Rapid Visual Flow: How Fast Is Too Fast?

It is becoming increasingly common for user interfaces to use zooming visual effects that automatically adapt to user actions. The MacOs X ‘dock’ icon panel, for instance, uses a fisheye distortion to assist users in targeting items. Another example is ‘speed-dependent automatic zooming’, which has been shown to improve scrolling by automatically varying zoom level with scroll speed—when scrolling fast the document is zoomed out, but when scrolling slowly the document is fully zoomed in. When implementing automatic zooming interfaces, designers must calibrate the behaviour of their zooming systems so that the visual effects allow rapid navigation without stressing the human visual system. At present, these calibrations are derived from trial and error. This paper describes an attempt to determine metrics of visual flow to answer the question “how fast is too fast”? Our main focus is on automatic zooming in document scrolling tasks. We performed an experiment to measure participants’ preferred and maximum-tolerable scrolling speeds at two different magnifications. We found that magnification affected the length of time that data needed to remain on screen. We also used the data to provide estimations regarding the appropriate calibration of threshold values in speeddependent automatic zooming systems.