SPATIAL MEMORY

Spatial memory pertains to the spatial structure of outdoor spaces, buildings, rooms, and maps; it includes knowledge of where objects are, of routes from place to place, and of distances and directions between locations. The evolutionary success of humans has depended, in part, on abilities to navigate in unfamiliar territory, to locate sources of food and water, and to be able to return to those sources and to home at a later time. In contemporary societies, people rely on their spatial memories for activities as mundane as reaching out in the morning darkness to shut off an alarm and as consequential as escaping from an office building during a raging fire. The spatial memories of insects, rodents, and nonhuman primates have been investigated extensively (Gallistel, 1990), but this chapter will focus on aspects of human spatial memory.

Route versus Survey Knowledge

Large-scale environments cannot be viewed in their entirety from a single vantage point and therefore can only be learned via navigation. When people learn a large-scale environment without the aid of a map, their knowledge initially consists of routes from place to place. With sufficient experience, people may learn the straight-line (Euclidean) distances and directions between locations and perhaps gain maplike or survey knowledge of the environment (Thorndyke and Hayes Roth, 1982). At one time researchers thought that route knowledge had to precede survey knowledge (Siegel and White, 1975). Recent studies have shown that the type of knowledge acquired depends on the goals of the learner, irrespective of the learning experience. For example, people perform better on survey knowledge tasks (e.g., drawing a map) when their goal is to learn the overall layout of an environment than when their goal is to learn routes, regardless of whether they learn the environment from a map or from navigation (Taylor, Naylor, and Chechile, 1999).

Orientation Dependence

An important property of spatial memories is that information is easier to retrieve from some perspectives than from others. Commit Figure 1 to memory. Then make the following judgments without looking at the figure: (a) Imagine you are standing at the book and facing the wood. Point to the clock. (b) Imagine you are standing at the wood and facing the shoe. Point to the book. Problem (a) is easier than (b), even though the pointing direction is the same. This phenomenon is an example of orientation dependence, and it is observed in many tasks and in memories of maps, rooms, and large-scale environments, even when several views are learned (Shelton and McNamara, 2001). Although there may be situations in which spatial memories are orientation independent, such that familiar and unfamiliar views are retrieved and recognized equally efficiently (Evans and Pezdek, 1980), these situations are the exception.

Orientation dependence has typically taken the form of better performance on familiar views and perspectives, as in (a), than on unfamiliar views and perspectives, as in (b), but other patterns have also been observed (Mou and McNamara, 2002). An important consequence of the orientation dependence of spatial memories is that people sometimes get lost when returning from a destination. The environment looks different coming and going.

Spatial Reference Systems

The concept of location is inherently relative. One cannot describe or specify the location of an object without providing a frame of reference. The location of a chair in a classroom, for example, can be specified in terms of the room itself (e.g., the chair is in the corner by the door), other chairs in the room (e.g., the chair is in the first row and second column), or an observer (e.g., the chair is in front of me). The primate brain represents spatial information using many types of spatial reference systems (Anderson, Snyder, Bradley, and Xiang, 1997).

Spatial reference systems fall into two categories: egocentric reference systems, which specify location and orientation with respect to the observer (as in, the chair is in front of me); and environmental reference systems, which define spatial relations with respect to elements of the environment, such as the perceived direction of gravity, landmarks, or the floor, ceiling, and walls of a room (as in, the chair is in the corner by the door).

Human spatial memories rely primarily on environmental reference systems (Shelton and McNamara, 2001). When people learn a map, locations of objects in a room, or even larger spaces, they select a reference system in the environment for representing its spatial structure. The particular reference system that is selected depends on the person's experiences, the structure of the environment itself, and spatial and nonspatial properties of objects in the environment. This process is similar to determining the "top" of a figure or an object (Rock, 1973; Tversky, 1981); in effect, conceptual "north" (and perhaps, south, east, and west) is assigned to the layout, creating privileged directions in memory of the environment (conceptual north need not correspond to true or magnetic north or any other cardinal direction). Retrieval of spatial relations is more efficient in directions aligned with this reference axis than in other directions. In Figure 1, for instance, an observer viewing the space from the position of the arrow might use the axes defined by the walls of the room and the intrinsic structure of the layout (the objects can be grouped into rows and columns parallel to the walls) to construct a reference system for remembering the locations of objects in the room. Egocentric spatial relations must be represented at the perceptual level for the purpose of guiding action in the environment (Sholl and Nolin, 1997). It is an open question whether egocentric spatial relations are represented in long-term spatial memories.

