Switch Access using Scanning and Encoding

Chapter 8 Switch Access using Scanning and Encoding  Mechanics of scanning  Compares different scanning techniques  Considers good practice for designing selection sets

Switch Access Quick Assessment Guide The user can use 4 or 5 switches… The user can hit 1 or 2 switches…  Repeatedly with good timing  With good timing  Hold, and then release a switch with good timing  But has difficulty with timing

Assessment Continued The user can operate the scanner but…  Often selects incorrect items  Writing it unacceptably slow

What is scanning? Technique for sequential display of a set of items and selection using a small number of switches Scanning System  Controlled by a switches  Different scanning methods (ex: Row-column)  Different scanning movements (ex: Groups)  Layouts and items for individual users and tasks

Who might use scanning? Severe physical impairments Control of one or small muscle group Learning disabilities People without patience  Can not use Keyboard Mouse voice

Scanning Methods Autoscan  Single switch, with automatic start  Users… Control 1 or 2 switches Good timing to activate switch, but can hold it down Needs to simplicity of one switch

Scanning Methods Userscan  1 switch, with dwell select  2 switches  Users… Can control 1 or 2 switches Can activate, hold and release switch Impatient, anxious, and stressed waiting to press the switch Trouble activating the switch with good timing

Scanning Methods Step Scan  Single and 2 switch  Users… Can control 1 or 2 switches Activate and release repeatedly Can not wait becomes anxious Learning disabilities

Matching Scanning Methods to User Skills Different scanning methods demand different control and operational skills Suggestions for assessing switch activation, release and timing skills

Control Demands Demands1-switch Autoscan 1-switch Userscan 1-switch Stepscan WaitHIGHMEDIUMLOW ActivateHIGHLOWMEDIUM HoldLOWHIGHLOW ReleaseLOWHIGHMEDIUM Motor Fatigue LOWMEDIUMHIGH Sensory/ Cognition HIGH LOW

Demands2-S.Auto2-S.User2-S.StepDirect User WaitHighLow ActivateMed to High Low HoldLowHighLowHigh ReleaseLowMed- High LowMed-High Motor Fatigue Low-MedMed- High LowMed-High Sensory/ Cognitive Med LowMed

Scanning Movements Simple Scan Movement Group Scan Movement  Row-column  Column-row  Nested scanning (Half-scan) Directed Scan Movement

Other Scanning Techniques & Features Canceling the scan  Wait for the program to go through the certain number of scan cycles  Cancel buttons at the beginning of rows Next scan item  ‘Home’ Scan delay on First item  On fast scan speeds anticipates next item

Introducing Scanning Prerequisites (Blackstone, 1989) Seating & positioning must facilitate function Movement, control site, and switch options must be specified Switch and device must be correctly positioned The user may need explanation and training in how the scanning works

Introducing Scanning Tasks…  Develop motor and visual scanning skills  Develop motor and visual scanning, plus cognitive skills  Develop motor and visual scanning, plus cognitive skills, plus communicative skills

How can scanning accuracy be improved? Seating and positioning Change the scan speed Use switch filtering (increase post- acceptance) Adjust the first item

How can scanning speed be increased? Increase the accuracy Change scan method Change scan rate Change selection set design and layout Change scanning movement Use acceleration techniques

Access with Switches and Encoding Switch Encoding  Using 1 or 2 switches and an extended version of Morse code  Fast method, user needs to have sufficient memory and sequencing skills A. (dit) – (dah) B -… C -.-. Space..--

Mouse control for switch users Scanning directions  Selecting direction from selection set  Rotating Pointer Key combinations Markers and Hot Spots  Buttons for marking locations on the screen Automatic Computer Access

Input Filtering Input acceptance filtering Repeat filtering Post acceptance filtering