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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 • 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 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 • Called Hemispatial Neglect Disorders of Orienting • Hypothesis: Parietal cortex somehow involved in orienting attention into contralesional space Disorders of Orienting • Posner and colleagues – Use cue-target paradigm to investigate attentional abilities of parietal lesion patients Disorders of Orienting • Posner and colleagues – Use cue-target paradigm to investigate attentional abilities of parietal lesion patients – Prediction ? 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 Disorders of Orienting Here is what you might predict: invalid - contralesional target valid - contralesional target invalid - ipsilesional target valid - ipsilesional target 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 Disorders of Orienting • Interpretation: – Patients have difficulty disengaging attention from good hemifield so that it can be shifted to contralesional hemifield 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 Disorders of Orienting • Disengage - Shift - Engage Model – Parietal Cortex notices events and disengages attention Disorders of Orienting • Disengage - Shift - Engage Model – Parietal Cortex notices events and disengages attention – Superior Colliculus moves attention Disorders of Orienting • Disengage - Shift - Engage Model – Parietal Cortex notices events and disengages attention – Superior Colliculus moves attention – Pulvinar Nucleus reengages attention 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 Disorders of Orienting • Orienting mechanism can be interfered with in normal brains Disorders of Orienting • Orienting mechanism can be interfered with in normal brains – changes that are not accompanied by transients are hard to detect 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 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 Neural Correlates of Selection • Since attention has a profound effect on perception, one would expect it to have some measurable effect on the brain 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 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) Neural Correlates of Selection • Single Unit Recordings: Delayed Match-toSample task MONKEY FIXATES CENTRE CROSS Neural Correlates of Selection • Single Unit Recordings: Delayed Match-toSample task “CUE” APPEARS AT FIXATION Neural Correlates of Selection • Single Unit Recordings: Delayed Match-toSample task DELAY SEVERAL SECONDS Neural Correlates of Selection • Remember that different neurons have a “preference” for different features • Some stimuli excite a given neuron and others do not Neural Correlates of Selection • Single Unit Recordings: Delayed Match-toSample task DELAY SEVERAL SECONDS Neural Correlates of Selection • Single Unit Recordings: Delayed Match-toSample task MONKEY MAKES EYE MOVEMENT TO TARGET Neural Correlates of Selection • Single Unit Recordings: Delayed Match-toSample task • Question: does attention modulate spike rate of neurons that respond to visual stimuli? 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 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 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 Neural Correlates of Selection • Is this a neural correlate of consciousness? Next time: • memory