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Harish Jose


Weber’s Law at the Gemba

Be surprised

Published: Thursday, January 16, 2020 - 13:02

In today’s column, I’m looking at Weber’s Law. It’s named after Ernst Heinrich Weber (born June 24, 1795, died Jan. 26, 1878), a German physician who was one of the pioneers of experimental psychology. I highly recommend the Numberphile YouTube video that explains this in detail.

A simple explanation of Weber’s Law is that we notice things more at a lower intensity than at a higher intensity. For example, the light from your phone in a dark room may appear very bright to you. At the same time, the light from your phone in a bright room may seem insignificant. This type of perception is logarithmic in nature. This means that a change from 1 to 2 feels about the same as a change from 2 to 4, or 4 to 8. The perception of change for an increment of one unit depends on whether you are experiencing it at a low intensity or a high intensity. At low intensity, a slight change feels stronger.

This is explained in the graph below. The green ovals represent the change of 2 units (2 to 4), and the red ovals represent the same change of 2 units (30 to 32). It can be seen that the perceived intensity is much less for the change from 30 to 32 than for the change from 2 to 4. These are represented by the oval shapes on the Y-axis. To achieve the same level of perceived intensity (i.e., change from 2 to 4), we need to create a large amount of intensity (~ change from 30 to 60, a difference of 30 units).

All of this fall under psychophysics. Per Wikipedia: “Psychophysics quantitatively investigates the relationship between physical stimuli and the sensations and perceptions they produce.”

What does all this have to do with the gemba and lean?

How often were you able to see problems differently when you came to the production floor as an outsider? Perhaps you were asked by a friend or colleague for help. You were able to see the problem in a different perspective, and you saw something that others missed, or you had a better perception of the situation. Most often, we get so used to the problems on the floor that we miss seeing things. We don’t notice problems until things get almost out of hand, or the problems become larger. Small changes in situations don’t alert us to problems. This, to me, is very similar to what Weber’s law teaches us. Small changes in intensity do not appear on our radar unless we are in the low-intensity area.

A good example is to imagine a white sheet of paper. If there is one black spot on the paper, it jumps out to us. But if there are many spots on the paper, an additional dot does not jump out. It takes a lot of dots before we realize things have changed. One of the experiments that is used to demonstrate Weber’s law has to do with dots. It’s easier to see the change from 10 to 20 dots than it is to see the change from 110 to 120 dots.

Ohno and Weber’s Law

Taiichi Ohno was the father of Toyota Production System. I wonder how his perceptive skills worked and whether his skill set followed Weber’s Law. I would like to imagine that his perceptive skill set was linear rather than logarithmic. He trained his perceptive muscles to see a small change, no matter what the intensity was. Even if he was used to his gemba, he was able to see waste regardless if it was small, medium, or large. Ohno is famous for his Ohno circle, which was a chalk circle he drew on the production floor for his supervisors and engineers. He would have them stand in the circle to observe an operation, trying to see waste in it. Waste is anything that has no value. Ohno was an expert who could differentiate a little amount of waste. If Ohno’s ability to see waste was plotted like Weber’s Law, it might appear to be linear instead of logarithmic, when compared to a student like me.

What we can learn from Weber’s Law is that we need to improve our perception skills to perceive waste as it happens. We shouldn’t get used to “waste” as an everyday, invisible element of production. When there is already so much waste, the ability to perceive it is further diminished. It would take a larger event to make us notice problems on the floor. We lack the ability to perceive waste accurately. We can only understand it based on what has been perceived already. This means that we should go to the gemba more often, and each time try to see things with a fresh perspective. As the Toyota saying goes, we should think with our hands and see with our feet. Change spots from where you are observing a process. Understand that gemba not only means the actual place, but also includes people, equipment, parts, and the environment. We should avoid going with preconceived notions and biases. As we build our understanding, we should try to include input from the actual process users and operators as much as possible. We must learn to see differently.

Final words

One of the examples I came up with for this column is about cleaning rooms. Have you noticed that cleaner rooms get messy fast? Actually, we perceive a slight increase in messiness when the room is clean vs. when it’s not. An already messy room requires a larger amount of mess to make a noticeable difference. What Weber’s Law shows us is that our natural instinct is not to think linearly.

Humans evolved to notice and minimize relative error. As noted on an article on the Science 2.0 website:
“One of the researcher’s assumptions is that if you were designing a nervous system for humans living in the ancestral environment, with the aim that it accurately represents the world around them, the right type of error to minimize would be relative error, not absolute error. After all, being off by four matters much more if the question is whether there are one or five hungry lions in the tall grass around you than if the question is whether there are 96 or 100 antelope in the herd you’ve just spotted.

“The STIR researchers demonstrated that if you’re trying to minimize relative error, using a logarithmic scale is the best approach under two different conditions: One is if you’re trying to store your representations of the outside world in memory; the other is if sensory stimuli in the outside world happen to fall into particular statistical patterns.”

Perhaps all this means is that we learn to see waste and solve problems on a logarithmic scale. And as we get better, we should train to see and solve problems on a linear scale. Any small amount of waste is waste that can be eliminated and the operation improved. It does not matter where you are on the X-axis of Weber’s Law plot.

I will finish with an excellent anecdote from one of my heroes, Heinz von Foerster, who was also a nephew of Ludwig Wittgenstein. I have slightly paraphrased the anecdote.

Let me illustrate this point. I don’t know whether you remember Carlos Castaneda and his teacher, Don Juan? Castaneda wants to learn about things that go on in the immense expanses of the Mexican chaparral. Don Juan says, “You see this...?” and Castaneda says, “What? I don’t see anything.” Next time, Don Juan says, “Look here!” Castaneda looks, and says, “I don’t see a thing.” Don Juan considers this problem for awhile because he really wants to teach Castaneda how to see. Finally, Don Juan has a solution. “I see now what your problem is,” he says. “You can only see things that you can explain. Forget about explanations, and you will see.”

We become surprised when we abandon our preoccupation with explanations. Therefore, we are able to see.

I hope you will continue to be surprised.

First published Nov. 17, 2019, on Harish’s Notebook.


About The Author

Harish Jose’s picture

Harish Jose

Harish Jose has more than seven years experience in the medical device field. He is a graduate of the University of Missouri-Rolla, where he obtained a master’s degree in manufacturing engineering and published two articles. Harish is an ASQ member with multiple ASQ certifications, including Quality Engineer, Six Sigma Black Belt, and Reliability Engineer. He is a subject-matter expert in lean, data science, database programming, and industrial experiments, and publishes frequently on his blog Harish’s Notebook.