Two-Point Threshold: Example, Use & Definition

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  • 0:00 Perception Reduced to Points
  • 0:54 Distinguishing Tactile…
  • 1:30 How Is This Knowledge Used?
  • 2:19 Differences of Theory
  • 3:32 Lesson Summary
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Lesson Transcript
Instructor: Gaines Arnold
This lesson focuses on the idea of two-point threshold. This concept is described and defined and its uses are discussed. This lesson also looks at the value of the measure and whether there are other measures that are better.

Perception Reduced to Points

Jillian told Tommy that she could prove that he only had one finger instead of four, excluding the thumb. He called her a mocking name and said that of course he had four fingers! Knowing Jillian, he then asked whether she was talking about amputation. She assured him it had nothing to do with removing any fingers. Jillian told Tommy to line his fingers up with no spaces in between and then hold his hand horizontally, pointing away from him. 'See?' she said. 'You can only see one finger!'

Being able to see only one object when multiple objects are lined up together is easy to demonstrate, but it's also possible to do the same thing with touch. The mind can easily be tricked into believing that more than one item is just one. But what is this convergence of tactile sensation called and why does it happen?

Distinguishing Tactile Sensations

Just as Jillian proved that more than one item can appear to be one, the two-point threshold proves the same thing. The two-point threshold is the distance between two points at which an individual recognizes they are being touched by two objects rather than one. It's a spatial measure. For example, if you take a pair of tweezers, squeeze the two points together, then touch yourself on the arm with the tweezers it will feel like one point is touching you rather than two. The two-point threshold is that distance between the points of the tweezers when your brain recognizes that you're being touched by two points instead of just one.

How Is This Knowledge Used?

The test is used to both understand the limit of the subject's perception of stimuli and to see if the individual's perceptive abilities fall within a predetermined range. Perception is defined as how an individual sees the world. It's used in this application to determine when the perception of two points of touch as differentiated from a single point occurs.

The perception of the individual is also used to make sure that he or she falls within what has been determined as a normal range. For example, most people have a two-point threshold of 2 to 4 mm on the lips, which expands to between 30 to 40 mm on the back. The reason for this is the incidence of nerve endings in a particular location, meaning that there are more sensing points on the lips than there are in the skin of the back. The lips are, therefore, more sensitive to touch.

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