The Human Factors of Hypertext
This item is not the definitive copy. Please use the following citation when referencing this material: Dillon, A. (1990) The human factors of hypertext. International Forum on Information and Documentation, 15(4), 32-38.
The present paper reviews the human factors issues pertinent to the design and use of hypertext documents. It is argued that many of the claims for the new medium are based largely on subjective impressions of its advocates rather than empirical demonstrations of its advantages. Hypertext applications are presented here as a structured subset of an information world that the user can access though an interface. Research relevant to all aspects of reading from screens is reviewed and conclusions for the development of more usable electronic documents are presented.
Electronic text is now more common than ever before and reading from computer screens is an activity that many workers in a variety of situations regularly perform. The pace of change has been slower than expected however. In 1982, Jonassen  avered that:
"in a decade or so, the book as we know it will be as obsolete as is movable type today." p.379
Eight years on, paper documentation shows no signs of obsolescence but the recent emergence of hypertext has provided the speculators with further chances to dismiss paper as a medium of presentation with a future. Now the standard argument is that paper constrains the reader and writer into linear modes of creation and access. Hypertext on the other hand, is said to liberate and support information structures more naturally reflecting the information processing characteristics of the human mind (see e.g. )
Despite the rhetoric, there is little supporting evidence for the supposed benefits of hypertext and much empirical work has shown that for certain tasks and texts paper remains as good as if not better than hypertext . A major problem with the new medium is that people prefer reading paper to electronic text and the human factors issues associated with interface design are rarely applied effectively to hypertext systems. The present paper reviews some of the relevant work on system design and presents some guide-lines for developing hypertext systems to support effective use.
2. The Interface as a physical and representational concept
Human-computer interaction can be conceptualised as a communicative dialogue whose purpose is to complete a task. The interface is therefore the communication channel afforded by the computer, allowing transfer of modality independent information between machine and user. As a communication channel the interface is both physical (keyboard, mouse, display) and representational (iconic, metaphoric) i.e., it offers the means of control as well as providing a model of its operations, whether this model is made explicit (e.g. the Macintosh desktop) or not (e.g. the MS-DOS operating system). The physical aspects are becoming reasonably standard across systems, the representational ones can vary even at the application level.
3. Users, Tasks and Information Spaces
To understand the development of user interfaces effectively one needs to conceptualise the design in terms of three factors:, the users, their tasks and the information space in which the task is being performed. The first two terms are self-explanatory but information space is a vaguer term by which is meant the document, database, texts, etc. that the user works on. This information space varies tremendously and can be shown to interact with both users and tasks i.e., people utilise information differently depending on its type, their experience and what they want from it .
There is a glaring lack of applicable knowledge on how people satisfy their information needs. By applicable, I mean knowledge that can be used reliably by designers to constrain the number of design choices they must make and guide their attempts at interface design. This may seem surprising given the long history of a variety of disciplines in studying such phenomena such as information science (how people access stored documents), psychology (how people process textual information) and typography (how characteristics of text structure and lay-out affect reading) to name some, but is a real problem for designers not skilled in these disciplines and wanting unambiguous answers to questions.
The goal of much human factors work is to provide relevant knowledge in a form suitable for consumption by designers. Ultimately, I propound the view, outlined in the present paper, that the hypertext system in total is the interface between a user and an information space. The advantage of this approach [which I refer to as "the system is the interface " or "the interface is everything" approach] is that it emphasises focusing very early on in the design on the most important aspects of the application: the user, the information and the task.
This view is far wider than that adopted by many computer scientists, and indeed by some other human factors professionals who view the interface as a conceptually narrow communication channel or as the physical (but non-representational) aspects outlined above (for further discussion on this issue see  ).
Thus the user interacting with a system to gain some information must be viewed as task-driven. Their behaviour may appear chaotic and error-prone, or smooth and efficient, depending on numerous factors such as skill, experience and so forth, but it is nonetheless purposive. The information they seek may vary from the general (e.g.,"Is this text interesting" ) to the specific (e.g., "What does this error message mean?") but the interface is the medium through which they obtain access an information world that provides the relevant data. In other words there exists a need (N), an information world (IW) that hopefully contains information which satisfies the need, and a means of entering and selecting from this world that can be called the user interface (UI). Thus, UI places some boundary on IW (the universe of information is not yet contained in a single system) and offers the means of interrogating IW to satisfy N. The careful design of UI is of paramount importance for the effective use of IW .
