Book Definition

The smallest amount by which a stimulus can be changed and the difference be detected half the time. The stimulus can only be detected half the time.

In Your Own Words

  • When something is changed, it is the least amount of change needed before you can tell the difference.
  • When something has changed to the point where you can sense even the slightest difference.
  • The least amount of stimuli needed to notice a difference.
  • Difference threshold is the exact same thing as JND (Just Noticeable Difference).


  • Your sister is in another room and asks you to turn the volume down. You turn it down as little as possible, and she may not hear a difference...If you hear a change, then it exceeds your own difference threshold, but not her's.
  • A light is at its maximum brightness and you dim it slightly, hardly anyone notices. The change is too subtle to cross their difference threshold.
  • You are tasting a dish, and you add salt. The point where you notice a difference in taste is your difference threshold.
  • You are playing a song on the piano and you change one note and you can tell that you did.
  • You are making your own perfume and you add one little ingredient that makes it smell slightly sweeter.
  • Everyday you made the exact same fruit smoothie for your friend. One day you add a single vegetable (a carrot) into the fruit smoothie, you changed the ingredients. If your friend doesn't notice the difference, it does NOT cross her difference threshold. If she noticed the difference it WOULD cross her difference threshold. If you wanted to find the JND you would keep adding more amounts of carrot until she notices.
  • When your cell phones brightness is all the way dim and you slightly turn the brightness up, the point when you can just see your screen/ screens light, that would be crossing your difference threshold.

Additional Resources


external image MR900434501.jpgJUST

external image MR900434509.jpgNOTICEABLE

external image MB900434489.jpgDIFFERENCE

JND is the same as difference threshold.