Week 8: Attention and its Disorders

• Covert Attention


  • Attention to an object without an eye movement towards it.

  • Shift of visual attention to a spatial location without eye movements
• Endogenous System

  
  

  Controlled by PP’s intentions and is used when central cues are presented
• Exogenous System


  Automatically shifts attention is involved when uninformative peripheral cues are presented. Stimuli that are different from other stimuli, like colour, are most likely to be attended using this system.
• Describe the top-down approach proposed by Corbetta & Shulman

  Top-down-Endogenous-Dorsal System

  •      The brain network involved in the goal-directed attentional system

  •      Consists of a dorsal fronto-parietal network 

  •      Under the influence of goals, expectations, knowledge

  •      Responds to predictive cues about incoming stimuli
• Describe the bottom-up approach proposed by Corbetta and Shulman

  Bottom-Up-Exogenous-Ventral System

  •      A stimulus-driven attentional system

  •      Provides a “circuit-breaking” function

  •      Unexpected, salient, or threatening stimuli

  •      Distractors resembling task-relevant stimuli

  •      Consists of right hemisphere (primarily) ventral fronto-parietal network
• Neglect

  Lack of awareness of stimuli presented to the contralesional side to the brain damage
• Egocentric or spaced-based neglect

  Damage to the right hemisphere, which causes a lack of awareness of stimuli on the left visual field
• Allocentric or object-centred neglect

  Lack of awareness to the left side of objects
• What brain areas are affected in neglected patients, and what type of system is involved?

  Damage to bottom-up/ventral attention network rather than brain areas.
• Extinction

  
  

  Failure to detect a stimulus presented to one visual field (typically left) when another stimulus is simultaneously presented to the other side
• Describe Posner's cueing paradigm.

  Participants had to respond as quickly as possible to the onset of a light.

  Shortly before the onset of the light, showing:

  1) a neutral cue (central cross)

  2) a central cue (the black arrow) or

  3) a peripheral cue with blue contour around box

  These cues were mostly valid, but sometimes they were not, i.e. they did not correctly announce where the light would appear.

  
• What did Posner's cueing paradigm find?

  Reaction times - (fastest) Valid cues > neutral > invalid (slowest)

  Same pattern for central & peripheral cues
• Which aspect of these study's results led Posner to propose two relatively separate visual attention systems?


  Peripheral cues as they were not ignored and still affected performance.
• What did Corbetta and Shulman (2002) argue, in essence, when they carried out a meta-analysis of brain-imaging studies


  Brain areas are most often activated when PP expect a stimulus that has not yet been presented from the dorsal attention network. In contrast, when PP detect low-frequency targets from the ventral attention network, brain areas are most often activated.
• Hahn et al. (2006) tested Corbetta and Shulman’s (2002) theory by comparing patterns of brain activation when top-down and bottom-up processes were required. What did they find?


  
  

  Little overlap between the brain areas associated with top-down and bottom-up processing.
• Why was Chica et al.'s 2011 study different to other neuroimaging studies?


  Used TMS that interfered with brain processing in a given area.
• What did Chica et al. 2011 find?

  Found that TMS applied to the right intraparietal sulcus impaired the functioning of both attention systems
• What did Chica et al. 2011 conclude?

  The two attention systems work together.
• Summarise the three developments in the approach Corbetta and Shulman (2002) that have occurred in recent years.

  1.      Greater understanding of the interactivity between the two attention systems.

  2.      Added clarification to how long/duration the dorsal attention network is active immediately before presenting an activated visual stimulus.

  3. Brain networks relevant to attention additional to those already identified are found.
• What were the findings of Rorden et al. (2012) in relation to these 2 forms of neglect? What do the findings suggest?

  F: Found a strong correlation between the 2 forms of neglect and similar brain regions associated with each form of neglect

  C: Supports the notion that egocentric and allocentric neglect are from a single disorder
• Which brain areas are damaged in neglect patients?

  Right hemisphere and superior temporal gyrus, inferior frontal gyrus, insula, supramarginal gyrus and angular gyrus.
• What task did Vuilleumier et al. (2002) use to study extinction?

  PP shown objects either on LVF/RVF and had to name the object.
• What were Vuilleumier et al.'s (2002) findings?

  When a pair of objects is shown, only the things shown RVF are named. The LVF pictures had a facilitation effect, indicating they had been processed.
• According to them, how does the damaged ventral system impair the functioning of the dorsal attention network?

  Damage to ventral system impairs function of the undamaged dorsal, goal-directed system

  a.      Unbalanced processing favouring the left hemisphere

  b.      Reduced alertness & attentional resources
• What are the two main assumptions of de Haan et al. 's 2012 theory of extinction?


  1. Often found in patients suffering from neglect, but…

  2. Problems in simultaneous (not sequential) processing: biased competition mechanism
• Summarise the Riddoch et al. study, its findings, and their implications


  T: Presented things often paired together: wine bottle and glass, and things never used together: wine bottle and ball

  F: Extinction PP identified both objects more often in the first condition than the second.

  C: When two stimuli are integrated, it can reduce competition and extinction.
• What did Roberston et al. (1998) find?


  The slower detection of stimuli in LVF compared to RVF was no longer present when warning sounds were used to increase alertness.
• Who examined the idea that neglect patients have reduced attentional resources?

  Bonato and Cutini (2016)
• What tasks were PP asked to complete in Bonato and Cutini?


  Compared neglect PP ability to detect visual targets with/without a second attention-demanding task
• What were the results of Bonato and Cutini?


  Detected half as many targets in LVF than RVF when performing another task
• What was the conclusion of Bonato and Cutini's study?


  Show neglect patients have limited attentional resources
• Who examined the prediction that neglect patients have an intact dorsal attention network (goal-directed, intentional system) ?


  Duncan et al.
• What task did Duncan et al. ask PP to do?


  Presented arrays of letters and neglect PP only recalled those in a specific colour
• What was the IV / main variable of Duncan et al?


  PP recalled coloured letters only so that the dorsal attention network was used to select appropriate letters.
• What were the results of Duncan et al.?


  Neglect PP and healthy PP did the same, showing equal recall of letters presented to each side of visual space.
• What did Duncan et al.'s findings imply?

  Neglect PP have an intact dorsal attention network, especially since its use is facilitated.