The role of design is to select from and structure the IW effectively and provide a suitable UI to support interaction. A designer can do little more than bring a user and information together and make sure that the UI is usable, after that the skill and desires of the user take over. Unfortunately to date, many hypertext systems pay no attention to usability or proper structuring of IW. An implicit assumption is present in much of the work on hypertext that it is so obviously better than paper or previous attempts at electronic text not to need careful design.
A schematic representation of the human factors issues involved in using hypertext is proposed here (see figure 1). This is a three-tier framework based on the size of information space.
Fig.1. Issues involved in hypertext design as a function of document size
Though generic, this representation gives an indication of what human factors issues need addressing when designing hypertext. According to this classification, the important issues change as a function of document or information space size. At the lowest level, for very short pieces of text such as notes or memos, the major research issues concern visual ergonomics. As the documents become larger and the reader must use physical manipulations to access parts of it, facilities supporting searching or paging become more pertinent to usability. Finally, for very large documents, research on such issues as navigation through electronic space are now gaining much attention.
Positively correlated with the size variable is the breadth of issue involved. At the lowest level, visual ergonomics address narrower and more specifiable constructs such as image quality than work on information structure which invokes such abstract psychological concepts as schemata and mental models. Negatively correlated with size is the specificity of prediction we can make about reading from screens on the basis of current knowledge. Thus for short texts requiring no manipulation, it is possible on the basis of published work to predict likely outcomes for electronically presented text though for large hypertexts, research provides much less guidance.
The following section describes the relevant literature in more detail. In accordance with the classification in Fig. 1 this is dealt with at each of the three levels.
4. Empirical Findings
4.1 Basic ergonomic issues
In terms of specificity there is an established literature on the visual ergonomic issues of screen technology. Surprisingly, most work on hypertext overlooks this even though, for the conceivable future, users of such systems are likely to be reading from VDUs. Much of the work on this area in the last 15 years has addressed the issue of likely differences between reading from screens as opposed to paper (for a detailed review of this work see ). Empirical investigations of the area have suggested five possible outcome differences between the media:
It seems certain that reading speeds are reduced by 20-30% on typical VDUs and accuracy may be lessened for cognitively demanding tasks. Fears of increased visual fatigue and reduced levels of comprehension as a result of reading from VDUs remain unsettled, the latter issue in particular is unlikely to yield a simple answer as comprehension is a difficult variable to measure reliably. With respect to reader preference, top quality hardcopy seems to be preferred to screen displays, which is not altogether surprising.
No one variable seems responsible for the observed differences. Gould et al  have shown that the speed and accuracy deficits could be overcome on short texts by using a high quality screen that combined positive presentation, high screen resolution to avoid flicker and anti-aliased characters. This equates more typically with the type of screen on which many hypertext applications are presented though as an issue of empirical comparison between paper and hypertext it tends to have been overlooked. For different task with lengthier texts it is difficult to accept the image quality hypothesis as sufficient.
Interestingly, any empirical attempt explain the differences in terms of such factors as the orientation of the display (paper is usually read in a horizontal position while screens are vertical), aspect ratio (paper tends to be portrait rather than landscape, the reverse holds for screens), visual viewing angle, or user characteristics (such as age, sex and experience in reading from screens) which are popularly supposed to affect screen reading, has failed to provide reliable effects .
As hypermedia, not just hypertext, become more commonplace, ergonomic issues pertaining sound quality and the interaction of sound and visual images are likely to emerge.
4.2 Manipulation Facilities
As information spaces increase in size other issues than those covered above come into play and need to be considered. With paper, users have acquired a range of physical and cognitive skills for manipulating text and the relatively standard format of texts allows for easy transfer of these skills across the spectrum of paper documents. It is less clear how hypertext should be designed to facilitate equally easy use. Several relevant human factors issues which have been investigated are:
The advent of hypertext applications with selectable buttons and linked nodes of information has brought a new sophistication to text manipulation facilities and it seems plausible that the ability to "point-and-go" has distinct advantages over paging or specifying goto jumps on a menu. However not all information is so easily manipulated and where information nodes are large or depend heavily on context, other factors such as display size, scrolling etc. come back into play. Specific work on these issues would be useful.
