Spatial metaphors and disorientation in hypertext browsing HANHWE KIM and STEPHEN C. HIRTLE Department of Information Science, 708 LIS Building, University of Pittsburgh, Pittsburgh PA 15260, USA; email
[email protected]
Abstract. The spatial metaphor can be used as a framework for explaining and designing tools that alleviate disorientation problems in hypertext systems. The approach based on this metaphor would involve developing tools analogous to navigational aids in physical environments and applying analogous concepts from research on human spatial processing and navigation in physical . . soaces. Research on hvoertext browsing with respect to the spatial metaphor is reviewed and contrasted with the larger task context where users are trying to explore, learn, analyse, and summarize the contents of the hypertext space.
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1. Introduction A problem faced by users browsing hypertext systems is the disorientation problem, where users have difficulty deciding which link to follow next. This problem has been described as 'being lost in hyperspace' and can lead to frustration in using hypertext systems (Edwards and Hardman 1989). This paper discusses the application of cognitive research in human spatial processing and wayfinding, as applied to the disorientation problems that occur when browsing hypertext systems. We wish to examine the extent that such research can provide explanatory frameworks for the disorientation problems and guidelines for designing tools and hypertext features for dealing with those problems. Through this review, we suggest several methods to reduce or eliminate disorientation, which are based on the principle of spatial cognition. As such, this paper presents a research agenda for future exploration of hypertext navigation tools. Hypertext systems are databases composed of a collection of nodes of data items and where relations between nodes are represented by explicit links. Such systems include a user interface that allows users to view the nodes by traversing the links. The browsing process allows users to explore the database, learn about related concepts and, through the
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exploration process, refine their information goals (Foss 1989a.. Foss 1989b. - , McAleese 1989). ~, The disorientation problem occurs when the user 'gets lost' in the display network or has difficulty deciding which node to view next (Dillon et 19907 Gygi 1990, Edwards and Hardman 1989). The decision concerning which node to view next involves understanding one's current location in the network, selecting potentially useful routes and executing the selected routes. Users must perform these navigational tasks in conjunction with informational tasks of summary, analysis, and comparisons of the contents and relationships between the nodes for understanding (Foss 1989b). The performance of multiple tasks furthermore requires an overhead for task management. Thus, there is a high load upon the browser's cognitive resources, and the navigational tasks, informational tasks, and task management become difficult (Conklin 1989, Foss 1989a, Foss 1989b, Utting and Yankelovich 1989). Users have reported 'feeling disoriented' when using hypertext systems, which result in degraded performance in tasks involving the use of hypertext systems (Foss 1989a, 1989b, Gray 1990). The situation faced by a user browing a hypertext database has been compared to that of a person wayfinding through a physical space (Hammond and Allinson 1987). Browsing in hypertext databases includes many of the same tasks as wayfinding in physical spaces such as: finding one's current location, planning a route that will accomplish one's task goals, and execution of the planned route (Garling and Golledge 1989). Research on human spatial processing and navigating in physical environments can be applied to the problem of disorientation in hypertext systems (Dillon et al. 1990, Edwards and Hardman 1989). If the similarities between wayfinding tasks in a physical environment and perusal tasks ~
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in hypertext databases are strong, then a spatial metaphor, where hypertext databases are compared to physical spaces, can serve as an explanatory framework concerning user difficulties, and a design framework for helping users deal with such difficulties. By comparing and contrasting cognitive processes in wayfinding and hypertext perusal, it may be possible to explain many of the difficulties that hypertext users have by identifying system features that are analogous to those of disorienting physical environments. Using the spatial metaphor as a framework for design would suggest providing navigational aids analogous to things as maps and guided tours available for navigating in physical environments, as well as provide guidelines for designing hypertext system features that are easier to peruse. We begin with a review of hypertext browsing with focus upon classifying the disorientation problems and clarifying the definitions (Foss 1989a, 1989b, Edwards and Hardman 1989). The disorientation problem is discussed in terms of navigational difficulties as well as specific task difficulties. Next, research in spatial processing and wayfinding in physical environments will be examined. The goal will be to examine how closely the cognitive aspects of navigation in physical environments match those of browsing in a hypertext system. Findings concerning cognitive maps, route, and survey knowledge of physical environments, and the design of navigational aids in physical environments will be discussed. The concluding sections will examine the application of such research in dealing with the disorientation problems. There are two approaches for helping users deal with disorientation problems. The first approach is to aid the wayfinding tasks directly, while the second approach is to help with specific informational tasks and task management. thereby lessening the overall cognitive load (Hammond and Allinson 1988, Foss 1989a, 1989b, Utting and Yankelovich 1989).
Browsing strategies can be classified in terms of the specificity of the user's goals (McAleese 1989), or in terms of the topology of the network (Parunak 1989). While the iterative refinement of information goals while browsing can provide flexibility in access, the cognitive demand of making many levels of navigational decisions while trying to integrate the contents can be cognitively demanding. This leads to disorientation problems where users have difficulty deciding what to read next. The following subsections refine and clarify these definitions.
2. Browsing and disorientation problems in hypertext perusal
2.2. Hypertext topologies and navigational strategies
Browsing in hypertext systems is defined as visiting a set of related nodes through traversal of links. It is described in contrast to retrieval by queries based upon keywords or field-value pairs (McAleese 1989). The browsing process allows users to explore the database, learn about related concepts and refine their information goals as they learn more through exploration (Foss 1989a, 1989b). The iterative refinement of information goals can be useful in situations where the user would initially have trouble formulating a useful query. The price of the increased flexibility of access by browsing is an increased cognitive load on the user, which results in disorientation problems. This section will examine the nature of browsing and the disorientation problems associated with it.
