Group scanning

Also called Block scanning, Group-item scanning, Quadrant scanning

The screen is split into blocks; pick a block, then a row within it, then a cell. A third pass that pays for itself on a big vocabulary.

What it is

Group scanning adds a step before rows. The device first highlights large blocks of the screen (halves, quarters, or blocks of a few rows), the person picks a block, and then scanning continues within it, usually by row and column. Three presses reach any cell.

It exists because on a big grid, even row-column scanning gets slow. Cutting the screen into quarters first means each later pass has a quarter of the distance to travel.

Who it can help

Switch users on large page sets: 48, 60 or 80 cells, or a full keyboard with prediction. People who are literate and building sentences word by word, or spelling. Adults with motor neurone disease and children with cerebral palsy who have outgrown a small grid.

It asks for more from the person: they must know roughly where on the screen their word lives, and hold three levels of choice in mind. For a person who is still learning the layout, or who has trouble with the change of direction in row-column, it is a step too far. And on a grid under about 40 cells the extra press costs more than it saves.

How it works

On an 8 by 10 grid, row-column scanning averages about nine highlights per selection. Split the grid into four blocks of 4 by 5 and it drops to about two block highlights, plus two rows, plus two or three cells: seven. That saving compounds over a sentence.

Devices differ in how they group: fixed quarters, top and bottom halves, or blocks of two or three rows. Some also group within a row (halves of the row) for very wide keyboards. The best layout puts words that are used together in the same block, so a person rarely has to leave it mid-sentence.

Getting started

Only try this once row-column scanning is fluent. Then, in the device's scan settings, turn on block or group scanning and start with two blocks (halves), not four. Give it a week. Move to quarters only if the person is choosing the right half without hesitation.

Redesign the page for blocks. If the person's most-used words are spread across all four quarters, the pattern will feel slower than it is. Gather core words into the block the scan reaches first.

Where to get help

This is specialist set-up and it belongs in an AAC assessment; in England the specialised AAC services handle exactly this kind of user. The ACE Centre and CALL Scotland publish guides on scan patterns, and Smartbox and Tobii Dynavox document the block-scan options in their own software.