Book Definition: This concept says that the size of a JND is proportional to the intensity of the stimulus. The JND is large when the stimulus intensity is high and is small when the stimulus intensity is low.


In Your Own Words



  • The more intense something is, the harder it is to notice a change, but if the intensity is lower, it is easier to notice the change.
  • The louder or brighter something is, the more change is needed to notice the difference.
  • The more there is of something, the more change is needed to pass your difference threshold, whereas the less there is of something, less change is needed to pass your difference threshold.
  • The more intense the stimulation is, the more of a change is needed to be able notice the difference.

Examples/Functions



  • If the volume of a television is high, turning it down by a few decibels will not be a very big difference.
  • When you start with 50 cans of soda, the sample size is large, if someone drinks a soda it will be harder to notice a missing soda. As the sample size gets smaller, 2 cans, when someone drinks a soda it is easier to notice a soda missing.
  • If you are benching a weight of 200 pounds you wouldn't notice if 5 pounds were added, but if 20 pounds or more were added the person benching would now be able to tell the difference in the weight.
  • If you add hot pepper to something that is not spicy AT all, you will notice the change after only using a little bit. Whereas, if you are adding hot pepper to something that already has a kick to it, it will take more and more hot pepper to finally get you to notice a difference.
  • Changing the brightness level on your cell phone. If the brightness of the screen is intense, the dimmer the screen needs to be. If the screen is very dim already, it only needs a slight adjustment for the screen to appear brighter.
  • You are driving. You notice the difference from being completely stopped to moving 5 miles per hour. But when you are driving on the highway you don't notice a 5 mph increase from 60 to 65.
  • You are upstairs jamming to your favorite music out MAX volume of 30. Your mom says it is too loud and you need to turn it down. Turning the volume down A LOT will be easy to notice. But if you only turn it down a few punches it will seem extremely loud still.
  • When a tree changes color in winter and becomes really bright (such as the one on our school grounds), it's still changing color daily but it is harder to notice than when it was a less intense color.
  • When your at the movies and your Iphone screen is really bright, you go to brightness to dim it down until its less noticable to the people surrounding you.
  • When you have a messy room, picking up one or two items isn't noticeable, however when you clean up 15 items the room will start to look less messy.
  • A pickpocket. For Example, if you were a pickpocket, the perfect time for you to steal something would be in a very large crowd of people because then, the person you are pickpocketing will mostly likely not notice the small change in weight in their left pocket. However, if you were to try and steal from someones pocket in a much smaller crowd of 10-15 people, it would be much easier to notice the change and you would most likely get caught. (and no one wants to be a terrible pickpocket)
  • when you are sitting at home watching TV if your listening to the television on its max volume of 55 because it was hard to hear with all the backround noise you wont notice someone turn it down to a max of 50 because you didnt see them physically do it and your not just paying attention to the T.V but to the people talking in the back also, but if you were to watch them while they turn it down you would notice the diiffrence in how loud it was because your focused on the sound coming out of the T.V and you see the volume bar getting lower so your body will react to it.
  • When you are taking 6 bags of groceries in the house and someone adds another bag you wouldn't notice it because of Weber's Law.

Additional Resources



  1. http://www.britannica.com/EBchecked/topic/638610/Webers-law
  2. http://www.sizes.com/units/webers_law.htm
  3. http://www.alleydog.com/glossary/definition.php?term=Webers%20Law