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

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Presentation on theme: "Lecture 8 Attention (Dr Roger Newport) u Attention u Extinction Neglect u Bàlints Syndrome Simultanagnosia Ocular Apraxia Optic Ataxia Anosognosia."— Presentation transcript:

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

2 A brief word about the PDFs online

3 Attention Pop-out Feature presentFeature absent Serial search

4 T L L L L L L L L L L L L L L T L L T L L T L T L T T T L L Find the TFind the RED T 1 feature2 feature conjunction

5 Retina SC Brainstem eye command LGNV1 PreFrontal Association area FEF LIP Fast Slow

6 ++++ 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

7 Spotlight Zoom lens Internal eye

8 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

9 + rTMS over parietal cortex induces extinction in normals rTMS over occipital abolishes target detection Pascual-Leone et al., (1994). Induction of visual extinction by rapid-rate transcranial magnetic stimulation of parietal lobe. Neurology Dec;44(12):2419. Extinction

10 It has been suggested that extinction results from a)an inability to disengage from the ipsilesional stimulus b)weakened or delayed afferent inputs to the affected hemisphere c)competition or capacity-limited processes Baylis et al - maximal extinction at simultaneous presentation Not a) as ext. reduced when ipsi item leads Not b) as b) predicts maximal ext. when contra item leads ipsi Neuropsychologia 40 (2002) 1027–1034 Visual extinction with double simultaneous stimulation: what is simultaneous? Baylis, Simon, Baylis & Rorden Also ipsilesional stimuli seem to have a temporal advantage over contra

11 Not caused by primary sensory deficits

12 Line Bisection

13 Albert Task Line Bisection Shape cancellation


15 Grapple Apple (omission) Fraction Traction (substitution) Acupuncture Picture (both) CopyingDrawing from memory Reading Patient RB

16 Anton Raderscheidt Self-portrait painted during recovery from a right hemisphere stroke which resulted in left hemispatial neglect Sketches drawn by the artist Tom Greenshields before and after his stoke BeforeAfter

17 Image courtesy of Dr Yves Rossetti Apple pie

18 How does neglect affect reaching? Curved hand paths in neglect (Goodale et al, 1990). control N+ Distortion of visual space or general distortion of space?

19 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

20 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

21 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.

22 Normal view Neglect Patients view

23 Size judgement task - Patient LC + HORIZONTAL BARS + VERTICAL BARS + SHAPES LEFT SMALLERSAME SIZERIGHT SMALLER CONDITION % Horizontal bars Vertical bars Shapes % left-smaller responses

24 Prisms and neglect - Rossetti et al., 1998


26 Curved hand paths in neglect Jackson et al., (2000)

27 Jackson & Newport. (2001). Prism adaptation produces neglect-like patterns of hand path curvature in healthy adults. Neuropsychologia –814

28 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

29 Patient RM

30 Patient JJ

31 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.

32 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 Balints, but also seen independently following bilateral damage to the superior parts of the visual association areas of the occipital lobes (BA 18/19)



35 JJ:... a man with a jar, a girl, another girl (pointing to the mother), a tap, a boy, curtains, a hedge and a cup.


37 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



40 JJ Control

41 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

42 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).

43 Disconnectionist account De Renzi, 1982 Misreaching deficitDisconnection 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)

44 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). But…there are two broad categories of optic ataxia: foveal and extra-foveal and disconnectionist model does not work for non-foveal optic ataxia.

45 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

46 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

47 LEFT HAND Control (foveating) 10° right of fixation 20° right of fixation 30° right of fixation RIGHT HAND Control (foveating) 10° right of fixation 20° right of fixation 30° right of fixation Target Fixation point Magnetic misreaching: Mrs D - Carey et al., 1997

48 Bimanual reach-to-grasp task a.b. c. Patient JJ - optic ataxia Jackson et al., (2003). Action binding and the parietal lobes: some new perspectives on optic ataxia

49 April 2001: Bimanual trials - Effects of gaze angle Gaze leftGaze right



52 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"

53 Motor 'intentional' activation system Motor system Effector Comparator or 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.

54 Frith, Blakemore and Wolpert. (2000). Forward model Desired state and predicted state match Actual state feedback is absent or ignored


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