2.1. Browsing strategies and user goals One would not expect consistent browsing behaviour from all users as the specificity of the user's information goals varies widely (Canter et al. 1985, McAleese 1989). Several classifications have been proposed in the literature. Some classifications are applicable to all electronic databases. For example, Canter et al. (1985) delineate five discernible browsing strategies of scanning (covering a large area without depth), browsing (following a path until a goal is achieved), searching (explicit goal search), exploring (finding the extent of information), and wandering (unstructured globetrotting). McAleese (1989) applies the strategies of Canter et al. (1985) to a hypertext context and discusses how different interfaces can foster different browsing strategies in a hypertext system. Embedded links, where the links are embedded in the views of the node contents, can foster scanning and browsing strategies. Maps, where the nodenode connectivity is depicted graphically, are suitable for seeing the extent of information. Finally, in situations where the user has a specific goal that can be described in terms of node characteristics, query mechanisms, instead of hypertext browsing, can be more efficient.
Whereas McAleese (1989) defines browsing strategies in terms of user goals, Parunak (1989) defines navigational strategies, the specific methods that can be used while browsing, and the constraints upon the navigational strategies imposed by hypertext topologies from a graph theoretic perspective. He compares navigation strategies in physical spaces and hypertext topologies, and identifies five strategies that people use in navigating physical spaces: (1) Identijier strategy: A unique identifier or description is associated with each entity of interest. This strategy requires an exhaustive search, but it can be applied to any topology. (2) Path strategy: A procedural route description of how to get to the target is provided. It is used if the number of
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places directly accessible from a particular place is much less than the total number of places. If this is not the case, then finding the next step in a path is not easier than directly going to the target itself. (3) Direction strategy: The searcher uses a global frame of reference to avoid exhaustive search (north-south, east-west). The strategy depends upon the texture and comparability of the space. (4) Distance strategy: The search is bounded to a circle around one's current position. Distance can be used in conjunction with a direction, and is always defined in spaces where paths exist. (5) Address strategy: Direction is refined by establishing an orthogonal coordinate system in the space. The definition of orthogonal dimensional coordinates reduces the computational complexity of the search. Parunak (1989) then defines five classes of topologies which hypertext systems can have based upon graph-theoretic concepts. In increasing order of complexity, the classes are linear and ring, hierarchy, hypercube and hypertorus, directed acyclic graph, and arbitrary structure. Pamnak (1989) notes that simpler topologies allow users to use a wider variety of navigational strategies, with the linear and ring structure allowing all five of the strategies, whereas the arbitrary structure allows only for the default identifier strategy.
2.3. The cognitive load of browsing While browsing a hypertext database, the user must carry out multiple tasks concurrently. These tasks can be clarified into three categories: (1) navigational tasks: planning and executing routes through the network; (2) informational tasks: reading and understanding the contents presented in the nodes and their relationships, for summary and analysis; and (3) task management: co-ordinating informational and navigational tasks (e.g., keeping track of digressions to incidental topics). Performance of these tasks exacts a high cognitive load upon the user (Conklin 1989, Foss 1989a, 1989b). There are two factors that further increase the user's workload. The first is the weakening of the 'literary contract' between the author and reader, and the second is the lack of discourse cues (Gygi 1990). The 'literary contract' defines the division of authority and responsibilities between authors and readers. In traditional paper-based media, authors are expected to organize a coherent sequential presentation of ideas, which readers are expected to follow. In hypertext systems, there are multiple paths through the network. The reader has greater flexibility but also greater responsibility in selecting an appropriate path from which sense can be made.
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Traditional print media also has a rich set of standard discourse cues: organization into chapters and sections, conventions concerning the placement of topic sentences, and typographical conventions that help the reader decide what parts to read in detail, and what parts to skim over (Foss 1989b, Oren 1990). Such conventions have not been established with hypertext systems yet (Oren 1990). The reader must make 'extensive meta-level decisions' concerning what to read next in hypertext systems without the aid of established discourse conventions (Gygi 1990). 2.4. Disorientation in hypertext systems The disorientation problem, 'feeling lost', not knowing one's current location with respect to the overall topology, and having difficulty 'selecting which node to read next' have been frequently reported by users of hypertext systems (Gygi 1990, Edwards and Hardman 1989). Researchers have tried to clarify these subjective accounts of disorientation. Edwards and Hardman (1989) classify different forms of 'feeling lost': (1) not knowing where to go next; (2) knowing where to go but not knowing how to get there; and (3) not knowing the current position relative to the overall hypertext structure. Foss (1989a) approaches the disorientation problems in terms of performing tasks ('deciding what to read next') under high cognitive loads as well as spatial navigation terms ('feeling lost'). She proposes three classes of disorientation problems and lists observable symptoms associated with each class of problem (Foss 1989b). (1) Navigational disorientation problems. Navigational disorientation problems are caused by incorrect or imperfect knowledge of topological organization, unfamiliarity with access tools, and not knowing the extent of the hypertext in terms of how much has been visited and how much is left. Symptoms of this problem can be seen by looping, inefficient paths to target nodes, and query failures. (2) Embedded digression problem. This problem occurs when high cognitive demands lead to difficulties of planning, managing and executing digressions. The symptoms of this problem are disorganized screen layouts with many windows open at once, and repeated retracking. (3) Art museum problem. When one spends a long day at a museum gazing at many paintings, without studying a few paintings in detail or thinking about the characteristics of a particular school of art, it is difficult to remember any particular painting in detail or understand how various styles influence each other. In hypertext systems, high cognitive demand leads to similar problems of remembering and summarizing contents that have been read, and lack of memory for details of any particular
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part. This is compounded by the lack of established discourse cues. Symptoms of this problem are short reading times indicating only cursory examination of node contents and restrictive search paths (Foss 1989b). Disorientation while browsing hypertext systems is the cost aspect of a trade off made by the reader between greater flexibility at the expense of higher cognitive loads. Complex hypertext topologies, while providing greater expressiveness, restrict the navigational strategies available to the reader. This restriction and the current lack of discourse cues and conventions for hypertext databases, further complicate the reader's task. The next section will examine research in human spatial processing and wayfinding that can help further explain and provide insights into dealing with the disorientation problems.