4.3 Structuring the Information Space
While the preceding sections are often not considered directly relevant to hypertext applications by many researchers and developers, the issues relating to re-structuring of information together with the nature and amount of linking involved with hypertext have become central questions. It is almost taken on faith by many that traditional documents consist of a linear format which demands serial reading while hypertext allows non-linear formats which offer more flexible and "natural" methods of use. Hypertext is often proposed as the liberator, freeing the user from the confines of traditional linear documentation. Such a distinction is dubious. It assumes for example that paper text can only be read in one way and that readers will prefer to have texts re-structured into linked nodes. There is little evidence to support either assumption and indeed fresh evidence on these matters suggests the opposite  .
Navigation through hypertext is the most commonly cited difficulty  and major research effort is now expended on developing browsing facilities and maps for users. Wright and Lickorish  provide evidence that the suitability of the navigation facilities varies with the task and information space again highlighting the need to consider the relevant attributes of users, tasks and information in designing usable hypertext interfaces.
It is clear that readers form mental representations of a paper document's structure in terms of spatial location  and overall organisation . Such representations or models are derived from years of exposure to the information type (e.g. academic journal articles) or can be formed in the case of spatial recall from a quick scan of the material. Such models are useful in terms of predicting where information will be found or even what type of information is available. Consideration of existing models is vital in the design of new versions so as to avoid designing against the intended users' views of how the information should be organised. These issues are discussed further in 
To date most work on hypertext has been discursive rather than experimental but of the studies that have been carried out it is obvious that hypertext will not be a universal panacea to problems of information presentation. It comes as a surprise to many that most comparative experimental work in the area has shown that users perform better or at least as well with paper [19,21]. This is not always so (Egan et al  provide evidence for improved performance by students using the SuperBook over a paper text on statistics though there evidence is open to interpretation) but is typical. However such findings must be interpreted in terms of the users, tasks, and information spaces being investigated as their will be many instantiations of the hypertext concept available in many different task domains to many different users. To assume that all hypertext are better (or worse) than paper on the basis of several limited empirical examinations is clearly short-sighted.
This is a large and ever-expanding literature. The present paper is an attempt at providing a perspective on it that supports its access and use by the uninitiated as well as an attempt at providing some form of guidance to those concerned with electronic documentation for whatever purpose. To aid documentation workers interested or concerned with hypertext and all electronic text forms I will summarise some steps that should be taken when seeking to design (or influence the design of) such text for usability:
The first step is important and will provide information of direct relevance to the next three steps. The last step is probably the most important although is often seen as a luxury that cannot be afforded. Failure to test the design is bound to lead to problems as no theoretical models or formal guidelines exist that can even approximate the quality of information obtained from observing real users interacting with a system. These steps will not guarantee success but they offer better prospects of achieving it than any others.
For those not concerned with design but interested as potential users of such systems, my advice is be critical. Do not accept a designer's view of how you should interact with documentation as better than your own. Hypertext offers exciting opportunities but it also provides designers with the scope for creating unusable documents in a way that paper could never be. There are many unknowns at present and only through refinement and informed analysis will genuine progress be made.
References Beeman, W., Anderson, K., Bader, G., Larkin, J., McClard, A., McQuillan, M. and Shields, M. (1987) Hypertext and Pluralism: From lineal to non-lineal thinking. In: Proceedings of Hypertext'87. University of North Carolina. 67-88.
 Cakir, A., Hart, D. J. & Stewart, T. F. M. (1980) Visual Display Terminals. Chichester: John Wiley and Sons.
 Card, S., English, W. and Burr, B (1978) Evaluation of mouse, rate-controlled isometric joystick, step keys and text keys for text selection on a CRT. Ergonomics, 21, 601-613.
 Creed, A., Dennis, I. & Newstead, S. (1987) Proof-reading on VDUs. Behaviour and Information Technology, 6(1), 3-13.
 Dillon, A. (1991 in press) Readers' models of text structures: the case of academic articles International Journal of Man-Machine Studies.
 Dillon, A. (1990) The Interface to Hypertext Systems. In D.Jonasson and H. Mandl (eds.) Designing Hypermedia for Learning. Heidelberg: Springer-Verlag.
