Lecture 8 Attention

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• Lecture 8 Attention
• (Dr Roger Newport)
• Attention
• Extinction
• ? Neglect
• Bàlints Syndrome
• Simultanagnosia
• Ocular Apraxia
• Optic Ataxia
• ? Anosognosia

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A brief word about the PDFs online
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Attention
Feature present
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Find the T
Find the RED T
1 feature
2 feature conjunction
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PreFrontal Association area
FEF
LIP
LGN
V1
Brainstem eye command
SC
Retina
Fast
Slow
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Posner cueing task
Right parietal patients slower at invalid trials
when R box cued. Asymmetry between the
attentional capabilities of each hemisphere R
ltgt Lgtonly
delay
valid
invalid
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Spotlight Zoom lens Internal eye
Spotlight
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Premotor Theory
Premotor Theory shifting attention is nothing
more than preparing an eye movement that will not
be executed
Perry and Zeki found Right SMG activation
(visual areas/FEF etc) when making eye saccades
and for covert attention shifts (equal for left v
right shifts
Fits parietal patient data
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Extinction
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• It has been suggested that extinction results
  from
• an inability to disengage from the ipsilesional
  stimulus
• weakened or delayed afferent inputs to the
  affected hemisphere
• competition or capacity-limited processes

Also ipsilesional stimuli seem to have a temporal
advantage over contra
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Not caused by primary sensory deficits
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Line Bisection
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Albert Task
Line Bisection
Shape cancellation
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Patient RB
Copying Drawing from memory Reading
Grapple Apple (omission) Fraction Traction (subst
itution) Acupuncture Picture (both)
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1
Before
After
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Sketches drawn by the artist Tom Greenshields
before and after his stoke
Anton Raderscheidt Self-portrait painted during
recovery from a right hemisphere stroke which
resulted in left hemispatial neglect
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Apple pie
Image courtesy of Dr Yves Rossetti
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How does neglect affect reaching? Curved hand
paths in neglect (Goodale et al, 1990).
N
control
Distortion of visual space or general distortion
of space?
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• Heilman Attention - Intention model
• Neglect may occur as consequence of failure to
  ATTEND or INTEND towards contralateral stimuli
• Processing of spatial information is divided into
  left and right hemispheres
• RH has special role in space-related behaviour -
  RH does left and right. LH only does right
• Neglect is attributed to hypoarousal of damaged
  hemisphere

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Kinsbourne Vectorial model Space-related
behaviour is directional Each hemisphere is
reponsible for directing attention in the
horizontal plane contraversively
The LH is dominant and must be inhibited by the
RH Damage to the RH lessens this
inhibition Resulting in a pathological rightward
attentional bias
e.g. Ladavas
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Bisiach Representational model Space is
topographically represented across the two
hemispheres
Different models explain different aspects of the
syndrome. How the syndrome is defined determines
which model appears to be the most attractive.


