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Charlene O’Connor July 20, 2005 Cognitive Neurology

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1 Charlene O’Connor July 20, 2005 Cognitive Neurology
Attention Charlene O’Connor July 20, 2005 Cognitive Neurology

2 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”.

3 Attention Required! 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”.

4 Outline What is attention? Neuroanatomical structures of attention
Models of attention: Posner & Petersen Orienting Application: neglect Alerting Executive Attentional Impairments

5 “Attention can be likened to a spotlight that enhances the efficiency of the detection of events within its beam” Posner et al (1980). Perhaps the simplest way to understand attention… But, as you already know, in psychology—nothing is ever this simple! Attention is a multi-dimensional concept—it is not a unitary system. Therefore, it can be understood within several dimensions.

6 Understanding attention
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.

7 Attentional Networks (Mesulam, 1990)
Attention is not a property of a single cell nor the collective function of the whole brain

8 Reticular Activating System

9 Superior Colliculus

10 Thalamus

11 Parietal Lobe

12 Anterior Cingulate Cortex

13 Frontal Lobes

14 Models of Attention: Posner & Petersen (1990)
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

15 Posner & Petersen’s Model of Attention
Orienting: directed attention disengage and shift attention Alertness: (Sustained Attention/ Arousal/ Vigilance) maintaining focus over a period of time Executive: Target Detection; Supervisory Control

16 Anatomy Orienting: Posterior attentional system Alertness: (Sustained Attention/ Arousal/ Vigilance) Right lateralized, frontal-parietal-thalamic network Executive: Anterior attentional system

17 Orienting: Posterior Attention System
Visual locations Overt Covert Three Cognitive Operations of Orienting Disengaging Shifting Re-engaging/Reading

18 Posner’s Cued Attentional Task

19 Anatomy of Posterior Attention System
Disengaging  posterior parietal lobe Shifting  superior colliculus Re-engaging/Reading  lateral pulvinar nucleus of the postereolateral thalamus

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21 Lesion Effects Damage to posterior parietal
inability to disengage from attentional focus to a target located in a direction contralateral to lesion site Neglect/behavioural inattention Damage to superior colliculus inability to shift attention regardless of whether attention is directed elsewhere initially Supranuclear palsy Damage to pulvinar slowed response to a valid or invalid cued target on side contralateral to lesion LaBerge & Buchsbaum (1990)

22 Pulvinar & Gating Function
N O Q W M R A S O Right Visual Field Left Visual Field LaBerge & Buchsbaum (1990)

23 Hemi-neglect 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

24 Movie: Neglect

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30 Hemi-neglect Problem in unilateral visual neglect is in disengaging from non-neglected side to shift to neglected side?

31 Simultanagnosia and visual extinction
Often exhibited by individuals with visual neglect. Simultanagnosia, characterised by inability to “see” more than one object concurrently.

32 Neglect of other “spaces”
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.

33 Spatial vs. Object Based Attention
Most of the evidence for the posterior attentional system derived from spatial tasks Space-based theories What about objects? Can attention be object-based? Is the same posterior parietal attentional network engaged in object-based bottom-up attentional tasks?

34 Object-based Attentional Processing
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)

35 Posner & Petersen’s Model of Attention
Orienting: directed attention disengage and shift attention Alertness: (Sustained Attention/ Arousal/ Vigilance) maintaining focus over a period of time Executive: Target Detection; Supervisory Control

36 Alerting: Vigilance & sustained attention
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.

37 Neuroanatomy of Sustained Attention
Evidence from lesion & neuroimaging studies (i.e. Sturm et al., 1999) R-lateralized network DLPFC, posterior parietal cortex, subcortical (thalamic) PPC RDLPFC MD Thalamus

38 Impaired Sustained Attention
Sustained attention is sustained control Pathological “Time on Task” effects

39 Role of sustained attention
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.

40 Posner & Petersen’s Model of Attention
Orienting: directed attention disengage and shift attention Alertness: (Sustained Attention/ Arousal/ Vigilance) maintaining focus over a period of time Executive: Target Detection; Supervisory Control

41 Anterior Attentional System
Executive control of directed attention Top-down processing overt, intentionally controlled orienting system involves frontal areas E.g. divided attention Allocation of attentional resources

42 Anterior Attentional System
Executive control of directed attention: involved in both selective and sustained attention Top-down processing Components of the anterior attentional/supervisory system: concentration of attention sharing attention (divided attention) suppressing attention shifting attention preparatory attention setting attention sustaining attention (Stuss et al., 1995)

43 Major Neuro-anatomical Structures:
Frontal lobes & Anterior Cingulate

44 Another Model: Distributed Network
Sensory Representation: Directed Attention Executive Control of Attentional Direction Thalamus Parietal Frontal Motivational Representation AC Reticular System (Mesulam, 1985) Arousal

45 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.

46 Complaints of subjects two years after severe brain injury, in percentages:
- forgetfulness - mental slowness - poor concentration - mental fatigue - unable to do 2 things - intolerance of bustle

47 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”.

48 Ponsford and Kinsella (1991), Attentional Rating Scale 0 - 4
mental slowness inability 2 things easily distracted

49 Attention Deficit and Hyperactivity Disorder
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)

50 Conclusions “….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).

51 Conclusions 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).


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