Invisible Power Effects
Invisible Power Effects and Defensive Powers
A character cannot abort to a defensive power to counter an attack or effect that he or she cannot perceive, nor can a character take advantage of a defensive maneuver, that isn’t constant, to counter a inobvious or invisible power effect. So, for example, a character who is already blocking could not block an attack that he or she does not see.
A character could, on the other hand, block an inobvious power that is perceived. However, the act of discerning the inobvious effect generally incurs a -3 penalty to OCV unless the character makes the Perception roll significantly (3 or more).
Invisible Power Effects and Triggers
An unperceived attack or effect cannot trigger a power. This includes, say, damage that the target cannot perceive. A character with healing, triggered whenever the character gets to 1/2 stun, would not trigger if the effect of the damage were invisible.