Just-Noticeable Difference

The smallest detectable difference between two stimuli that a person can perceive. In accessibility contexts, JND is commonly applied to color, contrast, and audio levels—determining the minimum change needed for users to distinguish between two values. For color vision, JND defines the boundary between colors that appear identical and colors that appear different to a specific user. Assistive technologies and accessible design tools use JND measurements to ensure that color choices, text-background contrast, and audio signals are perceptibly different for users with varying sensory abilities.