A document detailing the processes surrounding hemispheric neglect and extinction, how these processes can be explained, and the cognitive explanation for ADHD, the etiology and treatment for ADHD.
, Neglect and Extinction
• As we have seen so far, there are different sub-functions of attention
which likely also rely on different brain structures. Studying brain
damaged patients can shed light not only how a given brain area
contributes to a given cognitive function, but it can also provide novel
insights into cognitive functions that cannot be gained from healthy
brains (e.g., when a certain cognitive function is impaired by a brain
lesion, and this function might not have been regarded as a “module” in
cognitive theories)
• Lesions to the “what path” will typically lead to specific impairments in
object recognition, including impaired recognition of certain classes of
objects like faces. Lesions to “where path” will lead to deficits in spatial
attention.
• In the lecture on visual search and feature binding, we already
discussed that Balint’s syndrome is one dysfunction of spatial attention
resulting from bilateral damage to the parietal lobes
• Another group of syndromes classified as spatial attention deficits
following brain damage to the “where stream” is neglect/extinction.
o Neglect is characterized by a very substantial failure to pay
attention to half of the world (typically the left side of space).
o Other than Balint’s syndrome, neglect typically occurs after a
unilateral brain damage (affecting only one of the two
hemispheres), in far the most cases lesions to the right side.
The failure to attend and respond occurs for stimuli presented to
the contralesional side of space. Performance with stimuli
presented to the ipsilesional side is relatively intact.
▪ Contralesional: the visual field that projects onto the
lesioned hemisphere (see slide). For instance, the left
visual field projects onto the right hemisphere. Therefore,
the left visual field will be the contralesional side of a right
hemisphere lesion.
▪ Ipsilesional: the visual field that projects on the intact
hemisphere (see slide). The right visual field projects onto
the left hemisphere. Therefore, the right visual field will be
the ipsilesional side of a right hemisphere lesion.
o Spatial neglect can be demonstrated using a variety of simple
visual tests:
▪ Cancellation task: patients are presented with an array of
small line segments (e.g., spread across an A4 page) and
are asked to manually cancel out all the line segments
they can find. Neglect patients tend to perform accurately
with lines appearing within the ipsilesional side of space
but to miss out many of the lines appearing within the
contralesional side of space (see slide).
▪ Line bisection task: patients are presented with a series
of horizontal lines and are asked to mark the middle point
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