“everyone knows what attention is… william james, 1890
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What is visual attention?. ... It is the taking possession by the mind, in clear and vivid form, of one out of what seem several simultaneously possible objects ”. “Everyone knows what attention is… William James, 1890. Levels of analysis: 1. Subjective (W. James). - PowerPoint PPT PresentationTRANSCRIPT
“Everyone knows what attention is… William James, 1890
What is visual attention?
... It is the taking possession by the mind, in clear and vivid form, of one out of what seem several
simultaneously possible objects”
Levels of analysis:1. Subjective (W. James)
2. Functional - cognitive (joke)
3. Neurological
1. Subjective level (phenomenology)
- if you don’t pay attention to it, you don’t see* it
* perceptual awareness
In normal subjects
Go mist
Change blindness
In patients with hemispatial neglect
move your eyes (& your attention)
you ‘see’ the change -- you are ‘perceptually aware’-- at the attended location
You are unaware at the unattended locations
Try to find the difference between these two pictures
Look for waldo
Steps to find Waldo1. Fixate attention
2. Decide: Is that him?
3. Disengage attention
4. Move attention
5. Fixate onto a new location
These are the Cognitive processes
Find the letter T
T
L
T
T
T
L
Anne Treisman
2. Cognitive Processes: Visual Search
2. Cognitive processes: How to study visual attention?
• Visual search (Treisman)– Overt movement (i.e., moves eyes)– It’s difficult to isolate specific steps (e.g. disengage)
• Covert orienting task (Posner) (aka spatial cueing task)– No eye movements – Isolates each step of the process
time
Covert orienting task
Mike Posner+
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+
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invalid20%
Valid80%
1 sec
0.5 sec
Mike Posner
250
270
290
310
330
350
Valido Invalido
RT (ms)
Covert orienting task
Arrow Onset
. Voluntary engagement of attention
Target onset at opposite location (invalid trial)
. Detect surprising event
. Disengage attention from initial site
. Move it to the opposite location
Covert orienting task
Voluntary Attentional System (dorsal).
<-Attention at the cued location
<-
15 sec delay
* Detect stimulus at unattended location
Automatic attentional system (ventral)Corbetta et al, nature neuroscience
Interaction between the two systems
Left IPS
Right IPS.
Right TPJ
balance
Modulated by expectations
Alerted by Unexpectedstimulus
Hemispatial NeglectAnatomy
TPJ, horizontal cut
Temporo-parietal junction (right)
Lesion can extend
toward frontal lobe
Interaction between the two systems post-stroke
SPI izq.
SPI der.
UTP der
IMBALANCE Alert by unexpected
stimulusGreatly reduced
LESION
Sintoms:??
Covert orienting task
Hemispatial neglect, clinical
- eye gaze: right side bias
- neglects stimulus in left visual field (bumps wall, misses food on that side of tray)
- low arousal (sleepy)
-Muscular weakness (hemiparesis): unrelated
Cancelation task
Line bisection
Star crossing
Clinical assessment
drawings
Bias in writing
- Extincion
Clinical evaluation (cont’d)
Q Does the disordered attentional mechanisms associated with visuospatial neglect alter patient’s representation of space ?
normal
neglect
Self portrait by Anton Raderscheidt, at different stages of recovery
3
21
4Drawings by Tom Greenshields
pre- and post-stroke
Before After
Visual search: Eye movements