i think it is more auditory and has to do with out ability to error correct. Actually there is a really fascinating section in james gleick's "the information" on African drum communication which is essentially a much less dense version of spoken language since you say everything using a long sentence which essentially reduces the possibility of it being misinterpreted despite most of the sounds of normal spoken language are missing. Not sure if more scholarly work supports this idea but if this is the case then a written or thought language could certainly be denser...like symbolic algebra or python.