3. Human spatial processing and navigation cognitive science research on human spatial processing and wayfinding based upon information processing theoretical perspectives, assume the existence of a cognitive map, a mental model encoding knowledge about physical spaces ( ~ ~andl ~ i ~~ l ~1989, l ~ d and ~ Heidom ~ 1993). studies examined here are those pertinent to explaining the disorientation problem in hypertext systems. They are studies of (1) the representation, processing, and acquisition of cognitive maps; (2) environmental characteristics and their effects upon performance of tasks involving navigation; and (3) studies of navigational aids for physic. environments.
3.1.1. Representation formats: One classification of spatial knowledge considers three distinct representations: place, route and survey knowledge (Hirtle and Hudson 1991, Stem and Leiser 1988). Place knowledge includes the salient aspects of places encoded in a declarative form. People can thus know of the existence of places and can recognize them when they are encountered (Gkling and Golledge 1989, Gopal et al. 1989). Route knowledge is considered to be represented in terms of choice points (e.g., intersections) where decisions are made between places and represented procedurally (Gopal et al. 1989, Leiser et al. 1987). Gopal et al. (1989) note that children can recognize photographs of choice points better than photographs of other points along routes. Survey knowledge concerns the spatial layout of the salient places. Directions and distances between the salient places are represented. Another aspect about representation of cognitive maps is their structure. There is strong evidence of hierarchical organization. An example is the misconception that Reno, Nevada is east of San Diego, California, when in fact it is west of Sari Diego (Stevens and Coupe 1978). This is explained by a hierarchical organization where places in California are encoded to be west of places in ~ e v a d a ~. v e nfor spaces without predefined hierarchies, strong hierarchical organization exists within cognitive maps (Hirtle and Jonides 1985, McNamara et 989). Related to structures are frames of reference. Gopal et al. (1989) identify egocentric, environmental, and global frames. Egocentric frames are centred On the navigating individual. Environmental frames are based on reference points in a local environment. Global frames are independent of both navigator and local environment.
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3.1. Cognitive maps and navigation
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Cognitive maps are mental representations of physical spaces used for navigation. They encode knowledge about place characteristics and knowledge about spatial relations between places (GWing and Golledge 1989). Knowledge of spatial relations includes knowledge of routes, and survey knowledge: directions and distances between salient places. Navigation within a physical environment is a complex multi-level task, which involves orientation, and route planning and execution. Orientation is a process of recognizing the current location based upon perceptual features and locating perceptually non-available places based upon one's cognitive map. In unfamiliar environments, spatial orientation might depend upon perspective transformationsto note where one is relative to previously visited places. Route planning involves selection of a route based upon matching one's goals with place, route, and survey knowledge encoded in cognitive maps. Execution of the route plan involves sub-levels of decision making concerning what to look for, what to expect in the environment (Gkling and Golledge 1989).
3.1.2. Acquisition of cognitive maps: The representation formats of place, route, and survey knowledge have implications for their acquisition. Route and survey knowledge are hard to acquire compared to place knowledge since spatial configurations are not always directly perceivable. Route and survey knowledge have to be acquired piece-meal in complex spaces (Gkling and Golledge 1989). Survey knowledge is harder to learn than route knowledge from direct travel. Putting together a plausible layout of the places from episodic encounters requires additional effort, and does not develop automatically in environments with confusing layouts (Moeser 1988). However, exposure to maps does help in the acquisition of survey knowledge. Similar problems have been seen in computational models. Yeap (1988) provides a computational model of integrating temporal encounters of direct travel into a cognitive map representation from which survey knowledge can be retrieved. Initially, the model constructs route representations of paths of adjacent local spaces without explicit reference to survey representations. While discussion focuses on constructing place representations that integrate spatial and
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non-spatial knowledge, he notes it is possible to generate a coarse grained survey representation from the route representations. To do so, the model retraces paths through previously traveled closures in a manner analogous to 'mental walkthroughs' while applying two dimensional constraints to form a plausible layout. The model reflects the difficulty of acquiring survey knowledge from direct experience. 3.1.3. Processing of cognitive maps and navigational behaviour: Leiser et al. (1987) note that different study methods yield different performance on different tasks requiring either route or survey knowledge. Subjects, who studied an environment through simulated travel (practising routes), tended to initiate responses faster than subjects who learned through map study (survey knowledge). This and other supporting evidence lead Leiser et al. (1987) to hypothesize that, while subjects with route knowledge could directly retrieve familiar routes from memory, subjects with only survey knowledge had to perform processing to generate a route from retrieved survey knowledge. The ease of acquisition and thus the availability of route and survey knowledge has implications concerning navigational behaviour. Generally, people will tend not to have good survey knowledge. In cases where both route and survey knowledge are available, people will tend to retrieve familiar routes rather than try to deduce a new route from survey knowledge in route planning, unless motivated to do so (Ggiling and Golledge 1989). The availability of survey knowledge will also result in different strategies for error recovery. If survey knowledge is available, it may be possible for a lost person to reorient oneself and plan a corrective route. Without survey knowledge, the person will have to rely on some form of backtracking to a familiar location.
3.2. Environmental factors, and the acquisition andprocessing of cognitive maps While environmental factors that affect navigation performance and learning of cognitive maps are interesting from apractical view, it is difficult to generalize empirical findings across different environments, tasks and individuals. Garling and Golledge (1989) emphasize that the complexities of the navigational process imply that there can be a large amount of interaction between navigational task characteristics, individual characteristics, and environment characteristics, and that consideration of all such factors must be taken into account. G2rling and Golledge (1989) tentatively list some environmental factors that do affect navigation performance and acquisition of cognitive maps. They are differentiation, visual access, and path complexity. Differentiation is the
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distinguishability among different places. A building with halls and rooms all painted the same colour would generally be harder to navigate than if the same building were painted with a colour coding scheme. Visual access is the degree that targets are visible directly or indirectly. Path complexity is defined by the number of decision points in a path. The effects of environmental factors identified by GWing and Golledge (1989) were demonstrated in a study by Moeser (1988). In a notoriously difficult to navigate hospital building with poor visual access and complex paths due to segmented comdors, and irregular shapes of rooms, it was discovered that even experienced nurses had difficulty acquiring correct survey knowledge. They extensively relied on route knowledge and signs to navigate. Although more experienced nurses had developed more comprehensive cognitive maps in terms of the place and route knowledge, they did not demonstrate greater survey knowledge. Although maps showing the layout were placed on walls at various locations, they were seldom used (Moeser 1988). Thus the extent to which maps will be useful is most likely to be dependent upon the complexity of the space.
