disorders of object and spatial perception · category specific agnosias . akinetopsia failure to...
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Disorders of Object and
Spatial perception Dr John Maasch
Brain Injury Rehabilitation Service
Burwood Hospital.
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Take Home Message 1
Where there are lesions of the posterior
cerebrum and posterior temporal lobe,
screen for disorders of spatial perception
and object agnosia.
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Take Home Message 2
The Parietal Lobe presents space in order
to move in that space.
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Visual
processing More than half of the
posterior cerebrum is
devoted to visual
processing
Visual processing areas
are hierarchical and
increasingly specialised
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Vision processing and
modulation
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Two visual processing streams
A dorsal occipito-
parietal stream (the
“where” stream) for
spatial processing.
A ventral occipito-
temporal stream (the
“what” stream) for
object identification
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How we perceive space We use multiple senses-visual, auditory, Tactile esp proprioception
and vestibular.
The right hemisphere controls spatial perception in both hemispaces
The left hemisphere only controls spatial perception in the right
hemispace.
It has been found that patients with right hemisphere lesions may
have bilateral impairments of spatial perception and movement
while those with left hemispheric lesions may not show any obvious
spatial perceptual abnormality.
Verbal stimuli are responded to better when presented in right
hemispace and non-verbal stimuli responded to better when
presented in left hemispace.
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How we perceive space In patients with a left hemispatial perceptual disorder if two stimuli presented
side by side in right hemispace, the person will respond slower to the left
sided stimulus.
Carr and Shepherd (2010) report moving cues more compelling in reducing
symptoms of UHA indicating an intentional bias to spatial perception.
Also report action-intention movements into neglect hemi space improves
motor recovery.
In macaque monkey single neurons in the parietal lobe not only sensitive to
location in space but also to action that must be directed towards the
target e.g reach or saccades.
Snyder et al concluded therefore that parietal lobe not only codes for
spatial attention but spatial intention.
The parietal lobe might present space in terms of the action to be carried out in that space
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Terminology
Unilateral hemispatial neglect
Unilateral hemispatial
Inattention
Unilateral hemispatial agnosia
Disorder of spatial perception
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Classification by modality
Sensory Neglect
Visual neglect
Somatosensory neglect(tactile)
Auditory neglect
Proprioceptive neglect
Vestibular neglect
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Classification by modality
Motor Neglect
Akinesia
Directional akinesia- hypometria
- hypokinesia
- bradykinesia
Mixed
Buccal hemi neglect
Dysphagia neglect
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Classification by Spatial
representation
Egocentric
neglect
Allocentric neglect
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Classification by range of
spatial neglect
Personal Neglect-of body
Peripersonal Neglect-on body and within
reach of body
Extrapersonal Neglect- outside reach of
body
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Agnosias
“Lack of Knowledge/recognition” viz
agnostic
Ventral occipito-parietal stream
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Apperceptive visual agnosia-
recognition
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Apperceptive visual agnosia:
copy
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Matching
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ASSOCIATIVE VISUAL AGNOSIA -associative visual agnosia patients derive normal visual
representation but cannot use this information to recognize
things
-patient is unable to recognize the object despite an
apparent perception
-can copy a drawing rather accurately (indicating a
coherent percept), match it to another object, use the
object correctly, but cannot identify it
-the problem seems to be situated at the level of
association between the visual representation of the
object and its semantic links (stored information about the
object, category function)
-bilateral lesion of the anterior inferior temporal lobe
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Associative visual agnosia
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Associative VA-copy from memory
-can copy an anchor, can
define it, but cannot draw it
from memory demonstrating a
deficit in accessing a mental
image of the object
-failure of object recognition is
a memory defect that effects
not only past knowledge
about the object, but also
acquisition of new knowledge
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Category specific agnosias
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Akinetopsia Failure to detect motion and direction of
motion.
Beware of crossing roads. Patient might not have a visual hemispace inattention but might not perceive a car is approaching or the speed.
Problem in the hMT lobe.
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Final comment
If you suspect a spatial
perceptual or visual agnosia
difficulty, refer for further
neuropsychometric screening
and evaluation.