and directions become easier to calculate (THORNDYKE and HAYES-ROTH, 1982).

The same sort of contrast between perspective-biased and perspective-free representations seems to hold for mental models acquired from text. First, readers generally construct simple mental models from some preferred perspective. When changes in perspective

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are implied by a text, subjects experience inco- herence, and their recall is distorted to be consistent with their existing perspective (BLACK et al., 1979).

Retrieval time is likewise affected. To illustrate this, we can again consider the spatial framework. Its use requires that readers adopt the embedded perspective around which objects are positioned (BRYANT et al., 1992; F~N~IN and TVERSKY, 1990; FRANKLIN et al., 1992). Under some circumstances, as when a single environment is described with respect to several embedded observers, assign- ing a spatial framework to each observer’s perspective would require multiple mental models. It may be more efficient in such a case to use a mental model with an external perspective that incorporates all spatial relations between objects and observers simultaneously. Although use of an external perspective allows subjects to maintain a single mental model rather than many, it precludes use of the spatial framework, and the pattern of retrieval times is described by a different set of considerations (FRANKLIN er al., 1992).

Readers have been found under some circumstances to use mental models with apparently flexible perspectives. In TAYLOR and TVERSKY (1992), subjects read about an extended environment from either a route-perspective description (which used egocentrically-defined directions) or a survey- perspective description (which used canonical directions). Learning involved studying the description extensively, and the verification task that followed encouraged multiple perspectives. Subjects judged a series of true-false statements that each expressed a spatial relation from either the perspective of the text or from the alternative perspective. Speed and accuracy did not depend on whether the perspective implied by statements matched those encouraged at learning. With repeated study of the text, subjects appeared to have a perspective-free spatial representation that could be instantiated according to an embedded or survey view. Further, subjects’ subsequent map drawings were highly accurate regardless of the type of text, further indicating that route- learners could translate the embedded perspective of the text into a survey perspective.

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Are representations t~~~el~es really spatial?

We have seen that spatial features are represented in and can affect processing of memory representations, whether they are derived from perceptual experience or description. Some of the findings, like linear scanning functions, suggest continuous representation. Others, like regional priming effects or other discon- tinuous distance effects, suggest categorical processing. Clearly, memory representation must be capable of including semantic info~ation {e.g. history, function, and visual details) and must be organized so that some certain properties can affect processing.

McNamara and his colleagues have argued that this can be accomplished with a partial hierarchy (McNA- MARA, 1986; McNAMARA et al., 1989; SHER- MAN and LIM, 1991). That is, the representation is not as if subjects had a true map in memory. Rather, it is as if the spatial information were organized with respect to boundaries, regional associations, and other semantic information as well as with respect to Euclidean distance and direction. For example, the representation of a configuration segmented into multiple regions could be a hierarchy with multiple branching structures. Euclidean distance can be represented by proximity within the hierarchy or by distance tags, and regional association can be represented by branch. Thus, the representation can include and can be affected by distance without being map-like.

The effects of region membership, and of partial hierarchy, are reflected in recall clustering (SHER- MAN and LIM, 1991), route planning (PAILHOUS, 1969), errors in spatial judgments (STEVENS and COUPE, 1978), distance and direction judgments (MAKI, 1981; SHERMAN and LIM, 1991) and spatial priming (SHERMAN and LIM, 1991) for previously viewed configurations. As for other semantic information in memory, it appears that the spatial and nonspatial information are indeed strongly enough ‘associated that one can prime the other. For example, McNAMARA ef al. (1991) found that a keyword from a recently learned fact about a location facilitates spatial judgment about a nearby location but not about a location farther away. This spatial priming effect suggests that factual and configurational information are associated together

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within memory of previously viewed scenes. A partial hierarchy that is not strictly map-like provides a structure in which such association can take place.

It appears that mental models are generally not strictly map-like either. Like representations derived from perception, they appear typically to represent categorical properties and to sometimes represent analog properties. We saw that spontaneous distance effects for spaces learned solely through description are most likely when distance is confounded with region or scene membership. We also saw that retrieval times for space surrounding oneself and retrieval times for locations that are or are not foregrounded can be described categorically.

