The Physiology of Attention

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The Physiology of Attention
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Physiology of Attention

• Neural systems involved in orienting
• Neural correlates of selection

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Disorders of Orienting

• Lesions to parietal cortex can produce some
  strange behavioural consequences

Parietal Lobe
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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

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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
• Called Hemispatial Neglect

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Disorders of Orienting

• Hypothesis Parietal cortex somehow involved in
  orienting attention into contralesional space

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Disorders of Orienting

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

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Disorders of Orienting

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

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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 dont matter

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

• Interpretation
• Patients have difficulty disengaging attention
  from good hemifield so that it can be shifted to
  contralesional hemifield

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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

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Disorders of Orienting

• Disengage - Shift - Engage Model
• Parietal Cortex notices events and disengages
  attention

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Disorders of Orienting

• Disengage - Shift - Engage Model
• Parietal Cortex notices events and disengages
  attention
• Superior Colliculus moves attention

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Disorders of Orienting

• Disengage - Shift - Engage Model
• Parietal Cortex notices events and disengages
  attention
• Superior Colliculus moves attention
• Pulvinar Nucleus reengages attention

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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

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Disorders of Orienting

• Orienting mechanism can be interfered with in
  normal brains

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Disorders of Orienting

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

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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

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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

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Neural Correlates of Selection

• Since attention has a profound effect on
  perception, one would expect it to have some
  measurable effect on the brain

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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

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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)
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Neural Correlates of Selection

• Single Unit Recordings Delayed Match-to-Sample
  task

MONKEY FIXATES CENTRE CROSS
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Neural Correlates of Selection

• Single Unit Recordings Delayed Match-to-Sample
  task

CUE APPEARS AT FIXATION
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Neural Correlates of Selection

• Single Unit Recordings Delayed Match-to-Sample
  task

DELAY SEVERAL SECONDS
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Neural Correlates of Selection

• Remember that different neurons have a
  preference for different features
• Some stimuli excite a given neuron and others do
  not

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Neural Correlates of Selection

• Single Unit Recordings Delayed Match-to-Sample
  task

DELAY SEVERAL SECONDS
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Neural Correlates of Selection

• Single Unit Recordings Delayed Match-to-Sample
  task

MONKEY MAKES EYE MOVEMENT TO TARGET
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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?

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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
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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

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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

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Neural Correlates of Selection

• Is this a neural correlate of consciousness?

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Next time

• memory