One test used to diagnose schizophrenia is called the DAP test, or “draw a person” test. It involves asking the patient to draw a person; if the drawing is incoherent (body parts not connected correctly, too few or too many or in the wrong place, etc.) that can be symptomatic of schizophrenia. I was reminded of this by this image, which could probably serve as a diagnostic of some form of cognitive decline (i.e. if a patient responds to this positively, some critical faculty has deteriorated)