In their2014 article for Contemporary Education Psychology, C. M. Bohn-Gettler andP. Kendeou further note how “These verbalizations can provide a measureof the actual cognitive processes readers engage in during comprehen-sion” (208)
Have to look this up, but this might be dependent on culture and historical moment -- how important is the verbalization of writing (and often scripture). Thinking here of Plato's time when reading aloud was seen as the easier one to understand in contrast to repetition from memory. Or the Romans and early Christianity where silent reading was not as common.