16. Perceptual Disorders as a Higher Level Dysfunction Flashcards
What two factors determines what we perceive?
Physical stimulus input and cortical processing
Visual illusions describe visual images that are .... There is an ... of the physical stimulus.
Hallucination is an experience involving the ..., without any ....
The ... is responsible for most of our conscious visual perception of the environment. The mechanisms that helps ... is the driver of perception disorders.
Visual illusions describe visual images that are not the same as physical reality of the stimulus. There is an alteration of the interpretation of the physical stimulus.
Hallucination is an experience involving the apparent perception of something that is not present, without any visual input.
The brain is responsible for most of our conscious visual perception of the environment. The mechanisms that helps fill in information in the blind spot is the driver of perception disorders.
Negative visual phenomena makes up most of .... Thes include the ... e.g. ... → see things wavy, mishapen = ..., ....
Positive visual phenomena are due to .... These can also affect ..., ..., and .... E.g. ... (phosphines, ...) due to ... = white flashes; due to ... from optic nerve stimulation/ compression.
Negative visual phenomena makes up most of visual distortions due to eye disease. Thes include the reduction or losses e.g. AMD → see things wavy, mishapen = metamorphopsia, scotoma.
Positive visual phenomena are due to abnormal retinal/ cortical processing. These can also affect auditory, olfactory, and visual senses. E.g. Flashes (phosphine's, entoptic phenomena) due to vitreo-retinal traction = white flashes; due to elevated IOP from optic nerve stimulation/ compression.
Illusions are ... or .... This occurs in an ... as this requires ... to occur. This can be due to ..., abnormal ....
Illusions that result from normal neural processing are shared by most people, these are called ....
Illusions are distortions or misinterpretations of visual inputs. This occurs in an awake person with eyes open as this requires visual input to occur. This can be due to surround/ expectation/ other influences, abnormal brain/retinal/ neural processing.
Illusions that result from normal neural processing are shared by most people, these are called optical illusions.
Pathological illusions are due to .... There can be ocular or cortical causes.
Ocular causes can be either ... which is due to ... (difference in ...) caused by ... or ... (difference in ...); or can be retinal due to ....
Cortical causes includes ... and ....
“Pathological illusions are due to aberrant image procesing. There can be ocular or cortical causes.
Ocular causes can be either optical which is due to aniseikonia (difference in image sizes) caused by astigmatism or anisometropia (difference in prescription); or can be retinal due to vitreo-retinal traction.
Cortical causes includes palinopsia and Alice in Wonderland syndrome. “
How can ocular and cortical causes be differentiated? (3 different indications)
- One eye (retinal) vs one hemifield
- If homonymous (same side in both eyes) & respects the vertical midline = cortical
- Higher order distortions give complex perceptual illusions e.g. shape, depth
Palinopsia are .... This is characterised by:
* Increased duration of ...
* Reduced ... to form an ...
* ... become noticeable with routine eye movement
* ... may form, which appears as ...
This is an isolated condition associated with ... and can be experienced periodically by .... Individuals who had ingested ... may also experience this due to .... There are no ... for palinopsia, but management of ... have been found to help.
Palinopsia are extended/ exaggerated afterimages. This is characterised by:
* Increased duration of afterimages/ trailing
* Reduced amount of time to form an afterimage
* Positive afterimages become noticeable with routine eye movement
* Negative afterimages may form, which appears as inverted coloured afterimages
This is an isolated condition associated with brain/ cortical dysfunction or pathology and can be experienced periodically by migraine sufferers. Individuals who had ingested hallucinogens may also experience this due to serotonin receptor excitotoxicity. There are no treatments for palinopsia, but management of migraines have been found to help.
Alice in Wonderland Syndrome (AIWS) is a distortion that lasts ... to ..., but typically last for ... minutes. This is characterised by:
* ... e.g. ... & ...
* ... → most prominent & disturbing symptoms = ..., confusion in ... of parts or all of the body. This can occur in other or ...; changes in ... of inanimate objects
* Some also experience transient ... and ... (inability to talk)
AIWS is associated with ..., ..., cerebral lesions, ....
