Perhaps I should have gone into more depth? I understand we are talking about psychological types. Van der Hoop is a Jungian and is exactly talking about that.
Introverted Intuition is the part of our cognition that sees imagery in our minds, generated from the unconscious.
When Ni goes...
A great book that tackles personality type and mental illness is Conscious Orientation by J.H.Van der Hoop. He was a Jungian who spoke about certain illnesses in certain types.
I have BPD and Anxiety. Very poor Ni can be seen in schizophrenics.