An Explanation of Fits’ Law-like Performance in Gaze-Based Selection Tasks Using a Psychophysics Approach

Abstract

Eye gaze as an input method has been studied since the 1990s, to varied results: some studies found gaze to be more efcient than traditional input methods like a mouse, others far behind. Comparisons are often backed up by Fitts’ Law without explicitly acknowledging the ballistic nature of saccadic eye movements. Using a vision science-inspired model, we here show that a Fitts’-like distribution of movement times can arise due to the execution of secondary saccades, especially when targets are small. Study participants selected circular targets using gaze. Seven diferent target sizes and two saccade distances were used. We then determined performance across target sizes for diferent sampling windows (“dwell times”) and predicted an optimal dwell time range. Best performance was achieved for large targets reachable by a single saccade. Our fndings highlight that Fitts’ Law, while a suitable approximation in some cases, is an incomplete description of gaze interaction dynamics.