A wide range of specific issues must be addressed in order to answer these questions.
Five articles included in this special issue address a number of important aspects of the study of individual differences. A common theme that underlines all the articles in this issue is how to strike the balance between individuals' abilities and the demanding task for understanding, interpreting, and utilizing structural information conveyed through virtual environments.

Individual Differences and the Conundrums of User-Centered Design: Two Experiments
Bryce Allen

Allen (1999) focuses on the theme of how to optimize the match between users and system configurations in order to optimize their search performance. A key user interface feature in Allen's experiments is a word map. It is a multidimensional scaling model of 100 most frequently occurring words in a collection of bibliographic references. In this case, the intrinsic structure is reflected through the interrelationships in this bibliographic collection. The word map and a multi-window display are referred to collectively as design features in his article.

Allen's article is thought provoking. It demonstrates the power of theories and methodologies developed in (Egan & Gomez, 1985; Stanney & Salvendy, 1995; Vicente & Williges, 1988). More importantly, it shows how one can adapt and apply these theories and methods to the new generation of systems with greater emphasis on individual differences in virtual environments. Further work is necessary to clarify why high spatial individuals were found to perform better without the word map, as in Allen's experiments, and without the spatial-semantic virtual world, as in Chen's experiments. An ideal user interface design would not only compensate for low-spatial users, but also help high-spatial users to improve their performance.

Spatial-Semantics: How Users Derive Shape from Information Space
Andrew Dillon

The ability to perceive structure in abstract information spaces is crucial to navigation and search performance. Dillon's article distinguishes the role of spatial and semantic cues and explains why this conceptualization may lead to new insights into existing and emerging data. Dillon also introduces the concept of shape as the structural component of the working model of an information space. This is most apparent in Geographical Information Systems (GIS) but is less obvious or conceptualized in abstract information environments.  Dillon's article delineates the argument between top-down versus bottom-up approaches with a range of empirical evidence found in the literature.

Individual Differences in a Spatial-Semantic Virtual Environment
Chaomei Chen

The central theme of the special issue is how individuals differ in their performance in a virtual environment which requires an in-depth understanding of its underlying structure. Chen's article presents two studies of individual differences in searching through a spatial-semantic virtual environment. Qualitative and process-oriented studies are therefore called for to reveal the complex interaction between individuals' cognitive abilities, domain knowledge, and direct manipulation skills.  A call of an investigation of deeper knowledge structures is made based on previous studies of similar knowledge-intensive displays, e.g., (Rewey et al., 1991; Stanney & Salvendy, 1995).

Cognitive Styles and Virtual Environments
Nigel Ford

Nigel Ford's article focuses on the distinction between holists and serialists in learning, and its implications for supporting individual users through user interface design.  Of particular interest to the theme of this special issue, Ford addresses some interesting behavioral patterns of holists and serialists. While holists like to use concept maps, serialists prefer keyword indices. A concept map, or the overview of an underlying structure, is designed for global orientation regarding the overall structure of the subject matter.

Having recognized the fuzzy nature of identifying individuals' cognitive styles and learning strategies, Ford introduces a modeling approach based on Kohonen self-organizing feature maps, an artificial neural-network based classification technique. This self-organized approach has potential as a possible route for further research and development of adaptive virtual environments. Virtual environments provide a wider framework for integrating and directly manipulating global and analytic aspects of an information space.

Ford's article also draws our attention to the connection between field-dependence and cognitive styles in terms of individuals' behavioral patterns in navigation of hyperspace. Like holists, field-dependent individuals use overview maps more often than field-independent individuals. In the next article, Palmquist and Kim examine the effects of field-dependence in Web search.

Cognitive Style and On-Line Database Search Experience as Predictors of Web Search Performance
Ruth A. Palmquist and Kyung-Sun Kim

The Web has captured the imagination of millions of users all over the world. It is crucial for Web designers and indeed for all of us to understand how individuals with different cognitive style, different cognitive abilities, and different background in information systems interact with the vast amount of information presented on the Web. At the heart of the organization of information on the Web, it is the notion of association, as manifested through hyperlinks connecting information that is associated in one way or another. Once again, the ability to understand an abstract structure of information, or derive a coherent structure by articulating fragmented documents becomes a challenge to individuals' ability to find and make the best use of the information available. The significance of accommodating individual differences on Web search is clear.