W11 - Attention Flashcards
What the task examining voluntary attention? What are other names of voluntary attention
Posner Cueing Task
- Meaures Endogenous/Covert attention
- covert = not moving eyes
What is endogenous attention and why does posner cueing task examine this
Orientation of attention to the cue is
- Driven by goals (internally)
- Not due to environment/physical features
What is unilateral spatial neglect
- Symptom of patients behaving as though parts of objects, and or the world around them do not exist
- They are largely unaware of this deficit
- Show extinction (unlike heminaopia)
What brain damage is associated with unilateral spatial neglect
- Stroke
- Brain injury to right parietal and frontal cortex
Do patients with stroke always have unilateral spatial neglect. Why?
- People with stroke largely loses this neglect.
- Stroke = Pressure
- So after stroke dissipates, pressure goes back to normal, neglect dissipates
How do we examine unilateral spatial neglect.
At what spatial scales are these neglects
Line cancellation test
- Neglect may arise at different spatal scales within the same patient
- e.g. may ignore left page in book/left sided words
What is extinction?
Failure to perceive a stimuli contralateral to leision when presented simultaenously with stimuli ipsilateral to lesion.
How do we draw a distinction between spatial neglect and visual feild deficits?
Extinction
- Spatial Neglect:
- Will still repsond to unilateral presentation
- Visual Field Deficits
- Visual Field Damage
- Will not respond to unilateral presentation.
There are many studies showing different associations between neglect and brain regions. Why are there large variability?
- Different methods (e.g., CT, fMRI, DTI)
- How participants are selected, how long since stroke, what test used to measure neglect
-
Location of stroke (Naturalistic lesions)
- Some patients die after stroke, can’t locate…
What are the brain regions associated with neglect after confluence of imaging studies
- Posterior parietal lobe
- Temporoparietal junction (including STS)
PPL and TPJ (+STS)
What are the results of primate studies on neglect?
- Posterior pareital (by itself) does not cause neglect,
- Both posterior paretal cortex, TPJ (includes STS) together causes it
- Neglects are often temporary, not permanent
In a lot of structural work, what do studies often miss out
They often ignored where white matter damager occur, that might have disconnected frontal, temporal and parietal cortices
- Might be a disconnection syndrome
Other than TPJ, STS, and Posterior Parietal Lobe, wich other region has been found to cause neglect? What is the caveat
Damage to subcortical nuclei (caudate, putamen).
- Thought this might be due to disconnection: cortical hypoactivation to regions important for neglect like TPJ
Is neglect more common after left/right hemisphere damage
Right hemisphere damage is more common
(far less common in left-handed participants)
What are the models suggesting why neglect is more prominent after right-hemispheric damage?
- Representational Model
- Attentional Bias Model
Elaborate on the representation model of unilateral spatial neglect
- Right hemisphere represents right and left
- Left hemisphere tepresents right only
- Damage to left no neglect because right can maintain
Elaborate on the attentional bias model of unilateral spatial neglect
- Left and right have natural bias towards contralateral attention
- Bias is assymmetrical with left hemisphere being more strongly biased towards right hemispace
- that’s why we sit on the left
Saliency in Neglect Patients. What does it suggest
Saliency of objects in neglected / contralesional field is impaired
- Exogenous and endogenous (goal-driven) components of selective spatal attention are equally impaired
- Abnormally high salience of ipsilesional stiuli can prevent them from being filtered when task-irrelevant but they are a minority of examples
Saliency in dark room. Results and Implications?