Alice in Wonderland Syndrome (AIWS) is a distortion that lasts minutes to days, but typically last for 20 minutes. This is characterised by:
* Sensory distortions e.g. touch & hearing
* Visual distortions → most prominent & disturbing symptoms = altered body image, confusion in size and shape of parts or all of the body. This can occur in other or themselves; changes in size of inanimate objects
* Some also experience transient numbness and aphasia (inability to talk)
AIWS is associated with migraines, epilepsy, cerebral lesions, schizophrenia.
Visual hallucinations do not require ..., unlike illusions. Thes are caused by .... There are 6 major causes of visual hallucinations:
* Hallucinations that are isolated findings: ..., ...
* Hallucinations associated with ... or ...
* Hallucinations as part of specific pathology: ... and ....
Visual hallucinations do not require visual input, unlike illusions. Thes are caused by aberrant inhibition or over-excitation of the brain. There are 6 major causes of visual hallucinations:
* Hallucinations that are isolated findings: drug induced, subsequent to vision loss
* Hallucinations associated with sleep or trance
* Hallucinations as part of specific pathology: dementia and psychoses.
Hallucinations that arise subsequent to vision loss:
Cortical syndromes → ... (PCA)
Ocular syndromes → ... - visual hallucinations after ...
Hallucinations that arise subsequent to vision loss:
Cortical syndromes → Posterior Cortical Atrophy (PCA)
Ocular syndromes → Charles Bonnet Syndrome - visual hallucinations after eye diseases
Posterior Cortical Atrophy (PCA) is the lesion of the ..., ..., ... or .... PCA is a type of ... and is considered a variant of .... This results in ... and ... impairment, where 25% of px experience ....
Damages is needed across ... or to a network of ... to give hallucinations. These damages affects .... The lack of ... causes cortical activation of the ... and generates spontaneous .... This is the ....
Posterior Cortical Atrophy (PCA) is the lesion of the primary visual cortex, visual pathway, midbrain or thalamus. PCA is a type of dementia and is considered a variant of Alzheimer's. This results in spatial and perceptual impairment, where 25% of px experience visual hallucinations.
Damages is needed across multiple sites or to a network of interconnecting structures to give hallucinations. These damages affects inhibitory signals. The lack of inhibitory signals causes cortical activation of the lateral infero-temporal cortex and generates spontaneous hallucinations. This is the cortical release phenomenon.
Charles-Bonnet Syndrome (CBS) is more common in ..., ... eye diseases, mostly commonly presents with .... Px with CBS have intact ..., therefore is not a form of .... The 3 typical causes are ..., ... and .... CBS have been found to be ... in studies. Visual field loss in CBS can ... and .... CBS formed hallucinations can be ... or .... The timing and frequency of the hallucinations can ... but they usually last for ..., but can also be ....
Charles-Bonnet Syndrome (CBS) is more common in binocular, low VA eye diseases, mostly commonly presents with bilateral vision loss. Px with CBS have intact cognition, therefore is not a form of dementia. The 3 typical causes are bilateral AMD, glaucoma and cataracts. CBS have been found to be under-recognised in studies. Visual field loss in CBS can central and bilateral. CBS formed hallucinations can be vivid and clear or abstract and not fully form. The timing and frequency of the hallucinations can vary widely but they usually last for several minutes, but can also be seconds or hours.
How should Charles Bonnet Syndrome be managed?
- Reassurance & education - use less stigmatised language e.g. visual phantoms, bonnet images, phantom images, visions
- Improve visual function e.g. low vision aids or treat eye disease
- Increase social interaction
- Improve home lighting
- Direct to support group
Anton-Babinski syndrome is a form of ..., which is a condition where a person ..... This is very rare and occurs in conjunction with a ... e.g. ischaemic vascular cerebral disease. Px is blind due to ..., but will behave as if they can see. These px are often hospitalised ... and the visual disorder can take some time to be recognised as they are ....
Anton-Babinski syndrome is a form of anosognosia, which is a condition where a person does not recognise or have insight to their own illness. This is very rare and occurs in conjunction with a sudden bilateral occipital dysfunction e.g. ischaemic vascular cerebral disease. Px is blind due to bilateral occipital lobe damage, but will behave as if they can see. These px are often hospitalised post injury and the visual disorder can take some time to be recognised as they are not reported by the px.
