Neuroscience of attention

Question 1

What is selective attention?

Answer 1

o mechanisms that enable us to process relevant inputs, thoughts, or actions out of many possible items
o while ignoring irrelevant ones
o we can direct our visual attention (awareness) to locations and objects without necessarily moving the eyes (covert)
 can pay increased attention through listening rather than just looking
o Attention serves to facilitate processing of information within this focus or ‘spotlight’

Question 2

What did a study by Hermann von Helmholtz (1894) do/show?

Answer 2

• He kept his eyes fixated on central cross on a screen
• He covertly directed his attention to letters in a particular location away from centre cross
• When the room was briefly illuminated, he found he could perceive the letters located within the attended region
• but not those at other locations
• results showed that attention can be covertly directed

Question 3

What are the 2 general categories of attention?

Answer 3

1) Voluntary attention (endogenous)
- our ability to intentionally attend to something
- It’s a top-down goal-directed process
o e.g. paying attention in these lectures
2) Reflexive attention (exogenous)
- when a sensory event captures our attention
- is a bottom-up stimulus-driven process
o e.g. the fire alarm suddenly went off in hallway

Question 4

What ave EEGs showed in relation to auditory attention?

Answer 4

• Earliest physiological studies of attention in humans used the EEG method – ms timing (Hillyard et al, 1973)
• Recorded ERPs (average responses from EEG participants) from the scalp while volunteers attended or ignored sounds presented to both ears via headphones
• dichotic listening task like the cocktail party effect (Cherry)
  o Auditory ERPs (N1 wave) were enhanced for attended ear info
   Brain response to the stimulus (sounds) at approx. 100 milliseconds, were enhanced for the information they were attending to
  o Occurred ~90ms to peak after onset of the stimulus
  o Not just behavioural effects, brain activity was enhanced when attending to the stimulus

Question 5

What have EEG and MEG scans shown of auditory attention?

Answer 5

• Woldorff and Hillyard (1991) extended these studies with more subjects and trials, and better equipment
• As well as N1, early modulation found for the P20-50 effect
  o 20ms is time required for sound to reach auditory cortex
  o Very early modulation of activity in the brain
• Supports early-selection models of attention i.e. early modulation
• Subsequent MEG study (1993) using MRI scans indicated P20/50 signal arose from the auditory cortex (A1: Heschl’s gyrus)
• N1(M1) localised to later auditory cortex
• I.e. very early on, if you are attending to something, processing power is enhanced

Question 6

What have ERP’s shown of voluntary visual attention?

Answer 6

• Spatial attention increases the amplitude of visual ERPs in the extrastriate cortex => P1 (~70-90ms after stimulus onset)
  o but NOT initial V1 potentials (i.e. not in primary visual cortex)
• ‘early’ effect not found for attention to ‘non-spatial’ aspects
• e.g. colour, orientation, type of object etc…

Question 7

What have ERP’s shown of reflexive visual attention?

Answer 7

• Facilitation of attention IS evident - with shorter RT’s (<250 ms)
• Shows enhanced neural processing also occurs for reflexive attention to sensory event (same as voluntary attention)
• The brain process info attended to better than unattended info

Question 8

What have fMRIs shown about the modulation of visual processing?

Answer 8

• Showed blue and orange line segments arranged in sectors radiating from a central fixation point
• The orientation and colour of each sector changed every 2 seconds – attended location shown in red
  o Area attending to changed throughout
• Results showed enhanced activity in the visual cortex, but with patches of enhanced activity in the cortex that were associated with the location of the attended sector in their visual field
  o Where they were looking, the visual cortex in relation with that area would enhance in activity with the moving spotlight
• Therefore, attention modulates visual cortex activity at the attended versus unattended locations – spotlight of attention

Question 9

What can participants be told to pay attention to in neuroimaging studies?

Answer 9

o Colour
o Form
o Motion
o Location

Question 10

What happens when participants are told to focus on one part of a neuroimaging study?

