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,