Neural Basis of the Oblique Effect

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Neural Basis of the Oblique Effect

• Baowang Li, Matthew R. Peterson, Ralph D. Freeman

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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.

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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

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Alternatives continued

• Width/shape of tuning curve (measurement slope
  of tuning curves)
• Type of cell
• Effect exists outside of V1 (retina, LGN, V2)
• Some combination of the above

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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

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Results
Fig 2
Fig 4
Fig 3
Fig 5B
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Results continued
Fig 6
Fig 10
Fig 7A
Fig 7A
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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.

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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.

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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.

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