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 valid - contralesional target valid - ipsilesional target invalid - contralesional target invalid - ipsilesional target Here is what you might predict:

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

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-to- Sample task MONKEY FIXATES CENTRE CROSS

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

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

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

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?

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, 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