Textbook of Usability

Change blindness is the surprising failure of human observers to notice changes in a visual scene when the change coincides with a visual disruption — a saccade, a blink, a screen flash, or any brief interruption of the visual signal.

Classic demonstrations have shown people failing to notice the substitution of one person for another during a conversation, or large objects disappearing from photographs across brief flicker-interruptions. The phenomenon illustrates that the visual system does not maintain a complete internal representation of the scene; it samples the world as needed and fills in the rest.

In interface design, change blindness manifests when:

• A value updates during a page transition and goes unnoticed
• A status indicator changes between screen refreshes
• Monitoring dashboards show gradual drift that the user fails to detect
• Animations complete while the user's attention is elsewhere

Mitigations include animation (drawing the change out over time so it's caught in the act), highlighting (briefly flashing or colour-changing the updated element), persistent indicators (showing that something changed rather than just showing the new value), and explicit notification (a banner or badge).

Change blindness is especially dangerous in safety-critical monitoring where detecting changes is the primary task.