1. Electrophysiology of Visual Attention

2. 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?

3. 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

4. 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

5. 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

6. 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?

7. 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

8. 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

9. Visual Search Recall that visual search seems to entail scanning the “spotlight” of attention through the scene

10. 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)

11. Visual Search Find the green square: left visual-field target

12. Visual Search Find the green square: Right visual-field target

13. Visual Search Find the green square: Probe occurs at 250 ms at target location

14. Visual Search Find the green square: Probe occurs at 250 ms at distracter location

15. Visual Search Prediction: the probe at the target location should elicit enhanced P1 and N1 relative to a probe at a non-target location

16. 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

17. Then you watched a video