Eye Position Signals Modulate Early Dorsal and Ventral Visual Areas

Paper written by: Joseph F.X. DeSouza, Sean P. Dukelow and Tutis

Vilis

Presenter: Nachum Abraham Psychology 3890: Indep. Study

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)

Background:Anatomy :

Visual System

V4/V8

MT

MST

Figures 2A, 2B, and eye

http://www.livescience.com/health/051128_eye_works.html

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

How does our world stay stable? Motion

Transformations

Activation of Ventral collateral sulcus: V4v

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

Methods: Subject and training5 paid male and 2 female paid subjects

3 training sessions1 day prior to experimentDirectly before experiment During experiment

Methods: Optic Flow StimulusFixation

Optic Flow StimulusAlteration: FR, FLof, FL, FRof, FR, FLof, FL, FRof, FRLength: 16 seconds per epoch, 4-6 reps

Methods: Data Acquisition & Image analysis 4.0 T Varian UNITY INOVA (whole body

imaging)

BOLD imaging technique

Brain Voyager 4.3

Results: Mapping Optic FlowStationary fixation stimulus as control

Optic flow produces activation in MT and V4v/V8

Collateral sulcus activation had retinotopic representation

Results: Signals During Visual FixationComparing left and right fixations

MT after 9 seconds (avg)

V4v/V8 after 7 seconds

Key figures: 4B, 4D, 5A, 5B

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

Results: Figure 7Visual fixationOptic flow

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

Questions?And Thank You Joe!