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The Physiology of Attention

The Physiology of Attention. Physiology of Attention. Neural systems involved in orienting Neural correlates of selection. Disorders of Orienting. Lesions to parietal cortex can produce some strange behavioural consequences. Parietal Lobe. Disorders of Orienting.

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The Physiology of Attention

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  1. The Physiology of Attention

  2. Physiology of Attention • Neural systems involved in orienting • Neural correlates of selection

  3. Disorders of Orienting • Lesions to parietal cortex can produce some strange behavioural consequences Parietal Lobe

  4. 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

  5. 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 hemifieldbut they are not blind • Called Hemispatial Neglect

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

  7. Disorders of Orienting • Posner and colleagues • Use cue-target paradigm to investigate attentional abilities of parietal lesion patients

  8. Disorders of Orienting • Posner and colleagues • Use cue-target paradigm to investigate attentional abilities of parietal lesion patients • Prediction ?

  9. Disorders of Orienting • Posner and colleagues • Use cue-target paradigm to investigate attentional abilities of parietal lesion patients • Prediction: stimuli in ipsilesional field always faster than stimuli in contralesional field and cues don’t matter

  10. Disorders of Orienting Here is what you might predict: invalid - contralesional target valid - contralesional target invalid - ipsilesional target valid - ipsilesional target

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

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

  13. 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

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

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

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

  17. 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

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

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

  20. 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

  21. 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

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

  23. 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

  24. 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)

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

  26. Neural Correlates of Selection • Single Unit Recordings: Delayed Match-to-Sample task “CUE” APPEARS AT FIXATION

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

  28. Neural Correlates of Selection • Remember that different neurons have a “preference” for different features • Some stimuli excite a given neuron and others do not

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

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

  31. 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?

  32. Neural Correlates of Selection • Remember that different neurons have a “preference” for different features • If a “good” stimulus appears, neurons tuned to the features of that stimulus are initially excited, but remain so only if attention is focused on that stimulus Chellazi et al. (1993). A neural basis for visual search in Inferior Temporal Cortex. Nature. 363, 345-347 Stimulus is distractor Stimulus is target

  33. 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

  34. 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 is a neural correlate of the perceptual suppression of unattended information

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

  36. Next time: • memory

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