Transcript Lecture 18 Powerpoint File

Electrophysiology of Visual Attention
Does Visual Attention Modulate Visual Evoked
Potentials?
• The theory is that Visual Attention modulates visual information at the
level of visual cortex
• How would you design an experiment to test this theory?
Does Visual Attention Modulate Visual Evoked
Potentials?
• Sustained visual selective attention based on location (attend left or
attend right)
• Eyes remain fixed at centre (covert attention)
• Detect onset of a specific target
• Record the visual ERP in response to stimuli
Does Visual Attention Modulate Visual Evoked
Potentials?
• Result: several components of the visual ERP are modulated by attention
– P1 and N1 are larger for attended relative to unattended stimuli
Does Visual Attention Modulate Visual Evoked
Potentials?
• P1 effect has
topography
(isopotential voltage
maps and scalp current
density maps)
consistent with sources
in extrastriate cortex
Does Visual Attention Modulate Visual Evoked
Potentials?
• Transient visual spatial attention also enhances perceptual abilities for
attended relative to unattended stimuli
• The theory is that transient visual attention causes a P1 and N1 effect like
sustained visual attention
• How could you test that?
Does Visual Attention Modulate Visual Evoked
Potentials?
• Cue – Target Paradigm:
Responses are faster and more accurate for validly cued stimuli
Notice that the target stimulus is identical across the attention conditions
Does Visual Attention Modulate Visual Evoked
Potentials?
• Both P1 and N1 effects are observed
• Effects are most pronounced over contralateral cortex
• Note this is different from the auditory transient attention case
Visual Search
• Recall that visual search seems to entail scanning the “spotlight” of
attention through the scene
Visual Search
• The theory is that the attentional processes engaged by visual search are
the same ones as sustained attention and the cue-target paradigm
– Remember that just because it seems like these are the same thing from the
outside doesn’t mean that they are!
– How could you test this? (Hint: it’s not as straightforward as the sustained
attention and orienting)
Visual Search
• Find the green square: left visual-field target
Visual Search
• Find the green square: Right visual-field target
Visual Search
• Find the green square: Probe occurs at 250 ms at target location
Visual Search
• Find the green square: Probe occurs at 250 ms at distracter location
Visual Search
• Prediction: the probe at
the target location
should elicit enhanced
P1 and N1 relative to a
probe at a non-target
location
Visual Search
• Prediction: the probe at
the target location
should elicit enhanced
P1 and N1 relative to a
probe at a non-target
location
• Early P1 and N1 effects
are similar but not
identical to other
attention effects
• Then you watched a
video