Dwell selection needs an adjustable threshold
Aliases: dwell click · Midas touch · gaze threshold
What it is
Eye-gaze often treats “looked long enough” as a click. Too short, a glance fires — Midas touch. Too long, aiming becomes a wait, and fatigue and drift collapse the selection. Dwell selection has to let the user set the threshold. There is no universal “right number of seconds.”
Why it happens
Gaze, on an eye-tracker, does two jobs at once: looking, and choosing. Reading, searching, checking whether this is the target, all require the eyes to rest somewhere; if the device treats every rest as a choose, reading and selecting collide. The threshold is the cut between those gazes: shorter counts as looking, longer as selecting.
The cut moves with the person and the hour. Stability, calibration, lighting, fatigue, medication, spasm all shift the distribution. The same person differs morning to afternoon. Hard-coding one dwell time assumes every eye shares one boundary, which is the opposite of what this device is for. Adjustability is not an extra setting; it is the condition under which dwell can work as a selector.
Studying it
Sweep dwell times in an eye-gaze system (0.4, 0.8, 1.2 s). Have people read a passage, then hit a target button. Record false fires (meant to look, selected) and misses (meant to select, did not wait long enough).
Independent variables: dwell threshold, target size, whether the task is browsing or selecting. Dependent variables: false-select rate, miss rate, reported fatigue, the threshold the user finally keeps.
Letting the user tune until the task completes is closer to real use than an experimenter-chosen “standard dwell.” Check whether the app honors the system accessibility dwell setting.
Where it stops holding
Eye-gaze that confirms with a blink, sip-and-puff, or hardware key is not using dwell as the selector; the claim does not hold — the problem becomes anti-misfire on that confirm channel. Switch scanning does not dwell. A short, well-calibrated demo can make one fixed value look “just right”; another person, another light, another hour overturns it. An app that implements its own dwell and ignores the system value lets the user tune a control that does nothing.
Applying it
- Follow the system accessibility dwell threshold; do not hard-code milliseconds in the app.
- If the app must expose dwell, give a range and apply the current value immediately, without a restart.
- How to check: set system dwell very short and watch for false selects; set it very long and watch whether selection can still finish. If the app does not follow, the threshold is not adjustable. Then try two people with different gaze stability and confirm that no single fixed value works for both.