These are subjective experiences that can only be determined by asking the patient about them.
Disorders in perception and self-perception are:
Illusion/Illusionary Deception.
- Relates to a mistaken interpretation of a true sensory stimulus, such as mistaking a shrub or tree for a human being. On closer examination, one usually corrects such an interpretation. An illusion does not indicate psychopathology, but is indicative of a clouded consciousness, e.g. drugs.
Hallucination.
- During the anamnesis, a given patient may display behaviour that suggests perceptual disturbances, e.g. patient talking or arguing with a non-existent interlocutor.
- There are five distinct types of hallucinations:
- Auditory hallucination; hearing sounds or voices. Auditory hallucinations are indicative of psychotic disorders and delirium, but may occur on their own in the general population without additional evidence of a psychiatric disorder.
- Visual hallucination; seeing ghosts, people or objects. Visual hallucinations are a indication of delirium, schizophrenia, intoxication and drug dependency withdrawal symptoms (amphetamines, cocaine, alcohol), but also of epilepsy and visual impairment (Charles Bonnet syndrome).
- Olfactory hallucination, the smelling of odours. Olfactory hallucinations are indicative of non-psychiatric disorders, but also of an emotional disorder in which a scent memory is important for the patient. Patients with depression may indicate smelling an odour of death.
- Gustatory hallucination; tasting or having the sensation of a taste in the mouth. Gustatory hallucinations are indicative of neurological disorders, including epilepsy, but also of a psychotic disorder.
- Haptic hallucination; feeling something on or under the skin or inside the body. Haptic hallucinations are indicative of schizophrenia, but also for substance abuse (hallucination/illusion of insect infestation/fornication).
Derealisation.
- This is a usually unpleasant, subjective sensation of alienation from one’s surroundings. The patient is aware of the unreal character of the experience. Derealisation is indicative of acute stress disorder, panic disorder and of cannabis use (usually an overdose).
Depersonalisation.
- This is a usually unpleasant, subjective sensation of alienation from oneself and one’s body. The patient is aware of the unreal character of the experience. It is a specific indication of a depersonalisation disorder, but can also occur when using drugs such as amphetamine, cocaine and cannabis.
Body Perception Disorder.
- This is the case when a patient denies presence of their body or body parts. On the other hand, preoccupation with an exaggerated or non-existent defect in body physical features is indicative of body dysmorphic disorder. Body image distortion is a frequent symptom in patients with anorexia nervosa, where they view themselves as being overweight, despite clear evidence of the contrary.
