The psychiatrist is certainly not in a position to discern the authenticity of apparitions, locutions etc. His contribution in the process of discernment is to differentiate between those who are mentally ill and those who are not. The mentally ill person may have other symptoms of psychopathology. He may draw unnecessary attention to himself. This contrasts with the behaviour of St. Bernadette and the children of Fatima who went out of their way to avoid publicity.
Mental illness is characterised by disordered thinking and loss of goal-directed activity.
Extraordinary manifestations are not treated with sensible caution by the mentally ill. In contrast, authentic seers are prepared to await further judgement. The mentally ill person does not have much reticence in talking about his experiences. He is often fascinated by the incredulity of others. It is also worth noting that the number of apparitions of Our Lady that have been accepted is small indeed in comparison to the number of claims made.