Difference Threshold: Examples & Definition

Lesson Transcript
Sarah Collins
Expert Contributor
Michael Lee

Michael obtained his PhD from the University of Manitoba in Psychology. He has been teaching for the psychology department at the University of Winnipeg for the last 20 years.

Learn about the difference threshold phenomenon and some of its practical applications. Understand what affects your perception of change and why, sometimes, you do not notice differences that exist. Updated: 04/09/2021

Noticing the Difference

'I just want the ends trimmed,' you say to the hair stylist. Little do you know that you are her very first customer. Inside, she is shaking like a leaf. She nervously holds up a section of your hair - about one inch - and asks if that's an okay amount. You nod your head 'yes,' and then start reading an article about a couple in Hollywood that you don't really care about. She timidly begins to cut your hair.

When she's finished, you inspect your hair and are surprised to see that it looks the exact same as when you sat in the chair. You ask, 'Did you cut my hair?' She points to the clippings on the floor, and they're barely the length of doughnut sprinkles. She was so scared to make a mistake that she only cut off 1/16th of an inch! So, technically your hair is shorter, but why weren't you able to notice the change? It's because that 1/16th of an inch did not hit your difference threshold.

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What is the Difference Threshold?

A difference threshold is the minimum amount that something needs to change in order for a person to notice a difference 50% of the time. The concept of difference thresholds applies to all areas of perception: hearing, touch, sight, taste and smell all have thresholds that need to be met before any changes in stimuli are sensed. For example, if I were to give you a pile of five marshmallows and then give you one more, you'd probably notice the difference. It only took adding one marshmallow for you to notice a change, so the difference threshold was one marshmallow.

However, it's important to not just look at difference threshold as a flat number, but also as a percentage of change. If you had started with 100 marshmallows, one more would not have produced a noticeable difference. So, if I added 20% to your pile of 100 marshmallows (as I did when I added one marshmallow to your five), you would definitely notice a difference of 20 marshmallows. In these examples, the difference thresholds were 1, 20 or 20%.

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Applying Difference Thresholds to Everyday Life


You can try out the difference threshold on a volunteer by placing two weights of the same unit in the palms of the person's hand. At first, they should say that they feel equal. Add more weights to one of the hands incrementally until the person notices that the weight in that hand feels heavier. That is the difference threshold.

The difference does not only apply to detecting differences among physical stimuli.

For example, think about when you go shopping and how your decisions about what to buy or not to buy can be influenced by difference thresholds. Consider that you want to buy a cup of coffee. One coffee will cost you $4 and another coffee will cost you $6. Next, consider that you are looking to purchase a more expensive item, such as a new smart TV. One of the televisions you like costs $395, while the other one costs $397.

  • How would you characterize the choices you, or most other people, are likely to make in the above examples?
  • In what ways did the price differentials affect your decisions?
  • How could you explain this behaviour based on what you understand about difference thresholds?

Possible Answers:

Most would choose the 4 dollar cup of coffee because two dollars more seems like a big difference. Even though the difference is still only 2 dollars, when the amount of something is much higher (the $395 television) the difference doesn't appear to make much difference to us at all.

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