PERCEPTION

Perception is the awareness of objects, qualities and relations that follow stimulation of peripheral sensory organs as distinct from awareness that results from memory.

DISORDERS OF PERCEPTION

Perception: The process of becoming aware of what is presented through the sense organs.

Imagery: A sensory experience over which the subject has voluntary control and experiences as taking place within the mind.

- Eidetic imagery

- Pareidolia

I. SENSORY DISTORTIONS

A real object is perceived distorted: intensity or quality may be altered.

e.g.: - hypo / hyperaesthesia

- micro / macropsia.

- dysmegalopsia.

Changes in the emotional quality and associations of real percepts

- Splitting of perception.

II. FALSE PERCEPTION

Illusions

An illusion is a perceptual misinterpretation of a real external sensory experience.

It is often dictated by dominant affective state, e.g. anxiety which may lead to threatening distortion of visual experiences.

Three types:-

1. Completion illusion.

2. Affect illusion.

3. Pareidolic illusions.

Hallucinations

This is an apparent perception of an external object in the absence of an adequate sensory stimulus. An internal psychological event is mistakenly attributed to an external source.

Any sensory modality may be involved: it may refer to external surroundings or to bodily function.

When caused by organic factors there may be impaired consciousness. Organic causes include hallucinogenic drugs, epilepsy, delirium due to toxic agents or alcohol/barbiturate withdrawal states. Psychogenic causes include schizophrenic psychosis, which typically occurs in the setting of clear consciousness. Hallucinations may be hypnagogic (preceding sleep) or hypnopompic (on waking).

Features:-

1. A perception in the absence of an external stimulus

2. Appears real has the full force and impact of a real perception.

3. Unwilled, occurs spontaneously, not readily controlled.

Aggernaes (1972) - features shared between hallucinations and true percepts:

1. Experienced as a sensation, distinguishable from thought or fantasy.

2. Relevance (one realises the percepts possible relevance for ones self).

3. Objectivity. Same object could be experienced in another sensory modality.

4. Object constancy.

5. Involuntary. Unalterable, even if this were wished for.

6. Independence. Percepts is not felt to be due to own mental state. But not pubIicness.

Pseudo hallucinations

located in subjective space

- perceived with inner eye (or ear)

- differs from imagery by being perceived as involuntary

Functional Hallucinations

- a normal perceptual stimulus in one modality provokes an hallucination in the same modality. (e.g.: tap and voices)

Reflex Hallucinations

- an hallucination in one modality is precipitated by sensory stimuli in other modalities. some authors use the term synaesthesia

Hallucinations may be described according to:-

1. Complexity (elementary or complex)

2. Sensory modality

3. According to special features of their content

SPECIAL TYPES OF HALLUCINATION

Auditory HaIIucination

- 2nd person.

- 3rd person.

- Two or more voices arguing or discussing.

- Gedankenlautwerden

- Echo de Ia pensee

- running commentary Visual hallucinations

- Lilliputian

- Extracampine

- Autoscopic

Hallucinations of body sensation

- Superficial (thermic, haptic, hygric) (temp., touch, fluid)

- formication

- Paraesthesia (pins and needles tingling)

- Kinaesthesia

· Visceral

Olfactory and Gustatory hallucinations

- often with related delusions