Hierarchical Representations

Spatial knowledge is stored in the brain hierarchically (Stevens and Coupe, 1978). When people learn the locations of objects in an environment, they group the objects into ever larger clusters. For example, a hierarchical representation of an office may specify that the telephone and coffee cup are on the desk, that the desk is next to the chair, and that the desk and chair are in the office. Objects are grouped on the basis of their properties (e.g., the functional relation between a chair and a desk), aspects of the environment (e.g., barriers), and even organizational strategies unique to a particular person (McNamara, 1986; McNamara, Hardy, and Hirtle, 1989).

One way to interpret these findings is that people represent spatial relations in locally defined reference systems and these reference systems are then related to one another in higher-order reference systems (Poucet, 1993). For example, locations of objects in a room might be represented by a reference system local to the room. Such a reference system could then serve as an "object" in a reference system defining the spatial relations among the rooms on the same floor of a house; these could then serve as "objects" in a reference system relating floors of the house to one another.

Spatial Memory and the Brain

Functional neuroimaging using PET (positron emission tomography) and fMRI (functional magnetic resonance imaging) are proving to be powerful methods for investigating areas of the brain involved in spatial learning and navigation. This research is new, but consistent findings are emerging. The parahippocampal gyrus seems to be involved in a variety of spatial tasks (Epstein and Kanwisher, 1998). The hippocampus, predominantly on the right, is associated with the recollection of familiar routes (Maguire, Frackowiak, and Frith, 1997). Dorsal areas of the brain (e.g., the posterior parietal cortex) seem to be recruited for processing the locations of objects, whereas ventral areas (e.g., the lingual and fusiform gyri) seem to be recruited for processing the appearance of objects and scenes (Aguirre and D'Esposito, 1997). This dorsal-ventral dissociation is analogous to that observed in vision (Mishkin, Ungerleider, and Macko, 1983). Recent evidence indicates that route and survey learning recruit a common cortical network in the brain and that survey learning recruits a subset of the route-learning areas (Mellet et al., 2000; Shelton and Gabrieli, 2002).

Language and Culture

Spatial memories are not insulated from language and culture. The Mayan language Tzeltal uses an environmental reference system to describe the spatial relations among objects. This reference system corresponds to cardinal directions established by the mountainous terrain in which the speakers live (e.g., downhill = north, uphill = south, across = east or west). Tzeltal does not have the egocentric spatial terms left and right. When shown an array of objects on a table and asked to reconstruct the array on another table behind them after turning 180 degrees (see Figure 2), Tzeltal speakers reconstruct the array preserving its orientation with respect to the environmental reference system, not with respect to their egocentric perspective (Levinson, 1996). In contrast, speakers of Dutch (and presumably speakers of most Western languages) preserve egocentric, not environmental, spatial relations (e.g., plate to the left in the reconstructed array). Almost superhuman navigational abilities have been documented in several cultures, including those of the Australian Aborigines (Lewis, 1976) and Puluwat Islanders (Gladwin, 1970); experiments have shown that Aboriginal children perform substantially better than white children on tests requiring the children to remember the locations of objects (Kearins, 1981).

Gender Differences

There is a long history of research on gender differences in spatial ability (Maccoby and Jacklin, 1974) but relatively few studies have examined spatial learning and memory of room-sized and larger spaces. Those studies have shown that males perform better than females or that the genders do not differ (Montello, Lovelace, Golledge, and Self, 1999). Recent experiments have documented an intriguing dissociation between females and males in spatial abilities. Females perform better than males on tasks that require memory of the locations and identities of objects, whereas males perform better than females on tasks that require keeping track of orientation in large-scale environments (Montello et al., 1999; Silverman et al., 2000). (There is, of course, large variability within genders, with some men performing better than some women on object-location tasks, and some women performing better than some men on orientation tasks.) How can this dissociation be explained? According to the hunter-gatherer theory, spatial sex differences arise from a sexual division of labor between hunting and gathering during human evolution (Silverman and Eals, 1992). Tracking and killing animals, a predominately male activity, required monitoring one's location and orientation over large distances, whereas foraging for edible plants, a predominately female activity, required memory of the locations of plants and other immobile foods and then relocating them in subsequent growing seasons.

Conclusion

Spatial memories of large environments are composed of route knowledge and survey knowledge. Route knowledge is usually acquired before survey knowledge, but the learner's goals affect what is learned. Some perspectives of a familiar environment can be retrieved more efficiently than others. This orientation dependence arises because people store knowledge about location and orientation in terms of reference directions or axes. The use of different reference directions or axes in different locales may explain why spatial memories are hierarchical. Emerging evidence indicates that different areas of the brain specialize in representing and processing specific kinds of spatial memories. Gender, language, and culture influence the development and pattern of spatial capabilities.

See also:SPATIAL LEARNING: ANIMALS

Bibliography

Aguirre, G. K., and D'Esposito, M. (1997). Environmental knowledge is subserved by separable dorsal/ventral neural areas. Journal of Neuroscience 17, 2,512-2,518.

