Invariants, in terms of signs, refers to the seeming "basic residua" or essence of a sign. Though the letter s may appear in many different forms--different sizes, different fonts, different text styles, different handwritings--there seems to be some common essence that allows us to determine that it is still simply an s. The same is true of spoken words--despite different volumes, pitches, or accents, we still can identify a particular word.
Yet, as Cherry points out, this ability to recognize signs in their myriad forms does not necessarily imply a core invariant. We often use a number of different kinds of clues to recognize a sign. We may determine that a particular letter is an s or a particular word is dog based on the signs around it or the context of the discourse, rather than some invariant of the sign itself.
Western philosophy has long supposed an internal and external world. That is, there exists some objective material world that we all share and experience. But this external world generates or prompts experiences "within" us. That is, we have personal qualia ("mental sensations") that other people cannot examine directly in the same way that they can examine the constituent aspects of the external world.
If we adopt this world view (and it is difficult not to, considering our language often encodes a difference between an external objective world and an internal subjective one), we are faced with a number of interesting questions. How exactly does this external world prompt our internal experiences? How do our internal experiences prompt changes in the external world? That is, how does my intangible mind move my tangible body, and yet move only my tangible body?
Communication then faces a number of problems: how do we encode our internal thoughts into external signs? How do we interpret or filter external stimuli to decode the meaning of a sign? (This is exactly the debate over an existence of invariants as discussed above.) And if all of our transfers of meaning must be mediated by an external world, can we ever really fully communicate? Can we ever form true interpersonal relationships, or are we, in a sense, "imprisoned" in our bodies?
Assuming an internal-external model of reality means these questions are important when we try to understand communication. However, a different model of reality could well render these questions irrelevant, nonsensical, or at least much less important.
Memory, abstraction, and redundancy are all important aspects of pattern-matching and learning.
When we communicate, we tend to transmit redundant data, which allows the receiver to accurately determine sign "invariants". This is an abstraction process, wherein the receiver is determining the essential forms of the signs from the complete environmental stimuli. The receiver generally disregards non-essential aspects of the sign, such as the font or accent.
We perform this abstraction process based on our experience with particular signs. We must have a memory in order to retain signs, both to encode new messages and to decode received messages. Memory also means we have a variety of associations with different signs and experiences. Coupled with our ability to abstract, we can apply problem-solving techniques to situations that appear on the surface to quite different.
Interestingly, the metaphor used to conceptualize computers is often that of the human mind. Now, however, since computers have become so common-place and we have such extensive experience with them, we now often conceive of the mind in terms of a computer. There are many surface similarities. Both can save data for later retrieval. Both can process information in a logical, algorithmic fashion. Both generate patterns that can not be adequately described in terms of the underlying system of electrical signals. That is, a program may compute pi to the 100th digit running on system of off-on voltage changes in silicon circuits. And a person may compose and utter a sentence, which requires a system of correctly firing neurons. But the correctness of the calculation or whether the sentence is a lie cannot be described solely in terms of voltage level or neuron firings.
Of course, there are also a number of differences. A brain is living and organic, while a computer is not. A computer follows a set of predetermined instructions, while the brain does not. Human brains can spontaneously generate emotions, insight, novel creations, and self-awareness, while computers can not. Computers can be shut off and turned back on with much less damage than human brains.
Of course, all these difference and similarities are true only depending on your model of the human brain, or of a computer for that matter. Perhaps we are as programmed and fated by our past experiences as any computer. Perhaps we can never be truly logical. Perhaps computers can learn and create, though whether they can depends on your definition of those two activities.
The comparison between brain and computer will persist, because both produce intangible "mental" or "computational" results using a tangible, physical "hardware". In order to understand our own mental processes, we need a model, analogy, or conceptual metaphor. And it seems the closest candidate in terms of similar processes is either animal and computer cognition.
Cherry, Colin. On human communication: a review, a survey, and a criticism. Cambridge: Technology Press of Massachusetts Institute of Technology, 1957.
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