Home > Encyclopedia of Psychology > Just Noticeable Difference

Scientific calculation of the average detectable difference between two measurable qualities, such as weight, brightness of light, loudness of sound.

When we try to compare two different objects to see if they are the same or different on some dimension (e.g., weight), the difference between the two that is barely big enough to be noticed is called the just noticeable difference (JND). Just noticeable differences have been studied for many dimensions (e.g., brightness of lights, loudness of sounds, weight, line length, and others).

The human sensory system does not respond identically to the same stimuli on different occasions. As a result, if an individual attempted to identify whether two objects were of the same or different weight he or she might detect a difference on one occasion but will fail to notice it on another occasion. Psychologists calculate the just noticeable difference as an...