Week 3 - Visual Agnosia

Visual Agnosia

A neurological disorder which interferes with the ability to recognise visual stimuli.

Distortions of perception with visual agnosia can not be explained by:

can not be explained by:

• memory

• attention

• language problems

• lack of familiarity

what perceptual systems can agnosia affect

Visual, auditory and somatosensory

apperceptive agnosia

Inability to accurately perceive visually presented stimuli as a whole.

What can and can’t a person with apperceptive agnosia do?

Can:

• see visual stimulus

• can describe/verbally name objects

• identify using non-visual cues

Can’t:

• perceive or process visual stimulus as whole

• draw an image of visual stimulus

• recognise stimulus

what is apperceptive agnosia caused by?

• dementia

• physical injury

• oxygen deprivation

• carbon monoxide poisoning

• brain tumor

• damage to posterior of brain

associative visual agnosia

inability to recognise/retrieve knowledge from memory despite being able to perceive visual stimuli.

What can and can’t a person with associative agnosia do?

can:

• perceive visual stimulus

• draw visual stimulus

• describe physical features of object

can’t:

• recognise and name objects visually

• recognise faces or words (severe)

what is associative agnosia caused by?

• injury

• lesion in temporal lobe

Differences between apperceptive and associative agnosia

Apperceptive:

• lesions to parietal and occipital lobe

• Unable to process or perceive visual stimuli

• Unable to recognise stimulus

• Unable to draw or copy a drawing of stimulus

Associative:

• lesions to temporal lobe

• Able to process or perceive visual stimuli

• Unable to translate perception into recognition

• Able to draw or copy a drawing of stimulus

Prosopagnosia

Inability to recognise familiar faces.

What cues must someone with prosopagnosia rely on to identify people?

• hair

• tattoos

• age

• gender

• way a person walks

• voice

What causes prosopagnosia?

• autism

• lesions in occipital and temporal lobe (linked with facial perception)

• Alzheimers

Agnostic Alexia

Also referred to as pure agnosia or letter by letter reading, the inability to read words but are able to write and spell them.

What is the cause of Agnostic Alexia?

When language functions remain intact but have an impairment when recognising words. Has to do with visually identifying words rather than a language imparement.

What causes Agnostic Alexia?

Lesion in occipital lobe

What can and can’t someone with Agnostic Alexia do?

can:

• recognise objects, people, symbols without difficulty

• write normally

• understand spoken language perfectly

can’t:

• read fluently

colour agnosia

Inability to distinguish difference of colours despite having functional colour vision.

What can and can’t someone with colour agnosia do?

can:

• name a colour individually

• name an object individually

• see colour

can’t:

• correlate an object with it’s associated colour

• verbally describe colours of an object

what causes colour agnosia?

damage to the temporal and occipital lobe on the left hemisphere.

akinetopsia

inability to perceive motion. Can be present in either two forms: permanent or transient

What can akinetopsia look like depending on severity?

complete → seeing motion as a series of images

inconspicuous → seeing motion as slowed/blurred

What can and can’t someone with akinetopsia do?

can:

• perceive motionless objects

• recognise static facial expressions

• identify slow movement

can’t

• perceive continuous motion (objects jump from one place to another)

• pour liquids accurately

What causes akinetopsia? And where does it occur?

• damage to MT/V5 in brain

• bilateral damage

• medication

• seizure/migraine

simultanagnosia

inability to perceive multiple objects at once caused by damage in the posterior parietal lobe.

What can and can’t someone with simultanagnosia do

can:

• perceive one object at a time

can’t:

• perceive multiple objects at once

• see a visual scene as a whole

topographical agnosia

inability to perceive location in relation to familiar environments.