Perceptions

Perception is the process of attaining awareness or understanding of sensory information. What any individual perceives is a result of the interplays between past experiences, culture and their personal interpretation of the object of perception. Perceptions are subjective experiences which may be shared by other but are essentially those of the individual patients. It is highly important to assess these carefully as perceptual disturbances can be present in many psychiatric disorders.

Abnormal perceptions are classified into three - illusions, hallucinations and dissociations.

Illusions
An illusion is an abnormal perception of a real external stimulus in other words an illusion describes a misinterpretation of a true sensation. Theoretically they can occur in any of the senses however visual / optical illusions are the most well known and understood.

It is important to distinguish between hallucinations and illusions when interviewing a patient. Careful questioning of the patient is necessary - for example, establishing that hearing voices regardless of the environment would be a hallucination, whereas hearing demonic screams and screeches whenever the alarm goes off would be an illusion.

'Have you ever seen (heard, tasted, felt, or smelt) things which others around you saw (heard, tasted, felt, or smelt) differently to you?'

'Do things ever seem different to how they normally seem?'

'Have you ever experienced seeing (hearing, tasting, feeling, or smelling) a normally familiar thing as totally unfamiliar?'

Hallucination
A hallucination is a false perception occurring in the absence external stimulus. Hallucinations can occur in any of the five sensory modalities (sight, sound, taste, touch, or smell). True hallucinations cannot be accounted for by the person's religious or cultural background.

Certain psychiatric disorders are more likely to be associated with certain hallucinations e.g. Auditory hallucinations are a common symptom of schizophrenia., Somatic/tactile hallucination (formication) is a common side-effect of the extensive use of cocaine or methamphetamine

Inquire about insight into the hallucination; the patient may be fully aware may be aware that the perceptions are false or the may believe what they are seeing, hearing, tasting, feeling, or smelling is completely real and have a delusional system interpretation of the hallucination.

'Have you ever experienced seeing, (hearing, tasting, feeling, or smelling) something when nothing was there?'

'Have you ever see (hear, taste, feel, or smell) things that other people don't?'

'Do you ever experience a constant smell or taste when you haven't smelt or tasted anything?'

'Do you ever hear anything that has no obvious source?'

'Do you think that what you saw (heard, tasted, felt, or smelt) was absolutely real or could it have some explanation?'

Dissociation
Dissociation occurs when the mind separates a person's thoughts, memories, perceptions, actions, or sense of identity from their normal consciousness. Dissociation can occur along a spectrum of severity. Dissociated mental contents may resurface spontaneously or through triggers.

Experiencing dissociation does not necessarily mean that that person has a dissociative disorder or other mental illness for example a mild degree of dissociation occurs in people who have gone without sleep for a long period of time. Patients with acute stress disorder, post-traumatic stress disorder (PTSD), conversion disorder, or somatization disorder may develop dissociative symptoms.

Dissociative amnesia
In dissociative amnesia there is an inability to remember important personal information to a degree that cannot be explained by normal forgetfulness. It is not associated with experiencing a change in identity. Often it occurs as a result of a traumatic accident or witnessing a violent crime.

Establish if a patient has experienced a recent traumatic event.

‘Have you recently experienced forgetting personal details like your friends names (car, workplace, family names)?’

Depersonalisation
Depersonalisation is a symptom in which there is a sense of detachment from the self. It can be associated with sleep deprivation or "recreational" drug use. Patients sometimes describe depersonalisation as feeling like a robot or watching themselves from the outside. Depersonalisation disorder may also involve feelings of numbness or loss of emotional "aliveness."

'Do you ever feel distant or detached from yourself as if you were not real or different to normal?'

'Have you ever felt like you where outside of or separated from your normal self?'

'Do you ever feel like you are emotionally separated from what is going on around you?'

Derealisation
Derealisation is where objects in an environment appear altered to an individual. It is often accompanied by depersonalisation. Normal things may seem strange, unreal, distant, or two-dimensional.

'Do you ever feel distant or detached from everything around as if everything was not real or somehow different to normal?'

'Do things around you ever seem unreal?'

Descriptive Word List [psychiatric dictionary]
Hallucinations	Perceptual disturbance
Auditory Gustatory Hypnagogic Hypnopompic Kinaesthetic Lilliputian Mood congruent Mood incongruent Olfactory Somatic Trailing Visual	Alcoholic Hallucinosis Macropsia Micropsia Depersonalisation Derealisation Fugue Hysterical anaesthesia
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