Neuronal mechanisms of attention – Hemispatial Neglect Flashcards
what is a stroke
When someone has a stroke a blood clot breaks off and travels up the artery until it gets caught and blocks the blood flow to one side of the brain.
Blood flow is restricted to one half of the brain leading to neuronal death and eventually a fluid-filled cavity shown here in white on an MRI scan.
what is a lesion
area of brain damage
what is Contralesional stimuli:
• Contralesional stimuli: Things occurring on the opposite side to the lesion
what is Ipsilesional stimuli:
Things occuring on the same side as the lesion
what are cancellation tests
Because of the crossed nature of the human sensory system, a right hemisphere lesion affects the left side of space and vice versa.
This is a standard test for hemispatial neglect, requiring the patient (who has a right hemisphere lesion) to cross out all of the lines on the page. As you can see, the patient only crosses out lines on the right, ignoring all those on the left.
what is anatomy of neglect
Temporoparietal junction (TPJ) is the most common area but neglect can occur after damage to all of these regions.
example of extinction in aquired brain injury
As the patient recovers, neglect often resolves into extinction.
In extinction, the patient can perceive individual touches on the left and the right side. However, when presented with a simultaneous touch on both sides, the patient only perceives the one on the right.
It is the same with visual stimuli – patients can see things on either side individually but will generally miss things on the contralesional side (the side opposite the lesion) when presented together with things on the ipsilesional side (the same side as the lesion).
patients wiht lesion can detect what
contralesional stimuli, just not when they occur simultaneously with ipsilesional stimuli
what did rees et al find
When the face on the left is presented simultaneously with an object on the right, the patient reports no awareness of the face. However, there is still activation in visual cortex (albeit reduced). Therefore, the visual cortex is still processing the object despite the lack of (conscious) awareness.
what was Mattingley, Davis and Drivers 1997 study
- In this study Mattingley and colleagues wanted to test whether attention operates at a late stage in processing, i.e. after low level visual processing
- They presented subjects with Kanizsa figures, in which removing a segment of each circle produces the illusion of an object in the centre.
what did Mattingley, Davis and Drivers 1997 find
- They found that extinction of left sided circles was substantially reduced when an illusory surface was formed.
- Suggests attention operates after the low level visual processing has occurred – even after stimuli in the environment have been interpreted as objects.
what was Vuilleumier and Schwartz (2001)’s study
- They tested patients with extinction on a task where they were asked simply to identify what they could see.
- Patients were presented with two pictures at a time, which could either be fearful (e.g. spiders) or neutral (e.g. a ring).
what did Vuilleumier and Schwartz (2001) find
- They found that extinction was highest in all patients when the stimulus on the left was neutral but that extinction was reduced when the stimulus on the left was fearful.
- This suggests that despite the patient not being aware of information on the left side of space, if the information is sufficiently meaningful, or important, the stimulus can ‘break through’ the attentional filter
- Parallels with the cocktail party effect from the previous lecture.
what was Vuilleumier and Schwartz (2000) study
condition 1:
• Here subjects were shown two words, either the same (e.g one one) or different (e.g. one two)
• The first thing to note is that extinction was higher when the words were the same demonstrating that the meaning of the word is processed preattentively.
condiiton 2:
• So next they showed subjects words that looked different but with either the same semantic meaning (e.g. one 1) or a different meaning (e.g. one 2).
what was manly et al 2002’s material
cancellation test (also showed perservation behaviour)
what is perservation behaviour
recross out stars that they already crossed out
what did manly et al 2002 find about preservation behaviour
Perseveration behavior reduced when targets were removed from the left (unattended) side – suggests influence of unseen targets on behavior to seen targets
This effect could be driven by an overall reduction in clutter.
So in the next experiment they again removed targets from the left but this time replaced each target with a distractor.
Thus, the number of items (clutter) remains the same but the number of targets reduces.
what did Manly et al 2002’s replication change
stars on the left have been replaced by distractors- reduced targets but still clutter
what did manly et al 2002’s second study show?
They found that perseveration still reduced dramatically with the number of targets.
Again suggests that the unseen targets on the left can influence responding.
This demonstrates a really interesting aspect of attention, which is that although things are not perceived, they can still influence our behaviour.
Parallels with influence of unattended stimuli in dichotic listening task.
All evidence that attention operates at a late processing stage.
what did Bisiach and Luzatti do>
Bisiach and Luzatti asked Italian patients with neglect to recall a famous landmark in Florence and asked them what they could see in their minds eye.
what did Bisiach and Luzatti find?
The patients mostly reported seeing the buildings, cafes, shops on the side of space ipsilateral to their lesion (their ‘good’ side). It was as if they had lost the representation of things on the left side of space, even those that only existed in their memory or imagination, not simply in the external world.
what did Bisiach and Luzatti find when they asked people to imagine looking at the scene from the other end?
This time, they recalled all of the previously neglected information and again couldn’t report all of the contralesional information (the information they had previously recalled correctly!)
This finding suggests that attention operates also on ‘internal’ representations (e.g. memory, imagination) as well as ‘external’ representations (perception)
what did Wojiulik et al 2011 find?
patients made more perservations for Os than objects when marks were invisible.
This suggests a deficit in working memory.
what did Wojiulik do
Given attention operates on internal representations, possible neglect patients will show a deficit not only in attention but also in spatial working memory.
These authors gave patients a cancellation task and asked them to cancel either the Os or the objects with either visible or invisible marks.
What you tend to find normally on this task is that patients revisit previously cancelled targets (perseveration) i.e. they actually cross out the same targets over and over again.
what did Behrmann & Tipper 1994 do
In this study patients were presented with a barbell stimulus and a target (small white square) could appear in either end of the barbell.
In the static condition the barbell appeared and then the target appeared. In the moving condition, the barbell appeared and subsequently rotated and then the target appeared.
what did Behrmann & Tipper 1994 find
The study showed that in the static condition, patients with right hemisphere lesions were slower to detect targets on the left, as you would expect.
However, in the rotating condition, the direction of their neglect suddenly reversed – targets that appeared on the right side of the barbell (which was previously on the left side of space) were now detected slower.
This shows that attention is more focused on objects than spatial locations. Attention operates in an object-based frame of reference.
what was Posner et al 1984’s study
Reflexive attention has also been studied using the Posner cueing paradigm, but in this version subjects are cued exogenously.
This means that a flash of light or something attention grabbing occurs in a peripheral location, and then a target appears either in the location of the flash (called a cued trial) or in the other location (uncued trial).
what was Posner et al’s results
As you can see, RTs are much higher for the uncued contra condition indicating a problem disengaging attention from cues on the ipsilesional side.
what does Posner et al’s study suggest
- Suggests patients have trouble disengaging from stimuli on the ipsilesional side to focus on contralesional stimuli
- Spatial attention is a competitive process
reflective attention has been studied using what
Posner cueing paradigm
what is Balint’s syndrome
This is a rare disorder where patients have had strokes damaging both sides of their brain encompassing both parietal lobes.
In this case, the attentional disorder is not spatial but patients lose the ability to attend simultaneously to two objects – again demonstrates the competitive nature of attention
