What the Frog’s Eye Tells Its Brain

Or, How a Frogs Brain Constructs Its Visual World.

Receptive Fields

• 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

• Simple Cortical Cells

• Complex Cortical Cells

• Binocular Disparity detector

• “Novelty” detector

• Columnar organization