Visual attention

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Visual attention

• Functional principles and neuronal mechanisms of

Niko Kriegeskorte, Neurocognitie, FdP,
Universiteit Maastricht
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Content-general versus content-specific attention

• Content-general arousal and alertness
• (for an overview see Koelega 1996)

• Content-specific uneven allocation of limited
  processing resources to a number of concurrent
• tasks
• stimuli
• (see Pashler 1997, Palmer 1999)

Common principle prioritization
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Basic concepts ofcontent-specific attention

• overt covert(e.g. eye movements)
  (internal)
• top-down bottom-up
• single focus multiple foci
• space- feature- object-based
• visual auditory tactile, etc.
• sensory motor

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Covert attentionhas measurable effects!

• Behavioral effects
• shorter RT
• finer perceptual discrimination(e.g. of spatial
  structure, contrast and color)
• Neuronal effects in specialized visual areas
• Specialized visual areas show increased activity
  when their type of content is attended.
• additive effect (baseline shift) upon attention
  onset
• multiplicative effect (gain modulation) upon
  stimulus onset
• The effects are stronger in areas higher in the
  visual hierarchy.

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The cooperation ofcovert and overt visual
attention

• Covert visuospatial attention and high-level eye
  movement control are coupled to the degree of
  being indistinguishable (by current methods) at
  the neural level.
• When focussed covert attention is maintained at a
  peripheral location for seconds, it feels
  unnatural not to make a saccade to that
  location.
• Conversely, it has been shown that a saccade to a
  location is necessarily preceded by a short
  moment of extremely focussed attention to the
  target location. (Deubel Schneider 96)

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Hierarchical controlof active visual exploration

• Body movements(minutes)
• Head movements(seconds)
• Eye movements(hundreds of milliseconds)
• Covert attention shifts(tens of milliseconds)

costs of operation energy time
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Some experimental paradigms of visual attention

• Space-based visual attention
• (Posner 1980)
• Feature-based visual attention
• (also called filtering, e.g. Kahneman
  Treisman 1984)
• Visual search
• (e.g. Wolfe 1998)
• Object-based visual attention
• (e.g. OCraven et al. 1999)

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Visual attentional space
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Mechanisms of covert spatial attentiontarget
enhancement and distractor suppression
target distractors
cf. Treisman (1960) and LaBerge Samuels (1974)
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Metaphorsfor covert spatial attention
spotlight
zoom lens
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Object-based attention

• In object-based attention, either all or none of
  the features of an object are attended.
• If two objects overlap in the visual field,
  spatial attention cannot separate them.
• Their features must somehow be disentangled.

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Brain areas involved in visual attention

• Frontal, parietal and thalamic areas are involved
  in the control of many forms of visual
  attention.
• Specialized visual areas implement the effect of
  attention. They show increased activity when
  their type of content is attended.
• V1 V2 form
• V4 color
• V5 motion
• FFA (fusiform face area) faces
• PPA (parahippocampal place area) houses, rooms

strength of the effect of attention
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How attention affects the time course of activity
in a specialized visual area
activity S caddA cmultSA
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The functional neuroanatomy ofcovert spatial
attention
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The temporal aspect of attention

• Three phases of attentional modulation can be
  distinguished.
• prestimulus preparatory activation (relation to
  imagery, not to be shown with ERPs.)
• immediate poststimulus modulation (Neurons
  respond more sensitively to the first feedforward
  signal from the stimulus reaching them. Shown for
  IT in the monkey, see above.)
• delayed poststimulus modulation (e.g. in V1,
  possibly due to adaptive resonance that takes
  time to establish itself)
• The latency of attentional gain modulation after
  stimulus onset diminishes as one moves up the
  visual hierarchy.
• V1 is modulated by attention, but the modulation
  begins only about 200ms after stimulus onset.
• In early extrastriate visual areas, attentional
  modulation begins earlier about 70-100ms after
  stimulus onset. (Martinez et al. 99, Hopfinger et
  al. 00)
• Monkey physiology (Desimone et al.) has shown
  attentional modulation in IT immediately after
  stimulus onset.
• Long-term effect learning
• Attention plays a central role in the formation
  of explicit and implicit memories.
• Attention is required for the reorganization of
  cortical maps through experience (Merzenich et
  al.).

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The relation betweenattention and imagery

• Attention and imagery are both processes that
  involve sensory content and can operate
  independently of sensory perception.
• Whereas imagery creates internal representations
  of objects that are not present, attention merely
  modulates sensory perception processes.
• Just like attention, imagery leads to increased
  activity (baseline shift) in visual areas
  specialized for the type of visual content in
  question.
• Attention and imagery might reflect a single
  fundamental psychological mechanism.

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Effects of imagery in areas specializedfor
high-level object recognition
single-subject, non-averaged fMRI signal
(OCraven Kanwisher, in press)
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Introductory literature

• Kanwisher, N. Wojciulik, E. (2000). Visual
  attention insights from brain imaging. Nature
  Reviews 1, 91-100.
• Driver, J. Frith, C. (2000). Shifting baselines
  in attention research. Nature Reviews 1, 91-100.
  147-148.
• Section on Attention in Gazzaniga, M.S. (2000).
  The New Cognitive Neurosciences. MIT Press.

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Crude functional anatomy of attention

• Reticular formation (in the brain stem) and basal
  forebrain unspecific activation (sleep, waking,
  alertness).
• Frontal lobe high-level control of spatial and
  object-based visual attention.
• Parietal lobe mediation of spatial attention via
  spatial index map.
• Ventral path mediation of object-based attention
  via complex object codes.
• Thalamic nuclei (e.g. pulvinar) cortically
  controlled highly specific (down to features and
  retinotopic locations) modulation of other
  cortical areas via thalamocortical positive
  feedback loops.
• Functionally specialized perceptual areas
  biasing of the representation of perceptual
  content according to thalamocortical modulation.

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Theoretical considerationson attention

• When one attempts to define the concepts
  attention, imagery, feedback and internal state
  clearly, they all seem to come to the same
  thing.
• Space may be special as a feature dimension of
  attentional selection in that a spatial
  restriction can operate in conjunction with any
  other visual feature restriction, whereas two
  nonspatial feature restrictions cannot operate in
  conjunction.

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Target enhancement versus distractor suppression

• target-enhancement(related metaphors spotlight,
  zoomlens)
• distractor-suppression(related metaphors gate,
  filter)
• a combination of both
• (adapted from LaBerge 2000)

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Functions of sensory attention

• Sequential analysis each part of the currently
  perceived scene is selected in turn for a
  particular kind of in-depth processing (e.g.
  object recognition).
• Continuous prioritized perception a certain
  aspect of the perceptual stream (e.g. a piece of
  music in a café) continuously receives a greater
  share of the cognitive resources than other
  aspects.
• Preparation of perception the system gets set to
  perceive a certain type of event. The preparation
  improves perceptual performance (e.g. RT,
  perceptual thresholds or perceptual precision).
• (following LaBerge 2000)