Introduction to Psychophysics

Meaning

          The word Psychophysics is made up of Psychology and Physics.

Psychology = Psychological variables (Specially Sensation and Perception) of an individual.

Physics = Physical Properties of Stimulus

          Means studying the relationship between psychological phenomenon and physical properties of a stimulus.

 Definition

          The branch of psychological science that study relationship between psychological phenomenon and physical properties of a stimulus.

          The relationship between stimuli and the sensations they evoke has been studied in a discipline, called psychophysics (NCERT, XI).

          “The analysis of perceptual processes by studying the effect on a subject's experience or behaviour of systematically varying the properties of a stimulus along one or more physical dimensions” (Bruce et al., 1996 quoted by Wikipedia).

Introduction

          The term psychophysics was coined by Gustav Theodore Fechner in 1860 to describe mathematically the relationship between body and mind. He was German physicist and philosopher who used this in his book (in German) named as ‘Elements of Psychophysics’. Prior to his work while working at Leipzig University, Ernst Heinrich Weber proposed the concept of JND based upon the senses of touch and light which is commonly referred as Weber’s law. It states that the amount required to produce JND is a constant proportion of the value of the original stimulus or reference intensity. The concept of modern Psychophysics is based on the work Weber and Fechner.

 
In psychophysics the intensity of stimuli that activate the five senses are objectively quantified.

The two important concepts of psychophysics: -

(i)       Absolute threshold or limen (AL) – It is also known as Detection Threshold or point of subjective equality (PSE). The minimum amount, intensity, value or weight of the stimulus to get noticed or perceived by human sensory system. AL varies across individuals and situations depending upon various psycho-physical and situational factors. So to measure AL the number of trials forms the base. When the stimulus is perceived correctly in 50% of total trials than the particular intensity or value of the stimulus is referred as AL.

(ii)      Differential threshold of limen (DL) – It is also known as Just Noticeable Difference (JND) or Discrimination Threshold. The smallest difference in the values of the two stimuli that helps in detecting the difference between them. As AL, DL also measured using number of trials i.e. the minimum amount of change in the value of a stimulus which is capable enough to be detected correctly in 50% of the trials.

Methods of Psychophysics

          To measure the relationship between intensity of stimulus and perception Fechner developed following three methods. : -

(i)       Methods of Limits

(ii)      Method of Constant stimuli

(iii)     Method of Adjustment

          These methods are used to measure the threshold of the intensity of the stimulus required to perceive it which is known as Absolute threshold or Absolute Limen (AL).

References:

1.       NCERT, XI Psychology Text book.

2.       Bruce. V., Green, P. R. & Georgeson, M. A. (1996). Visual perception (3rd ed.). Psychology Press.

3.       https://www.britannica.com/science/Webers-law.

4.       https://en.wikipedia.org/wiki/Psychophysics.

5.       https://www.britannica.com/science/ psychophysics.

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