What the Frog Eye Tells The Frog’s Brain We will talk about…. Kinds of visual information which may be useful for frog to survive Four operations on the image in frog’s 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

Frog’s 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

Frog’s 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

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

Large Receptive Fields 4 “Basic” operations small receptive fields Sustained contrast detectors Net convexity detectors Moving edge detectors Net dimming detectors Large Receptive Fields

Sustained contrast detectors Light intensity in receptive field Ignores general illumination level Responds similarly to large and small objects

Net convexity detectors “Bugs detectors” Ignores general illumination level Responds only to objects which lie interior to receptive field

Moving Edge detectors Nearly ignores general illumination level Responds to darklight AND to lightdark transitions Frequency of discharge increases with velocity

Net dimming detectors Ignores general illumination level Large receptive field Response depends only on decrease of light in receptive field

Conclusion Frog’s 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

Retina Higher brain levels Frog VS Human Low level implementation = more effective, fast, BUT non-adaptive, inflexible