Sunday, May 13, 2012

Direct vs. Indirection Selection?

Selection Options for Device Use:

When evaluating an assistive technology device,  the selection method is one of the most important aspects of the evaluation.  The if the appropriate type of selection method is not being utilized then the user cannot be as efficient and might become frustrated with the device use. These selection methods can be used with computer access, communication devices (AAC or SGD), and environmental control units.

Direct Selection:  Direct selection simply is just what it sounds like; you press a switch and your "selection" is made.  An everyday example of direct selection is a light switch; you "flip" the switch and the light turns on or off.  Other examples of direct selection is the left or right buttons on the mouse, dwell click software, or touch screen use/access for computer skills.  Direct selection can be a very quick form of access for the appropriate individual.  If it is not appropriate, then the individual might spend an extended amount of time to fix errors or be unable to effectively access the device at all.  Direct Selection does not need to be performed with a hand but any body part or technical device in order to make a selection.

Indirect Selection or Scanning:  Indirect selection is also known as scanning which is an indirect way of accessing a device.    

The user will access a switch which will begin intermdiate steps or scanning in order to make a choice.  There are several different types of scanning.  Either one or two switches can be used with scanning; these switches are mounted or positioned at the body part with the best strength or that will not create fatigue with use over time.  

The most common form of scanning or indirect selection is linear scanning.  With linear scanning, the user accesses their switch which begins the scan.  This scanning moves row by row.  When the scan gets to the line with the letter or choice that the user wants, they access the switch again; this begins a column scan.  Once the scan gets to the desired choice, the user accesses their switch again and the desired action happens.  This could be a pre-saved phrase for communication or a letter for typing with an on screen keyboard.

Inverse Scanning is performed with the user holds their switch down to being the scan.  The user holds their switch down until the desired choice is highlighted and lets go to have their choice made.

Group Scanning:  With group scanning, the user accesses their switch and groups are highlighted.  As the group with the desired choice is highlighted, the user accesses their switch.  It then will narrow the choices with a linear scan.

Item by Item Scanning:  The user accesses their switch to move the highlight or cursor in order to make a choice.  This method requires multiple switch access "hits" in order to get to the desired choice.

Other, individuals are concerned that scanning is slower than direct selection.  Points to consider are if the individual is unable to perform direct selection without making a considerable amount of mistakes, indirect selection will be more efficient and less fatiguing.  

Indirect selection is appropriate for an individual with limited movement.  For example, if the user has only one area of movement such as one finger, scanning would be an appropriate access method for access of the computer or a communication device.

Positioning is very important for scanning use.  The switch must be mounted to the area with the best strength so that the user will not become fatigued over time.  Switches can be mounted to any surface such as a wheelchair, tabletop, or bedrail.

Considerations with scanning is that it requires a higher cognitive load.  The user must be able to anticipate the scan and understand the cause and effect of indirect selection.

There are many features that can be modified with scanning.  These include:
  • The rate of the speed of the scan
  • The type of scan
  • The type of feedback
    • Audio
      • Click sounds
      • Reading the scan choices out loud
    • Visual
      • Highlight color
      • Magnification of the scan
  • One or two switches
When evaluating an assistive technology device, the type of selection is one of the most important parts of the evaluation and consideration of particular devices.  It is important to remember that the most appropriate access method might not be established within the first session; it can take time to figure out the best method as well as the modifications required to make this method the most appropriate.

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