The word psychophysics is derived from two words (psycho, which means mind or experience and physics that means physical events). Psychophysics studies the relationships between physical activities, physical aspects of the stimuli, and our psychological experience to them.

Psychophysics played an important role in the development of the field of psychology. The German psychologist Gustav Fechner (1801-18877) found psychophysics, who studied the relationship between the strength of a stimulus and a person’s ability to detect the stimulus.

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Fundamental Concepts in Psychophysics

1. Absolute Thresholds:

Our sense organ cannot detect every stimulus. So, when does a stimulus become powerful enough to be detected by our sense organs? To know the answer, we should understand the concept of absolute threshold.

An absolute threshold is the smallest intensity of a stimulus that can be detected. The concept of an absolute threshold is not so clear cut. As the strength of the stimulus increases, the probability that it will be detected increases gradually. It is also important to note that at a low level, participants might be able to detect the stimulus part of the time. Technically, the absolute threshold is the stimulus intensity that is detected 50% of the time.

2. Difference Thresholds

The difference threshold (or just noticeable difference) refers to the minimum change in stimulation required to detect the difference between two stimuli.

German physiologist Ernst Weber (1795 – 1878) discovered that the ability to detect differences depends not so much on the size of the difference but the size of the difference with the absolute size of the stimulus. For example, if you have a tea with a teaspoon of sugar, adding another teaspoon will make an enormous difference in taste. But if you added that same volume of sugar to a cup of coffee that already had 6 teaspoons of sugar in it, then you probably wouldn’t taste the difference as much.

Weber’s law also helps to explain why a person in a quiet room is more startled by the ringing of a telephone than is a person who is already in a noisy room.


Understanding Psychology – Robert S Feldman
Introduction to Psychology – CT Morgan
Introduction to Psychology –