Linear scanning

Also called Item scanning, Single-item scanning, Sequential scanning

The highlight visits one cell at a time, in order, and the person presses on the one they want. Slow, but there is nothing to learn.

What it is

Linear scanning moves through every choice one after another: first cell, second cell, third, until the person presses. There are no rows to pick and no change of direction. One press, one choice.

It is the pattern people start on, and for a small set of choices it is the pattern many people stay on for good.

Who it can help

Beginners of any age, because the rule is the simplest there is: wait for your thing, press. People with two to eight choices on a page. People who find the row-then-column switch of direction confusing, including some people with a learning disability or a brain injury, and people whose page is a list rather than a grid: a menu, a set of quick phrases, a choice board.

It is the wrong pattern for a large grid. On 36 cells the last word is 36 highlights away, and most words are half that. Nobody should be spelling on a linear scan.

How it works

The device highlights each cell for the scan rate, then moves on. After the last cell it either loops (usually two or three times) or stops and waits for a press to restart. The order is normally left to right, top to bottom, but on many devices it can be set so the most-used cells come first.

The maths is honest: average selection time is half the number of cells times the scan rate. Six cells at two seconds is six seconds a choice. Twenty cells is twenty. That number, not the person's ability, is what should move them to row-column scanning.

Getting started

Make a page of four things the person cares about, put it on a linear scan at a slow rate, and use it at the moment those things are wanted: snack, telly, music, out. Say the timing out loud as the highlight moves so they hear the rhythm.

Once the presses are landing reliably for a week, add cells two at a time and watch the wait. When the wait starts to feel like a punishment, and it will, it is time to move to rows. That day is a success, not a failure.

Where to get help

Any speech and language therapist working in AAC can set up a linear scan, and the ACE Centre and CALL Scotland publish free introductory guides. Communication Matters is the UK membership organisation for people who use AAC and their families.