Several possible kinds of representations can account for such findings. One possibility is a representation organized according to both spatial and semantic properties, perhaps as a simplified or schematic spatial representation, or a map-like representation with categorical labels. Another possibility (SHARP and McNAMARA, 1991) is a nonspatial mental model, which represents the described situation rather than the text but whose schematic structure is not directly isomorphic to a spatial structure. A nonspatial mental model can represent spatial relations, even emergent spatial relations not mentioned in the description, but all relations are represented as semantic labels in a propositional structure. Through simple rules of association and inference-derivation, nonspatial mental models seem to be able to account for the findings we have discussed, both continuous and categorical.

Detailed questions about the organization of memory for space have yet to be answered satisfactorily for either images derived from perceptual experience or mental models derived from text. We do know quite a bit, though, about the behavior of these representations under various experimental circumstances, and we can expect that any memory organization to be considered must predict the effects of spatial features that have been observed in the literature.

Factors influencing whether mental models are used

Besides asking how the circumstances affect a mental model’s organization, we can ask what factors deter-

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mine whether one is formed at all. To this there are some clearer answers. The text, referent situation, task, and subject can all affect the likelihood of using mental models. With regard to text, subjects are unlikely to create mental models if the spatial information is presented incoherently or discontinuously (EHRLICH and JOHNSON-LAIRD, 1982; DENIS and DENHIERE, 1990) or is indeterminate (MAN1 and JOHNSON-LAIRD, 1982; STENNING, 1981). In such cases, they are likely to retain a representation of the text only (MAN1 and JOHNSON- LAIRD, 1982), although they might construct a mental model by imposing default specifications (e.g. right turn) that limit the situation to a single determi- nate case (STENNING, 1981). With regard to subject characteristics, individuals who are classified as poor readers or poor imagers appear less able and less likely to construct mental models than are individuals scoring high on these skills (SHARP and McNA- MARA, 1991). With regard to the described situation, subjects are unlikely to construct a mental model if the configuration is simply too complex (PERRIG and KINTSCH, 1985). As for task, subjects are unlikely to construct mental models if they have been told to expect a memory test for the text itself (GARNHAM, 1981). These findings fit with the argument that creating mental models (or the failure to do so) is not strictly a product of descriptions of space but is rather a reasonable solution to the problem of constructing a representation given a description of space, an anticipated task, and limitations of one’s own working memory.

Conclusion

Memory for space is versatile. Complex reorganiz- ations can take place that would allow otherwise computationally expensive inferences to become trivial. We saw that this occurs whether the source of input is perceptual or descriptive. Spatial information acquired from extensive route learning in physical environments can be reorganized so that the learner has survey relations available. In addition, information about space that was originally presented according to the organizational principles of coherent text (THORNDYKE, 1977) is likely to be spontaneously translated by subjects into a representation that is apparently organized according to spatial characteristics.

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Further, details of the memory organization generally seem to reflect one’s typical interactions with the represented space. Tasks involving immediately surrounding space primarily consist of local navigation and of perception and manipulation of nearby objects. Accordingly, organization appears to be gov- erned by salient aspects of one’s interaction with nearby space and objects. Memory for larger-scale space should be and does seem to be organized according to other considerations. At the level of a familiar but large environment (say, one’s city of residence), interactions with the environment often involve planning one’s extended route, which in turn requires estimating direction and distance and updating one’s perspective. Interactions with space on the largest (e.g. global or national) scale involve primarily judging spatial relations among locations (rather than, say, between a distant object and oneself).

From the cases discussed here, the organization of mental models appears to depend on the same factors (e.g. nature of the environment, degree of one’s learning, and task demands) as do perceptually- derived representations. Source of learning seems to interact little with these factors; it appears to have a greater effect on the richness of content than on whether spatial factors affect processing.

Note

1. Representation of spatial relations that are learned exclusively from description is one of many topics studied in the mental models literature, but the current paper will focus on this single use of the term.

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