Answer 10

• Attention to colour, form and movement each led to increased activity in different areas of the visual cortex
  o Even though the info seen was the same each time!
• The neural activation was greater in the dedicated brain region for each particular stimulus feature when it was attended to
• Thus, paying attention to a certain feature means enhanced processing in area of brain that processes that type of information
  o Reduced responding to information that was not attended

Question 11

What is the biased competition model?

Answer 11

Desimone & Duncan, 1995; Duncan, 1996

• Sometimes different stimuli in visual field may fall in the receptive field of a particular visual neuron
• Therefore, two different visual stimuli are ‘competing’ for control of the firing of that neuron
• This model suggests that attention resolves this competition – the neuron fires to the stimulus that is attended to

Question 12

What is the faces-houses fMRI study?

Answer 12

O’Craven et al, 1999

• Used pictures with transparent images of houses and faces superimposed onto each other – occupied same space and were both transparent
• One of objects moved while other was stationary – subjects told to pay attention to either faces, houses, or motion
• Looked at activation in the FFA (face area), PPA (place area), and in MT/V5 (motion area)

Question 13

What are the results

Answer 13

• It was found that when subjects attended to faces there was increased activity in FFA, but not PPA
• When subjects attended to houses, there was increased activity in PPA but not in FFA
• When subjects attended to motion activity in MT/V5 increased, as well as in brain area for that object (FFA or PPA)
• So even though the info coming into the brain was the same each time, by selectively attending to one type of information or the other the corresponding neurons in the brain that process that information were more enhanced in activity whereas the other areas of the brain were reduced when compared to them

Question 14

How can attention act as a distraction?

Answer 14

Bantick et al, 2002
- Used fMRI to look at neural effects of an attention distraction task to reduce pain perception
- People in scanner received painful stimuli while:
o doing a low demand neutral task
o doing a high cognitive demand distraction task
- Counting Stroop task – had to count items in list
- Doing Distraction task (minus Neutral task) caused:
o greater activity in ACC for interference processing (task)
o alongside reduced activity in pain areas of the brain

Question 15

How might attention act as a control network?

Answer 15

• Showed participants a Posner type cuing task with stimuli on both sides of the screen
  o an arrow in centre indicated the side to direct attention
• pressed a button if stim was grey, but only on attended side
• A top-down network for attention was engaged by the cue
• None of these areas involved in sensory processing of info
• these areas ‘control’ our attention mechanisms i.e. (the source of attention)

Question 16

How may attention source relate to attention site?

Answer 16

• Some areas of the brain are involved in controlling attention: goal-directed
  o Include areas of the frontal, temporal, parietal cortex (top-down)
  o These are the sources of attention
• Other areas of the brain are involved in sensory and perceptual processing
  o Activity in these areas is modulated by attentional processes from sources

Question 17

Attention source versus attention site –>

Answer 17

• ‘Source’ of attention (top-down) = Black
• ‘Site’ of attention (bottom-up) = Purple
• Top-down may change background firing rates of neurons
• Improve their sensitivity to respond to stimuli (priming?)

Question 18

What damage may lead to neglect syndrome?

Answer 18

Unilateral damage to the inferior parietal lobe (IPL) can result in problems with attention and orientation – neglect to the side of space opposite the lesion (lesions often on the Right side)

Can be referred to as hemi-neglect, hemispatial neglect, visual neglect, visuo-spatial neglect, unilateral neglect etc…

Occurs most often following damage to the right Inferior Parietal Lobe (IPL)

Question 19

How has damage to the right parietal cortex been linked to neglect syndrome (painting)?

Answer 19

• Self-portraits during recovery from a stroke to Right parietal cortex that caused a neglect syndrome
• 2 months post-stroke the artist made the upper left portrait, virtually no left side to the face in the painting
• 31/2 months post (upper right), some detail there on the left side but not nearly as much as on the right
• At 6 months (lower left) and 9 months post (lower right), there is increasing info in the left side of the painting

Question 20

What is neglect?

