Two point threshold experiment in psychology

 Hello guys today I will talk about the point threshold experiment in psychology. 


Introduction: the smallest distance between two points of stimulation on the skin at which the two stimuli are perceived as two stimuli rather than as a single stimulus. Also called spatial threshold.

Purpose: To determine the two point threshold on the volar surface of the fore-arm of the subject with the method of minimal changes.

Material used: Aesthesiometer, Blindfold, Metronome, paper, pen.

Subject’s Details: Age… gender……………..educational



Preliminary set up Aesthesiometer was checked. A table was made to record the responses of the rough threshold wherein 2.5 is the midpoint (five above and five below 2.5 with a distance of 0.5 between all). Metronome is checked and set at 60 beats per minute.

Procedure: The subject was called to the laboratory. The subject was properly blind folded. Rough threshold was identified. For this a line of 5 cm line was drawn on the volar surface of the fore arm of the subject. Thereafter the subject was given the following instructions:“I will be putting a blindfold on your eyes thereafter you will experience the sensation of one or two points on your forearm. You have to carefully feel the same and tell me whether you experience one point or two points on all the trials that I will take.’

After ensuring that subject has understood what he/she has to do he was given the signal of ‘ready’. Thereafter, the metronome was started. The aesthesiometer was put on the line drawn taking care that the pressure applied on each presentation of the scale from 0-5.00 cm is the same. Each stimulus was presented for two beats (2seconds) and with the gap of two beats between successive stimuli. The responses were recorded in terms of (+) and (-) to indicate two points and one point. After this ascending trial another ascending trial and two descending trials were taken. The rough threshold was calculated with the help of the midpoints of the transitional zones. After obtaining the rough threshold another series was made keeping the rough threshold at the centre of the series (with five above and five below with a distance of 0.2 between each successive stimulus). The two point threshold with this series was taken out taking five ascending and five descending trials (alternate). The two point threshold is calculated after identifying the transitional zones and midpoints.


1.The aesthesiometer was not shown to the subject.

2.The pressure of aesthesiometer was kept same throughout all the trials.

3.The aesthesiometer was touched on the forearm of the subject only for two seconds.


Table one for rough threshold

Distance in cm A D A D
5.0 + + + +
4.5 + + + +
4.0 + + + +
3.5 + + + +
3.0 + + +
2.5 + + +
2.0 + + +
1.5 +
Mid point of transition 1.75 3.25 1.75 1.25

Rough threshold=1.75+3.25+1.75+1.25/4

Rough threshold=2.0c.m.

Table 2 for calculating two point threshold

Distance in cm A D A D A D A D A D
3.0 + + + + + + + + + +
2.8 + + + + + + + + + +
2.6 + + + + + + + + + +
2.4 + + + + + +
2.2 + + + + +
2.0 + +
1.8 +
Mid point of transition 2.1 2.5 1.9 2.5 2.1 2.3 2.1 1.7 2.5 2.5

Mean of ascending order=2.14

Mean of descending order=2.30

Two point threshold 

Now for checking significant of mean you have to check t test between ascending and descending order. In the end you have to write interpretation of this experiment.

You can read also these experiments 


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