Attention

1. 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 • Application: neglect • Executive • Application: neglect • 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).

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 • Orienting • 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

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. N O Q W M R A S Pulvinar & Gating Function O Left Visual Field Right 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

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. PPC • Neuroanatomy of • Sustained Attention • Evidence from lesion & neuroimaging studies (i.e. Sturm et al., 1999) • R-lateralized network • DLPFC, posterior parietal cortex, subcortical (thalamic) 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 54 - mental slowness 33 - poor concentration 33 - mental fatigue 30 - unable to do 2 things 21 - intolerance of bustle 19

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 2.78 inability 2 things 2.44 easily distracted 2.14

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).