Choosing the right switch is a feature match between the student's skills and features needed in the switch.
The motor pattern identified on the sensory assessment guides the switch selection, just like the sensory preferences of the student guide the switch consequences
Mechanical switch:requires 5 actions and graded force (locate, touch, press, hold, release
Electronic switch: requires 2 actions and no force (locate, release), require a power source
There are exceptions of course but typically electronic switches are the way to go for students who have trouble exerting force or exertion causes extraneous uncontrolled movement.
Big Picture: # of switches/Types of scanning
We use Linda Burkhart’s "Stepping Stones To Success" article to guide us, once we have all the components of the equation in place
How do we determine number of switches?
If the student understands the use of switches and has two motor patterns, move on to two switches as soon as you can.
If you’re not sure, move on and try it, give them many opportunities for the movement to become consistent and predictable.
Giving a student two switches gives them much more control and increased engagement.
If the student has two body parts they can access switches with it allows for a lot more growth and will help determine which type of scanning will be best eventually, after moving through the stepping stones.
Types of Scanning
Automatic Scanning: array is highlighted at a predetermined auditory or visual scan, student activates switch to select
Inverse Scanning (array is highlighted at a predetermined auditory or visual scan, st activates switch to start scan & must hold throughout, release the switch to select) only available on certain dynamic display communication devices.
2 switch step scan (one switch steps through choices each time it is pushed and the 2nd switch is used to select the choice)
Mouse emulation (one switch can toggle between moving the cursor up/down and another between moving the cursor left/right), may need an additional switch site to “click with the mouse”.
Benefits of Two Switch Step Scanning
Active Control Vs Passive Control
Does not require timing, rhythm, or waiting
Allows for distraction and interruptions
Allows for more appropriate social skills and pragmatics
Separate function for each switch
Allows for more growth beyond cause and effect
Student may be able to move to mouse emulation (using three switch sites to control the cursor)