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In direct selection, the user directly selects the desired item from the selection set using the control interface. The augmentative communication user makes his or her selection by using hand, finger, voice, eye, head, or some other body movement. All of the elements in the selection set are available for selection at any time. Direct selection techniques are the most straightforward and cognitively simple approaches to use in a human/technology interface. The downfall of direct selection is that it requires fine motor control. For this reason, indirect selection methods have been developed.
Indirect selection is different from direct selection in that intermediate steps are required to select an item from the selection set. The most common method of indirect selection is scanning. Items in the selection set are presented to the user one at a time for the user to select from by activating the control interface at the proper time. There are a number of scanning methods available for the user to operate. Methods such as linear scanning, circular scanning, multi-dimensional scanning, directed scanning, and encoding will be discussed.
Linear and Circular Scanning
In linear scanning, the items in the selection set are presented to the augmentative communication user one at a time until the user selects the desired item. The only difference between linear and circular scanning is that items are presented in a circle instead of a horizontal or vertical line. Linear and circular scanning are the slowest of all possible scanning methods; therefore, they are primarily used for training, assessment, or for individuals with a limited vocabulary.
Multi-dimensional scanning, or group-item techniques were developed to increase the rate of scanning. In group-item scanning, there are several items in one group and several groups to select from. The groups are presented one at a time and the user selects the group in which the desired item is in. The items within the selected group are then scanned one at a time. To make the final selection, the user activates the control interface to select the desired item. The most common method of group-item scanning is row-column scanning. In row-column scanning, or two-dimensional scanning, there are several rows of items located in columns. The rows are sequentially lit up until the user activates the desired row. Once the row is selected, the columns in the selected row are presented to the user one by one until he or she selects the correct item.
In directed scannning, the augmentative communication user activates the control interface to select the direction of the scan, whether it is vertical or horizontal. As long as the switch or joystick is activated, the items are then scanned in the preset pattern. The user then selects the desired item by releasing the switch or joystick.
Encoding is a technique in which the user gives multiple signals in order to specify the correct item from the users selection vocabulary. Examples include Morse code and Darci code. Encoding is basically used to decrease selection time or to increase the number of items in the selection set. Encoding methods are generally implemented in three ways: memory-based, chart-based, and display-based. Memory-based encoding requires the user to memorize the codes for the communication device, which may become very difficult. Chart-based encoding is essentially the same as memory-based, but with the exception that the codes are displayed on a chart. This eliminates the need for memorization. In display-based encoding, the user responds to a display rather than sending a code that is memorized or selected from a chart. The user simply sends signals that control the movement of the cursor light on the display to select the item desired