Session Twelve (Attention and Neglect) Flashcards
(36 cards)
What is Attention?
- Our brains only have a limited capacity
- Attention is the mechanism by which we select which information to spend further effort processing
- Enables for detailed processing of important sensory inputs (normally those that are loudest/ brightest/ suddenly appearing)
Acts in two ways:
- Focuses on chosen items, deemed important
- Filters out stimuli we don’t need which might hinder processing of important stimuli
What are the two aspects of attention?
Exogenous: Automatic control of your attention by the characteristics of the stimulus (bottom-up)
Endogenous: Control by your chosen intentions and interest (top-down)
How did Posner et al (1980) investigate the two attention paradigm?
Cuing test:
- Participants shown a series of 3 slides
- Slide 1 = Blank, P pays attention to dot in centre
- Slide 3 has the test stimulus e.g. a letter which the P will be asked to repeat
- Slide 2 is different depending on which paradigm is being tested
- If Exogenous (automatic attention), slide 2 will have a dot appear over the location of the test stimulus for slide 3
- Tests P’s ability to automatically divert attention there
- If Endogenous (chosen attention), slide 2 will show an arrow in the centre pointing to where the test will appear on slide 3
- Patient has to read the arrow, then make the decision to divert their attention along its lines
What did Posner et al (1980) actually show?
- Faster response time and lower error rates in Exogenous paradigm
- Poorer when Endo paradigm
- When they made the arrow right only about half the time, people began to ignore it
- Shows you can consciously modulate which form of attention you use
What did Rees, Russell, Frith and Driver show about attention in their 1999 study?
- Participants shown a series of slide with a red image and a green word over each other
- In some cases they were asked to look for repetitions of the word, in others for repetitions of the image
- Found that the occipital lobe (visual interpretation) activated only in the image tests
- Left hemisphere (reading) activated only in the word tests
- Suggests that our attention selection abilities are so strong they can prevent our brains from processing words/images even when we are staring right at them
What did Pardo, Fox and Raichle show about Attention in their 1991 study?
Tested the sustainability of attention
- Compared PET scans of people into conditions
- Having to detect pauses in very light touches to the left or right big toe
- Having to detect brightness changes in a central fixation point
Areas of activation:
- Right parietal lobe for all tasks
- (left parietal regions when monitoring right toe)
- Suggests this area is crucial to maintaining our attention on one stimulus
What categories of stimuli is our attention capable of diverting to?
- Features e.g. shape, colour etc
- Locations (overlap between areas of the brain related to attention and spatial awareness)
- Whole objects (studies have shown we can interpret objects as a whole)
How does our brain pay attention to specific features?
“Pop out search”
Our brain can easily distinguish one feature that is different amongst a group of similar stimuli, finds it much harder if we try and identify multiple abnormal features (e.g. colour as well as shape)
What evidence exists to suggest our brain is capable of interpreting location as a form of attention?
- There is a crucial overlap between regions of our brain controlling spatial representation and attention
- Single-cell studies have shown that directing attention to a particular location enhances response in visual cortex neurones coding for that specific part of space
DeYoe et al (1999):
- Subjects were cued to different segments of their visual fields
- Compared firing of neurones in vision to firing when paying direct attention
- Showed that when your attention is directed at one area only, your visual cortex only processes that one area
What does Whole Object Selection mean and what evidence exists that our brains are capable of doing this?
Our brain’s ability to pay attention to all information relating to an object, not just shine a spotlight on a small part of it.
Downing et al, 1999:
- fMRI study on attention to entire objects
- Face overlaid on object + motion element
- Subjects task was to monitor for repetition of face/place/motion
- When participants were asked to pay attention specifically to motion, parts of their brain associated with facial recognition also lit up
- Shows that attention spreads to different features of the same object
What is inattentional blindness?
- The process by which paying attention to one stimulus prevents us from noticing another
- Might even render it invisible to us, regardless of how obvious and attention grabbing it should be, if our attention is diverted elsewhere
- Eye tracking tests have shown that you can even pass your eyes over the stimulus but not register it
- Suggests that there is more to vision than just seeing, there is also an attentional aspect
What did the Russell and Driver (2005) study show us about inatentional blindness?
Showed that while we can’t SEE these stimuli on some level they still get processed.
- 3 slide task
- Attention diverted elsewhere
- Asked to state wether dots on slide 3 were arranged the same as dots on slide 1
- Evidence of some congruency effect, demonstrating a degree of implicit/unconscious processing of unattended background stimuli
- Suggests that attention only prevents CONSCIOUS perception of things outside of its focus
How did Lavie et al (1995) explain research evidence suggesting Implicit Processing of Unattended Stimuli?
