Enneads IV 5: [On Sight]

This is another brief tractate primarily concerned with physics rather than metaphysics.

IV 5: Problems of the Soul (3) [Also Entitled "On Sight"]

We hold that sight operates through the sympathy of observer and object; for both are part of the same Cosmic Body, enjoined by the unity of Soul, and this is the only way we can see of dealing with the many difficulties presented by a more mechanical explanation (such as some kind of contact occurring between observer and object). However, it is clear that this sympathy is carried out through the operation of the observer's bodily sense organs with light acting as an intermediary, and that light needs no other medium (such as air or water) for its operation.

Hearing operates similarly to sight, except that air itself—rather than light—acts as an intermediary. However, while it is obvious how air can transmit volume, it is less clear how it can transmit quality of sound, or timbre. By this we suppose that, just like with sight, sympathy of the soul with the cause of the sound must transmit this information.

On the side I've been picking at Porphyry's Sentences. One of them has been giving me trouble, reading thus:

VI. It is not the case that everything which operates on another thing produces the effects that it produces by contiguity and contact; in fact, even those things which operate by contiguity and contact only employ contiguity incidentally. [tr. Dillon]

I wonder if this "sympathy of soul" is what is being talked about?