Answer 20

• Patients behave as though one half of world does not exist
  o they’re completely unaware of missing half - and don’t miss it!
• How does this manifest itself in everyday life?
  o only dress or shave one side
  o only eat half dinner, bump into doors
  o ignore sights & sounds from left side
  o reading errors

Question 21

What is extinction?

Answer 21

• Failure to perceive or act on stimulus in the opposite visual field when 2 stim are present - prominent feature of neglect
• If one stimulus presented at a time – normal detection
  o shows it’s not primarily just a general ‘visual’ problem
• When two presented simultaneously – responds only to the stimulus in the unaffected visual field (right)

Question 22

How can we test for neglect?

Answer 22

Line bisection test
- Neglect of contralesional space diagnosed by neuropsychology tests
o e.g. the line bisection test
- Patient given sheet of paper with many horizontal lines and asked to bisect the lines precisely in the middle with a vertical line
- Patients with RH lesions bisect the lines to the right of the midline

Question 23

What is the attentional bias model?

Answer 23

• LH & RH biased to their opposite visual fields
• Bias is asymmetrical – LH is more strongly biased to R field and Inhibitory connections normally keep a balance
• With a Right side lesion
  o The stronger bias to R visual field is now unopposed
  o No longer inhibition from RH to LH, bias increases
• LH lesion less severe bias
• Versus representational model

Question 24

What are the functional deficit(s) in neglect?

Answer 24

• Neglect is not a deficit of seeing, hearing, or moving
  o but instead of looking, listening, exploring etc.
  o attention is an active process, and it is this difficulty in ‘doing’
• Other potential explanations…
  o Skewed motor intentions?
  o Distortions in mental representations?
  o Distortions in perception or memory?

Question 25

How has neglect been shown through mental representations?

Answer 25

• Bisiach & Luzzati (1978) studied neglect patients in Italy who were very familiar with their own city landmarks
• They asked patients (in lab) to imagine themselves in the local piazza standing in a certain location and to describe the piazza and the buildings surrounding it
  o in descriptions from memory, they neglected things on side of the piazza opposite to their lesion from their perspective
  o when they were then asked to describe the piazza as if standing at the opposite end of the town square - they now neglected the side of piazza they had previously reported!
  o as the town was well known to them, and they were clearly able to report the buildings on both sides (although only one perspective at a time) - its clearly NOT a memory deficit
   this finding showed that attention to ‘parts’ of the recalled images was biased by their parietal damage

Question 26

What are copying and memory skills like in neglect patients?

Answer 26

• Patient NS was a famous cartoonist who suffered right-sided stroke- he typically neglected the left of objects he copied
• When drawing from memory, he could do a complete representation
• However, when asked to copy what he’d drawn, he neglects the left side again - his mental image of the person is unimpaired - so it’s just ‘perceptual’ neglect (info still stored within memory)

Question 27

How has implicit processing been seen to occur in patients with neglect?

Answer 27

• Unattended stimuli, although not available to conscious awareness, can still impact on behaviour
  o A parallel to the phenomenon of Blindsight in vision
• patient sees 2 depictions of a house that are identical on the non-neglected (right) side - but differed on the left (flames)
• Patients claimed not to be able to perceive the difference between them (no awareness), but when forced to choose said they would rather live in the house without the flames!
  o Illustrates neglected information is implicitly coded to a level that supports meaningful judgements to be made
   Some degree of processing going on, even though it is outside of awareness and consciousness, it is not outside of processing

Question 28

What individual variations should be remembered in regard to neglect?

Answer 28

o Some people have worse attention and then if they obtained damage to an area then it would be found that there is decreased attention there

Question 29

Summarise the neuroscience of attention –>

Answer 29

• Attention helps us deal with a flood of sensory and perceptual information – more than we can handle
• Attention facilitates processing of key information
  o This reduces processing of less important information
• It does this through increased neural processing of attended information versus unattended (site)
• This is ‘modulated’ by top-down mechanisms which aren’t involved in sensory processing (source)
• Neglect leads to attentional deficits in processing items/information in the environment or thoughts