Metamerism and keys

What do the colors have to do with the keys to the apartments? Much more than it seems. Indeed, reasoning about keys and apartments will allow us to reveal an error behind a notion very dear to psychologists: metamerism.

Let’s start with the simple case. I live in a condo which, like many others, has a shared entrance and door. Nothing special so far. This simple circumstance, however, obliges each condominium to have two keys: one for his apartment and one for the door. A few weeks ago a novelty arrived: the administrator had all the keys and locks replaced, both in the apartments and in the door. The biggest novelty is that now there is no need for two keys anymore, but each one has only one key that opens both the front door of his home and the door of his home and, lo and behold, does not open any other door.

At first, it surprised me.

How could the same key open both the door and the door of my house and not anyone else’s door?

And then I realized that the solution to the mystery is simple:

Each key is a combination of two keys, one for the door and one for its own door.

The apparent magic arises from the wrong assumption that since the administrator has given me a piece of compact metal (the new key), it must be a single key. The solution of the trick is simple: they are two keys soldered together.

What does all this have to do with metameric stimuli? A lot, as we will see. First, however, two words to say what metameric stimuli are. They are all those phenomena which, although different, are perceived identically. For example, two materials that, while reflecting light differently, have the same color. Or two different chemicals that taste the same for us.

In all these cases, the standard explanation of psychology is the following:

there are two distinct physical phenomena and, for various reasons, our perceptual system makes us perceive a single sensation (a single color, a single smell, a single flavor).

Since the sensation is the same even if the phenomena are different, it would follow that sensation and physical phenomena are different.
The traditional explanation is reasonable, but deeply wrong! And the example of the keys will help us understand it very well. Let’s go back to our condominium and examine two condominiums: Riccardo and John. It all depends on how we tell things.

If we say that John and Riccardo have one key each, we can say that, with respect to the common lock of the door, the two keys seem the same. But this way of telling the story, obviously, depends on considering the piece of metal, which John or Riccardo have in his pocket as if it were a single key, instead it is made of two keys soldered together.

So there is no magic (as always in the real world).

Similarly, when there are two molecules that are perceived as having the same taste, it is because those molecules can be divided into two parts: one that has no role in stimulating our perceptual systems and one that is instead the one relevant for the our perceptive system. That is, from the point of view of interaction with our body, there is not a single molecule, but two.

Therefore it is not a mystery that two phenomena appear/look the same, because the part that interacts with the body is the same.

Even with colors, the same explanation obtains. An optical phenomenon can be divided into two parts, one that is relevant to our perceptual system (for example the relationship between RGB components) and one that is not relevant (for example, the exact shape of the spectrum). It is as if there were two keys. In the case of metameric colors, the different part is not relevant to our eye while the relevant part is obviously different.

The psychological and philosophical tradition, as well as the layman, has been deceived by on over-simplistic notion of the stimulus and that has prevent us from seeing the simple double-keys mechanism that nature (and my condominium administrator) have used.

Nature never appears different 
from what it is.
Nature is always what it is and
we too, being nature,
are always what we are.
There are no tricks in nature,
only in our theories!

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