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Vision the Eye and the Visual Receptors

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Vision the Eye and the Visual Receptors 10/13/2015 (Book Fig. 6.7) (Billionths of a meter) Vision The Eye and the Visual Receptors Stimulus which activates visual receptors: light waves in the visible spectrum Light waves are a small range of wavelengths (~350-750 nanometers) of electromagnetic energy. (book Fig. 6.4) Transparent Cornea • Curve of cornea helps to focus light waves on retina • “Astigmatism” causes 2 focal points instead of 1 Of Macula Green Muscular Iris & Black Pupil Hole • Muscles of iris under ANS control- • Symp: dilate pupil • Parasymp: constrict Light travels Of Macula in straight lines Lens becomes less flexible later in life – need reading glasses 1 10/13/2015 Looking Into Left Eye: Optic Disk or “Blind Spot”- Center (Macula) of Retina Needed for Detail Vision axons exit eye to form optic nerve (Fovea especially) You can locate your own blind spot with the demo on p. 156. Book Fig. 6.5 Macular Degeneration Loss of the critical central region of retina Smoking is #1 preventable cause What you might see Rods vs Cones 6.8 • ~120 million/eye • ~6 million/eye • more in periphery • most in center, especially in the fovea • very sensitive (low threshold) • Need bright light to reach threshold • ~100 rods share same (photopic vision) optic nerve fiber to • have more private lines brain to brain- good for detail • night vision (scotopic vision or “acuity” vision) • color vision 2 10/13/2015 Turning Light Waves Into Electrical TRANSDUCTION Messages (Transduction) 6.12 . Rods & cones have molecules of light sensitive photopigment embedded in cell membrane. Rods – rhodopsin Cones – 1 of 3 iodopsins . Like metabotropic transmitter receptors, except they receive light! . But receiving light has a surprising effect 2 Theories of Color Vision Proposed in 1800’s Trichromatic Theory (“Component Theory”) – 3 Cones different types of color receptors work together to represent all colors of the spectrum. 3 different . Opponent Process Theory – cells in the visual types, pathway receive input about pairs of colors (R-G or absorbing B-Y). One color makes them fire faster, the other different makes them fire slower. ranges of wavelengths . Supports the Color “Opposites” on Trichromatic the Color Wheel theory Short wavelengths long wavelengths “Afterimages” of strong Book Fig 6.2 & 6.19 visual stimuli appear in opposite colors Primary Visual Pathway 6.13 Visual Fields • Each half of your brain sees the opposite half of your visual world 3 10/13/2015 “Dorsal stream - Many Regions of Cortex Involved in Visual where is it, what are its dimensions & how Processing do I get to it or reach . Primary visual cortex is just the first level of cortical for it pathway processing . Damage here”cortical blindness” . Secondary “visual cortex” has separate regions 6.21& 6.25 devoted to shape, color, location, & movement that extend beyond occipital lobe. Ventral stream – what or who is it, what color is it pathway Damage to either of these “streams” can impair these visual abilities Visual Agnosia (not recognizing) Visual Processing Cases . Damage to different parts of this system lead to different kinds of . Object Agnosia visual agnosia (object agnosia, color agnosia, movement agnosia) . http://www.youtube.com/watch?v=rwQpaHQ0hYw . Object agnosia & trouble locating visual stimulus . Prosopagnosia- can’t recognize individual faces (or similar members . http://www.youtube.com/watch?v=dG8JGg-d2Pk&feature=related of other complex classes of visual stimuli) – most often seen after . Prosopoagnosia (“face blindness”) damage to the inferior temporal lobe’s fusiform gyrus (in pink) . http://www.youtube.com/watch?v=vwCrxomPbtY&list=UU943Unaj Vxe9SpFJpwxpLsQ&index=8 . Motion blindness . http://www.youtube.com/watch?v=B47Js1MtT4w&list=PL22D01B36165478AD . “Blindsight” https://www.youtube.com/watch?v=ny5qMKTcURE p. 164 4.
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