This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE TRANSACTIONS ON HUMAN-MACHINE SYSTEMS 1 Automatic Lock of Cursor Movement: Implications for an Efficient Eye-Gaze Input Method for Drag and Menu Selection Atsuo Murata and Waldemar Karwowski, Senior Member, IEEE Abstract—This study proposed a method—automatic lock of cursor movement (ALCM)—that locks a cursor at the center of a target at the instant the cursor enters the target. The method is intended to suppress irritating subtle cursor movements that occur when an eye-gaze input system transforms involuntary eye movement (e.g., drift) into cursor coordinates. The effectiveness of the proposed ALCM was verified using pointing performance (speed and accuracy) in two types of HCI tasks. In a drag task, we compared mouse input versus eye-gaze input with use of a backspace (BS) key or voice input. The key or voice facilitates target selection once the eye gaze was aligned with a target. In a menu selection task, we also compared mouse input with eye-gaze and the use of two voice input conditions. This task required gaze alignment with a menu and menu item by use of voice input for selection. Whether the ALCM function was added to the eye-gaze input system or not was a within-subject factor. The input method and target sizes were within-subject factors. The study concluded that the ALCM improved pointing accuracy for all eye-gaze input methods and all two tasks. Index Terms—Automotive lock of cursor movement (ALCM), click, drag, HCI, involuntary eye movement, menu selection, point- ing time, prediction accuracy. I. INTRODUCTION S INCE the initial proposal of an eye-gaze input system using an eye tracking system [1]–[3], enhancements in the accu- racy and resolution of the eye tracker have enabled researchers to design HCI tasks using eye-gaze input systems that are faster and more intuitive than a mouse [4]–[7]. HCI techniques that incorporate eye movements into a human–computer dialogue have found that eye-gaze input systems ensure faster pointing [8]–[15]. Sibert and Jacob [5] and Murata [6] observed faster target acquisition performance using eye-gaze with short (less than 150 ms) dwell times than using a mouse. Agustin et al. [16] suggested that an eye-gaze input would be promising even in game interactions, provided that the eye tracker is sufficiently accurate and responsive and that a well-designed interface is available. Manuscript received July 26, 2018; revised November 13, 2018; accepted November 18, 2018. This paper was recommended by Associate Editor S. Landry. (Corresponding author: Atsuo Murata.) A. Murata is with the Department of Intelligent Mechanical Systems, Gradu- ate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan (e-mail:, murata@iims.sys.okayama-u.ac.jpand). W. Karwowski is with the Engineering and Management Systems, University of Central Florida, Orlando, FL 32816 USA (e-mail:, wkar@ucf.edu). Digital Object Identifier 10.1109/THMS.2018.2884737 Previous studies have also considered an optimal and effec- tive click method [14], [17], a menu selection method [18], and a character input method [19]. According to Bader and Bey- erer [7], these techniques diverge from natural gaze behavior to trigger events such as click, drag or menu selection, which are frequently used in a variety of HCI tasks. Although movements corresponding to a mouse’s cursor movements can be executed naturally by moving the eye line of gaze from point to point, the left click function used in mouse interfaces, for example, forces participants to carry out unnatural eye movements, such as constant-duration fixation instead of the mouse’s left click. Bader and Beyerer [7] emphasized the importance of achieving more natural eye movement in order to enhance an eye-gaze input system’s usability. A number of drawbacks to the input system need to be ad- dressed before it can be put to practical use in actual HCI tasks. In particular, drift or jittering of the cursor caused by involuntary eye movements during fixation, which occurs when transform- ing the location of the eye gaze into a cursor, can be irritating to the users of an eye-gaze input system who are attempting to click, drag or perform menu selection tasks. The studies cited above [8]–[15], [17]–[19] did not take this issue into account. This problem may undermine the potential for the widespread use of eye-gaze input systems in HCI tasks. It is impractical to rely only on eye-gaze inputs when execut- ing relatively complicated tasks such as menu selection, even though, as Bader and Beyerer [7] suggested, using only eye- gaze is more natural. One solution to this problem may be to combine eye-gaze input with voice input or key pressing. How- ever, this technique also has its disadvantages. With an eye-gaze input system, involuntary eye movement occurs when executing fixation and uttering for voice input or executing key presses. This produces a subtle fluctuation of the cursor. This makes it difficult to concentrate on gazing at a target, and the cursor unintentionally moves out of the target. Therefore, the cursor movement corresponding to the eye line of gaze (fixation point) may unintentionally deviate from the intended target. Such de- viation degrades the accuracy and speed of pointing. This would be attributable to the interference between the perceptual and visual system and the muscular or auditory system for keys or utterances [20], [21], which in turn would produce inaccurate and slow pointing. Partala et al. [20] studied the benefit of comparing the com- bination of gaze pointing and facial-muscle EMG clicking to 2168-2291 © 2018 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications standards/publications/rights/index.html for more information.