Contrast threshold task

You will see a box containing a symbol. Use the Lighter and Darker buttons (or the ↑/↓ keys) to adjust the box until the symbol is just barely visible. Then press Just visible (or Space).

The double-arrow buttons move in larger steps (or hold Shift with the arrow keys). Hold any button to repeat.

Please sit at your normal viewing distance and avoid changing your screen brightness during the task.

Participant:

Where are you?
How bright is the light around you?
Your screen brightness setting