How Does Split Brain See The World

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How Does Split Brain See The World?

• Arash Afraz

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Corpus Callosum
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• Roger Sperry (1958)
• Animal Studies.
• Human Studies.

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Splenium resection Splitting visual world
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Sagittal T2W/TSE MRI section of MDs brain. The
splenium andmost of the corpus callosum is
resected .
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Match-to-Sample ExperimentBilateral Condition
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Visual Crowding in Split Brain!Non-Crowded
Condition
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Crowded Condition
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Results of Crowding Exp.
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• Some Inter-hemispheric spatial interactions can
  take place even without Splenium

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Distracter-Target-Distance (DTD)
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Results of Crowding Exp.
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Cortex lt gt Sub-cortex ?

• Texture-Defined shapes!

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Results of Texture-defined Crowding Exp.
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What remained unanswered
Crowding is a distracter effect! Is there any
gateway remained in the absence of splenium- for
transferring of spatial information? Looking
for a positive spatial effect!
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Visual Object Tracking!
Behrad Noudoost, S.R Afraz, M Vaziri P, H Esteky
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The task Fixate at the bulls eyeand track the
marked item covertly
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2 seconds
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8 more seconds with identical items
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Tracking one among three itemsSlightly better
performance for uncrossed trials
0.027
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Tracking one among three items But the crossed
trials was performed far above chance level!
0.000
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Tracking one among three items Even with a new
definition of chance level Destination Visual
Field Chance Level
0.000
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Control Experiment

• A strip of about 2 degrees in the vertical
  meridian of the retina is shared between two
  visual cortices.

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Tracking one among three itemsin the presence of
occluders
Comparison of Crossed Trials between occluded and
non-occluded condition The performance was
slightly lower for occluded condition however it
was not significant (0.108). But the same minor
decrease in performance was observed for the
within hemifield up-down crosses.
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So, Transfer of Spatial Information is possible
in the absence of splenium of corpus callosum,
While transfer of shape information is lacking
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Next Question

• Possible contribution of a temporally coded
  signal from one hemisphere to the other one at
  the crossing time

More quantitative spatial and temporal
investigation
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Tracking one among five itemsin two conditions
Single and double controlled.
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Double controlled condition The target and
co-target are painted with different colors.
Please note that all balls are identical in the
main experimental display. The shifter bar is
also schematic.
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P 0.555
P 0.005
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Is the difference between single double
controlled crossed trials really imply that
there is a temporal signal?

• The objects are spaced relatively denser in the
  double controlled condition!

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Analysis of spatial and temporal interactions at
the time of crossing
Logistic Regression of Distance among two
objects Temporal cross offset
p0.006 p0.498
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Summary
Performance in five objects condition was a
little bit lower than conditions with three
objects But when another object escorts the
target this co-transfer in the midline leads to a
lower performance due to some spatial
interactions rather than temporal arrival
ambiguity
This experiment gives us some clue about
selective decrease of spatial resolution in the
vertical midline. But we need some more direct
information
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Match to position experiment

• Task
• Stimulus
• Three conditions
• Staircase method
• 6 steps of resolution

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Match to position experiment
Ln(Correct/1-Correct) 0.546 Hemifield 0.32
Spatial Offset 0.052
0.043
0.001