Our ways to think depend in part on how we're raised. But at the start, much more depends upon the wiring in our brains. How do those microscopic features work to influence what happens in our mental worlds? The answer is, our thoughts are largely shaped by which things seem most similar. Which colors seem the most alike? Which forms and shapes, which smells and tastes, which timbres, pitches, pains and aches, which feelings and sensations seem most similar? Such judgments have a huge effect at every stage of mental growth — since what we learn depends on how we classify.
For example, a child who classified each fire just by the color of its light might learn to be afraid of everything of orange hue. Then we'd complain that the child had generalized too much. But if that child classified each flame, instead, by features that were never twice the same, that child would often be burned — and we'd complain that it hadn't generalized enough.
Our genes supply our bodies with many kinds of sensors — external event-detecting agents — each of which sends signals to the nervous system when it detects certain physical conditions. We have sensory-agents in our eyes, ears, nose, and mouth that discern light, sound, odors, and tastes; we have agents in the skin that sense pressure, touch, vibration, heat, and cold; we have internal agents that sense tensions in our muscles, tendons, and ligaments; and we have many other sensors of which we're normally unaware, such as those that detect the direction of gravity and sense the amounts of various chemicals in different parts of the body.
The agents that sense the colors of light in human eyes are much more complex than the redness agents of our toy machine. But this is not the reason that simple machine can't grasp what Redness means to us — for neither can the sense detectors in our human eyes. For just as there is nothing to say about a single point, there's nothing to be said about an isolated sensory signal. When our Redness, Touch, or Toothache agents send their signals to our brains, each by itself can only say, I'm here. The rest of what such signals mean to us depends on how they're linked to all our other agencies.
In other words, the qualities of signals sent to brains depend only on relationships — the same as with the shapeless points of space. This is the problem Dr. Johnson faced when creating definitions for his dictionary: each separate word like bitter, bright, salt, or sweet attempts to speak about a quality of a sensory signal. But all that a separate signal can do is announce its own activity — perhaps with some expression of intensity. Your tooth can't ache (it can only send signals); only you can ache, once your higher-level agencies interpret those signals. Beyond the raw distinctiveness of every separate stimulus, all other aspects of its character or quality — be it of touch, taste, sound, or light — depend entirely on its relationships with the other agents of your mind.