Events speed past us, compelling us to reassess our assumptions – our previous formed images of reality. Research topples older conceptions of man and nature. Ideas come and go at a frenetic rate. (A rate, that, in science at least, has been estimated to be twenty to one hundred times faster than a mere century ago.) Image-laden messages hammer at our senses. Meanwhile, language and art, the codes through which we transfer image-bearing messages to one another, are themselves turning over more rapidly.

All this cannot – and does not – leave us unchanged. It accelerates the rate at which the individual must process his imagery if he is to adapt successfully to the churning environment. Nobody really knows how we convert signals from outside into images within. Yet psychology and the information sciences cast some light on what happens once the image is born. They suggest, to begin with, that the mental model is organized into many highly complex image-structures, and that new images are, in effect, filed away in these structures according to several classificatory principles. A newly generated image is filed away with other images pertaining to the same subject matter. Smaller and more limited inferences are ranged under larger and more inclusive generalizations. The image is checked out for its consistency with those already in file. (There is evidence of the existence of a specific neural mechanism that carries out this consistency-checking procedure.) We make a decision, with respect to the image, as to whether it is closely relevant to our goals, or whether, instead, it is remote and hence, for us, unimportant. Each image is also evaluated – is it "good" or "bad" for us? Finally, whatever else we do with the new image, we also judge its truth. We decide just how much faith to place in it. Is it an accurate reflection of reality? Can it be believed? Can we base action on it?

A new image that clearly fits somewhere into a subject matter slot, and which is consistent with images already stored there, gives us little difficulty. But if, as happens increasingly, the image is ambiguous, if it is inconsistent, or, worse yet, if it flies in the face of our previous inferences, the mental model has to be forcibly revised. Large numbers of images may have to be reclassified, shuffled, changed again until a suitable integration is found. Sometimes whole groups of image-structures have to be torn down and rebuilt. In extreme cases, the basic shape of the whole model has to be drastically overhauled.

Thus the mental model must be seen not as a static library of images, but as a living entity, tightly charged with energy and activity. It is not a "given" that we passively receive from outside. Rather, it is something we actively construct and reconstruct from moment to moment. Restlessly scanning the outer world with our senses, probing for information relevant to our needs and desires, we engage in a constant process of rearrangement and updating.

At any given instant, innumerable images are decaying, dropping into the black immensity of the forgotten. Others are entering the system, being processed and filed. At the same time, we are retrieving images, "using them," and returning them to file, perhaps in a different place. We are constantly comparing images, associating them, cross-referencing them in new ways, and repositioning them. This is what is meant by the term "mental activity." And like muscular activity, it is a form of work. It requires high energy to keep the system operating.

Change, roaring through society, widens the gap between what we believe and what really is, between the existing images and the reality they are supposed to reflect. When this gap is only moderate, we can cope more or less rationally with change, we can react sanely to new conditions, we have a grip on reality. When this gap grows too wide, however, we find ourselves increasingly unable to cope, we respond inappropriately, we become ineffectual, withdraw or simply panic. At the final extreme, when the gap grows too wide, we suffer psychosis – or even death.

To maintain our adaptive balance, to keep the gap within manageable proportions, we struggle to refresh our imagery, to keep it up-to-date, to relearn reality. Thus the accelerative thrust outside us finds a corresponding speed-up in the adapting individual. Our imageprocessing mechanisms, whatever they may be, are driven to operate at higher and higher speeds.

This has consequences that have been as yet largely overlooked. For when we classify an image, any image, we make a definite, perhaps even measurable, energy-investment in a specific organizational pattern in the brain. Learning requires energy; and relearning requires even more. "All the researches on learning," writes Harold D. Lasswell of Yale, "seem to confirm the view that 'energies' are bound in support of past learning, and that new energies are essential to unbind the old ..." At the neurological level, he continues, "Any established system appears to include exceedingly intricate arrangements of cell material, electrical charges and chemical elements. At any cross section in time ... the somatic structure represents a tremendous investment of fixed forms and potentials ..." What this means in brief is very simple: there are costs involved in relearning – or, in our terminology, reclassifying imagery.

In all the talk about the need for continuing education, in all the popular discussions of retraining, there is an assumption that man's potentials for re-education are unlimited. This is, at best, an assumption, not a fact, and it is an assumption that needs close and scientific scrutiny. The process of image formation and classification is, in the end, a physical process, dependent upon finite characteristics of nerve cells and body chemicals. In the neural system as now constituted there are, in all likelihood, inherent limits to the amount and speed of image processing that the individual can accomplish. How fast and how continuously can the individual revise his inner images before he smashes up against these limits?

Nobody knows. It may well be that the limits stretch so far beyond present needs, that such gloomy speculations are unjustified. Yet one salient fact commands attention: by speeding up change in the outer world, we compel the individual to relearn his environment at every moment. This, in itself, places a new demand on the nervous system. The people of the past, adapting to comparatively stable environments, maintained longer-lasting ties with their own inner conceptions of "the-way-things-are." We, moving into high-transience society, are forced to truncate these relationships. Just as we must make and break our relationships with things, places, people and organizations at an ever more rapid pace, so, too, must we turn over our conceptions of reality, our mental images of the world at shorter and shorter intervals.

Transience, then, the forcible abbreviation of man's relationships, is not merely a condition of the external world. It has its shadow within us as well. New discoveries, new technologies, new social arrangements in the external world erupt into our lives in the form of increased turnover rates – shorter and shorter relational durations. They force a faster and faster pace of daily life. They demand a new level of adaptability. And they set the stage for that potentially devastating social illness – future shock.