3.3. Designing navigational aids of physical spaces The large amount of interaction between task, environment, and individual characteristics in navigational tasks makes it difficult to prescribe comprehensive guidelines for design of navigational aids. Careful consideration of user and task characteristics must be taken. Passini (1984: 158-196) proposes a methodology for designing less disorienting architectural environments. He emphasizes the careful definition of wayfinding tasks, user and environmental characteristics. Building upon such definitions, it is possible to deduce the information needed by people in making various wayfinding decisions. Thus, the architect can make decisions concerning the visual access of pathways and places, placement of signs and other information sources in a rational manner. Studies by Streeter et al. (1985) and Kovach et al. (1988) in designing a user interface for a vehicle navigational aid also illustrate the need for consideration of task and user characteristics. The studies compared formats for presenting navigational information for drivers attempting to follow routes in an unfamiliar city. Customized maps were compared with verbal presentations of the same information. The customized maps included information on limited access roads and landmarks that people were found to use extensively when wayfinding. Conventional maps lacked such information. The verbal instructions also were carefully designed to avoid ambiguities and avoid counting (e.g., '8 blocks after the light'). In both sets of experiments, the researchers confirmed that verbal presentations are better than maps, since map reading is a cognitively demanding task
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This section will discuss the spatial metaphor and its extent and limitations as a design reference for dealing with hypertext browsing difficulties. Several approaches to helping users avoid disorientation problems while browsing hypertext systems have been proposed. They are conventions that can help authors create less disorienting hypertexts, and tools to help users perform browsing tasks. The conventions and tools aim to improve general wayfinding, and help in specific informational tasks and task management. conventions and tools inspired from the spatial metaphor are stronger in aiding general wayfinding.
alleviate difficulties analogous to those in the domain of the metaphor (Hammond and Allinson 1987). On the basis of the spatial metaphor, electronic databases, in general, and hypertext systems, in particular, are similar to the worst environments for wayfinding identified by Giirling and Golledge (1989) in terms of differentiation, visual access, and route complexity. Screenfuls of text look homogeneous, and generally do not provide the visual differentiation one finds in the typographic cues of printed matter (Nielsen 1990). Visual access is restricted by screen space and resolution and the extent of the hypertext database is frequently not shown to users. In a hypertext with much linking between nodes, the route complexity can be high. Using the spatial metaphor as a reference for design will focus attention upon dealing with general wayfinding difficulties, and suggest approaches inspired from wayfinding in physical spaces. The limitation of such a design reference is that it does not address the difficulties of other tasks that users perform concurrently while browsing. These are difficulties with the informational tasks of summary and analysis of the database contents, and the task management overhead involved in keeping track of navigation while analyzing and summarizing. There can be task specific approaches focusing upon helping users perform these concurrent tasks that complement the general wayfinding approaches.
4.1. Spatial metaphors and hypertext browsing
4.2. Approaches to reducing disorientation
Hammond and Allinson (1987) discuss the process through which metaphors are used to convey information about a computer system and guide design. By using metaphors, users can predict system behaviour by matching features of the system and the metaphor and generalizing behaviour in the metaphor to the system (Hammond and Allinson 1987). If the matching is inappropriate, the user performs a more cognitively demanding problem solving task to infer the system's behaviour. Metaphors need not be appropriate descriptors in every level of detail, but it is important for metaphors to be explicitly inappropriate for features that do not match: If the key features are only partially matched, the user will make errors due to overgeneralization. A common overgeneralization error made by typists who are novice users of word processors is trying to use the space bar for cursor movement, when the space bar in word processors is used exclusively for space insertion. For designers, metaphors provide a frame of reference for design activities. Designers can make decisions concerning the features of a system based on the information conveyed by the metaphor. System features analogous to positive features in the metaphor's domain can be added, and characteristics of the system can be used in novel ways to
The approaches to help reduce disorientation in hypertext browsing are establishing conventions for less disorienting hypertexts and the design of browsing tools. Browsing tools are supplementary facilities provided by the hypertext system. Some tools can help with general wayfinding while others aid in specific informational tasks or task management. The general wayfinding tools are inspired from analogous objects in the spatial domain (e.g., maps and guided tours). They impose simpler topologies upon subsets of the nodes and links in the database, foster the acquisition of useful mental models of hypertext topologies, and aim to improve visual access of the topology. The task specific tools do not have analogous objects in the spatial domain and are complementary to the general wayfinding tools. They make use of annotation facilities, and session histories. These tools help users keep track of digressions (task management), and summarize and analyse contents (informational tasks).
that would be difficult to do while driving (Streeter et al. 1985, Kovach et al. 1988). The high degree of interaction between the environment, task, and individual characteristics makes generalizable studies and the design of general guidelines for wayfinding difficult. Environments with good visual access, high differentiation between places, and simple paths are generally easier to navigate. In designing navigational aids, careful consideration must be given to specific task factors and cognitive loads. No single navigational aid is going to be best for all situations.
