Neural mechanisms of feature- based attention Taosheng Liu.
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Transcript of Neural mechanisms of feature- based attention Taosheng Liu.
What is attention?
“Everyone knows what attention is. It is the taking possession by the mind in clear and vivid form, of one out of what seem several simultaneously possible objects or trains of thought.”
-William James (1890)
• Types of visual attention– Overt attention– Covert attention
• Spatial
• Feature-based
• Object-based
Outline
• The effect of feature-based attention on visual cortex– How does attention modulate sensory
representations?
• The control of feature-based attention– What is the source of control and how is control
implemented?
• Attention and object recognition
The effect of FB attention to motion
Treue & Martinez-Trujillo, 1999, Nature
Respons
e
Atte
nd ‘u
p’At
tend
‘dow
n’
Questions:• Does feature-based
attention modulate neuronal subpopulations in the attended location?
• If so, how does it correlate with behavior?
MT
Respons
eAt
tend
‘up’
Atte
nd ‘d
own’
upward preferring units
More adaptation for a upward test stimulus when attending ‘up’ vs. ‘down’
Respons
edownward preferring units
Use adaptation to assess feature selectivity
fMRI adaptation
• A voxel contains many neurons.
• fMRI adaptation can assess feature selectivity within a voxel.
Behavior: tilt aftereffect (n=8)
+20°-20°
0°
. . . . .
Adapter (4 s) Test (0.5 s)1 s…
Pre-adaptation (40 s)
Attend +20 Attend -20 Attend +20 Attend -20
fMRI adaptation protocol
. .. ..
Adapter (4 s) Test (1 s)
1 s 1.2 s
Attended
Unattended
Blank
…Pre-adaptation (40 s)
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Task inside the scanner: report the orientation of the test stimulus.
fMRI details
• Siemens 3T Allegra • Surface coil• 21 coronal/oblique slices • 3 mm isotropic voxels• TE = 30 ms, FA = 75º• TR = 1.2 s• Bite bar to minimize head
motion
Surface reconstruction and retinotopic mapping
QuickTime and aᆰMicrosoft Video 1 decompressorare needed to see this picture.
Retinotopic mapping and localizer
QuickTime and aᆰYUV420 codec decompressor
are needed to see this picture.
real data (TL)
fMRI response to the test stimulus
Unattended
Attended
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Time (s)
fMR
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adapter test
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Attended
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Time (s)
fMR
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onse (%
)
A model relating psychophysical and imaging data
neutralattended
-90 -45 0 45 900
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Neu
ral resp
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Preferred orientation (deg)
-90 -45 0 45 900
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Preferred orientation (deg)
-90 -45 0 45 90-10
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Sh
ift in p
refe
rred
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Preferred orientation (deg)
Dragoi et al, 2000, 2001
-90 -45 0 45 900
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Preferred orientation (deg)
Psychophysics
fMRI
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Summary & conclusion
• Feature-based attention enhances activity of neuronal subpopulations when the attended and unattended features are processed in the same retinotopic region.
– Attentional modulation of orientation-selective fMRI response adaptation.
– Attentional modulation constant across visual areas, suggesting a feed-forward mechanism.
– Significant correlation between TAE and AMI only in V1.
Liu etal, 2007, Neuron
The control of feature-based attention
• Components of attentional control– Disengage/shift– Engage/maintain
• Goal:– Separate different
components– Feature-based
attention
Sustained effect for motion
R SPL/IPL
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% sig
nal ch
ang
e
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Time (sec)
color to motion
MT+: effects of attention for motion.
FEF, SPL/IPL: sustained attentional control for motion.
Time (sec)-5 0 5 10 15
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0.20L ITG (MT+)
motion to color
hold motion
hold color
Transient shift activity
color to motion
motion to color
hold motion
hold color
Precu, IPS, PCG: transient control of attention shift.
Summary
• Effects of attention: – MT+ (motion) and V4 (color)
• Attentional control: – Transient control: disengage/shift (superior parietal lobule, left
intra-parietal sulcus, left pre-central gyrus).
– Sustained control: engage/maintain (frontal eye fields, superior-inferior parietal lobule for motion; superior frontal gyrus for color).
Liu etal, 2003, Cerebral Cortex
Current and future plans
• Attentional control within feature dimensions– What are the ‘shift’ regions?– What are the ‘hold’ regions?--attentional priority
The representation of attentional priority
• Spatial attention– Higher areas with a
spatiotopic map send feedback signals
• Feature-based attention– Are there neurons that
encode the attended direction in higher areas?
FEFLIP
Decoding of brain activity Kamitani & Tong (2007)
• Classifier scheme
• Classifier can reliably decode orientation information in early visual cortex
Learning sequence of views of three-dimensional objects:
The effect of temporal coherence on object memory
How do we recognize shapes?
Temporal association: object views appearing close in time are associated.Wallis & Bulthoff (1999)