paper written by: joseph f.x. desouza, sean p. dukelow and tutis vilis presenter: nachum abraham...
TRANSCRIPT
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Eye Position Signals Modulate Early Dorsal and Ventral Visual
AreasPaper written by: Joseph F.X.
DeSouza, Sean P. Dukelow and Tutis Vilis
Presenter: Nachum Abraham Psychology 3890: Indep. Study
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Objectives:1) To describe how MT/MST and V4 areas act as visual
motion processing sections of the human brain
2) Provide evidence to support that transformations of Retinotopic to egocentric coordinate frames are necessary for guiding action and recognition in humans
3) Depict how transformations are modulated by eye positions for humans (the difference in preferred direction of eye position signal reflects differences in transformation)
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Background:Anatomy :
Visual System
V4/V8
MT
MST
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Figures 2A, 2B, and eye
http://www.livescience.com/health/051128_eye_works.html
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Helmholtz corollary discharge for eye position used
to achieve consistency
Shifting Locus
Transforming reference frame
How does our world stay stable?
http://www.physics.gla.ac.uk/Physics3/Kelvin_online/Helmholtz.gif
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How does our world stay stable? Motion
Transformations
Activation of Ventral collateral sulcus: V4v
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HypothesisSimilar modulation by eye position is present
in the human equivalent model of the monkey
MT/MST and V4 areas
=http://williamcalvin.com/portraits/Chimp/Arnhem%20283sml.jpg http://www.oldunterrified.org/
sitebuildercontent/sitebuilderpictures/screaming.jpg
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Methods: Subject and training5 paid male and 2 female paid subjects
3 training sessions
1 day prior to experiment
Directly before experiment
During experiment
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Methods: Optic Flow StimulusFixation
Optic Flow Stimulus
Alteration: FR, FLof, FL, FRof, FR, FLof, FL, FRof, FR
Length: 16 seconds per epoch, 4-6 reps
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Methods: Data Acquisition & Image analysis 4.0 T Varian UNITY INOVA (whole body
imaging)
BOLD imaging technique
Brain Voyager 4.3
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Results: Mapping Optic FlowStationary fixation stimulus as control
Optic flow produces activation in MT and V4v/V8
Collateral sulcus activation had retinotopic representation
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Results: Signals During Visual FixationComparing left and right fixations
MT after 9 seconds (avg)
V4v/V8 after 7 seconds
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Key figures: 4B, 4D, 5A, 5B
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Results: Signals During Optic FlowComparing left and right flow stimuli
No significant eye position signal differenceOutliers
Variances
http://thailandy.files.wordpress.com/2006/11/eyes-3.jpg http://images.inmagine.com/168nwm/photoalto/paa073/paa073000001.jpg
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Results: Figure 7Visual fixationOptic flow
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DiscussionAbsence of moving stimulus and MT
Eye position signal may be to transform coding
retinal slip velocity into velocity regarding the head
Disappearing fixation modulation
Apposing V4v/V8 and MT data and coordinate
transformations
Ventral and Dorsal streams
http://www.biomedcentral.com/graphics/journal/imageofthemonth/1005/200711large.jpg
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Questions?And Thank You Joe!