Just my thoughts - The underlying mechanisation of reasoning in humans seems to be the use of symbols as abstractions that represent components in the real world. Hence we can think about things that are not currently present, or emotions which have no visible existence that we can point to. These symbols can be visual (road signs, sign language), auditory (a fire alarm), or written or spoken language. By far the most extensive and finely grained symbol representation is language, sign, written and spoken. I find maths easiest with written language, while working out a presentation is easiest spoken internally. I do not know, but I suspect that those deaf from birth might use sign language for internal reasoning?