NanoGuy

This is wrong and long disproven. For even the most rudimentary of perceptual mechanisms, like the first layers in the visual cortex, neurons can act as feature detectors by learning which neurons in lower levels are likely to fire together or which will not fire if others are firing. Further layers find out when those feature detectors neurons are firing together or not, and so on up. Go a few layers up and now the brain is effectively aggregating all those first neuron reponses into much more abstract things, like regions of rapidly varying light intensity or hue (edges of objects in the visual field) or regions of similar or slowly varying color (like surfaces). Later on this information gets glommed together with information from different senses, like our kinesthetic sense, so that at higher and higher levels of abstraction we can do more interesting simulations, like mental rotations of figures.
Every step in that process is "symbology", a little piece of machinery that compactly represents lower level sensory data. People do not have stored up memories of sensory experience at the level of photons impinging on the retina. We are not cameras that can be forced to replay a scene. Rather, the states of feature detector neurons, which can represent the gist of a scene, are remembered, and this information can be used in reverse, with the feature detectors now acting as feature controllers which re-activate lower levels of features, in order to approximately reconstruct scenes. Language is built on thoughts, which are made of concepts, which are abstracted from perception. And every one of those layers is supported by more math and science than found in that book.
There are no "signs" floating around in our minds. To develop a real understanding, you need to know what the neural machinery is doing and how that behavior implements relevant algorithms. And we do know a lot of that. And no, when the results came in, the answer was not that "language is actually the structure that the human mind is made of". Language comes from the human mind; saying, of absolutely any cognitive phenomenon or process that "language did it" can not be an explanation. It's like saying lightning is responsible for electromagnetism.