Switch scanning

Also called Scanning, Indirect selection, Scan access

The device lights up each choice in turn and the person presses when the highlight reaches the right one. One button, any vocabulary.

What it is

Scanning is what a device does so that a switch can choose. A highlight moves across the screen, from cell to cell or row to row, and the person presses their switch when it lands on what they want. Pressing at the wrong moment picks the wrong thing; not pressing lets it move on.

That is the entire mechanism. Everything else, row-column, linear, group, auditory, auto or step, is a variation on which choices are offered, in what order, and who moves the highlight.

Who it can help

People using switch access because they cannot point accurately enough to touch. It is used from early childhood (with two or three big pictures) to adulthood (with full keyboards and word prediction), and it scales from a single-message button to a novel.

It is not a soft option. Scanning needs the person to watch, wait, anticipate and time a press, hundreds of times a day. For someone who could use eye gaze or a head pointer it is usually the slower choice, and the honest answer for a person who cannot yet sustain attention on a moving highlight is partner-assisted scanning first.

How it works

The device has a scan pattern (the order it offers things), a scan rate (how long it pauses on each), and a selection rule (press to choose, or press to advance and pause to choose). A typical starting rate is 1.5 to 2 seconds per item, with a longer first-item delay so the person can settle after a selection.

With one switch and row-column scanning on a 36-cell grid, an average cell takes about six highlights to reach: three rows and three columns. At two seconds each that is twelve seconds a word, which is why scan users lean so hard on core vocabulary, word prediction and quick phrases. Layout is speed: put the most-used cells where the scan reaches them first.

Getting started

Turn scanning on in a tablet's own accessibility settings (Switch Control on Apple, Switch Access on Android) and use a Bluetooth switch or a big external button. Start with four large cells, a slow rate of two seconds or more, and something the person wants on one cell.

Do a fortnight of errorless practice: no testing, no "show me the dog". Model it yourself out loud, "I'm waiting for drink... there", so they see what timing looks like. Keep a note of the rate you used and the hits, and only speed it up when hits are consistent. Then read scanning speed and timing, because that is where most set-ups fail.

Where to get help

Your speech and language therapist can refer for an AAC assessment, and switch users with complex needs are eligible for the specialised AAC services. The ACE Centre publishes free guides on scanning set-up, and CALL Scotland has practical materials for schools. Communication Matters runs an annual conference where switch users teach the rest of us.