1. Disorders of Orienting Lesions to parietal cortex can produce some strange behavioural consequences –patients fail to notice events on the contralesional side –Patients behave as if they are blind in the contralesional hemifield but they are not blind

2. Disorders of Orienting Called Hemispatial Neglect - patients appear unable to process information in the contralesional hemifield

3. Disorders of Orienting Hypothesis: Parietal cortex somehow involved in orienting attention into contralesional space

4. Disorders of Orienting Posner and colleagues –Use cue-target paradigm to investigate attentional abilities of parietal lesion patients ContralesionalIpsilesional

5. Disorders of Orienting Results: Valid cue in contralesional field is effective invalid- contralesional target valid - contralesional target invalid - ispilesional target valid - ipsilesional target Results: Severe difficulty with invalidly cued contralesional target

6. Disorders of Orienting Interpretation : –Patients have difficulty disengaging attention from good hemifield so that it can be shifted to contralesional hemifield

7. Disorders of Orienting Interpretation: –Patients have difficulty disengaging attention from good hemifield so that it can be shifted to contralesional hemifield –Parietal cortex is somehow involved in disengaging attention

8. Disorders of Orienting Disengage - Shift - Engage Model –Parietal Cortex notices events and disengages attention

9. Disorders of Orienting Disengage - Shift - Engage Model –Parietal Cortex notices events and disengages attention –Superior Colliculus moves attention

10. Disorders of Orienting Disengage - Shift - Engage Model –Parietal Cortex notices events and disengages attention –Superior Colliculus moves attention –Pulvinar Nucleus reengages attention

11. Disorders of Orienting Disengage - Shift - Engage Model –Parietal Cortex notices events and disengages attention –Superior Colliculus moves attention –Pulvinar Nucleus reengages attention –Entire process is under some top-down control from Frontal Cortex

12. Disorders of Orienting Orienting mechanism can be interfered with in normal brains

13. Disorders of Orienting Orienting mechanism can be interfered with in normal brains –changes that are not accompanied by transients are hard to detect

14. Disorders of Orienting Orienting mechanism can be interfered with in normal brains –changes that are not accompanied by transients are hard to detect e.g. building appearing slowly orienting mechanism scans the scene aimlessly

15. Disorders of Orienting Orienting mechanism can be interfered with in normal brains –changes that are not accompanied by transients are hard to detect e.g. building appearing slowly orienting mechanism scans the scene aimlessly –changes accompanied by full-field transients are hard to detect e.g. change blindness orienting mechanism is blinded by the transient

16. Neural Correlates of Selection Since attention has a profound effect on perception, one would expect it to have some measurable effect on the brain

17. Neural Correlates of Selection Since attention has a profound effect on perception, one would expect it to have some measurable effect on the brain This has been confirmed with a variety of techniques: EEG, fMRI/PET, Unit Recordings

18. Neural Correlates of Selection Electrical activity recorded at scalp (EEG) shows differences between attended and unattended stimuli in A1 within 90 ms Hansen & Hillyard (1980)

19. Neural Correlates of Selection Single Unit Recordings measure signals from individual neurons

20. Neural Correlates of Selection Single Unit Recordings measure signals from individual neurons Remember that visual cortex neurons have receptive fields that are tuned to specific stimulus properties (e.g. color, motion)

21. Neural Correlates of Selection Single Unit Recordings: Delayed Match- to-Sample task MONKEY FIXATES CENTRE CROSS

22. Neural Correlates of Selection Single Unit Recordings: Delayed Match- to-Sample task “CUE” APPEARS AT FIXATION (not the same “cue” as in the cue-target paradigm)

23. Neural Correlates of Selection Single Unit Recordings: Delayed Match- to-Sample task DELAY SEVERAL SECONDS

24. Neural Correlates of Selection Single Unit Recordings: Delayed Match- to-Sample task MONKEY MAKES EYE MOVEMENT TO TARGET

25. Neural Correlates of Selection Single Unit Recordings: Delayed Match- to-Sample task Question: does attention modulate spike rate of neurons that respond to visual stimuli?

26. Neural Correlates of Selection During presentation of the “cue”, only neurons tuned to it’s properties are excited

27. Neural Correlates of Selection During the delay, those neurons do not return to baseline (is this memory?)

28. Neural Correlates of Selection During 1st 70 ms of search array, any cell will be excited if it’s preferred stimulus is presented

29. Neural Correlates of Selection Once attention is focused, only cells tuned to the attended object remain active

30. Neural Correlates of Selection Results: Neurons in visual system respond vigorously to certain stimuli but are then sharply suppressed if a different stimulus is selected by attention

31. Neural Correlates of Selection Results: Neurons in visual system respond vigorously to certain stimuli but are then sharply suppressed if a different stimulus is selected by attention Interpretation: this selection might be a neural correlate of the perceptual suppression of unattended information

32. Neural Correlates of Selection Is this a neural correlate of consciousness?

33. Next Time Memory