Section: New Results

Transfer functions for scrolling tasks

Participants : Géry Casiez [correspondant] , Nicolas Roussel.

Scrolling is controlled through many forms of input devices, such as mouse wheels, trackpad gestures, arrow keys, and joysticks. Performance with these devices can be adjusted by introducing variable transfer functions to alter the range of expressible speed, precision, and sensitivity. However, existing transfer functions are typically "black boxes" bundled into proprietary operating systems and drivers. This presents three problems for researchers: (1) a lack of knowledge about the current state of the field; (2) a difficulty in replicating research that uses scrolling devices; and (3) a potential experimental confound when evaluating scrolling devices and techniques. These three problems are caused by gaps in researchers' knowledge about what device and movement factors are important for scrolling transfer functions, and about how existing devices and drivers use these factors (Figure 2 ). We fill these knowledge gaps with a framework of transfer function factors for scrolling, and a method for analysing proprietary transfer functions demonstrating how state of the art commercial devices accommodate some of the human control phenomena observed in prior studies [22] .

Figure 2. Gain scale factors across input velocity (counts per second) with Mac OS X, Microsoft IntelliPoint (under Windows 7), and Logitech drivers under Mac OS X. Gain is measured as the level of amplification in the system's base unit (pixels per count for Mac OS X and Logitech; lines per count for Microsoft IntelliPoint), and is plotted at varying levels of each driver's respective UI sliders for acceleration.