Perceptual Load Theory:
- Predicted that the brain will process information that is not attended to so long as attentional capacity is not full
- Attention is ‘selective’ when capacity is full
- If there is spare capacity, brain can also process information outside the focus of attention
i. e
- If we are doing something that requires a lot of care and attention we might not perceive anything else
- If we are doing something that requires less attention then other things might be able to get through and be processed
What evidence is there in favour of Perceptual Load Theory?
Rees, Frith and Lavie (1997):
- Gave participants two word based tasks, one simple and one complex
- During the task, a moving dot appeared in the background of the screen, patients told to ignore it
- Measured fMRI activity in MT/V5, an area associated with motion detection
- Found that when performing the low effort task the area became more activated than the high effort task
- Essentially showing that we are more capable of noticing things in our surroundings in low attentional load situations
What is Visuo-spatial Neglect?
- Inability to perceive, report or orient to sensory info, on one side of space
- Happens when parts of the brain associated with attentional allocation (e.g the parietal lobe) are damaged
- Side neglected is contralateral to lesion
- Patients neglect items and objects on one side of space- including people and their own bodies
What is the difference between Neglect and Hemianopia?
- In neglect they can see that side but they can’t allocate any attention to it
- In Hemianopia they cannot see it but would be able to pay attention to it
- Key difference: Hemianopia works along the midline whereas neglect is less likely to
- Two can coexist but very hard to distinguish
Do individuals with VS neglect have difficulty reading?
Weirdly they don’t, can track the line along the page and know to move their head to compensate
How can you test for VS neglect?
Simple tests:
- Ask them to read a newspaper headline (less linear reading pattern therefore can be difficult)
- Ask them to bisect a line (especially useful as how far along they go gives you a good idea of clinical severity)
- Ask them to describe the room to you
More complex tests:
- Line cancellation tasks
- Coping and drawing things from memory e.g. a face or a house
- Can do eye tracking tests
What is Extinction (Inattention)?
A less severe form of VS neglect:
- “Pathological exogenous salience”, strong enough to prevent observation of objects on the other side
- But still capable of seeing both sides
- If presented with a single stimulus, on either side, will be able to say which side it was
- But if presented with two equal stimuli, will only become aware of the one on their favoured side
- Patients can present this way, or can recover from full blown VSN into this
What evidence proves that Neglect is not simply an issue of vision?
Luzzatti (1978):
- VSN patients from Milan asked to describe the Piazza del Duomo from one end of the square
- Only described the buildings on one side
- Were later asked to describe the square from the other side, described the other half of the square
- Shows its not that they can’t see it, its that they can’t pay attention to it
Furthermore, lesions that cause VSN are very rarely regions associated with vision, much more commonly in areas associated with attention, such as the right parietal lobe.
How can a patient with VSN be made to see stimuli on their neglect side?
- If they are placed in a fully dark room (no distractions at all) will be able to see stimuli on their bad side
- If patients are alerted to an item on that side they will momentarily be able to pay attention to it
Once again emphasises that this is a disorder of attention, not vision
What has VSN taught us about attention?
- Attention can indeed be directed at entire objects, otherwise it wouldn’t make sense that VSN patients can neglect a whole object
- Provides evidence for unconscious processing aside from awareness
- There is an interaction between sustained attention/vigilance and spatial attention
What evidence gathered from VSN patients supports the idea of Object-Based attention?
1) The fact that they do not simply neglect the contralesional side of space but also the contralesional side of individual objects
2) Behrmann and Tipper (1994):
- Barbell test
- Two balls linked by a bar, if asked to name which side a dot appears on they find it difficult as they view the whole image as one object
- If you take the bar away they can’t perceive it as a single object anymore and the results change
What evidence gathered from VSN patients supports the idea of Unconscious Processing Outside Awareness?
Number of studies have shown that even though VSN patients do not see the test stimuli, they still perceive them.
Volpe et al, 1979:
- Ps presented with two objects
- When asked to them all objects only named the one, on the CL side
- When asked to state if different or same were capable of doing it quite well
- Clearly processing both
Marshall et al, 1988:
- Presented with two houses, one normal one on fire on their CL side
- Couldn’t tell them apart
- However were able to identify the safe one when asked which house they’d rather live in.
Rees et al, 2000:
- Presented with a house on normal side, face on CL side
- When asked what they see said just house
- However brain scanner revealed activity in fusiform area, associated with facial recognition
