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Psycho physical methods

The branch of psychology which is concerned with the study of relationship between physical and psychological phenomenon is called psycho-physics. In this sense, the term psycho-physical methods may be referred to all those methods in which attempts are made to employ physical devices for the scientific measurement of some psychological experiences like sensation of weight, brightness, loudness and other such magnitudes. The other complicated psychological phenomena like sleep or span of memory etc., can also be studied through the use of such psycho-physical methods.

Three classical psycho-physical methods devised by the German physiologist and physicist Gustav Fechner (1801-1887), the father of psycho-physics are still in vogue. They are:

1. 
   The method of minimal changes or methods of limits.
   
2. 
   The method of constant stimuli or the method of right and wrong responses.
   
3. 
   The method of average or mean error.
   

These methods are primarily employed to measure absolute threshold and the difference threshold. Both the absolute threshold and the difference threshold are statistical concepts and both are measured in much the same way.

The absolute threshold may be defined as the minimum value of a physical stimulus that reliably produces sensation. Absolute threshold, thus, separates the sounds we can hear from those we cannot, the odors we can smell from those we cannot, the brightness of the light we can see that which cannot and so on.

The difference threshold may be defined as the minimum difference in value between two stimuli that can be perceived by the subject. For example, when one experiences a particular weight put on his hand, the difference threshold is the minimum weight that should be added to it so that the total becomes distinguishable from the first. Let us now give a brief idea of the three psycho-physical methods mentioned above.