What the Frog’s Eye Tells Its
Brain
Or, How a Frogs Brain Constructs Its
Visual World.
Receptive Fields
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Receptive fields
On Center – Off Surround
Off Center – On Surround
Diagramming neural circuits
Retinal circuitry
Operation of an edge detector
Edge Detectors
• Lateral inhibition and edge enhancement
– Demonstrations:
http://dragon.uml.edu/psych/illusion.html
• Lateral inhibition simulator
– http://serendip.brynmawr.edu/bb/latinhib_app.html
Types of Detectors
• Boundary Detectors
– Ex: one group responds to horizontal border that is
darker below and lighter above (surface of pond
detector?)
• Concave Boundary Detector
– Activated by concave line moving in the direction of
concavity (big mouth bass detector?)
• Changing Contrast Detector
– Responds most to high contrast edge moving fast
• Dimming Detector
– Responds to slowly changing brightness
Types of Detectors
• Bug detector
– Small, dark, moving spot detector
– Frogs eat live flies but will starve to death on a
pile of dead ones
• Frog’s visual system may actually be so
primitive that stationary objects actually
disappear. (Of course humans can’t see a
deer in the woods until it moves, either)
More Complex Detectors
• Newness Neurons
– Adapt immediately to movement in a particular
direction but still respond to movement through their
fields in a new direction
• Sameness Neurons
– Larger fields– do not respond immediately to an object
brought into the field, but once they “notice” it they
respond to it as long as it stays in the field, with stron g
bursts taking place every time it starts to move or
change direction (looses it if stationary for ~ 2 min)
More Complex Detectors
• Straight Line Detectors
• Movement Detectors
• Direction Detectors
Cortical Cells
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Simple Cortical Cells
Complex Cortical Cells
Binocular Disparity detector
“Novelty” detector
Columnar organization