This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Symptoms & Signs , Subject name: Psychiatry
Perceptual misinterpretation of a real object is 
Select and explain. 
A. Illusion, B. Delusion, C. Hallucination, D. Schizophrenia
A: Illusion
Answer: A: Illusion 
Explanation: Ans. is 'a' i.e. Illusion Both illusion and hallucination are perceptual disorders.In illusion there is misinterpretation of the actual stimulus whereas in hallucination perception occurs in the absence of any stimulus.Illusion -Misinterpretation of rope as snake.Hallucination - Able to see snake without any ropeDelusionIt is the disturbance in the content of thought.It is a belief based on incorrect inference about external reality and not consistent with patient's intelligence and sociocultural background.DeliriumIt is used as a general term for the quite cognitive impairment syndrome.Delirium is characterized by global impairment in consciousness, resulting in reduced level of alertness, attention, and perception of the environment.