One of the questions that has interested brain scientists and philosophers alike is that of self versus non-self. How do we distinguish what is part of us, versus what is part of the environment?

This sounds like a trivial question. When I see my hand move, I know it is part of me. That’s obvious. But in terms of perception, this is not trivial at all. It is the concept known across several disciplines as body schema.

In 1998 an interesting experiment was reported that has now become well known as the ‘rubber hand illusion’. A group of people were seated with their left arm resting on a table, hidden to their view by a screen. Then a rubber arm was placed in front of them, oriented in the same way as their real arm, and they were asked to look at it. The scientists used two paintbrushes and stroked both the subjects’ hands and the artificial arms at the same time. This created an illusion where the subjects believed that the artificial arm was actually theirs. This is such a strong illusion that if you were taking part in the experiment, you’d become distressed if someone were to stick a needle into the rubber arm. The experiment is tapping into the mechanisms we have in our brains that decide what is self and what is non-self.

Another interesting observation is that when we hold an object, we come to think of it as part of us (see this paper as an example). For example, if we have a rake in our hand, we see that rake as part of us perceptually. The same is true if we are wearing clothes: they become self versus non-self. Or if we are driving a car – this could explain some of the aspects of road rage. It could also go part of the way to explaining why some people identify so closely with their cars, and why cars are such a prominent part of conspicuous consumption. Status-obsessed people are very fussy about the car they drive. Interestingly, we don’t think of the car as self when we are a passenger in it. The car-as-self phenomenon seems to be caused by the act of driving, and the holding of the steering wheel and moving the pedals and gear stick, and seeing the effect of these actions. For this reason, will the appeal of driverless cars be limited? Will it be unsatisying to own a car that we don’t actually drive?

What about eating and drinking? When we hold a knife and fork, they become part of us. They become self. The food that the cutlery propels to our mouths is in the act of becoming self. When it is on our fork, it is our food, and shortly after this it becomes part of us in a more literal sense as we ingest it. And then there is the transition as the wine is absorbed and digested, and passes from our gut, which is the outside of our inside, to our true inside. The wine then interacts not only with our internal tissue, but also alters our mind – the ultimate stage of becoming us.

So when we have wine in our glass, does our relationship with that wine change? Does the act of wine drinking change the wine from non-self to self in this multi-step process? I think it does, and this transition could be important for the way that we experience wine. As we pick up a wine bottle and pour a glass, we are aware that soon this wine will become part of us. This adds an extra dimension to the appreciation of wine, but is one we rarely consider.