4. Designing hypertext systems to reduce disorientation
4.2.1. General wayfinding tools: Navigational aids presented to users through the spatial-travel holiday metaphor include 'maps' and 'guided tours' (Hammond and Allinson 1987). Maps depict survey knowledge of the hypertext topology, showing nodes and links graphically. Guided tours
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are author defined display sequences intended to give a tutorial guidance to novice users concerning the extent of the hypertext, and general familiarization. On the basis of his matching of possible navigation strategies and classification of hypertext topologies, Parunak (1989) notes that simpler topologies are easier to navigate since they offer more possible navigational strategies. The implication is that navigational aids will work by imposing simpler topologies upon hypertexts with complex topologies. He identifies several navigational aids provided with hypertext systems that impose simpler topologies:
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(1) beaten-path mechanisms, such as back-up stacks that provide a list of recently visited nodes and guided tours (path macros), impose a linear structure on parts of the hypertext network; (2) book-marks, which allow the user to designate nodes that can be accessed directly when the book-mark facility is activated impose a one-level hierarchy structure; (3) typed links and filtering on link types impose a hierarchical or other simpler topology on parts of the hypertext. Parunak (1989) further asserts that maps are useful only on topologies where path, direction and distance strategies make sense, or other restricted topologies. When paths, directions, and distances degenerate, map displays become spaghetti. In light of Parunak's (1989) graph theoretic analysis of maps, the customized maps provided by Hammond and Allinson (1989) in their studies should be distinguished from the graphic overview tools that automatically generate graphic schematics of the network. The maps provided by Hammond and Allinson (1989) do not display the connectivity of the network in terms of the all links but display only a subset of the links designed to give the user an overview of content organization that would be appropriate in the context of learning. In displaying only a subset of the links, the maps in Hammond and Allinson (1989) impose an appropriate simpler topology. The maps also include a wide range of annotation concerning the semantic contents of the nodes displayed. Overview tools that automatically generate schematics are deficient in that they do not convey semantic information, and the lack of filtering sometimes results in tangled displays of degenerate paths (Foss 1989a, 1989b). These schematic displays are closer to visual access tools that increase the visual access a user has of the network. To the extent that visual access of the network is increased, such tools can also help navigation. Research on such visual access tools has been to look for various ways to filter links automaticaliy to generate appropriate topologies for maps and ways that convey semantic information concerning the nodes (Gygi 1990).One of the approaches is to provide fish-eye views. Closer nodes are displayed in more detail than nodes that are farther away
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(McAleese 1989).A fish-eye view can be used in topologies where non-trivial distances exist. A fundamental limitation of using visual access tools is that the perspective transformations can be either inconsistent, if the topology is inappropriate for maps, or confusing, if the topology is not restricted to the dimensional constraints . of physical spaces. If a user generalizes the topology of a hypertext to a 3 or 2 dimensional space, incorrect inferences based upon misconceived survey knowledge could result in confusion (Utting and Yankelovich 1989). Foss (1989a, 1989b)notes several practical problems with visual access tools. The computational demands of generating a graphical presentation of a large network are high, and much of it is wasted in many cases where the user is interested in only a portion of the database. Also scrolling large overview screens can be unwieldy. Edwards and Hardman (1989) and Kerr(1990) caution that providing a multitude of wayfinding tools can confuse the user and slow the acquisition of appropriate mental models due to the mismatches in applicable wayfinding strategies between hypertext and physical topologies that the tools introduce. However in the studies by Hammond and Allinson (1989), users quickly learned to make use of multiple access mechanisms in a rational manner. When given specific research tasks, they used indexes and link browsing and when given more exploratory tasks they tended to use tours and 'excursions'. Hammond and Allinson (1987, 1988, 1989) argue that the mismatches introduced by alternate wayfinding facilities is explicit enough that users do not make errors of overgeneralization. 4.2.2 Task speciJic tools: The disorientation problem can be due to the high cognitive load of informational tasks and task management difficulties, as well as pure wayfinding difficulties. Foss (1989a, 1989b) proposes tools that address the 'embedded digression problem' and the 'art museum phenomenon' aspects of disorientation by aiding specific informational or task management tasks. The tools designed by Foss (1989a, 1989b) makes use of annotation facilities, history lists and automated marking of visited nodes. These also include some of the 'cognitive management tools' discussed by Gygi (1990). Possible tools are graphical history lists, history trees, summary boxes (Foss 1989a) and history matrices (Foss 1989b). Examples of the tools can be seen in figures 1 through 7 using an example based upon the public domain Hypercard stack on the Internet, authored by BBN. The graphical history list is primarily a visual access orientation tool with some support for managing digressions. The history tree is primarily a digression management tool with some support for summary. The summary box is primarily a summary tool. The history matrix makes explicit an implicit hypertorus topology, and is used for compare-and-contrast analysis. All of Foss's (1989a, 1989b)implementations,allow annotations
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Figure 1. A history list for a session on the internet hypercard stack. The seven cards listed on the left have been visited this session. by the user to help later summary, or goal tracking. Each of these tools are described in detail below. Graphical history lists, shown in figure 1, are an extension of the back-up stacks. From the history list, users can access a 'mini-browser' which displays the local neighbourhood of a node visited in the stack. The nodes that are referenced by and nodes that reference a selected node in the history list are shown. Previously visited nodes are marked. The mini-browser, shown in figure 2, displays the local neighbourhood of a node visited in the stack. The nodes that are referenced by and from the selected node are shown. Previously visited nodes are marked. Mini-browsers, thus, show the immediate neighbourhood of nodes in a hypertext database. In effect, a one-level fish-eye view is provided with indications of which of the neighbouring nodes have been visited before. History trees, as displayed in figure 3, display the path of a user in a hierarchical format rather than a list. However, a history tree also retains the temporal ordering of visits unlike
Figure 3. A history tree for the internet session. a history list. The history tree makes explicit the digressions one has taken. The connectivity in the hierarchy does not necessarily represent connectivity through links, since cards visited through query retrieval are displayed in their appropriate temporal order. After a browsing session, the history tree can be used as a summary of the exploration. Summary boxes, as shown in figure 4, are again extensions of the history list. When activated, each time a new node is visited, a 'twin node' in which users can take notes, is generated. When one of the nodes in the summary box is selected, it is displayed together with its twin. The display of the twin and the original node at the same time facilitates copy-paste operations for note taking. Figures 5 and 6 show the original card and the twin card that would appear when clicking on 89: Domain system in figure 4. History matrices, as shown in figure 7, are useful when a user is trying to perform a compare and contrast analysis on a hypertext containing nodes on several topics, or a classification task. The user is provided with a matrix, and along the top row the user specifies the dimensions for comparison, and the leftmost column provides identifiers for each of the cases, or classifications. In effect, tool provides
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Figure 4. An example for a summary box on a single card.