Anderson, R. A., Snyder, L. H., Bradley, D. C., and Xiang, J. (1997). Multimodal representation of space in the posterior parietal cortex and its use in planning movements. Annual Review of Neuroscience 20, 303-330.

Epstein, R., and Kanwisher, N. (1998). A cortical representation of the local visual environment. Nature 392, 598-601.

Evans, G. W., and Pezdek, K. (1980). Cognitive mapping: Knowledge of real-world distance and location information. Journal of Experimental Psychology: Human Learning and Memory 6, 13-24.

Gallistel, C. R. (1990). The organization of learning. Cambridge, MA: MIT Press.

Gladwin, T. (1970). East is a big bird. Cambridge, MA: Harvard University Press.

Kearins, J. M. (1981). Visual spatial memory in Australian Aboriginal children of desert regions. Cognitive Psychology 13, 434-460.

Levinson, S. C. (1996). Frames of reference and Molyneaux's question: Crosslinguistic evidence. In P. Bloom, M. A. Peterson, L. Nadel, and M. F. Garrett, eds., Language and space. Cambridge, MA: MIT Press.

Lewis, D. (1976). Observations on route finding and spatial orientation among the Aboriginal peoples of the western desert region of central Australia. Oceania 46, 249-282.

Maccoby, E. E., and Jacklin, C. N. (1974). The psychology of sex differences. Stanford, CA: Stanford University Press.

Maguire, E. A., Frackowiak, R. S. J., and Frith, C. D. (1997). Recalling routes around London: Activation of the right hippocampus in taxi drivers. Journal of Neuroscience 17, 7,103-7,110.

McNamara, T. P. (1986). Mental representations of spatial relations. Cognitive Psychology 18, 87-121.

McNamara, T. P., Hardy, J. K., and Hirtle, S. C. (1989). Subjective hierarchies in spatial memory. Journal of Experimental Psychology: Learning, Memory, and Cognition 15, 211-227.

Mellet, E., Bricogne, S., Tzourio-Mazoyer, N., Ghaëm, O., Petit, L., Zago, L., Etard, O., Berthoz, A., Mazoyer, B., and Denis, M. (2000). Neural correlates of topographic mental exploration: The impact of route versus survey perspective learning. NeuroImage 12, 588-600.

Mishkin, M., Ungerleider, L. G., and Macko, K. A. (1983). Object vision and spatial vision: Two cortical pathways. Trends in Neurosciences 6, 414-417.

Montello, D. R., Lovelace, K. L., Golledge, R. G., and Self, C. M. (1999). Sex-related differences and similarities in geographic and environmental spatial abilities. Annals of the Association of American Geographers 89, 515-534.

Mou, W., and McNamara, T. P. (2002). Intrinsic frames of reference in spatial memory. Journal of Experimental Psychology: Learning, Memory, and Cognition 28, 162-170

Poucet, B. (1993). Spatial cognitive maps in animals: New hypotheses on their structure and neural mechanisms. Psychological Review 100, 163-182.

Rock, I. (1973). Orientation and form. New York: Academic Press.

Shelton, A. L., and Gabrieli, J. D. E. (2002). Neural correlates of encoding space from route and survey perspective. Journal of Neuroscience 22, 2,711-2,717

Shelton, A. L., and McNamara, T. P. (2001). Systems of spatial reference in human memory. Cognitive Psychology 43, 274-310.

Sholl, M. J., and Nolin, T. L. (1997). Orientation specificity in representations of place. Journal of Experimental Psychology: Learning, Memory, and Cognition 23, 1,494-1,507.

Siegel, A. W., and White, S. H. (1975). The development of spatial representations of large-scale environments. In H. W. Reese, ed., Advances in child development and behavior. San Diego: Academic Press.

Silverman, I., Choi, J., Mackewn, A., Fisher, M., Moro, J., and Olshansky, E. (2000). Evolved mechanisms underlying wayfinding: Further studies on the hunter-gatherer theory of spatial sex differences. Evolution and Human Behavior 21, 201-213.

Silverman, I., and Eals, M. (1992). Sex differences in spatial abilities: Evolutionary theory and data. In J. H. Barkow, L. Cosmides et al., eds., The adapted mind: Evolutionary psychology and the generation of culture. New York: Oxford University Press.

Stevens, A., and Coupe, P. (1978). Distortions in judged spatial relations. Cognitive Psychology 10, 422-437.

Taylor, H. A., Naylor, S. J., and Chechile, N. A. (1999). Goalspecific influences on the representation of spatial perspective. Memory & Cognition 27, 309-319.

Thorndyke, P. W., and Hayes Roth, B. (1982). Differences in spatial knowledge acquired from maps and navigation. Cognitive Psychology 14, 560-589.

Tversky, B. (1981). Distortions in memory for maps. Cognitive Psychology 13, 407-433.

Timothy P.McNamara