Appearance-based gaze tracking algorithms, which compute gaze direction from user face images, are an attractive alternative to infrared-based external devices. Their accuracy has greatly benefited by using powerful machine-learning techniques. The performance of appearance-based algorithms is normally evaluated on standard benchmarks typically involving users fixating at points on the screen. However, these metrics do not easily translate into functional usability characteristics. In this work, we evaluate a state-of-the-art algorithm, FAZE, in a number of tasks of interest to the human-computer interaction community. Specifically, we study how gaze measured by FAZE could be used for dwell-based selection and reading progression (line identification and progression along a line) - key functionalities for users facing motor and visual impairments. We compared the gaze data quality from 7 participants using FAZE against that from an infrared tracker (Tobii Pro Spark). Our analysis highlights the usability of appearance-based gaze tracking for such applications.

Eye movements while reading with screen magnification (which requires manual scrolling to center the magnified portion of the screen within the viewport) pose interpretation challenges. Standard representations in terms of alternating fixations and saccades don't apply to this case. This is because, during scrolling, eyes often track a moving text element, generating a movement akin to smooth pursuit. We propose a new representation that uses information from the mouse (which the reader uses to move the center of magnification) to undo the effect of magnification and scrolling. After this "compensation" operation, gaze tracks can again be described as alternating fixations and saccades. We present an analysis of gaze tracks obtained by applying this transformation on an existing dataset, recorded from low vision readers using two modalities of screen magnification. This analysis highlights similarities and differences in terms of dynamic properties of compensated gaze tracks vis-à-vis gaze during regular reading.