I’ve expanded upon (but tried to refrain from modifying, at least based upon my interpretations) mental conflicts in my game. The way that it has been working:
We use three different types of mental attacks.
Psychic attacks are essentially psychic force directed against the opponent’s will. This allows the attacker to influence the opponent’s actions, dominate, control, etc. This type of mental attack will always be Lawbreaking (capital L for metaphysical consequences, even for sponsored magic, but how my group treats Lawbreaking and sponsored magic could be an entirely different post). These are Spirit magic. These must be defended against with Discipline barring specific stunt or declaration related circumstances on the part of the defender (hasn’t come up, but I provisioned for it anyway).
Sleep attacks are in many ways kid gloves version of psychic attacks, but do not inflict lasting (permanent, they can still inflict consequences for which recovery is just periods of good rest and relaxation) mental harm on the opponent. They make an opponent drowsy mentally (not physically tired, but still needs to sleep sort of like not getting enough sleep each night). I allow these as mental attacks based upon examples in the books as well as how the developers treated mental consequences related to spellcasting. These are Spirit magic and not Lawbreaking (but may be lawbreaking, little-l meaning Warden enforcement depending on context). They may be defended against with Discipline OR Endurance (see below for how Toughness powers interact).
Distraction attacks break your opponent’s ability to concentrate, distract and disorient. They inflict mental stress in the same way as walking into a room with four different songs playing at full volume and erratic strobe lights would inflict stress. They aren’t lawbreaking of any sort (unless flavored as causing the opponent to hallucinate rather than simply creating the images or sound, then it is Lawbreaking). They are the province of Spirit (for light) and Air (for sound) magic. They may be defended with either Alertness OR Discipline.
Discipline becomes the mental equivalent of Athletics in that it may be used to defend against any type of mental attack. Endurance and Alertness were choses both for thematic reasons, but also because they are common skills for most characters allowing for things to not have to be rewritten to improve defenses against a type of attack which would become more common.
Toughness (specifically Recovery) powers also make it easier to defend against sleep attacks. Inhuman provides +2, Supernatural +4, Mythic +6. Physical Immunity does not provide a bonus. This applies only to Sleep attacks and not other types of mental attacks and is extrapolated from the Vigorous and Tireless effects.
(Note: I have debated changing this to simply providing armor equal to half this value and may playtest it soon).
Echoes of the Beast grants a +1 bonus against Distraction attacks. Active Sight completely negates these types of effects (but will open them up to other types of mental stress, of course).
(Note: I’ve essentially allowed any power that boosts Alertness for anything other than Initiative to provide a bonus).
I'm sure I'm forgetting details, but this is the gist of it. Let me know (either on here or by PM) if you have further questions.