Disorders of perception Flashcards
Perceptual distortions
-stimulus is present, the object is perceived but the quality of the object is altered
Illusions
-stimulus is present but something else is perceived
Hallucinations
- stimulus absent
- perception without stimulus
Negative hallucinations
-stimulus is present but no object is perceived
Perceptual distortion
-stimulus is perceived as corresponding object but not accurately- changes in shape, colour etc
Change in shape of object
-dysmegalopsia
Change in size of an object
- micropsia
- macropsia
Eidetic imagery
- special ability of memory where visual images are drawn from memory accurately at will and described as being perceived current;y
- notes in 2-15% school goers
- may be part of religious experiences
- no pathology
Affect illusion
- prevailing emotional state leads to misconceptions
- often fearful, emotion provoking
- disappears on focussing the object with extra concentration
- e.g a depressed patient reading ‘deed’ as ‘dead’
Pareidolic illusion
- formed objects from ambiguous stimuli, coloured by prevailing emotion
- often playful and whimsical
- on paying extra attention the object intensifies
- e.g seeing cars in the cloud
- using psychodelics or delirium
Completion illusion
- stimulus that does not form a complete object might be perceived to be complete
- due to inattention
- disappearance on concentration is the rule
- CCOK is read as COOK
Elementary auditory hallucination
- unstructurede hallucinations
- seen in acute organic states
Musical hallucinations
- similar to Charles Bonnet Syndrome
- can occur in those with deafness
Lilliputian hallucinations
- seen in DTs
- tiny people, insects
Autoscopic hallucinations
- see oneself
- in depression
- phantom mirror images
- in negative autoscopy one looks into a mirror and sees no image at all
Palinopsia
- ‘again’ ‘seeing’
- visual disturbance causes images to persist even after their corresponding stimulus has left
- seen in LSD use, migraine, occipital epilepsy, head trauma
Coenesthetic hallucinations
- visceral hallucinations -pain deep in viscera
- suggest schizophrenia
- also seen in ETOH and benzo withdrawal
Formication
- from formic acid in ants
- special type of haptic hallucination
- unpleasant sensation of little animals or insects crawling on skin
- seeen in DTs and cocaine
- also seen in parietal seizures
Olfactory hallucinations
- can occur in the aura of TLE
- in depression it can be associated with nialism
Gustatory hallucinations
- bitter taste of poison can give rise to delusions of persecution in schizophrenia
- also seen in TLE
Extracampine hallucinations
- hallucinations outside the normal FIELD of perception
- e.g images behind your back, voices from Scotland
- occur in schizophrenia, epilesy and hypnagogic hallucinations of healthy people
Hypnagogic hallucinations
- when you are GOING to sleep
- 3x more common than hypnapompic
- 37% adults experience at least once
- more specific for narcolepsy
- EEG shows alpha rhythm
- hearing one’s name is most common
Hypnapompic hallucinations
-when you are waking up
Functional hallucinations
- external stimulus provokes hallucination
- voices heard whenever the noise of water running though the tap is heard
- same modality
Reflex hallucinations
- similar to functional
- hallucination in one modality is provoked reflexively by a stimulus in another modality
- seeing an angel when listening to music
Synaesthesia
- tasting music, hearing colours and smelling voices
- cross modality perception
- common in females 4:1 to 6:1
- runs in families
- colour-number synaesthesia is the most common form
- can be acquired in neurological disease
- can be induced by ingesting mescaline
