Transcript Neural Basis of the Oblique Effect

Neural Basis of the Oblique
Effect
Baowang Li, Matthew R. Peterson,
Ralph D. Freeman
What questions does the group ask
and why does anyone care?
• What is the neural
basis of the oblique
effect?
• To make inferences
about the architecture
of the visual system in
the brain.
• Reconciliation of
physiological data
with a behavioral
phenomenon.
Alternative answers to problem
1. Number neurons tuned to horizontal and
vertical vs. oblique orientations
2. Difference in tuning widths of neurons in
V1
3. Difference in response (firing rate) to
stimuli
4. Latency of response
Alternatives continued
5. Width/shape of tuning curve
(measurement: slope of tuning curves)
6. Type of cell
7. Effect exists outside of V1 (retina, LGN,
V2)
8. Some combination of the above
Methods
• Shone an oriented light stimulus in the eye
of anesthetized and paralyzed cats
• Used microelectrodes to make recordings
of single neurons in V1.
• Classified cell as simple or complex.
• Recorded: orientation preference, tuning
curve, spatial frequency, firing rate of cells
• Combined data from over 4,000 cells
Results
Fig 2
Fig 3
Fig 4
Fig 5B
Results continued
Fig 10
Fig 7A
Fig 7A
Fig 6
Conclusions
• Combination of alternatives were confirmed:
– The effect exists only for a subpopulation of cells:
simple cells in V1 with high spatial frequency.
– There are more cells tuned for cardinal orientations
and these cells exhibit a narrower tuning width at
horizontal angles.
– The slopes of the tuning curves are also steeper for
horizontal orientations.
• Response properties of individual neurons do
not change: rate and latency.
More Conclusions
• The effect is based on the population of
neurons in V1, not on changes in
individual neurons.
• Simple cells must directly project to higher
areas in addition to/instead of only to
complex cells.
Problems?
• Varying N value could be misleading
• Did not look at any cells outside of V1
• Cats were anesthetized. It has been
shown that anesthesia itself changes
neuronal response properties.
• Anesthesia also makes simultaneous
psychophysics in animals impossible.
 Direction of causality unclear.