Results
- Patients in dark room without stimuli show spatial lateralised bias (Bias to look to the right/ ipsilesional hemispace/’good side’)
- Eye movements reflect hemispatial bias. Gaze deviations are observed at rest
Implications
- Not a reduced salience of contralesional spatial deficits alone
- Also an imbalance in mechanism controlling in
- (a) controlling gaze; and
- (b) relevant to attention
Is spatial lateralised bias related to early/late visual process
Bias does not reflect early visual mechanism
There are 4 findings that supports inact early visual mechanism in neglect patients, which are
- Intact image segmentation of low-level visual features in the neglected visual field
- e.g. figure ground illusions in neglected side
- Normal contrast sensitivity
- Occipital cortex responds to visual stimuli in the contralesional hemispace, even under extinction presentation
- Contralesional visual stimuli prime faster response times for subsequent stimuli
- Unconscious processing
What is the thrid model of unilateral spatial neglect
(Hence why frontal and temporal regions contribute to neglect syndrome)
Deficits is not spatial in nature. 3 non-spatial deficits to account for neglect:
- Re-orienting of attentnion
- Detection of heaviourally relevant stimuli
- Difficult maintain arousal and vigilance
Evidence for deficits not being spatial in unilateral spatial neglect
1.) Re-orienting of attention
In posner cueing task, even though invalid cues slowed reaction times (All patients)
- Interaction effect where RTs significantly greater when invalid cue directed attention to ipsilesional hemsiphere (‘good’ side)
- An example of not being able to shift attention from the ‘good’ side to the ‘neglect’ side
Evidence for deficits not being spatial in unilateral spatial neglect:
2.) Detection of behaviourally relevant stimuli
1.) Other modalities
- Show deficits in target detection in simple paradigms (auditory)
- May reflect deficit in arousal and processing capacity
2.) Attentional Blink (not hemispheric)
- RH stroke showed significant longer attentional blink than controls
- RH stroke + neglect worsens the blink (See picture)
Evidence for deficits not being spatial in unilateral spatial neglect: Arousal and sustained attention
RH and neglect patients deficits in
(a) Arousal
* Reduced GSR to electrical stimulation
(b) Sustained attention
* Elevator counting test / GNG / SST
Cognitive task but giving an arousal boost (non-lateralised thing) before that reduces the neglect (assumed to be lateralised)
Neglect in left-handed patients is more common/less common
Less common
Monkey lesion studies have indicated that the region most likely to cause neglect-like symptoms is ____
Temporal-parietal junction / TPJ
The finding that neglect patients show deficits in non-spatial measures of attention has been argued to support what hypothesis?
The right hemisphere dominance of neglect reflects the laterality of mechanisms supporting reorienting, detection and arousal
The Rees et al. (2000) study of neglect patients identified significant occipital cortex activity associated with the presentation of visual stimuli in the neglected hemifield, which demonstrated?
Neglect is not caused by abnormal visual processing at early stages of visual processing
Localising the cortical mechanisms underlying neglect has been difficult because:
Neglect patients, especially those with enduring symptoms, typically have white matter damage which causes disconnection between cortical loci
An extinction test helps to discriminate unilateral spatial neglect from hemianopia because?
Damage in the visual pathway will cause the patient to be non-responsive to all unilateral visual stimuli presentation
Which type of visual deficit is most consistent with unilateral spatial neglect?
Fail to perceive a visual stimulus in the hemifield opposite (contralesionsal) to their brain lesion, when presented simultaneously with a stimulus in the ipsilesionsal hemifield
Define selective attention. What kinds are there?
Cognitive processes that enable organisms to process relevant inputs, thoughts or actions while ignoring irrelevant or distracting ones
- ) Voluntary (Endogenous): Top-down / Goal-directed
- ) Reflextive (Exogenous): Bottom-up / Reflexive
What is TBI
Traumatic Brain Injury
Brain damage by external mechanical force
Given that attention is limited capacity, what must the system decide
Decide:
- What is selected for extended processing
- What gains access to awareness
What are bottlenecks and what are the 2 theories
Bottleneck: Filtering of input that permit high priority information to gain access
- Early
- Stimuli need not completely perceptually analysed before selection for further processing or rejected as irrelevant
- Late
- Both attended and ignored inputs are processed equivalently and bottleneck occurs at higher level prior to awareness/further processing
What are the results of posner cueing task in relation to cue period length. Explain.
- RTinvalid > RTneutral > RTvalid
- Benefit increases with cue period length
- Because of internal shift in covert attention (‘mental spotlight’) to cued visual field
What is the P1 ERP? What does it occur and not occur for?
