Language is not the basis of thought. If someone thinks only with a mental narrative (in words, some language), then they're not really thinking in the broadest sense.
Being an emergent / adaptive organism, we are taught and learn models and metrics, and in turn project those outward upon the world.
Not shocking that the models and metrics form the scaffolding for thought as expressed in language.
“Does Language Shape Thought?: Mandarin and English Speakers' Conceptions of Time”
[1] http://www.sciencedirect.com/science/article/pii/S0010028501... [2] Which, also likely not a coincidence, calls into question the veracity of narrative structure, and instead frames narrative as an ideological tool and construct.
Visual, wherever the arbitrarily privileged line is drawn, is another convention.
To suggest that somehow the nebulous “visual domain” doesn't require reading would be to ignore much of art history and theory.
Again, there is no “visual” realm that is not steeped in vernacular; cliche, symbology, context, etc.
In this way, the visual domain is not somehow more elevated / pure / true than any other language, despite the sad reality that many have been unexposed to understanding it as such.
Not sure why you're arguing a priori that all thought must be "vernacular" - code for "linguistic", I'd assume. But thought is not merely verbalizing or grammatizing everything.