Transcript Psy393 Attention

Attention
Charlene O’Connor
July 20, 2005
Cognitive Neurology
Attention
William James (1907)
“Everyone knows what attention is. It is
the taking possession by the mind in clear
and vivid form of one out of what seem
several simultaneous objects or trains of
thought”.
Attention Required!
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Search for a blue thing.
Feel the seat against your back.
Listen to extraneous noise
Prepare to tap the desk next time you hear a
cough.
All require “attention” to different internal
or environmental information and “setting
up”.
Outline
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What is attention?
Neuroanatomical structures of attention
Models of attention: Posner & Petersen
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Orienting
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Alerting
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Application: neglect
Executive
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Application: neglect
Application: neglect
Attentional Impairments
“Attention can be likened
to a spotlight that
enhances the efficiency
of the detection of events
within its beam” Posner
et al (1980).
Understanding attention
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Attention is required to limit entry to a finite
capacity processing system by selecting only a
subset of all available information.
Attention itself is a resource of limited
capacity which can be divided between tasks.
Attention is responsible for vigilance over
time
Processing and attentional capacity is linked to
arousal and alertness.
Attentional Networks
(Mesulam, 1990)
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Attention is not a property of a single cell
nor the collective function of the whole brain
Reticular Activating System
Superior Colliculus
Thalamus
Parietal Lobe
Anterior Cingulate Cortex
Frontal Lobes
Models of Attention:
Posner & Petersen (1990)
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Attention system anatomically separate
Attention carried out by a network of
anatomical areas
Areas involved carry out different functions that
can be specified in cognitive terms
Posner & Petersen’s Model of
Attention
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Orienting:
directed attention
 disengage and shift attention
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Alertness: (Sustained Attention/ Arousal/ Vigilance)
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maintaining focus over a period of time
Executive: Target Detection; Supervisory Control
Anatomy
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Orienting:
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Alertness: (Sustained Attention/ Arousal/ Vigilance)
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Posterior attentional system
Right lateralized, frontal-parietal-thalamic network
Executive:
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Anterior attentional system
Orienting: Posterior Attention
System
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Orienting
Visual locations
 Overt
 Covert
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Three Cognitive Operations of Orienting
Disengaging
 Shifting
 Re-engaging/Reading
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Posner’s Cued Attentional Task
Anatomy of Posterior Attention
System
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Disengaging  posterior parietal lobe
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Shifting  superior colliculus
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Re-engaging/Reading  lateral pulvinar nucleus
of the postereolateral thalamus
Lesion Effects
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Damage to posterior parietal
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Damage to superior colliculus
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inability to disengage from attentional focus to a target located in a
direction contralateral to lesion site
Neglect/behavioural inattention
inability to shift attention regardless of whether attention is directed
elsewhere initially
Supranuclear palsy
Damage to pulvinar
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slowed response to a valid or invalid cued target on side contralateral to
lesion
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LaBerge & Buchsbaum (1990)
Pulvinar & Gating Function
N
M
Right Visual Field
O
Q
O
R A
W
S
Left Visual Field
LaBerge & Buchsbaum (1990)
Hemi-neglect
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Associated with right posterior parietal lesions.
Patients tested on Posner’s orienting tasks have
difficulty orienting attention to the neglected
side.
Deficit in attentional processing
Movie: Neglect
Hemi-neglect
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Problem in unilateral visual neglect is in
disengaging from non-neglected side to shift
to neglected side?
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Simultanagnosia and visual
extinction
Often exhibited by individuals with visual
neglect.
Simultanagnosia, characterised by inability to
“see” more than one object concurrently.
Neglect of other “spaces”
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Representational space (Bisiach and
Luzzatti(1978).
Sensory space (Bisiach 1988).
Object centred space.( e.g. Driver and
Halligan 1991).
Personal space
Suggests a very complex variety of “spatial”
systems within which attention can operate.
Spatial vs. Object Based Attention
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Most of the evidence for the posterior
attentional system derived from spatial tasks
Space-based theories
What about objects? Can attention be objectbased?
Is the same posterior parietal attentional
network engaged in object-based bottom-up
attentional tasks?
