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TNU 230 seems to be the guideline on this. I'll note, though, that all of the damage types are referencing 'reduction' in an Attribute. i.e. Confusion attacks "reduce your Intelligence [...]. If you have Psychic Armour, this must be reduced to zero before your Intelligence can be affected."What I'm wondering is...
Many of the spells and effects that are blocked by Psychic Armour have a "damage" associated with them (usually stat-point damage), and so I assume that you just take that damage to your Psychic Armour first. I'm not sure what to do with effects that don't have an associated damage die, however. Maybe roll the Hit Die of the character? That would mean that Fighters and the like can deplete Psychic Armour faster than Wizards and Scholars, which doesn't seem right. Or maybe a spell like Confusion (no damage listed) just can't affect someone with Psychic Armour unless some other effect depletes it?
My interpretation is that Psychic Armour behaves exactly like Disposition, it's just for damage conferred by things other than standard physical attacks.
A spell like Confusion doesn't do any damage, therefore it works regardless of whether one has any Psychic Armour. Characters and creatures are both generally allowed a Save against Magic, which will be their defense against the Confusion spell.