Seeing what isn't really there

My experience of a tree is nothing like the tree itself. The colors we see are not really there -- not there in the physical world, that is. Light reflected from the tree is composed of many different wavelengths, with most of the energy focused in what we call the "green" part of the visible spectrum. The cells in the eye detect how much light there is in three different parts of the spectrum (the three primary colors); and this information is then sent to the brain. But all that is passed on are electro-chemical impulses; there is no color here. The green I see is a quality created in consciousness. It exists only in the mind.

Similarly with sound, what I hear are qualities created in the mind. When the seventeenth century Irish theologian Bishop Berkeley argued that only what is perceived exists, a debate ensued as to whether a tree falling in a forest made a sound if no one was there to hear it. The answer is "No". There is no sound in the physical reality; vibrations of the air molecules, yes, but not sound. The sound itself exists only in the mind of the perceiver -- whether that perceiver be a human being, a deer, a bird, or an ant.

The same is true of all other sensory qualities. Molecules released from the tree's bark reach chemical receptors in the nose, leading to the perception of the smell of certain sap or resin. We imagine the smell is in the air; but it is not. That again is a construction in the mind. We may be able to isolate the combination of molecules involved, and even synthesize them to recreate the same sensation, but the aroma itself is a quality that exists only in the mind.

Even our perception of distance is a construction of the mind . Light falling on the retina of the eye creates a flat image; it gives no indication of how far away things are. The brain estimates distance by taking into account information from several sources. It analyzes slight differences between the images from the left and right eyes (the stereoscopic effect), and integrates this with information about where the eyes are focused, relative movements of objects, and previous experience as to the likely size of things. From this data it calculates that the tree is fifty feet away. A three-dimensional image of the world is then created with the tree placed "out there" in that world. Yet, however real it may seem, the quality of space and distance that we experience "out there" is actually a created of the mind.

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