The difference threshold is the smallest level of added (or reduced) stimulation required to sense a change.
It is also referred to as a just noticeable difference.
Weber's law states that a just noticeable difference is a constant proportion of the intensity of an initial stimulus.
Weber's law helps explain why a person in a quiet room is more apt to be startled by the ringing of a telephone than a person in an already-noisy room.
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