Glossary
Terms used in accessibility research and practice. Each entry has a definition, common aliases, and category tags.
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- Just-Noticeable Difference(also: JND, Difference Threshold, Differential Threshold)
- 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…
- Magnitude Estimation(also: Psychophysical Scaling, Stevens Method)
- A psychophysics research method where participants assign numerical values to stimuli based on their perceived intensity or magnitude. In accessibility research, magnitude estimation is used to determine how users naturally interpret sensory mappings—for example, what…
- Psychophysics
- Psychophysics is the scientific study of the quantitative relationship between physical stimuli and the sensations and perceptions they produce. Founded in the 19th century, it uses rigorous experimental methods to measure how humans detect, discriminate, and scale sensory…
- Visual Crowding(also: Crowding)
- A perceptual phenomenon in which the presence of nearby flanking characters or objects makes it harder to recognise a target character, especially in peripheral vision or when the target is small, low-contrast, or briefly viewed. Crowding jointly with limited visual span sets an…
- Weber's Law(also: Weber Ratio, Weber's Ratio, Weber-Fechner Law)
- Weber's Law is a foundational principle of psychophysics stating that the smallest detectable change in a stimulus — the just-noticeable difference — is a roughly constant fraction of the stimulus magnitude rather than a fixed absolute amount. For example, if a user can reliably…
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