BLATT-sight

Selective Channeling (page 132): Do I have to be able to see a creature in order to exclude them from the effect of my channeled energy?

Just like using a Target: creature spell, you must be able to see or touch a creature to affect it (or, in the case of this feat, select it to be unaffected). Pinpointing the square of an invisible creature isn't sufficient—you must be able to see or touch the creature.

Note that this works differently than an alchemist's precise bombs discovery, which allows the alchemist to exclude *squares* from his bomb's splash area (not targets).

—Sean K Reynolds, 07/14/11

They dont have to see you, you MUST see them.  Apparently Channel targets even though the word "target" isnt in the description.