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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 Disorders of Orienting • Called Hemispatial Neglect - patients appear unable to process information in the contralesional hemifield 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 Contralesional Ipsilesional 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 measure signals from individual neurons 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) Neural Correlates of Selection • Single Unit Recordings: Delayed Matchto-Sample task MONKEY FIXATES CENTRE CROSS Neural Correlates of Selection • Single Unit Recordings: Delayed Matchto-Sample task “CUE” APPEARS AT FIXATION (not the same “cue” as in the cue-target paradigm) Neural Correlates of Selection • Single Unit Recordings: Delayed Matchto-Sample task DELAY SEVERAL SECONDS Neural Correlates of Selection • Single Unit Recordings: Delayed Matchto-Sample task MONKEY MAKES EYE MOVEMENT TO TARGET Neural Correlates of Selection • Single Unit Recordings: Delayed Matchto-Sample task • Question: does attention modulate spike rate of neurons that respond to visual stimuli? Neural Correlates of Selection During presentation of the “cue”, only neurons tuned to it’s properties are excited Neural Correlates of Selection During the delay, those neurons do not return to baseline (is this memory?) Neural Correlates of Selection During 1st 70 ms of search array, any cell will be excited if it’s preferred stimulus is presented Neural Correlates of Selection Once attention is focused, only cells tuned to the attended object remain active 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 might be a neural correlate of the perceptual suppression of unattended information Neural Correlates of Selection • Is this a neural correlate of consciousness? Next Time • Memory