Switch Access using Scanning and Encoding

1. Switch Access using Scanning and Encoding

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

3. 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

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

5. 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

6. 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

7. 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

8. 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

9. 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

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

11. Control Demands

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

14. 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

15. 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

16. 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

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

18. 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

19. 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 ..--

20. 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

21. Input Filtering • Input acceptance filtering • Repeat filtering • Post acceptance filtering