In his work, Theaetetus, Plato wrote, "Perception, then, is always of what is, and unerring." However, Socrates contended that "perception is unerring--as befits knowledge." Of course, science has proven that the eyes do not actually see anything. They are simply organs of vision: When light hits the lenses of the eyes, nerves are excited and then carry messages to the brain. The brain then comprehends the messages of the nerves and the person "sees" the object(s) viewed. Since, each person's brain differs in its knowledge, then understanding of the messages from the nerves will necessarily differ.
A very simple example of this interpretation of visual perception can be witnessed as a student from a lower socio-economic class reads aloud. Since he/she has learned substandard English at home and in his/her environment, this student may read "he has seen" as "he seen" even though the Standard English is in print.