Virtual environments enable a given information space to be traversed in different ways by different individuals, using different routes and navigation tools. However, we urgently need robust user models to enable us to optimize the deployment of such facilities. Research into individual differences suggests that the notion of cognitive style may be useful in this process. Many such styles have been identified. However, it is argued that Pask's work on holist and serialist strategies and associated styles of information processing are particularly promising in terms of the development of adaptive information systems. These constructs are reviewed, and their potential utility in "real-world" situations assessed. Suggestions are made for ways in which they could be used in the development of virtual environments capable of optimizing the stylistic strengths and complementing the weaknesses of individual users. The role of neural networks in handling the essentially fuzzy nature of user models is discussed. Neural networks may be useful in dynamically mapping users' navigational behavior onto user models to enable them to generate appropriate adaptive responses. However, their learning capacity may also be particularly useful in the process of improving system performance and in the cumulative development of more robust user models.