Download What a Frog s Eye tells the Frog s brain

Psy/Orf 322
Human – Machine Interactions
Lecture 16
Spring 2004
What a Frog’s Eye Tells the Frog’s Brain*
*J.Y. Lettvin, Maturana, McCulloch, and Pitts, Proc. Of the IRE, Nov, 1959
Interesting Aspects:
Between the Rods & Cones (~1million) and the Ganglion Cells (~ 0.5 million; whose axons form the optic nerve) there is:
 A layer of connecting Neurons (bipolar, horizontal & Amacrines) (~3million)
o Each Rod/Cone connects to many Ganglia & each Ganglia connects to many Rod/Cone
 Does not make for good resolution of an image map of light intensity!
 Must do other things!
 The output from a Frog’s Eye is a set of 4 spatially distributed operations on the visual
image.
 These operations are independent of the general level of illumination
1. Local sharp edges and contrast
2. the curvature of edge of a dark contrast
3. the movement of edges
4. the local dimming produced by movement or rapid general darkening
 Each group of fibers serving one operation maps the retina continuously in a single sheet
of endings in the frog’s brain.
 There a re 4 such sheets in the brain corresponding to the 4 operations
 These maps are spatially registered
In effect what the above 4 operations do performs as a “bug detector”
 They respond best when a dark object, smaller than the receptive field, enters that field, stops, and
moves around intermittently thereafter. The response is NOT affected if the lighting changes or if
the background is moving (grass moving). There is no response if only the background, moving or
still, is in the field.
 They also respond when there is large changes in illumination over large parts of the receptive field
08/02/17 Psy/Orf 322 Human –Machine Interactions
Spring 2004