Auto scan or step scan

Also called Automatic scanning, Step scanning, Inverse scanning, Timed scanning

Does the highlight move on a timer, or only when the person presses? The choice decides who is in charge of the pace.

What it is

In auto scan the device moves the highlight by itself, on a timer, and the person presses once to choose. In step scan the highlight moves only when the person presses, and a second action (a second switch, or a pause) makes the choice. Same screen, opposite division of labour.

There is a third, less common option, inverse scanning: the person holds the switch down to move the highlight and releases to choose.

Who it can help

Auto scan suits people with one reliable movement who find repeated pressing tiring or painful, and people who can watch and time a press. It is the usual choice in motor neurone disease and for anyone with fatigue.

Step scan suits people who cannot time a press to a moving target but can press deliberately as often as they like: some children learning to scan, some people with cerebral palsy whose movement is effortful to start but easy to repeat, and people with an attention pattern that cannot sustain watching a timer. It costs a press per step, so it is tiring on a big grid. Inverse scanning suits a person who can hold but not tap.

How it works

Auto scan has a scan rate (the pause on each item, typically 1 to 3 seconds), a first-item delay, and a number of loops before it stops. The person's whole job is timing.

Step scan has no rate; it has a switch to advance and a way to select. With one switch, the selection is a pause: stop pressing for a set time (say 2 seconds) and the current item fires. With two switches it becomes two-switch scanning, the most controllable pattern of all. Inverse scanning has a rate like auto scan, but the highlight only moves while the switch is held.

Getting started

If auto scan is producing a lot of misses and the person seems to press "late" every time, try step scan for a week before you slow the rate any further. If step scan is producing accurate choices but the person is exhausted by lunchtime, try auto scan with a generous rate.

Both are in a tablet's own switch settings, and both can be changed in a minute, so trial them on real communication: the same four cells, the same wanted things, one mode for a few days, then the other. Count the hits and watch the face.

Where to get help

A speech and language therapist or occupational therapist with AAC experience will trial both during an AAC assessment. The ACE Centre and CALL Scotland both explain the scan modes in their free materials.