Penfield Homunculus: How Do We Sense the World?


Developing precise body control is not easy

Move your right hand up and down while moving your left hand back and forth. You must be a genius of body control if you can do this smoothly and easily. To the guests of our factory tour, I always ask to do this, but I’ve never seen anyone who can do it right. Our craftspeople move like this when surface-finishing a table top board with a wide belt sander.

Precise body control makes a smooth surface

A wide belt sander is a machine rotating a sanding belt on a platform that can slide back and forth. The craftspeople press the sanding belt to a table top board with their right hand while moving back and forth with their left hand the platform on which the table top board is placed. The sanding power is strong. If you apply too much pressure or apply appropriate pressure on a wrong point, you can never make a smooth surface. Making matters more difficult, they’re required to judge smoothness by a sense of touch.

How we sense the world

Have you ever seen the above image by the way? It’s a Penfield homunculus, a model to show how our brains recognize the world. As you can see that in the above image, the lips, tongue, and hands are designed much bigger than their actual size. When first seeing the grotesque model, I was surprised because I believed we saw the world mainly with the eyes. The importance of information through a sense of hand touch is bigger than many people would think.

A sense of hand touch

The homunculus also reminded me of a story in some small mold factory in Japan. The maximum tolerance of their molds is about 1 micron (1/1000 mm), and is detected by a sense of hand touch. Their molds look so smooth to me even if they’re before the final polishing, though. In addition, our hands are excellent not only as a sensor but also as a tool. We can easily hold things different in weight and intensity together, like cream puff and a stone, but this is very difficult for robot hands. They still need many sensors at all the joints, and it’s necessary to pre-enter a lot of data about things to be handled. Our hands perform such difficult missions every day.

The image of a hand with a sanding tool. The tool is applied to the wood chair frame.

The same as the above mold factory, it is a sense of hand touch of our craftspeople that affects the quality of our products. In order for high-quality things to be evaluated as such, however, your keen sense of hand touch is also necessary. Seeing something and wanting to touch it—this is highly likely to happen when things are good in design and quality like our furniture, I guess. Please confirm that with your own hands at a shop near you.

Shungo Ijima

He is travelling around the world. His passion is to explain Japan to the world, from the unique viewpoint accumulated through his career: overseas posting, MBA holder, former official of the Ministry of Finance.

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