Rule Clarification, Spirits affecting physical world Options

[Xel]

Hey guys,
Quick rule clarification question - for summoned spirits to use powers such as "Accident", it is my understanding that they must actually be materialized if their target is a physical being (read: pretty much anyone who isn't astrally perceiving). Is this true? If not, where in the rules does it explain what may be done in the physical world when NOT materialized? (My understanding is pretty much no interaction other than speaking when manifesting, but nothing more unless materialized).

Thanks,
--Xel