The whole idea behind the just-noticeable difference
is fundamentally flawed. The basic idea is that there is some minimum detectable difference in our perception before we can see the difference. So for example if I increase the brightness of a light by 0.001% it would be below the jnd and therefore you would be unable to detect any difference. I'm going to argue that this doesn't make any sense.
Assume that the jnd of temperature is 0.3K. Any difference below this in temperature would be unnoticeable. Therefore 30.2K feels the same as 30.4K and 30.4K feels the same as 30.6K. However, 30.2K does not
feel the same as 30.6K because the difference in temperature is 0.4K which is above the jnd of 0.3K. Am I the only one who sees the problem here?
It's like saying a = b, b = c and a != c. It's obviously wrong, it leads to a logical absurdity. It breaks the transitive property of equality. The jnd cannot exist.
I think the reason the jnd has been formulated is a result of the way we use language. If I held up two sticks which were exactly 1.0m and 1.0000000001m in length and asked "Are there two sticks the same length?" the vast majority of people would say yes. However, everyone would realize that it's actually impossible for them to be the same length. The variations would result from their atoms vibrating differently due to heat - their lengths would be constantly changing by incredibly small amounts. Since it is impossible to completely remove the effect of heat from any system this effect will always be taking place.
The reason the people say "yes they are the same lengths" is because they interpret the question as "Is the length difference of these sticks less than 1mm (or some similar value)" or "Has the manufacturer of these sticks put a large amount of effort towards minimizing the difference in length of the sticks". We unconsciously interpret the question in a way different to its literal meaning. If we didn't do this automatically, communicating would be very difficult and take a long time.
This directly leads me to disliking the word "negligible" because its definition is essentially "quantities smaller than the jnd". So I do avoid using the term negligible.
The broken concept of jnd makes people not improve things which could could be improved. We say things like "There's no point in increasing the frames per second beyond 60 because the human eye cannot detect it as a 1/60th increase is below the jnd" or "We shouldn't increase the DPI of this screen because an increase is beyond the resolution of the eye (Retina Display)".
This belief that there is a jnd is holding back our progress in many technologies and we should do everything in our power to make it clear that jnd does not exist. If anyone would help to get the jnd article removed from Wikipedia it would be greatly appreciated.