Single switch scanning
Theoretically single switch scanning is the simplest. An indicator (highlight, cursor or light) moves through all the options, one at a time, at a speed preset to suit the the user. When the required item is highlighted, the user presses the switch and that item is selected. If the user can always hit the switch when they require then single switch scanning can be a quick and easy selection method. However, single switch scanning demands considerable concentration and physical control.
Two common difficulties are that the user may tense up as the required location is approached and therefore be unable to activate the switch, or they may be so excited that they hit the location before or after the required. Slowing the scan rate may just cause the user to lose concentration or interest.
There are many variations on two switch scanning, but basically pressing one switch progresses the indicator systematically through the options available. When the required item is highlighted, the user presses the second switch to select the item. Hence one switch is the 'move' switch and the other the 'select' switch.
This method puts the user in total control and overcomes the tension around stopping the scan in the correct place.
Row-column scanning is much quicker than sequential scanning. Items to be scanned (i.e. the ‘keys’ or ‘cells’) are arranged in a grid. The rows of the grid are indicated one at a time. When the row containing the desired item is highlighted, the user presses a switch. The indicator then moves along the row, key by key. When the desired item is highlighted, the user presses again and the item is selected.
Row-column scanning can be used with either one or two switches.
(There are other scanning methods involving three or four switches but these are not often used.)