Threshold of Sensitivity 

       Threshold is an important term in psychophysics since it is concerned with studying the relationship between physical stimuli and the psychological response.

  1. Types of thresholds


      We can differentiate between four types of thresholds: absolute thresholds, recognition thresholds, difference thresholds and subliminal perception.

       Absolute thresholds represent the lowest amount of energy needed for a certain stimulus to be perceived, for example the absolute threshold of taste is one teaspoon of sugar in two gallons of water.

           Recognition threshold is the lowest amount of energy needed for a certain stimulus not only to perceived but to be recognized. For example if the absolute thresholds represents hearing a sound, recognition thresholds would not stop at that point, in recognition thresholds you will be able to know if that sound is a cat meowing or a dog barking for example.  

           Subliminal perception refers to the perception of stimuli below the thresholds of conscious awareness.

       Difference threshold is the amount of stimuli energy needed to be added or subtracted from a stimulus for a person to notice the difference.  Let us say for example that the difference thresholds of 6 pounds is 2 pounds, in this case if you carry 7 pounds you will not notice the difference but if you carry 8 pounds you will notice it. This difference can be referred to as the just noticeable difference(JND). However it is not majored the same way, in the example above the difference thresholds is two pounds so in this case 2 pounds will be considered one just noticeable difference (JND) and 2 JND will be considered 4 pounds.

  2.Psychophysical laws

  • Weber’s law

According to Weber what is important in producing a JND is not the absolute thresholds between the two stimuli but rather the ratio. So if we take the example above and consider that the absolute thresholds of 6 pounds is 2 pounds then in this case the ratio would be 6 subtracted from 8 and divided by 6 which will be 2/6. It should be known that the smallest the ratio the better is the sensitivity according to Weber.

  • Fechner’s law

Fechner’s law is quite impressive, you see according to Weber the JND is governed by a certain ratio that should be calculated. Fechner on the other hand thinks that sensation increases more slowly as intensity increases. Let me give you an example to make this idea more clear. Let say that you were carrying one book and you add another book on top of it, in this case the difference will be obvious to you. However if you were carrying six books and you add a book on top of them you will barely feel the difference or maybe you will not even notice any difference. Hence sensation increases more slowly as intensity increases.

  • Signal detection theory

This theory concentrates on the idea that non-sensory factors like experiences, motives and expectations influence what the subject says he senses. For example someone who is cautious would think twice before saying that he heard something, on the other hand someone who is less cautious can say that he heard something even if he just thought that he did.

In the signal detection experiment two types of signals are presented a true one “where the signal is real” and a false one “where the signal is absent”. The outcome would give either a hit “when the person identify a true signal”, miss “when the person do not identify a true signal”, false alarm “when the person identify false signal as true” and correct rejection “when the person do not identify a false signal”.  As a final step the outcome of the experiment is presented in a curve called Receiver operating characteristics (ROC). 

See Also:



Perception and experience