Patients in a new study were able to comprehend words that were written but not said aloud. They could write the names of things they saw but not verbalize them. For instance, if a patient in the study saw the word 'hippopotamus' written on a piece of paper, they could identify a hippopotamus in flashcards. But when that patient heard someone say 'hippopotamus,' they could not point to the picture of the animal.
Source: Medicine Science Daily