From the introduction: "Our work among the Quiché Indians of Guatemala has consisted partly in the preparing of literacy materials and teaching reading and writing [...]. A major problem for our beginning readers is the recognition of sentences and other large grammatical groupings with the punctuation that marks the borders of such units. It is clear that punctuation marks are necessary for the reader as a partial indication of the intonation of the spoken language, since the latter is not otherwise indicated in the orthography. It is, however, notoriously hard to teach such marks of punctuation, and we have found that only the highly skilled reader consistently recognizes them. This problem has led us to experiment with new ways of teaching punctuation to readers, and we have found a partial solution within the grammatical structure of the language itself."
Fox, David G.
"Some psycholinguistic considerations in Quiché literacy,"
Work Papers of the Summer Institute of Linguistics, University of North Dakota Session: Vol. 3, Article 3.
Available at: https://commons.und.edu/sil-work-papers/vol3/iss1/3