 Dillon, A., McKnight, C. and Richardson, J. (1988) Reading from paper versus reading from screens. The Computer Journal 31(5), 457-464.
 Dillon, A., Richardson, J. and McKnight, C. (1989) The human factors of journal usage and the design of electronic text. Interacting with Computers, 1(2) 183-189.
 Dillon, A., Richardson, J. and McKnight,C. (1990) The effect of display size and text splitting on reading lengthy text from screen. Behaviour and Information Technology 9(3) 225-237.
 Dillon, A., Richardson, J. and McKnight,C. (1990) Navigation in hypertext: a critical review of the concept. In D. Diaper (ed.) INTERACT '90. Amsterdam: North Holland.
 Duchnicky, R.L. and Kolers P.A. (1983) Readability of text scrolled on a visual display terminal as a function of window size. Human Factors, 25(6), 683-692.
 Egan, D., Remde, J., Landauer, T., Lochbaum,C. and Gomez, L. (1989) Behavioural evaluation and analysis of a hypertext browser. In Proceedings of CHI'89. ACM, New York.
 Elkerton, J. and Williges, R. (1984) Information retrieval strategies in a file search environment. Human Factors, 26(2), 171-184.
 Ewing, J., Mehrabanzad, S; Sheck, S; Ostroff, D. and Shneiderman, B. (1986) An experimental comparison of a mouse and arrow-jump keys for an interactive encyclopedia.International Journal of Man Machine Studies, 24, 29-45.
 Gould, J. D. (1986) Reading is slower from CRT displays than from paper: some experiments that fail to explain why. IBM Report RC 11709 (#52588), IBM Research Centre, Yorktown Heights, New York 10598.
 Gould, J.D., Alfaro, L., Finn, R., Haupt, B. and Minuto, A. (1987) Reading from CRT displays can be as fast as reading from paper. Human Factors 26 (5), 497-517.
 Jonassen, D. (1982) The Technology of Text. Vol I. Principles for Structuring, Designing, and Displaying Text. Englewood Cliffs, NJ: Educational Technology Publications.
 Kak, A. V. (1981) Relationships between readability of printed and CRT-displayed text. Proceedings of Human Factors Society - 25th Annual Meeting, 137 - 140.
 McKnight, C., Dillon, A., and Richardson,J. (1989) A comparison of linear and hypertext formats in information retrieval. In R. McAleese and C. Green (eds.) Hypertext: state of the art. Oxford: Intellect
 Milner,N. (1988) A review of human performance and preference with different input devices to computer systems, in: D.Jones and R.Winder (eds.) People and Computers IV, Cambridge: Cambridge University Press.
 Monk,A., Walsh, P. and Dix,A. (1988) A comparison of hypertext, scrolling, and folding as mechanisms for program browsing, in: D.Jones and R.Winder (eds.) People and Computers IV, Cambridge: Cambridge University Press.
 Richardson,J., Dillon, A., and McKnight, C. (1989) The effect of window size on reading and manipulating electronic text. in E. Megaw (ed.) Contemporary Ergonomics 1989. London:Taylor and Francis.
 Rothkopf, E. Z. (1971) Incidental memory for location of information in text. Journal of Verbal Learning and Verbal Behaviour, 10, 608-613.
 Schwartz, E., Beldie, I. and Pastoor, S. (1983) A comparison of paging and scrolling for changing screen contents by inexperienced users. Human Factors, 25, 279-282.
 Wilkinson , R.T. and Robinshaw, H.M. (1987) Proof-reading: VDU and paper text compared for speed, accuracy and fatigue. Behaviour and Information Technology, 6(2), 125-133.
 Wright, P. and Lickorish, A. (1983) Proof-reading texts on screen and paper. Behaviour and Information Technology, 2, (3), 227-235.
 Wright, P. and Lickorish, A. (1990) An empirical comparison of two navigation systems for two hypertexts. In R. McAleese and C. Green (eds.) Hypertext: state of the art. Oxford: Intellect
 Edwards, D. and Hardman. L. (1909) 'Lost in Hyperspace': cognitive mapping and navigation in a hypertext environment. In: R. McAleese (ed) Hypertext:theory into practice. London: Intellect.
Many of the arguments expressed in this paper are dealt with in much more detail in the book Hypertext in Context, by C. McKnight, A. Dillon and J. Richardson. (1991) published by Cambridge University Press.