The major issues that has become more clear to me is the way that the nervous system makes sense of the world is by receiving patterns of information from a variety of sources and then learning to interpret them (label them) as something. From color vision, we see that color is perceived based not only on the intensity of light (high light versus low light conditions), but also on the wavelength of light in high light conditions as well as the reaction in the receptor (cones). The light creates a reaction in the cones by a pattern of photopigments which will be different based on the wavelenght of light. Thus the nervous system receives a "code" of information from the type of receptor stimulated, the wavelength of the light and the photopigments used which it learns to interpret (and label) as a certain color. It seem our behavior, then, is based on our interpretation of patterns of input from many sources on the type of receptors stimulated, as well as from what is not stimulated (lateral inhibition). In high light conditions, a certain color creates a patterns of activity based on the cone photopic system which the brain learns to interpret as a specific color. Slight changes or variations in the color red will be detected because the pattern of activity will be slightly different. Thus our behavior is based on our ability to detect and transmit information, as well as our ability to code the pattern of activity and label it.
It seems that most sensory perception operates in a similar manner. Stimuli are detected, membranes are depolarized, a pattern of activity is transmitted (while other is inhibited) and the brain learns to interpret this in such a way that we begin to experience reality. The nervous system is set up to detect change or difference, and through detection and analysis of these differences it creates reality. Much like non color vision tells us mostly about the edges (or the change) color vision tells us about the difference of one wavelength versus another and about one photopigment in relationship to another (color mixing). In this way we perceive the world. Similarly, I would suspect our other sensory systems operate to detect change. The tactile system, for example uses information about the area of the skin stimulated (which receptors are stimulated) and which are inhibited (lateral inhibition) as well as information about how quickly the signal is being transmitted (intensity) and how sharp the stimulus is (based on comparison of areas stimulated and inhibited, to make a perception of what just happens. The nervous system learns to interpet this and thus uses this information to tell us about reality.
Yep, color vision principles certainly generalize to other systems. And detecting differences certainly important in all of them. So too the somewhat arbitrary character of the initial transduction. I think, though, you underestimate the nervous system a bit in saying that the brain "learns to interpret" this. Much of the "interpretation" and consequent creation of meaningful categories actually happens in the transduction and shortly thereafter. So, for example, it is the particular set of cone pigments which actually gives rise to the concept red, or at least to the kind of distinctive pattern of activity for which other parts of the nervous system need to develop a concept (in organisms that do such things). PG