Chapter 5: Single Switch Scanning

Single Switch Scanning (Auto-Scan) is the most common scanning method.

How it works

1. System automatically highlights items in sequence
2. User waits for desired item to be highlighted
3. User presses switch to select
4. System activates item and restarts scan

Auto-Scan Flow (Mental Model)

Start → Highlight Item → Wait → (Press?) → Select → Restart
                    ↘ No press → Next item ↗

Auto-Scan Variants

• Auto-while-held (user scan): the highlight moves only while the switch is held down.
• Auto-restart: restart from the first item or continue from last selected item.
• Initial item pause: extra time on the first item to help users prepare.
• Scan loops: stop after N passes (or infinite loops) to avoid endless waiting.

Timing tips

• Too fast → missed selections
• Too slow → frustration and low TER
• Just right → user feels in control

Variants You’ll See in Real Devices

• Auto-while-held: The highlight moves only while the switch is held down.
• Auto-restart modes: Restart from the first item or continue from last.
• Initial item pause: Extra time on the first item to help users get ready.

Why This Matters

For many users, auto-scan is the only feasible mode. The tradeoff is timing pressure: the user must anticipate the highlight and press at exactly the right moment. This makes scan rate, acceptance time, and error recovery critical (see Chapters 13 and 19).

Selection Methods

• Press-to-select: most common, a switch press selects the highlighted item.
• Dwell selection: selection occurs automatically after a set dwell time.
• Encoded selection: patterns like double‑press or long‑hold trigger special actions.

Auto-While-Held (User Scan)

In standard auto‑scan, the press stops the scan and selects. In auto‑while‑held, the logic reverses:

• Hold the switch to move forward.
• Release to stop and select (or dwell).

This can feel safer for some users because letting go stops the movement.

Demo