Visual attention

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Visual attention

• Michael Silver
• VS212B
• November 29, 2006

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What is attention?

• How is the word used?
• Examples
• something bright caught my attention
• I didnt see you, I was paying attention to the
  game
• I struggled to pay attention to the lecture
• I dont remember even cleaning the table, I must
  not have been paying attention
• Attention refers to many different kinds of
  mechanisms

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Attention and limits on information

• We need attention to limit the amount of
  information that is processed
• Why are there limits on the amount of information
  we can process?

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Attention and limits on information

• Human information processing is massively
  parallel, up to a point ? serial bottleneck
• limited sensory systems
• limited effector systems
• movements must be planned sequentially
• words can only be spoken sequentially
• It is the allocation of our attention that
  determines what is analyzed.
• Often, we are unable to process information that
  is unattended ? inattentional blindness

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Change blindness
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Covert attention
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Inhibition of return

• If we have attended a particular region of space,
  it is less likely we return to that region ? bias
  favoring novelty.

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Posner Cueing Task
Central cue
peripheral cue
cue
ISI
target
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Central cue
peripheral cue
cue
ISI
target
exogenous involuntary fast effortless disruptive
endogenous voluntary slow effortful interruptible
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Attention signals in visual cortex
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Spatial attention signals in early visual cortex
are retinotopically specific
Target annulus region 1.5 4.5 deg diameter
Peripheral region 15 30 deg diameter
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Split attention spotlight
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Filtering of distractors
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Filtering of distractors
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Neural correlates of attention in parietal cortex
Trained to fixate. Small response from parietal
lobe neuron when light comes on in periphery.
Trained to fixate until peripheral light comes
on, then must move eyes to look at the light.
Identical retinal stimulation. Much bigger
response (3x). Trained to move arm instead of
eyes. Same result (bigger response), i.e., not an
eye movement control signal. Rather more like the
neural correlate of attention.
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IPS1 and IPS2 contain maps of the contralateral
visual field, but these maps encode visual
attention, not sensory stimuli
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Gradient of responses to passive visual
stimulation
sensory
attention
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Control of visual attention
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Microstimulation of FEF (Tirin Moore)
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Microstimulation of FEF (Tirin Moore)
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Central cue
peripheral cue
cue
ISI
target
endogenous voluntary slow effortful interruptible
exogenous involuntary fast effortless disruptive
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Ventral attention system circuit breaker
TPJ temporo-parietal junction MFg medial
frontal gyrus IFg inferior frontal gyrus
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Visual Search
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Examples of Visual Search
Is there a threat?
Wheres Waldo?
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Is there a red circle?
MORE DIFFICULT
EASY
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Search times can be influenced by set size
is there a black circle?
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Feature-integration theory (Treisman Gelade,
1980)

• Different visual features are coded in parallel
  in separate feature maps.
• Visual search is easy (pop out) when it
  involves only a single feature that can be
  computed by a feature map no attention is
  required

orientation
size
color
E.g., find the blue circle
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Conjunction search

• Visual search becomes more difficult when
  conjunctions of features are involved
• e.g., is there is red circle?
• Theory states that attention is needed at a
  particular location to synthesize its features
  into an object
• Attentional spotlight can only be deployed
  locally ? viewer must apply serial search

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Serial Search

• Assumes that items are examined one at a time.
• Search terminates when the target is found or all
  items have been examined.
• If the target is present, on average, how many
  items need to be examined?
• roughly half
• (n1)/2
• where n size of the search set
• If absent, all items will be examined.

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RT curves for parallel / serial search
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Disorders of Visual Attention

• Neglect
• Failure to acknowledge objects in the field
  contralateral to the lesion
• Often no perceptual deficit
• Extinction
• Neglect patients sometimes detect a single
  stimulus presented to their left visual field,
  but fail to detect the same stimulus when another
  stimulus is presented to the right of it

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Neglect
Model
Patients copy
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Alberts Line Crossing Task
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Visual neglect syndrome can be object-based
Patients can neglect the left side of the object,
rather than the left side of space. This is
because the neglect is object-centered rather
than person-centered. Black lines show expected
left-sided person-centered versus red lines
showing actual point where the patient neglected.

Marshall and Halligan, 1993
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Visual neglect syndrome can be object-based
When a right neglect patient is shown a dumbbell
that rotates, the patient continues to neglect
the object that had been on the right, even
though it is now on the left (Behrmann Tipper,
1999).
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Il Duomo
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Bisiach Luzatti, 1978 Cortex
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Vallar Parani, 1986, Neuropsychologia
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Unilateral Spatial Neglect
Uncued contra
Uncued ipsi
Cued contra
Cued ipsi
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Summary (part 1)

• Two types of attention exogenous (stimulus
  driven) and endogenous (goal directed)
• Attention enhances visual perception
• Endogenous attention increases visual cortical
  activity, both in the presence and absence of
  visual stimulation
• Endogenous attention control areas in parietal
  cortex and FEF
• Exogenous shifts of attention activate TPJ, MFG,
  and IFG

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Summary (part 2)

• Visual search can be parallel (popout stimuli) or
  serial (conjunction search)
• Spatial neglect is a disorder of visual attention
• Neglect can be observed in object-based
  coordinate systems and even for visual imagery
• Neglect is associated with damage to the TPJ and
  with impairments in disengaging spatial attention

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What havent we talked about?

• Intermodal attention
• ADD, Alzheimers
• Neurochemistry of attention
• Attentional tracking
• Applied attention research