Ans: c) IllusionIllusion:Misinterpretation of stimuli arising from an external object. There are three types:i) Complete illusion: depends on inattention of the person. For eg: misreading words in newspapers / missing misprints, we read the word automatically as if it were complete. It also depends on our previous experience / interests. For eg: to the person with an interest in reading, _ook may be misread as 'book' even though the faded letter is '1'.ii) Affect illusions: Arising in the context of a particular mood state, eg: young child wakes up scared in the middle of the night and misinterprets a white towel as a ghost.iii) Pareidolia: Vivid illusions of excessive fantasy thinking. For eg: the subjects sees vivid pictures in fire/ clouds/pattems on walls.Hallucinations:Perceptions without an adequate external stimulus.Special types of hallucinations;i) Functional hallucinations: Hallucinations which require the presence of another real sensation. For eg: patient hears the voice of God (hallucination) as her clock ticked (real sensation).ii) Reflex hallucianations: Morbid form of synaesthesia.Synaesthesia: experience of a stimulus in one modality produces a sensory experience in another.For eg: patients can feel, taste and hear Flowers simultaneously in reflex hallucination: stimulus in one sensory field produces a hallucination in another. For eg: patient feels pain in her head (somatic hallucination) when she heard someone sneeze (the stimulus).iii) Extracampine hallucinations: it has hallucinations outside the limits of the sensory field. For eg: patient hears the voices of the people in Delhi when he is in Kerala.iv) Hypnagogic hallucinations: hallucinations which occur when subjects go to sleep.v) Hypnapompic hallucinations: hallucinations which occurs when subject wakes up from sleep.CHARLES- BONNET SYNDROME:Complex visual hallucinations occur in the absence of any psychopathology and in clear consciousness.Associated with central / peripheral reduction in vision.BODY IMAGE DISTORTIONS:i) Hyperschemazia: perceived magnification of body parts.ii) Aschemazia: perception of body parts as absent.iii) Hyposchemazia: perception of body parts as diminished.iv) Paraschemazia: feeling that body parts are distorted/ twisted/separated from the rest of the body.v) Hemisomatognosia: unilateral lack of body image- person behaves as if one side of body is missing.vi) Anosognosia: ddenial of illness.vii) Somatoparaphrenia: patients showing bizarre attitude to their paralysed limb. They feel they have too many/ distorted/ inanimate limbs.KORO: belief that the penis is shrinking and will retract into the abdomen and cause death.DELUSIONS: false, unshakable belief that is out of keeping with the patients social and cultural background.Special types:i) COTARD' S SYNDROME: extremely severe nihilistic delusion. Seen in severe depression. Eg: patient complains that their bowels have been destroyed and may never pass feces again.ii) CAPGRAS SYNDROME: patient believes that a person closely related to her has been replaced by a double.iii) FREGOLI SYNDROME: the patient believes that one or more people have changed their appearance to resemble familiar people, usually in order to persecute the patient.iv) INTERMETAMORPHOSIS : patient believes that a person/ persons have been transformed, both physically and psychologically into another person/ that people have exchanged identities with each other.v) Doppelganger: patient has delusion that another person has been physically transformed into his own self (syndrome of subjective doubles).vi) FOLIE A BEUX: person in a close relationship with somebody who already has an established delusional system develops similar ideas (shared/ induced delusional disorder).