Psycho-Physical is the science that investigates the quantitative relationships between physical events and corresponding psychological events or the investigation of quantitative relationships between stimuli and responses. In educational psychology they are used to study the problems of school noise, classroom illumination, fatigue, attention, perception, learning, remembering, forgetting and education of the children with sensory handicaps.
The main methods devised by the Psycho-Physical are:
1. The method of limits or minimal changes,
2. The method of adjustment. and
3. The method of constant stimuli.
In the first method, an absolute threshold is determined by minimally changing the stimulation in successive trails along some physical dimension until the sensation is felt or conversely is not felt. The differntional threshold can be determined by holding the standard stimulus constant a various the comparison stimulus in minimal steps till just noticeable difference is reported.
In the second method, the subject himself controls the stimulus until by increasing its intensity, it is just barely sensed or by decreasing its intensity, its sensation just barely disappears. A similar technique is used for determining differentials threshold.
In the third method, the stimulus values are presented in regular steps but in an irregular order. The subject responds to the stimulus and percentages of correct and incorrect response are calculated. The absolute threshold value is that stimulus intensity that is detected 50 percent of the times. For determining differential threshold through this method, the subject responds to a series of comparison stimuli which are passed repeatedly with standard stimulus. The subject has to indicate which comparison stimulus has a greater sensory value in his judgment. The actual differential threshold is then statistically calculated.