Row-column scanning

Also called Row/column scanning, Row-column scan

The device scans down the rows, the person picks one, then it scans across that row. The standard pattern for any grid bigger than a handful.

What it is

Row-column scanning offers the grid in two passes. First the highlight moves down the screen one whole row at a time. The person presses when the row holding their word is lit. Then the highlight moves across that row, cell by cell, and a second press picks the word.

It is the default on almost every communication aid because it is the best trade-off between speed and simplicity for a rectangular grid.

Who it can help

Anyone scanning a grid of more than about six cells. Below that, linear scanning is simpler and nearly as fast. Above about 40 or 50, group scanning adds a third pass and saves time again.

It asks for two things: the person must be able to hold in mind which row their word lives in while the rows go by, and they must cope with the highlight changing direction after the first press. Some people with a visual impairment or a field loss cannot follow a moving row and do better with auditory scanning.

How it works

On a 6 by 6 grid the worst case is six row steps plus six column steps, twelve highlights; the average is around six or seven. Linear scanning of the same grid averages eighteen. That is the whole argument for it.

Two settings shape it. The number of times the scan cycles through the rows before giving up (usually two or three) and whether a wrong row can be escaped, either by waiting for the row scan to finish or by a long press. Some devices scan columns first, which suits a vocabulary organised in columns by word class (semantic-syntactic grids). And the top row is reached first, so the most-used words belong there.

Getting started

If the person is already scanning linearly on a small grid and is accurate, this week is the time to try rows. Keep the grid the same and switch the pattern; nothing else. Expect a dip for a few days while the two-press rhythm settles.

Lay the page out for the scan, not for looks. Put "yes", "no", "help" and "more" in the top row. Leave the bottom-right cell for something that is rarely needed. If the person keeps missing the row, slow the row scan only; many devices let you set row and cell rates separately.

Where to get help

Your AAC service will set the pattern during an AAC assessment. The ACE Centre and CALL Scotland explain scan patterns in their free resources, and Communication Matters is the place to ask other switch users what they use.