Perceiving Window Geometry: An Experimental Study

The importance of incorporating the user's response capabilities into the design of user interfaces is now well established. Many experiments that measure basic user responses have concentrated on motor capabilities, such as Fitts's law [I]. The user's perceptual abilities, as they apply to the organization and interrelating of displayed information, are another important design factor. This paper describes an attempt to measure per· ceptual capabilities, specifically the ability of users to discriminate borders in window systems. These capabilities are used in parsing visual information that is displayed in multiple windows. Two aspects of this problem are considered, window occlusion, which is important in establishing the depth ordering of windows on the display surface, and window border design, which is important in providing visual separation between windows. The minimum occlusion needed to provide easy depth judgments is measured experimentally. This part of the paper provides an interesting example of closing the loop in interface design. The measured value is related to visual acuity, a very basic aspect of human vision. Additionally, it is used successfully in an experimental interface that is designed to minimize possible inter-window visual conflicts [2J. The experiments on border design are still in progress. However, it is already possible to provide some rules of thumb that are useful in border design.