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an explicit hypertorus or hypercube framework (Parunak 1989), that may not have been only implicit in the hypertext system, into which the nodes can be assigned. Foss (1989b) discusses an example of using the history matrix for a classification task, where users are supposed to identify correctly the names of 10 countries, based on nodes that had encyclopedic data on each of the countries in 7 attributes: people, economy, communication infrastructure, government, military, land, and water. The history matrix included a field in the leftmost column where the user could enter tentatively the name of the current best guesses. The matrix would facilitate comparison of several countries along several dimensions, and allow users to annotate pivotal information (marking the square in the matrix black) upon which the current judgement was made, and indicate which of the nodes had been examined or not. 4.3. Menus Maps have also been suggested to assist in navigation of hierarchical menus (Billingsley 1982, Webb and Kramer Domain Svstem(Twin) Twin card makes annotation easy
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was Copied from the orlglnal A postmaster at the reclplent's organlzatlon can provlde the correct address when you h 0 . r the the domain name of the organlzatlon Send a message requesting help to postmaster@domaln m e user can add comments and notes and link this
card to others. T h e "Edit Links" button on the lower right pops up the "Ilake Link" button and allows the user to select text for new llnks and reconfigure old ones bv clickinq on links. When "Edit Llnks" is off. Edit Links for conf iguring l h l s is a link
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Figure 6. Twin of card 89: domain system opened from the summary box.
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Figure 7. A history matrix for comparing five apartments on three criteria. The matrix indicates previously visited nodes with an asterisk (*), and allows the user to indicate 'good' (circle with dot) or 'bad' (x in square) aspects about each apartment.
1990). In a study by Billingsley (1982) subjects who were given the opportunity to study a tree diagram of menu items were faster at retrieval tasks when compared to either a control group or an index group that studied an alphabetized list of terms along with menu sequences. The items in this study were drawn from a set of animals and the tree represented the actual semantic structure of the set. Billingsley concluded that the pictorial representation facilitated the development of a usable mental model of the menu structure. A more recent study by Webb and Kramer (1990) suggests that providing an analogy of the space rather than an explicit map is more beneficial to subjects, especially over time when the specifics of the map may be forgotten. In the analogy conditions, subjects were given a generic description of the space as moving through a department or shopping in the mall, rather than an explicit map. This is consistent with a recent finding by Mohageg (1992), who found that novice users of a hypertext system performed retrieval tasks faster with an underlying hierarchical structure, rather than a network structure or linear structure. In discussing these findings, Mohageg (1992) notes the difficulty in conceptualizing network links when first using a system. As users gain expertise, he suggests that such nodes are easier to incorporate into one's working model of the system. Together, these studies suggest that good navigational tools are those that indicate to the user an appropriate mental model for understanding the structure of the space. Delays in retrieval time occur when the physical structure and the cognitive structure are in disagreement. Fisher et al. (1990) have suggested that the construction of menus start with a seed hierarchy that matches the user's structure of the menu concepts. The seed hierarchy can then be modified to result in optimal groupings and nestings so that the tree is neither too deep nor too wide (cf., Norman and Chin 1988).
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4.4. Extensions
5. Conclusion
As one compares the research conducted within the physical domain of wayfinding and with the experience of hypertext users, a large gap remains. The lack of differentiability at the local level or hierarchical structure at the global level leaves many users alone to wander among the frames with little guidance beyond leaving a trail of history makers, like dropping nuts along a trail in the forest. In critiquing YOU ARE HERE maps, Levine et al. (1984) point out that even accurate information may be misleading if the correct orientation is not readily available. Furthermore, the best YOU ARE HERE maps provide redundant information, which can reduce the cognitive load and resulting errors, dramatically. Clearly, additional cues, such as the relative position of a user, are needed for most hypertext applications. Within the hypertext domain, we discussed a number of excellent methods of providing route and survey knowledge, the two main classes of spatial knowledge, through guided tours and maps. As previously argued, the benefit of each depends entirely on the topology of space and the nature of the task at hand. It would not surprise us if there were large individual differences, as well, as has been seen in most spatial domains, with some preferring maps whereas others prefer route information. However much more work needs to be done on the differentiation problem. Nielsen (1990) shows how specifying different background designs for the presentation of nodes on the computer screen can increase the differentiability between nodes. Also, having different graphic designs for different classes of nodes can help users recognize landmarks with the topology and aid the meta-level decision making task (Gygi 1990). Thus researchers in hypertext are beginning to explore the importance of differentiation, which has long been known in the spatial domain. In addition to distinguishing node type by differentiation, it is also important to differentiate hypertext regions. In physical environments identical establishments might have similar architecture or logos, but seeing two identical McDonald's restaurants does little to distinguish uptown from downtown in a city. Therefore, in addition to classifying node types, node regions in the topology should be given identifying colours, textures or fonts. Users would be able to keep track of what cluster they are in and, if keys were coded in a similar manner, even the best way to move on to the next region. The research on cognitive mapping suggests that even in the most random topology, users will impose a hierarchical structure to make 'sense' of the space (McNamara et al. 1989). If users are going to impose a hierarchical structure, then it would be best if the designer provided the most logical one for the user. An explicit hierarchical structure also provides a natural pattern for the construction of local and global maps.'
