What is the Just Noticeable Difference?

• A. The smallest detectable difference between two sensory stimuli
• B. The loudness at which a sound is uncomfortable
• C. The minimum duration of a tone to be heard
• D. The maximum difference between two stimuli that is not noticeable

Answer: (A)

The Just Noticeable Difference is the smallest change in a sensory stimulus that you can detect. In psychophysics, this difference threshold means you’re comparing a baseline stimulus to a slightly altered one, and the JND is the point at which the change becomes detectable about half the time. In music perception, this could be the tiniest raise in loudness, a slight shift in pitch, or a brief change in duration that you can just perceive. Often, the size of the JND grows with the strength of the baseline stimulus (Weber’s law), so louder sounds require a bigger change to notice. The other options describe different limits (like when a sound becomes uncomfortable, or the minimum time needed to hear a sound) or misstate the idea as the largest undetected difference, which is not the standard definition.