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Vision.docx

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Department
Philosophy
Course
PHILOS 2D03
Professor
Joe Kim
Semester
Fall

Description
Vision Light  Amplitude: height of each wave, perception of brightness  Wavelength: distance between successive peaks, perception of colour  Purity: perception of saturation o Single wavelength light = pure light which is completely saturated o Desaturated light is combination of many wavelengths The Visible Spectrum  Bees see UV spectrum to perceive differences of colour  Snakes see light in infrared spectrum to detect body heat Light Passing Through the Eye 1. Cornea: begins focusing process!!! 2. Pupil 3. Iris: controls the size of the pupil; constricts muscles when too much light is reaches retina, dilate pupil when not enough light reaches retina 4. Lens: final focusing based on distance of objects  Curvature causes images to land on retina upside-down and reversed, but final image is product of brain activity  Accommodation: o Close object = lens gets rounded to produce clear image o Far object = lens elongates to focus the image on back of the eye 5. Vitreous humor: clear, jelly-like substance that comprises main chamber inside eyeball 6. Retina: translates light into neural signals Retina  Covers back of the eye  Neural cells arranged in three different layers  Photoreceptors in layer 1: translate light stimulus into neural signal o Retinal pigment epithelium provides nourishment for photoreceptors at back of eye o Photoreceptors would die without RPE Layer 1: Photoreceptors  Cones: o 6 million o day vision o colour o good visual acuity o concentrated in fovea: tiny spot in middle of retina that only contains cones; seeing something in detail, we focus our eyes so image falls on the centre of fovea  Rods: o 125 million o night vision o no colour o poor visual acuity o concentrated in periphery (around the fovea); seeing something that is dimly lit, we look at the side of the object because if we stare right at it, it falls on our fovea and cones will not produce a clear image. Layer 2 & 3  Neural signal passes through bipolar cells to ganglion cells  Axons of ganglion cells converge at the optic disc, then leave the eye to join the optic nerve which travels to the brain  Optic disc contains no photoreceptors (blind spot) Processing in the Retina  Some visual processing in the retina  Amacrine cells and horizontal cells allow information from adjacent photoreceptors to combine their information; the info from over 130 million rods and cones converge to travel along only 1 million axons in optic nerve Visual Acuity Receptive fields  Collection of rods and cones in the retina that affects the firing of a ganglion cell when stimulated Visual Pathways  Right and left halves of visual field processed by contralateral hemisphere of brain  Optic chiasm: the point where optic nerves from the inside half of each eye cross over to opposite hemisphere  After optic chiasm, info from each visual field arrives in opposite hemisphere, and the optic nerve fibres split and travel along two pathways oMost ganglion cell axons travel along main pathway and synapse in
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