The disorientation problem in hypertext browsing is caused by difficulties in wayfinding tasks, and difficulties due to the high cognitive load. Cognitive research in spatial processing and wayfinding help identify the specific properties of current hypertext systems that cause such difficulties and evaluate approaches to dealing with them. Certainly the lack of differentiability, visual access, and hierarchical structure need further consideration in hypertext systems. Successfully applying cognitive research in the design of physical wayfinding aids and the design of less disorienting physical environments requires detailed analysis of the specific task factors and their interaction with specific cognitive aspects (Passini 1984, Streeter et al. 1985, Kovach et al. 1988), as well as awareness of general aspects of the hypertext environment (Garling and Golledge 1989, Moeser 1988). There is a parallel trend in the development of approaches for dealing with the disorientation problems. Approaches that are readily inspired from the spatial metaphor and which focus upon general wayfinding aspects are complemented with task specific approaches. As experience with hypertext databases accumulates, our understanding of the wayfinding tasks, informational tasks, and task management involved in browsing will become more detailed. It will be possible to identify the information required by users for different browsing tasks, and match those requirements with various means of presenting the information. Then in addition to a refinement of conventions and browsing tools for improving general wayfinding based upon accumulated experience, it may be possible to define sets of browsing tool primitives from which specialized browsing tools can be constructed. Such a development would parallel developments in architecture such as Passini's (1984) design methodology for identifying and providing information for wayfinding tasks.
Note '1t is critical to realize that a cognitive hierarchical structure is independent of the topology of the space. A spider web that is painted red, green, and blue would consist of three clusters of nodes, while the topology remains a network, not a tree.
References BILLINGSLEY. P. A. 1982, Navigation through hierarchical menu structures: does it help to have a map? Proceedings of the 26th Annual Meeting of the Human Factors Society (The Human Factors Society, Santa Monica, CA) 103-107. BOTAFOGO, R. A. 1993,Cluster analysis for hypertext systems, inR. Korfhage, E. Rasmussen, and P. Willet (eds), SIGIR '93 Conference Proceedings (ACM Press, New York), 116-125.
Spatial metaphors in hypertext browsing CANTER, D., RIVERS,R. and STORRS, G. 1985, Characterizing user navigation through complex data structures, Behaviour & Information Technology, 4, 93-102. CONKLIN, J. 1987, Hypertext: an introduction and survey, IEEE Computer, 20, 1 7 4 1 . DILLON, A., MCKNIGHT, C. and RICHARDSON, J. 1990, Navigation in hypertext: a critical review of the concept, in D. Diaper (ed.), Human-Computer Interaction - INTERACT '90 (Elsevier, Amsterdam), 587-592. EDWARDS, D. W. and HARDMAN, L. 1989, Lost in hyperspace: cognitive mapping and navigation in a hypertext environment, in R. McAleese (ed.), Hypertext: Theory into Practice (Intellect Books, Oxford), 105-125. FISHER,D. L., YUNGKURTH, E. J. and Moss, S. M. 1990, Optimal menu hierarchy design: syntax and semantics, Human Factors, 32, 665-683. Foss, C. L. 1989a, Tools for reading and browsing hypertext, Information Processing and Management, 25, 4 0 7 4 18. Foss, C. L. 1989b, Detecting users lost: empirical studies on browsing hypertext, Technical Report (Rapports de rkcherche) No 972, INRIA, Sophia-Antipolis. GARLING, T. and GOLLEDGE, R. G. 1989, Environmental perception and cognition, in E. Zube and G. T. Moore (eds), Advances in Environment, Behavior, and Design, Volume 2 (Plenum Publishing, New York), 203-236. GOPAL,S., KLATZKY, R. L. and SMITH,T. R. 1989, Navigator: a psychologically based model of environmental learning through navigation, Journal of Environmental Psychology, 9, 309-331. GRAY,S. 1990, Using protocol analyses and drawings to study mental model construction during hypertext navigation, Interntional Journal of Human-Computer Interaction, 2, 359-377. GYGI,K. 1990, Recognizing the symptoms of hypertext ... and what to do about it, in B. Laurel (ed.), The Art of Human-Computer Interface Design (Addision-Wesley, Reading), 279-288. HAMMOND, N. and ALLINSON, L. 1989, Extending hypertext for learning: an investigation of access and guidance tools, in D. Diaper, and R. Winder (eds), People and Computers V: Proceedings of The Fifth Conference of the British Computer S o c i e ~Human-Computer interaction Specialist Group (Cambridge University Press, Cambridge), 75-90. L. 1988, Travels around a learning HAMMOND, N. and ALLINSON, support environment: rambling, orienteering, or touring, in E. Soloway, D. Frye, and S. B. Sheppard (eds), CH1'88 Conference Proceedings (ACM Press, New York), 269-273. HAMMOND, N. and ALLINSON, L. 1987, The travel metaphor as design principle and training aid for navigation around complex systems, in D. Diaper, and R. Winder (eds), People and Computers Ill: Proceedings of The Third Conference of the British Computer Socieo Human-Computer interaction Specialist Group (Cambridge University Press, Cambridge), 75-90. B. (1993), The structure of cognitive HIRTLE,S. C. and HEIDORN, maps: representations and processes, in T. Galing and R. G. Golledge (eds), Behavior and Environment: Psychological and Geographical Approaches (Elsevier, New York), chapter 7. HIRTLE, S. C. and HUDSON, J. 1991, Acquisition of spatial knowledge for routes, Journal of Environmental Psychology, 11, 335-345. HIRTLE,S. C. and JONIDES, J. 1985, Evidence of hierarchies in cognitive maps, Memory and Cognition, 13, 208-217. KERR,S. T. 1990, Wayfinding in an electronic database: the relative importance of navigational cues vs. mental models, Information Processing and Management, 26, 5 11-523. KOVACH, R. C. JR, S U R R E ~M. E , A. and AAMODT, M. G. 1988, Following informal street maps: effects of map design, Environment and Behavior, 20, 683-699.
