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Wavelength/frequency Intensity Location/position of source Reflects off some materials Refracted (bent) moving through other materials
Eyes categorize wavelength into relative intensities within wavelength bands RGB ~ Red, Green, Blue Long, medium, short wavelengths Color is a neural/psychological construct
Cornea - refraction (2/3 of total) Pupil - light intensity; diameter regulated by Iris. Lens - refraction (remaining 1/3; focus)
Retina - light detection ~ skin or organ of Corti Pigment epithelium - regenerate photopigment Muscles - move eye, reshape lens, change pupil diameter
Image inverted (up/down) Image reversed (left/right) Point-to-point map (retinotopic) Binocular and monocular zones
Central 1-2 deg of visual field Aligned with visual axis Retinal ganglion cells pushed aside Highest acuity vision == best for details
Outer segment Membrane disks Photopigments Sense light, trigger chemical cascade Inner segment Synaptic terminal Light hyperpolarizes photoreceptor! The dark current
From photoreceptors… To Bipolar cells <-> and Horizontal cells To Retinal ganglion cells <-> and Amacrine cells
Center region Excites (or inhibits) Surround region Does the opposite Bipolar cells & Retinal Ganglion cells -> Most activated by "donuts" of light/dark Local contrast (light/dark differences)
Black vs. white (achromatic) Long (red) vs. Medium (green) wavelength cones (Long + Medium) vs. Short cones Can't really see reddish-green or bluish-yellow "Oppose" one another at cellular/circuit level
Retinal ganglion cells 2nd/II cranial (optic) nerve Optic chiasm (\(\chi\) - asm): Partial crossing of fibers Nasal hemiretina (lateral/peripheral visual field) cross Left visual field (from L & R retinae) -> right hemisphere & vice versa Lateral Geniculate Nucleus (LGN) of thalamus (receives 90% of retinal projections)
Hypothalamus Suprachiasmatic nucleus (superior to the optic chiasm): Synchronizes day/night cycle with circadian rhythms Superior colliculus & brainstem