sed cum legebat, oculi ducebantur per paginas et cor intellectum rimabatur, vox autem et lingua quiescebant. saepe cum adessemus (non enim vetabatur quisquam ingredi aut ei venientem nuntiari mos erat), sic eum legentem vidimus tacite et aliter numquam, sedentesque in diuturno silentio (quis enim tam intento esse oneri auderet?) discedebamus et coniectabamus eum parvo ipso tempore quod reparandae menti suae nanciscebatur, feriatum ab strepitu causarum alienarum, nolle in aliud avocari et cavere fortasse ne, auditore suspenso et intento, si qua obscurius posuisset ille quem legeret, etiam exponere esset necesse aut de aliquibus difficilioribus dissertare quaestionibus, atque huic operi temporibus impensis minus quam vellet voluminum evolveret, quamquam et causa servandae vocis, quae illi facillime obtundebatur, poterat esse iustior tacite legendi. quolibet tamen animo id ageret, bono utique ille vir agebat. (Confessiones 6.3.3.)
"Now, as he read, his eyes glanced over the pages and his heart searched out the sense, but his voice and tongue were silent. Often when we came to his room--for no one was forbidden to enter, nor was it his custom that the arrival of visitors should be announced to him--we would see him thus reading to himself. After we had sat for a long time in silence--for who would dare interrupt one so intent?--we would then depart, realizing that he was unwilling to be distracted in the little time he could gain for the recruiting of his mind, free from the clamor of other men's business. Perhaps he was fearful lest, if the author he was studying should express himself vaguely, some doubtful and attentive hearer would ask him to expound it or discuss some of the more abstruse questions, so that he could not get over as much material as he wished, if his time was occupied with others. And even a truer reason for his reading to himself might have been the care for preserving his voice, which was very easily weakened. Whatever his motive was in so doing, it was doubtless, in such a man, a good one." (Translation from here)
Is this issue ever treated in Indian or Tibetan literature?