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LEISER, D., TZELGOV, J. and HENIK, A. 1987, A comparison of map study methods: simulated travel vs. conventional study, European Bulletin of Cognitive Psychology, 7 , 317-334. I. and HANLEY, A. 1984, The placement and LEVINE, M., MARCHON, mis-placement of You ARE HERE maps, Environment and Behavior, 16, 139-157. MCALEESE, R. 1989, Navigation and browsing in hypertext, in R. McAleese (ed.), Hypertext: Theory into Practice (Intellect Books, Oxford), 7-43. 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, 21 1-227. MOESER,S. D. 1988, Cognitive mapping in a complex building, Environment and Behavior, 20, 2 1 4 9 . MOHAGEG,M.F. 1992, The influence of hypertext linking structures on the efficiency of information retrieval, Human Factors, 34, 35 1-367. NIELSEN,J. 1990, Navigation through hypertext, Communications of the ACM, 33, 297-310. NORMAN, K. L. and CHIN,J. P. 1988, The effect of tree structure on search in a hierarchical menu selection system, Behaviour & Information Technology, 7 , 5 1-65. OREN,T. 1990, Designing a new medium, in B. Laurel (ed.), The Art of Human-Computer Interface Design (Addision-Wesley, Reading), 467479. PARUNAK, H. V. 1989, Hypermedia topologies and user navigation, in Hypertext '89 Proceedings (ACM Press, New York), 43-50. PASSINI,R. 1984, Wayfinding in Architecture (Van Nostrand Reinhold, New York). STERN,E. and LEISER,D. 1988, Levels of spatial knowledge and urban travel modeling, Geographical Analysis, 20, 140-155. STEVENS, A. and COUPE,P. 1978, Distortions in judged spatial relations, Cognitive Psychology, 10, 422437. STREETER, L. A,, VITELLO, D. and WONSIEWICZ, S. 1985, How to tell people where to go: comparing navigational aids, International Journal of Man-Machine Studies, 22, pp. 549-562. U~ING K., and YANKELOVICH, N. 1989, Context and orientation in hypermedia networks, ACM Transactions on Information Systems, 7 , 58-84. A. F. 1990, Maps or anologies? A WEBB,J. M. and KRAMER, comparison of instructional aids for menu navigation, Human Factors, 32, 25 1-266. YEAP,W. K. 1988, Towards a computational theory of cognitive maps, Artificial Intelligence, 34, 297-360.
Appendix: A practitioner's summary This section gives a summary of the features ?nd tools for reducing disorientation discussed in the paper. Each feature or tool helps wayfinding, informational, or task management aspects of the browsing task, but also has a set of implementation difficulties the author or designer must overcome, and limitations. A. 1. Differentiation of regions Differentiation of regions can help wayfinding by providing an explicit cognitive hierarchical structure for users. Differentiation can be achieved by giving backgrounds of nodes distinguishable colours, textures or layouts. To assist in defining appropriate clusters, Botafogo (1993) discusses automatic clustering techniques for hypertext systems where the similarity between two nodes is defined as the number of distinct paths between the two nodes.
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A.2. Maps
A.6. History list
Maps help wayfinding by providing survey information and orientation within the hypertext database. Maps show a subset of the nodes and links in a schematic form along with annotations about the contents, and the user's current location. The difficulty includes selecting an appropriate subset of the node and links appropriate for the map's purpose, fitting the schematic and annotations within a limited computer screen, and maintaining consistent orientations across different maps.
History lists help task management and orientation by showing the local neighbourhood of each node visited. They are extensions of the back-up stack, which lists previously visited nodes (Foss 1989a). The display distinguishes between visited and not visited neighbouring nodes. Such information helps users establish the context of each node they have visited and manage digressions. Providing this tool requires an extensible hypertext engine unless it is already built-in.
A.3. Guided tours
A.7. History tree
Guided tours help wayfinding by providing route information and information upon the extent of the hypertext database. The author defines a recommended path through the hypertext, which the user can follow by selecting clearly marked links. The user temporarily gives up the flexibility of open exploration for less disorientation. Guided tours are most useful for introducing the database to novices.
History trees help task management by explicitly showing digressions. Like the history list, it is an extension of the backup list. The history tree detects cycles in the user's traversal, where a previously visited node is revisited. The cyclic paths are treated as completed digressions and displayed as a branch of the tree with the revisited node being the root (Foss 1989a). A problem with this tool is that the display can become cluttered if the user makes many errors. Implementing history trees requires an extensible hypertext engine unless it is built-in.
A.4. Landmark nodes Landmark nodes help wayfinding by providing an explicit hierarchical topology amongst regions of the database. They are prominent nodes in the database defined by the author. They are usually nodes that have many outgoing links to other nodes and contain summary information on other nodes. The landmarks appear in maps, and are accessible from other nodes. Examples are introductory nodes (e.g., 'Home' cards in Hypercard) that provide a starting point for the hypertext system. For landmarks to be useful, the hypertext database must have defined regions.
A.8. Summary box tool Summary boxes help informational tasks. The summary boxes are twin nodes in which the user takes notes while perusing the database. The backup-stack displays the notes along with the original nodes. This helps the user summarize the information after viewing many nodes. This tool requires users to have annotation privileges to the hypertext database.
A.5. Fish eye views
A.9. History matrix tool
Fish eye views help wayfinding by increasing the user's visual access. They display the links and nodes local to the user's current position in varying detail. The close nodes are shown in great detail, while the further nodes are shown in diminishing detail. The difficulty is defining the distance to a node from the current position, and defining a way to display different levels of detail (Nielsen 1990).
History matrices help the informational task of classifying nodes by providing a framework for comparing and contrasting nodes. The top row specifies the dimensions for comparison, and the left-most column specifies the different classes. As each node is assigned to a class, the pivotal dimension is marked in the matrix. Implementing this tool requires an extensible hypertext engine unless it is built-in.