Object-based Attentional Processing
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Overlapping faces and houses (all in same
location), one stimulus moving
Attend to: Faces, House, or direction of Motion
Activity greater when attending to preferred
stimulus (eg. Fusiform face area greater during
faces)--object-based attentional modulation
since all stimuli in same location.
O’Craven et al. (1999)
Posner & Petersen’s Model of
Attention
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Orienting:
directed attention
 disengage and shift attention
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Alertness: (Sustained Attention/ Arousal/ Vigilance)
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maintaining focus over a period of time
Executive: Target Detection; Supervisory Control
Alerting: Vigilance & sustained
attention
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Vigilance requires constant monitoring for
signal occurrence.
Sustained attention is required once selection
has occurred and further processing is
necessary to complete task.
Both involve goal maintenance over time.
(More an issue of executive control.)
Related to arousal levels.
Neuroanatomy of
Sustained Attention
RDLPFC
•Evidence from lesion
& neuroimaging
studies (i.e. Sturm et al., 1999)
•R-lateralized network
•DLPFC, posterior
parietal cortex,
subcortical (thalamic)
MD Thalamus
PPC
Impaired Sustained Attention
Sustained attention is sustained control
 Pathological “Time on Task” effects
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Role of sustained attention
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Robertson and Manly (1999) suggest unilateral
neglect associated with non-lateralised attentional
deficits.
Right hemisphere (particularly dorsolateral
prefrontal) is more important for sustaining
attention than shifting it.
Contributions to neglect, extinction and
simultanagnosia may result from a more general
effect of reduced arousal, impaired spatial attention
and reduced attentional capacity.
Posner & Petersen’s Model of
Attention
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Orienting:
directed attention
 disengage and shift attention
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Alertness: (Sustained Attention/ Arousal/ Vigilance)
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maintaining focus over a period of time
Executive: Target Detection; Supervisory Control
Anterior Attentional System
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Executive control of directed attention
Top-down processing
overt, intentionally controlled orienting system
involves frontal areas
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E.g. divided attention
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Allocation of attentional resources
Anterior Attentional System
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Executive control of directed attention: involved in both
selective and sustained attention
Top-down processing
Components of the anterior attentional/supervisory system:
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concentration of attention
sharing attention (divided attention)
suppressing attention
shifting attention
preparatory attention
setting attention
sustaining attention
(Stuss et al., 1995)
Major Neuroanatomical
Structures:
Frontal lobes
&
Anterior
Cingulate
Another Model: Distributed Network
Sensory Representation:
Directed Attention
Parietal
Executive Control of
Attentional Direction
Thalamus
AC
Frontal
Motivational
Representation
Reticular
System
Arousal
(Mesulam, 1985)
Impairments of Attention
Cerebral Vascular Accident (stroke) - diverse
impairments, dependent on site, hemi-neglect
Alzheimers- impairments in control over focused
and divided attention, progressive
Brain Injury - slowness of information processing,
in some individuals impaired control as well. Some
recovery in slowness.
Complaints of subjects two years after
severe brain injury, in percentages:
- forgetfulness
54
- mental slowness
33
- poor concentration
33
- mental fatigue
30
- unable to do 2 things
21
- intolerance of bustle
19
Leclercq and Azouvi (2002):
“Impairments in control processes may be
demonstrated, apart from slowed processing,
- in more complex situations
- under time pressure
- under high working memory load
- in the more severely injured patients”.
Ponsford and Kinsella (1991),
Attentional Rating Scale 0 - 4
mental slowness
2.78
inability 2 things
2.44
easily distracted
2.14
Attention Deficit and
Hyperactivity Disorder
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Symptoms: distractibility, impulsivity and
overactivity
Poor at continuous performance tasks
Problems with sustained attention and shifting
attention (Brewer et al., 2001)
Poorer performance on sustained attention
related to smaller volume of white matter in
right hemisphere (Simrud-Clikeman et al., 2000)
Conclusions
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“….attentional computations are carried out
by a complex but specifiable anatomical
network and ... each area of the network has
its own computations.
Farah and Ratcliff (1998).
..attention ... a widely distributed state in
which several brain systems work on the
different properties and action implications
of the same selected object.”
Duncan (1999).
Conclusions
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A major challenge for the future is to determine
how these multiple attentional mechanisms
operate in a coordinated manner to maintain
unity of behaviour. (Posner and Petersen 1990).