The sense of perception requires the stimulation of receptors within the brain. This is usually done through one of our five senses of taste, smell, sound, sight or touch. Interestingly these senses all obey Weber's law or the Weber-Fechner law, which was initially discovered by the German anatomist and physiologist E. H. Weber in 1834.
Weber discovered that people holding different weights in each hand could tell which weight was heavier if the difference in the weights was greater than five percent of the total weight. They couldn't tell the difference if the difference was less than five percent. Therefore, they could tell the difference between 20 and 21 gram weights, but not between 20 and 20.5 gram weights. As Weber increased the amount of weight he had to increase the amount of the difference. Therefore, they could tell the difference between 40 and 42 gram weights, but not between 40 and 41 gram weights even though the difference was 1 gram as was necessary for detecting the difference in the 20 gram weights. As Weber experimented with higher and higher weights, he always had to increase the difference by five percent in order for the person to tell the difference. Therefore at 100 grams, he had to use 100 and 105 grams for people to tell or sense the difference in weights. This five percent difference became known as the "just noticeable difference".
This was a fundamental discovery into the brain's sense of perception that led subsequent researchers to explore this law more thoroughly. Subsequently, researchers discovered that Weber's law is valid for all of our senses. These findings led researchers to wonder how our sensory receptors can produce such a ratio preserving process. One insight into this process occurred when Lanzara discovered that a simple two pan balance also obeys Weber's law (see - http://www.bio-balance.com/Weber%27s_Law.pdf ). This insight demonstrated that a relatively simple object such as a balance obeyed the same physiological law as our sensory receptors.
How can this be? Well in order to understand why this may be correct, we'll need to learn a little about the pharmacology of how receptors work. In general, receptors are complex cellular molecules that are found on the surface of our cells. This is how our cells sense signals from other cells in our bodies. It is thought that these receptors exist in two possible states that are in a poised equilibrium, which is very similar to the equilibrium between the two pans of a balance. When a signal (usually a molecule) interacts with a receptor, then it shifts the equilibrium toward one state, which changes the receptor equilibrium. When this occurs, the receptor sends a signal to the cell. This is how our senses work.
This suggests that our brain's sense of perception functions very much like a balance that can tip from one side to the other. Sensory stimuli tip the receptor balance and trigger a signal. This remarkable finding can lead one down the rabbit hole if you care to explore further (see - http://www.bio-balance.com/Ref.htm ).