I'm not sure I understand the question. For the pre-test, that is done at the beginning of a session, before prepping the patient. It can be done with and normal spontaneous settings. You would see artifacts if the patient has metal.
For SSPs, that is done after a recording, as part of processing. SSPs can be used to find the artifact, typically it will be one of the first projectors. I suggest reading the tutorial on SSPs.
Hope that helps.