It sounds like it means that the range of choices was fewer in the written forms as compared with the visual forms, but as already commented it's very hard to be sure without the complete context.

I wouldnt say fewer choices, i would say that visual narrative was one of the forms of narrative that was used more than other literacy

Hi Mehrdadart: You could offer that conclusion but I think you might be "reading into" the statement more than is actually there. The sentence has two clauses, and both are widely divergent in meaning and intent. Let's see them. =========================== #1 "Once a society developed a certain degree of literacy, its members tended to gravitate toward certain forms. #2 "...the mode of visual narrative used was a choice among a range of possibilities." Clause #2 is virtually a redundancy for one thing. Everything in existence, can be understood generally as A---Choice---Among---A---Range---Of---Possibilities". That sort of conclusion is so generally as to be almost meaningless. Clause #1 does not identify any FORMS, so little can be concluded from it. Not all literary expression is NARRATIVE. Also, NARRATIVE does not define the set of Literary Forms. NARRATIVE is one of the literary forms. Clause #1 informs us that there are a number of forms. One form is VISUAL NARRATIVE. Your own question suggests that NARRATIVE ART is subdivided into another set of Forms; but the sentence does not inform us that NARRATIVE is subdivided.

It is hard to answer your question without knowing the full context of the article from which this paragraph presumably comes.