Download Visual form processing in primary and secondary visual

Visual Cognition laboratory
University of Fribourg
Visual form processing in primary and
secondary visual cortex of the tree shrew
Paolo De Luna, Jordan Poirot, Gregor Rainer
Dept. of Medicine, University of Fribourg
DAY OF COGNITION 2015 @ UNIFR – 07/10/2015
INTRODUCTION
VISUAL FORM PROCESSING
R(θ)
Polar
Hyperbolic
thal
Cartesian
θ
V2 V1
retina
 Orientation tuning
 Spatial frequency preference
 Spatial phase modulation
• Visual information is processed in a hierarchical fashion.
How is information represented and transformed?
• Investigation by means of Cartesian (parallel) gratings.
Naturalistic scenes are rich and complex.
V2
• Tree shrew as animal model for visual neuroscience.
Anatomical homology, and similar neurophysiology
of the visual system.
V1
RESULTS 1/5
EXEMPLAR NEURAL RESPONSE
Cartesian
Hyperbolic
Polar
Rmax = 64 spikes/s
Cartesian
Hyperbolic
Polar
Cartesian
Hyperbolic
Polar
Structure selectivity
index
0.73
0.55
0.56
Polarity sensitivity
index
0.23
0.30
0.02
1)
Selective responses to a broad range of
stimulus structures.
2)
Selectivity to complex patterns is not
predictable on the basis of responses to
Cartesian gratings.
RESULTS 2/5
GRATING PREFERENCE IN V1 AND V2
Pol
V1
.1
Car
.25
Pol
V2
.50
Hyp
Car
Hyp
Preference for Cartesian gratings, but also specialization for non-Cartesian stimuli in both V1 and V2.
RESULTS 3/5
GRATING SELECTIVITY: SPATIAL FREQUENCY
V1
Hyperbolic
Polar
Cartesian
100
100
75
75
% of neurons
% of neurons
Cartesian
V2
50
25
Hyperbolic
Polar
50
25
0
0
low mid high
low
mid
high
low mid high
low mid high
low
mid
high
low mid high
•
Borders extraction from visual scene
•
Enhancement of figure-ground segregation
RESULTS 4/5
GRATING SELECTIVITY: FUNCTIONAL DOMAINS OF THE CORTEX
Structure selectivity index
V1
V2
0.70
spiking
VEP
*
*
V1
0.60
0.50
0.40
V2
Cartesian
Hyperbolic
Polar
1)
V1 neurons are organized in local domains which compute complex patterns of polar gratings.
2)
V2 neurons receive converging tuned inputs onto individual neurons.
VEP: Visually evoked potentials.
Stimulus
feature
(SF) α
SF 
SF 
SF 
SF ε
RESULTS 5/5
STIMULUS POLARITY AFFECTS NEURAL SELECTIVITY
Hyperbolic
Cartesian
Polarity sensitivity index
0.30
V1
V2
Polar

•
In V2:
neurons retain similar levels of
polarity sensitivity to V1;
0.20
• no difference between grating classes.

In V1, polarity sensitivity for
hyperbolic gratings is higher than
0.10
C
H
P
C
H
P
for the other classes.
CONCLUSIONS
Non-conventional stimuli provide useful insights into the functional organization of the
early visual cortices (structure of polar gratings, and polarity of hyperbolic stimuli).
V1 and V2 neurons are selective for a wide range of visual patterns.
Neurons in tree shrew’s V2 exhibit emergent selectivity for polar-like stimuli.
REFERENCES
‐
‐
‐
‐
Bosking et al – J Neurosci (2000)
Cloherty & Ibbotson – J Neurophys (2014)
Gallant et al – Science (1993)
Gallant et al – J Neurophys (1996)
‐
‐
‐
‐
Hegdé & van Essen – J Neurosci (2000)
Hegdé & van Essen – Cereb Cortex (2007)
Mahon & deValois – Vis Neurosci (2001)
von der Heydt et al – Perception (1995)
ACKNOWLEDGEMENTS
‐ Visual Cognition laboratory (University of Fribourg)
‐ Animal caretakers and veterinarians at the Dept. of Medicine of the University of Fribourg