invented, and then the electrical telegraph, wireless telegraphy, the telephone, television, and so on at an accelerated rate of development.
We also communicate with others by making a picture on a surface (clay tablet, papyrus, paper, wall, canvas, or screen) and by making a sculpture, a model, or a solid image. In the history of image-making, the chief technological revolution was brought about by the invention of photography, that is, of a photosensitive surface that could be placed at the back of a darkened chamber with a lens in front. This kind of communication, which we call graphic or plastic, does not consist of signs or signals and is not so obviously a message from one person to another. It is not so obviously transmitted or conveyed. Pictures and sculptures are apt to be displayed, and thus they contain information and make it available for anyone who looks. They nevertheless are, like the spoken and written words of language, man-made. They provide information that, like the information conveyed by words, is mediated by the perception of the first observer. They do not permit firsthand experience--only experience at second hand.
The ambient stimulus information available in the sea of energy around us is quite different. The information for perception is not transmitted, does not consist of signals, and does not entail a sender and a receiver. The environment does not communicate with the observers who inhabit it. Why should the world speak to us? The concept of stimuli as signals to be interpreted implies some such nonsense as a world-soul trying to get through to us. The world is specified in the structure of the light that reaches us, but it is entirely up to us to perceive it. The secrets of nature are not to be understood by the breaking of its code.
Optical information, the information that can be extracted from a flowing optic array, is a concept with which we are not at all familiar. Being intellectually lazy, we try to understand perception in the same way we understand communication, in terms of the familiar. There is a vast literature nowadays of speculation about the media of communication. Much of it is undisciplined and vague. The concept of information most of us have comes from that literature. But this is not the concept that will be adopted in this book. For we cannot explain perception in terms of communication; it is quite the other way around. We cannot convey information about the world to others unless we have perceived the world. And the available information for our perception is radically different from the information we convey.
Ecological optics is concerned with many-times-reflected light in the medium, that is, illumination. Physical optics is concerned with electromagnetic energy, that is, radiation.