Kent L. Norman

Department of Psychology and the Human/Computer Interaction Laboratory
University of Maryland
College Park, MD 20742-4411


Email:, phone: (301) 405-5924, fax: (301) 314-9566



Usability and User-Centered Design


Cognitive Abilities, Menu Selection, Metaphors, Spatial Visualization Ability, User Interfaces, Visualization Techniques


The positive impact of computer-based technology varies in part as a function of interface design and the individual abilities of users. A model is proposed for how individual differences are expected to affect performance when technology is introduced. The primary cognitive factor driving differences in performance using computer-based technology is spatial visualization ability (SVA). Four techniques for mitigating the negative impact of low spatial visualization are discussed. The use of spatial metaphors and graphical user interfaces have been promising, but interface apparency, revealing hidden relationships and showing contingencies, and interface manipulatability, allowing users to directly manipulate objects and see intermediate steps, are most likely to benefit individuals with low spatial visualization ability. Past research on the use of spatial metaphors and graphical user interfaces suggest positive benefits across all subject populations, but they do not mitigate the individual differences. The current project explores the interface apparency and interface manipulatability. Two studies are proposed in which the hidden contingencies of a hierarchical control structure are revealed through a dynamic graphical screen display. Several methods of showing the contingencies will be compared. Two additional studies are proposed which allow users to manipulate objects through intermediate steps rather than having to infer or visualize those steps. In all four experiments spatial visualization ability will be assessed in relationship to the experimental conditions. The results of these experiments and the design concepts that are subsequently suggested by them will help to provide interface designers with graphical user interface (GUI) techniques that will provide gateways through the SVA barrier. Interface apparency and manipulability will help to off-load spatial processing from the user to the system and greatly enhance performance.


Butler, S. A. (1990). The effect of method of instruction and spatial visualization ability on the subsequent navigation of a hierarchical data base. (CAR-TR-488 and CS-TR-2398) Department of Psychology and the Human/ Computer Interaction Laboratory, University of Maryland, College Park, MD.

Norman, K. L. (1994). Navigating the educational space with HyperCourseware. Hypermedia., 6, 35-60.

Norman, K. L. (1994). Spatial visualization: A gateway to computer-based technology. Journal of Special Education Technology, 12, 195-205.

Norman, K. L., and Butler, S. (1989b). Search by uncertainty: Menu selection by target probability. (CAR-TR-432 and CS-TR-2230). University of Maryland, Center for Automation Research and the Department of Computer Science, College Park, MD.

Norman, K. L., and Singh, R. (1989). Expected performance at the human/computer interface as a function of user proficiency and system power. Journal of Behavioral Decision Making, 2, 179-195.


The design and evaluation of human/computer interfaces has become an extremely important area in interacive systems. As the use of computers and in particular, graphical user interfaces have increased, the design of menus and screen layout has become critical to the success of an application. Moreover, human/computer interfaces are becoming more and more complex as they are being designed for larger and more extensive systems.

The usability of such human/computer interfaces depends on how the cognitive abilities of the user are either facilitated or stressed by the interface. Interface design must be centered around our understanding of how the user perceives the interface, comprehends its functions, and can solve problems based on an understanding of how it works. An important cognitive ability that interacts with interface design is the user's spatial visualization ability, the ability to manipulate spatial objects in memory and to keep track of sequences of events.

The design of new human/computer interfaces should not only use graphics to display icons, images, and menus, but also maps, sequences, and animation to aid the user in knowing where he or she is and knowing how to get to the next desired step. Such systems will help to off-load the cognitively taxing effort of trying to keep track of the system's state in working memory and trying to anticipate the next step by mental manipulations of spatial visualization.


Carroll, J. M., and Mack, R. L. (1985). Metaphor, computing systems, and active learning. International Journal of Man-Machine Studies, 22, 39-57.

Mayer, R. E. (1989a). Teaching for thinking: Research on the teachability of thinking skills. In. I. S. Cohen (Ed.), The G. Stanley Hall Lecture Series (Vol. 9). Washington, DC: American Psychological Association.

Norman, K. L. (1991a). Models of the mind and machine: Information flow and control between humans and computers. In M. C. Yovits (Ed.) Advances in Computers, Vol. 32, pp. 201-254, New York: Academic Press

Norman, K. L. (1991b). The psychology of menu selection: Designing cognitive control at the human/computer interface. Norwood, NJ: Ablex.

Vicente, K. J., Hayes, B. C., and Williges, R. C. (1987). Assaying and isolating individual differences in searching a hierarchical file system. Human Factors, 29, 349-359.

Yates, L. G. (1986) Effect of visualization training on spatial ability test scores. Journal of mental imagery, 10, 81-92.


Adaptive Human Interfaces, Intelligent Interactive Systems for Persons with Diabilities, Virtual Environments


This project is related to other efforts of user interface design in which graphic techniques are used. The question is to what extent emerging designs solve cognitive problems for the user or create new ones. It is related to other projects that deal with individual differences and attempt to compensate for disabilities. Finally, the aspects of manipulation and spatial visualization may relate to projects in virtual environments in which the spatial manipulations can be seen rather than imagined.