Debrief: Making a just noticeable difference.

Abstract

Ernst Weber was a 19th-century German physician who first described the just noticeable difference, the JND, before the work was taken up by his student, Gustav Fechner, another pioneer in experimental psychology. The Weber–Fechner Law highlights how our senses and perceptions aren’t as robust and rational as we might like. They found that the JND in any variable is proportional to the magnitude of that variable. Weber did research using simple weights to see when people could detect a difference in weight. We’re best at detecting relative differences — as a weight gets heavier we need a bigger difference to feel it. This has clinical relevance as well. The JND is often the threshold at which people come to see us. It’s when they notice that they have lost weight, or their pain spills over, …