[Verse 1] Light comes knocking at your eye's front door But the story's twisted, there's so much more Passes through the layers, crystal clear Till it hits the back wall, photoreceptors here Counterintuitive design, nature's strange plan Signal flows backward then forward again [Chorus] Back to front, that's where light must go Through transparent layers, nice and slow Front to back, signals make their way Retina's wired in a backwards display Back to front, front to back Neural signals on a zigzag track [Verse 2] Rods and cones are waiting at the rear One hundred twenty million rods appear Six million cones in three different types Short and medium, long wavelength stripes Blue and green and red receptors shine Packed together in the foveal line [Chorus] Back to front, that's where light must go Through transparent layers, nice and slow Front to back, signals make their way Retina's wired in a backwards display Back to front, front to back Neural signals on a zigzag track [Verse 3] Rods work best when darkness fills the scene Saturate in daylight, can't be seen Periphery patrol, but fovea's bare Scotopic vision everywhere Cones need brightness, color is their game Photopic processing stakes their claim [Bridge] Photon hits retinal, twists the key G-protein cascade, transducin spree Phosphodiesterase breaks cGMP down Sodium channels close without a sound Hyperpolarize when light arrives Glutamate drops, that's how vision thrives [Verse 4] Horizontal cells spread signals wide Lateral inhibition, side to side Center-surround fields, contrast they make Ambient adaptation for vision's sake Bipolar cells split the signal stream ON and OFF channels, the retinal scheme [Verse 5] Ganglion cells process the final code Magno, parvo, konio on the road Large cells carry motion, fast and bright Small cells handle color, form, and sight Optic nerve bundles every visual tale Through the chiasm, cortical trail [Chorus] Back to front, that's where light must go Through transparent layers, nice and slow Front to back, signals make their way Retina's wired in a backwards display Back to front, front to back Neural signals on a zigzag track [Outro] From photoreceptors to ganglion's end Forward through the network signals wend Axons carry messages to the brain Back to front, then forward once again [Final Chorus] Back to front, that's where light must go Through transparent layers, nice and slow Front to back, signals make their way Retina's wired in a backwards display Back to front, front to back Neural signals on a zigzag track
← The framing to carry forward | The computation: center-surround and what it means →