Dwell selection

Also called Dwell, Dwell time, Dwell click, Hover select

Choosing by holding your gaze or pointer still on a cell for a set time. The setting that makes eye gaze and head tracking usable, or unbearable.

What it is

Dwell is a way of clicking without a button. Keep the pointer, whether it is driven by the eyes, the head or a joystick, over a cell for the dwell time, and the cell fires. Look away or move before then, and nothing happens.

It replaces a switch for people who have nothing to press, and it is why an eye gaze user can run a whole device with their eyes alone.

Who it can help

Eye gaze, head tracking and joystick users who cannot press a switch, or who want the speed of not having to. Anyone with a mouse pointer and no reliable click, on a computer, with a dwell-click program.

It is a poor fit for people who cannot hold still: a tremor, an involuntary movement, nystagmus. It is also tiring in a way a click is not, because the person can never simply rest their eyes on the screen; everything they look at for long enough is chosen. Good systems have a rest area or a pause gesture, and using them matters as much as the dwell time itself.

How it works

Dwell time is the setting: typically 0.5 to 1.5 seconds for eye gaze, a little longer for head tracking. A visual countdown (a shrinking circle, a filling cell) shows how long is left. Too short and the person selects things they were only reading; too long and every word is a slog. Many systems let the dwell time differ by cell type: short for letters, longer for "delete all" or "speak".

Three helpers make dwell survivable. A dwell "lock" or rest cell, where the gaze can sit without selecting. A pause gesture (look off screen, or at a corner, to stop the pointer). And a "one selection per dwell" rule so a gaze that stays on the cell does not keep firing it. Some people prefer a blink or a switch for selection and use dwell only for navigation.

Getting started

Start long. A dwell of 1.5 seconds on big cells for the first fortnight teaches the person that looking is choosing, and that looking away is safe. Then bring it down in tenths until selections start landing on the wrong thing, and go back up one step.

Set up a rest area on every page and show the person where it is: a plain cell in the corner that does nothing. Watch for the tell-tale of a dwell that is too short, which is a person who keeps their eyes shut or looks at the floor between words.

Where to get help

Dwell settings are set at an AAC assessment and revisited by the specialised AAC services for their users. The ACE Centre and CALL Scotland explain dwell in their eye-gaze guides, and AbilityNet covers dwell-click software for computers.