Weber’s Law

 Introduction

An approximately accurate generalization in psychology, the smallest change in the intensity of a stimulus capable of being perceived is proportional to the intensity of the original stimulus. Weber’s law explains why you don’t notice your headlights are on in the daytime. Psychophysics the concept that a just-noticeable difference in a stimulus proportional to the magnitude of the original stimulus.

            Weber’s law, also called Weber-Fechner law, historically important psychological law quantifying the perception of change in a given stimulus. The law states that the change in a stimulus that will be just noticeable is a constant ratio of the original stimulus. It has been shown not to hold for extremes of stimulation.

The law was originally postulated to describe researches on weight lifting by the German physiologist Ernst Heinrich Weber in 1834 and was later applied to the measurement of sensation by Weber’s student Gustav Theodor Fechner, who went on to develop from the law the science of psychophysics.  By stating a relationship between the spiritual and physical worlds, the law indicated to Fechner that there is really only one world, the spiritual. To others, the law meant the possibility of a scientific, quantitative psychology.  The combined work of Weber and Fechner has been useful, especially in hearing and vision research, and has had an impact on attitude scaling and other testing and theoretical developments.

        Weber law states that the ratio of the increment threshold to the background intensity in a constant. So, when you are in a noisy environment you must shout to be heard while a whisper work in quite room. And when you measure increment threshold on various intensity background, the threshold increases in proportion to the background. According to Weber’s law

∆1/1=K 

The fraction ∆1/1 is also known as the weber fraction (aka Fechner fraction) If we rearrange the equation to ∆1=1K , you can see that weber law predict the relationship between the increment threshold and the background intensity (Weber, 1834).   

Why Weber law is useful?

            Weber law is a useful way to summarize the relation between discrimination threshold ∆1 and the base intensity 1. In general, this relation holds true many different dimensions (but not always see below). if we know that Weber law holds for two dimensions, we can compare our sensitivity to change along those discrimination by comparing the Weber fraction. The Weber fraction is often expressed as a percentage. A Weber fraction 1% indicate a fairly high sensitivity to increments, while a Weber fraction 15% is rather poor or indicates lower sensitivity to increments.

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