- 70-90ms after visual stimulus onset in occipital lobe
- Larger when same stimuli appear at same location (Valid) compared to attention focused elsewhere (Invalid)
- Does not occur for other features such as colour, spatial frequency, orientation, or properties
What are fMRI findings in relation to posner cueing task
Stronger sensory processing of visual stimli when either covert or overt attention is applied to it (stronger when attended)
What is the length of reflexive attention. What other properties you get with reflexive attention? Why?
Short lived (<300ms)
- Inhibition of Return
- Reflexively attended location become inhibitied over time, slowing responses in those areas
- Necessary for coping with our dynamic environment, otherwise we’ll be constantly distracted during complex tasks…
What are the pathways of voluntary and reflexive attention
Voluntary: Top-Down
- Dorsal Pathway
- Intraparietal cortex and superior frontal cortex
Reflexive: Bottom-Up
- Ventral Pathway, lateralised to right hemisphere.
- Temporoparietal cortex and inferior frontal cortex
- Detecting behaviourally relevant or salient stimuli
- Acts as cirucit breaker for Dorsal
What is Balint’s syndrome. When does it occur?
Baliant’s Syndrome
- Severe disturbance of visual attention and awareness
- Perceive only one or a small subset of available ojects are perceived at any time
- Typically occurs after stroke/CVA
What are symptoms of balient syndrome
- Simultagonsia
- Deficit perceiving visual field as a whole
- Ocular Aprexia
- Deficit in eye movement to scan visual field
- Optic atoxia
- Deficit in visually guided hand movements
- Bilateral occipitotemporal lesion:
- Deficit in perceiving multiple objects in space
Define Vigilance
Sustained Attention/Vigilance:
State of readiness to respond to rare, unpredictive stimumli
Vigilance vs Selective Attention
Vigilance:
- Neuroanatomically sepaarate
- Basic attentional function that determines the efficacy of selective attention
What is a property of sustained attained task
Has to be long.
Generally need to engage participants for 30 mins plus before seeing any decreament, even TBI patients
What is the network for Vigilance/Sustained Attention. What is the evidence to support it? What NT is it sensitive to?
Right fronto-parietal network (IMPORTANT)
Reticular Activating System
- Basal forebrain projects to prefrontal/parietal regions to facliatate top-down regulation of vigilance
- Sensitivty to noradrenergic release
Evidence
- Increased activty of right frontal and parietal regions in vigilance task
What group of people is associated with vigilance deficits. Why?
- TBI (Traumatic Brain Injury)
- TBI affects frontal lobes and white matter
- Affects sustained attention
- Diffuse axonal injury disrupt reticular activating system
- TBI affects frontal lobes and white matter
- ADHD
What is the first task used to examine vigilance and what is the problem
- PASAT or CPT
- Confounded with other cognitive domains such as processing speed
- Vulnerable to rapid automatisation where limited attention still allow task performance
What are more modern tasks to examine vigiliance. What do they examine
Standard SART and Fixed Sequence SART
- Requiring inhibition of ongoing behaviour in context of a rare target
- Test both IC and Vigilance
- Distinction rest on whether vigilance is generated endogenously rather than exogenously
- If IC poor, standard performance will be poor but fixed sequence will be ok
- If TBI/vigilance poor, both will be poor
- Inability to maintain a sufficient level of vigilance
- Error rates at 25% or above despite sequence being entirely predictable
- Distinction rest on whether vigilance is generated endogenously rather than exogenously
What are some neurological and physiological features SART failures associated with physiologically and neurologically in TBI patients?
In TBI patients, SART failures are associated with…
- Decreasd right frontal parietal
- SCR
- Alpha Band
What are some neurological and behavioural SART failures associated with physiologically and neurologically in ADHD?
ADHD
- Increase response variability
- Rapid fluctuation in attention levels from trial-to-trial
- Decreased right fronto-parietal
What improves vigilance attention and what are other neurological associated outcomes in the task.
Methylphenidate
- Improved SART
- Increased right fronto-parietal activity
- Decreased variabiltiy in response times
MPH in TBI patients. What improves, and why?
Sustained attention, but also other cognitive domains
- Sustained attention thought to be the ‘gate’ for other domains.
