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Lecture 8 Attention(Dr Roger Newport)
Attention
Extinction
Neglect
Bàlint’s Syndrome
Simultanagnosia
Ocular Apraxia
Optic Ataxia
Anosognosia
A brief word about the PDFs online
Attention
Pop-out
Feature present Feature absent
Serial search
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Find the T Find the RED T
1 feature 2 feature conjunction
Retina SC Brainstemeye command
LGN V1
PreFrontalAssociation area FEF
LIP
FastSlow
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Posner cueing task
validinvalid
delay
Right parietal patients slower at invalid trials when R box cued.
Asymmetry between the attentional capabilities of each hemisphere
R <>; L>only
Spotlight
SpotlightZoom lensInternal eye
Premotor Theory
Premotor Theoryshifting 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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rTMS over parietal cortex induces extinction in normalsrTMS over occipital abolishes target detection
Pascual-Leone et al., (1994). Induction of visual extinction by rapid-rate transcranial magnetic stimulation of parietal lobe.Neurology. 1994 Dec;44(12):2419.
Extinction
It has been suggested that extinction results froma) an inability to disengage from the ipsilesional stimulusb) weakened or delayed afferent inputs to the affected
hemispherec) competition or capacity-limited processes
Baylis et al - maximal extinction at simultaneous presentationNot a) as ext. reduced when ipsi item leads Not b) as b) predicts maximal ext. when contra item leads ipsi
Neuropsychologia 40 (2002) 1027–1034Visual extinction with double simultaneous stimulation:what is simultaneous?Baylis, Simon, Baylis & Rorden
Also ipsilesional stimuli seem to have a temporal advantage over contra
Not caused by primary sensory deficits
Line Bisection
Albert Task
Line Bisection
Shape cancellation
GrappleApple(omission)
FractionTraction(substitution)
AcupuncturePicture(both)
Copying Drawing from memory Reading
Patient RB
Anton Raderscheidt Self-portrait painted during recovery from a right hemisphere stroke which resulted in left hemispatial neglect
3
21
4 Sketches drawn by the artist Tom
Greenshields before and after his stoke
Before After
Image courtesy of Dr Yves Rossetti
Apple pie
How does neglect affect reaching?Curved hand paths in neglect (Goodale et al, 1990).
control
N+
Distortion of visual space orgeneral distortion of space?
Heilman: Attention - Intention model
1. Neglect may occur as consequence of failure to ATTEND or INTEND towards contralateral stimuli
2. Processing of spatial information is divided into left and right hemispheres
3. RH has special role in space-related behaviour - RH does left and right. LH only does right
4. Neglect is attributed to hypoarousal of damaged hemisphere
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 biase.g. Ladavas
Bisiach: Representational model
Space is topographically represented across the two hemispheres
Damage to one hemisphere destroys the representational analogue of the contralesional real world
Different models explain different aspects of the
syndrome.How the syndrome is defined
determines which model appears to be the most
attractive.
Normalview
NeglectPatient’sview
Size judgement task - Patient LC
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HORIZONTAL BARS
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VERTICAL BARS
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SHAPES
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LEFT SMALLER SAME SIZE RIGHT SMALLER
CONDITION
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Horizontal bars
Vertical bars
Shapes
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Prisms and neglect - Rossetti et al., 1998
Prisms and neglect - Rossetti et al., 1998
Curved hand paths in neglect
a) controls b) MJH c) LGC d) RB300
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Jackson et al., (2000)
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VV/Base
VV/AH
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Jackson & Newport. (2001). Prism adaptation produces neglect-like patterns of hand path curvature in healthy adults. Neuropsychologia 39 810–814
Balint’s 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 Bálint’s 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
Patient RM
Patient JJ
Description of a Balint’s 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 can’t”. 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.
Simultanagnosia or spatial disorientation
An inability to see the visual field as a whole
Examples: difficulty in copying/drawing/writing 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 Balint’s, but also seen independently following bilateral damage to the superior parts of the visual association areas of the occipital lobes (BA 18/19)
JJ: “... a man with a jar, a girl, another girl (pointing to the mother), a tap, a boy, curtains, a hedge and a cup.”
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
JJ
Control
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.
Milner’s posting task
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).
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)
If areas are disconnected then OA’s should be impaired whenReaching 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.OA’s 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).
But…there are two broad categories of optic ataxia:foveal and extra-foveal and disconnectionist modeldoes not work for non-foveal optic ataxia.
Pointing movements in two optic ataxic patients
From Ratcliff and Davies-Jones, 1972
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
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
LEFT HANDControl (foveating) 10° right of fixation 20° right of fixation 30° right of fixation
RIGHT HANDControl (foveating) 10° right of fixation 20° right of fixation 30° right of fixation
TargetFixation point
Magnetic misreaching: Mrs D - Carey et al., 1997
Bimanual reach-to-grasp task
a. b.
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Patient JJ - optic ataxia
Jackson et al., (2003). Action binding and the parietal lobes: some new perspectives on optic ataxia
April 2001: Bimanual trials - Effects of gaze angle
Gaze left450
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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"
Motor'intentional'activation
system
Motorsystem
Effector
Comparatoror monitor
Heilman's intentional model
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.
Anosagnosia as a failure of monitoring
Heilman et al., 1998.
Frith, Blakemore and Wolpert. (2000).
Forward model
Desired state and predicted state match
Actual state feedback is absent or ignored
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