When I usually speak about the Art versus Language Perspectives, I usually couch it in a view that there are "different potential ways our society treats graphic images." As I just realized, stating it in this way maybe obscures the true intent of the distinctions.
Really, this is a hypothesis about cognition.
At the heart of my theory of visual language is the observation that we have three modalities by which we can convey our concepts: Sound, Body motions (faces/hands), and creating graphic images. That's it. To push it further, the theory is that when these modalities take on structured sequences governed by a system of constraints (a grammar), it becomes a type of language: speech, sign language, or visual language.
The "Language Perspective" assumes that all systems of conceptual expression work in similar ways — what we can maybe call "cognitive modality equivalence" or some such. Under such a view, we would expect for the graphic modality (drawings) to operate under the same principles as the verbal and manual domains.
If you look at the ways that speech and gestures (and sign language) grow developmentally in children and are used and treated in society, you see certain patterns — conventionality, imitation, communality, etc. While many of those patterns do emerge in the graphic domain, they appear "dampened", are dismissed, or just aren't recognized as such.
So, the question becomes raised: "Why don't you see these things fully in the graphic modality?" and/or "why don't we know them when we see them?"
The offered explanation is the Art Perspective — a cultural force that suppresses the patterns that would normally emerge from any other modality of conceptual expression. With polar opposite emphases, the Art Perspective works to dampen the "usual" course of development and treatment for graphic images.
So, given this, a new set of questions can be asked about this underlying "cognitive modality equivalence": What are the trends that a conceptually expressive system shows in development and society? How do modalities differ? Do these trends reflect broader cognitive processes than just conceptually expressing systems?