Perception without stimuli is

Delusion: False belief, based on incorrect inference about external reality, that is firmly held despite objective and obvious contradictory proof or evidence and despite the fact that other members of the culture do not share the belief. Delirium: Acute reversible mental disorder characterized by confusion and some impairment of consciousness; generally associated with emotional lability, hallucinations or illusions, and inappropriate, impulsive, irrational, or violent b Reference:p.922 chap 7.3 Signs and Symptoms in Psychiatry(Kaplan & Sadock's Comprehensive Textbook of Psychiatry, 9th Edition)