What the Frog Eye Tells The Frogs Brain

1
What the Frog Eye Tells The Frogs Brain

• We will talk about.
• Kinds of visual information which may be useful
  for frog to survive
• Four operations on the image in frogs retina
• How we can obtain information about these
  operations (from the frog)
• What are advantages and disadvantages of such
  information processing

• J.Y.Lettvin
• H.R.Maturna
• W.S.McCulloch
• W.H.Pitts

2
Frogs life

• Responds only to moving objects
• Treats all small moving objects as food
• Treats all large moving objects as enemy
• On danger jumps to darker place

Simple non-adaptive requirements on visual
system
3
Frogs retina

• Ganglion cells
• Only one layer of ganglion cells
• Enormous amount of overlap in input
• Several types with distinct dendritic patterns

Very likely that there is some nontrivial
processing
4
Testing a Frog

• Most of described recordings
• Done from optic nerve fibers
• Used dull black disk as a moving object

5
4 Basic operations
small receptive fields

• Sustained contrast detectors
• Net convexity detectors
• Moving edge detectors
• Net dimming detectors

Large Receptive Fields
6
Sustained contrast detectors
Light intensity in receptive field

• Ignores general illumination level
• Responds similarly to large and small objects

7
Net convexity detectors
Bugs detectors

• Ignores general illumination level
• Responds only to objects which lie interior to
  receptive field

8
Moving Edge detectors

• Nearly ignores general illumination level
• Responds to dark?light AND to light?dark
  transitions
• Frequency of discharge increases with velocity

9
Net dimming detectors

• Ignores general illumination level
• Large receptive field
• Response depends only on decrease of light in
  receptive field

10
Conclusion

• Frogs retina not just transfers but PROCESSES
  information, it calculates complex and important
  image properties including
• Local sharp edges and contrast
• Curvature of edge of dark objects
• Movement of edges
• Rapid local changes in light intensity
• Each property decoded in distinct type of fibers
  of the optic nerve

11
Frog VS Human

• Retina

Higher brain levels
Low level implementation more effective, fast,
BUT non-adaptive, inflexible