Damage to one hemisphere destroys the
representational analogue of the contralesional
real world
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Size judgement task - Patient LC
SHAPES
left-smaller responses
HORIZONTAL BARS
VERTICAL BARS
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Prisms and neglect - Rossetti et al., 1998
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Prisms and neglect - Rossetti et al., 1998
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Curved hand paths in neglect
Jackson et al., (2000)
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Jackson Newport. (2001). Prism adaptation
produces neglect-like patterns of hand path
curvature in healthy adults. Neuropsychologia 39
810814
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Balints Syndrome (1909) A cluster of
co-occuring visuomotor and visuospatial
disturbances Bálint's syndrome results from
bilateral damage to the posterior parietal lobes
(usually either progressive cerebrovascular
complications or lateral gunshot wounds) but
lesions often also take in parts of occipital and
temporal cortex as well as white matter
damage The triad of disorders associated with
Bálints syndrome are Simultanagnosia -
inability to see visual field as a whole Ocular
apraxia - deficit of visual scanning Optic
ataxia - inability to reach accurately under
visual guidance
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Patient RM
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Patient JJ
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Description of a Balints patient (JJ) a 65 year
old man with a history of recurrent cerebral
posterior haemorrhages affecting the occipital,
parietal and temporal cortices of both cerebral
hemispheres . He frequently bumps into objects,
unsure of where they are or not noticing them at
all. He says, I can see them but it is as if I
cant. He complains of difficulty in finding
objects and people around him. He has difficulty
in performing everyday tasks. For example, he may
misreach when trying to cut bread. Or he may
unsuccessfully spend over an hour trying to wire
an electric plug because he has difficulty in
placing his fingers in the right place. When
pouring tea, he may miss the cup entirely. He
often fails to eat all the food on his plate
because he does not see it, or knocks food off
the plate with cutlery.
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Simultanagnosia or spatial disorientation An
inability to see the visual field as a
whole Examples difficulty in copying/drawing/wri
ting because they are unable to see both the end
of the pen and what is on the paper at the same
time. Unable to describe complex scene (e.g.
Boston cookie theft). Spatial disorientation
inability to appreciate the spatial properties
of objects (e.g. relative distance and size
estimates are impaired, as are whole body
movements in space). Often seen as part of
Balints, but also seen independently following
bilateral damage to the superior parts of the
visual association areas of the occipital lobes
(BA 18/19)
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JJ ... a man with a jar, a girl, another girl
(pointing to the mother), a tap, a boy, curtains,
a hedge and a cup.
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Gaze or ocular apraxia An inability to move the
eyes voluntarily to points in the visual
field. Not due to basic oculomotor
deficit. Spontaneous, reflexive movements may be
spared. Eye movements towards auditory or
somatosensory stimuli spared. Functional gaze
restricted to narrow band, usually to the right
of the midline. Can appear similar to neglect
symptoms. Usually co-occurs with visuospatial
deficits
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JJ
Control
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Optic ataxia - an inability to reach accurately
under visual guidance Reaching accurately
involves reaching in the right direction, with
the correct grip scaling and grip
orientation/finger placement. Visual guidance
means being able to see both the target and the
hand throughout.
Milners posting task
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In humans optic ataxia is associated with
(usually unilateral) damage to intraparietal
sulcus/superior parietal lobe Optic Ataxia is
not due to basic sensory or motor deficit. How do
we know this? Can affect one limb in one or both
hemispheres (not purely visual or spatial
disorder) Can affect both or one limb in only
one hemisphere (not purely motor disorder) Optic
ataxia is not accompanied by a deficit of
position sense although this is often only
assessed by informal bedside clinical testing
(e.g. limb postion matching).
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Disconnectionist account
De Renzi, 1982
Misreaching deficit Disconnection
Both hands to contralesional field Visual information from damaged hemisphere to both (contra and ipsi) motor areas
Contralesional hand to contralesional field Visual information from motor area in damaged hemisphere only
Ipsilesional hand to contralesional field Visual information from damaged hemisphere to motor area in spared hemisphere
Both hands to both fields visual information from both to both motor areas (i.e. bilateral parieto-occipital junction damage)
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Butthere are two broad categories of optic
ataxia foveal and extra-foveal and
disconnectionist model does not work for
non-foveal optic ataxia.
If areas are disconnected then OAs should be
impaired when Reaching to both foveal and
non-foveal targets
Buxbaum and Coslett (1997) - OA a spatio-motor
transformation failure - a failure to encode the
target with respect to the position of the arm in
limb-based coord system. OAs ? rely upon
undamaged oculocentric coord system. Reaches ?
directed towards direction of gaze. Evidence DP
(Buxbaum and Coslett, 1997) and Mrs D (Carey et
al., 1997).
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Pointing movements in two optic ataxic patients
a) patient with left hemisphere lesion reaching
with left hand - note leftward error for both
right visual hemifields b) patient with right
hemisphere lesion reaching with left hand - note
rightward error for both left visual
hemifields H1 - misreaching toward the
ipsilesional space H2a - misreaching toward
fixation H2b - imbalance between foveal and
peripheral vision
From Ratcliff and Davies-Jones, 1972
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Magnetic misreaching Case of Mrs. D (Carey et
al., 1997) 76 year-old woman with a slowly
progressive bilateral parietal lobe
degeneration Mrs. D could only reach to the
point of fixation regardless of where the target
was with either hand. A manifestation of
parietal lobe dysfunction Breakdown in
sensorimotor transformation
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Magnetic misreaching Mrs D - Carey et al., 1997
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Patient JJ - optic ataxia
Bimanual reach-to-grasp task
a.
Jackson et al., (2003). Action binding and the
parietal lobes some new perspectives on optic
ataxia
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April 2001 Bimanual trials - Effects of gaze
angle
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Anosagnosia is the denial of illness which is
often seen in brain-injured patients. Frequently
associated with hemineglect.
Anosognosia
Landmark cases
Von Monokow (1885) - Reported a 70 year old
patient who had suffered bilateral damage to
posterior brain areas and exhibited loss of sight
of which the patient was not aware (patient
attributed visual deficit to loss of ambient
light).
Anton (1899) - Reported the case of Ursula Mercz
who was shown to suffer from cortical blindness
but denied this. (termed Anton's syndrome).
Patients pupils respond to light but the patient
is unable to demonstrate functional sight. Deny
any visual difficulty. Confabulate responses,
guess, and make excuses for deficit e.g., "the
room lights are too dim" or "I don't have my
glasses with me"
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Anosagnosia as a failure of monitoring
Heilman's intentional model
Motor
'intentional'
patients unaware of movement failure because the
comparator which contrasts intended and actual
movements receives no signal that a movement has
been intended. Because patients do not try to
move the paralysed limb they never discover that
it is paralysed. Can explain denial of
impairment, but not cases in which patients
apparently experience having made movements when
none have actually occurred.
activation
system
Comparator
Motor system
or monitor
Effector
Heilman et al., 1998.
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Forward model
Frith, Blakemore and Wolpert. (2000).
Desired state and predicted state match Actual
state feedback is absent or ignored
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