Option A - Sight and Wave Phemonena
Option A - Sight and Wave Phemonena
The Eye and SightThe Eye and Sight
The Eye and SightThe Eye and Sight The human eye The human eye
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How does the eye work?How does the eye work? Light refracts as it enters the eye.
Light passes through the cornea, aqueous humour, lens, and vitreous humour, then strikes the retina
Retina contains rods and cones (light sensitive cells)
Light refracts as it enters the eye.
Light passes through the cornea, aqueous humour, lens, and vitreous humour, then strikes the retina
Retina contains rods and cones (light sensitive cells)
Rods and ConesRods and Cones
Photopic visionColor visionNormal light levelsProvided by 3 different cone cells with peak sensitivity in short, medium and long wavelengths (S, M, L)
Photopic visionColor visionNormal light levelsProvided by 3 different cone cells with peak sensitivity in short, medium and long wavelengths (S, M, L)
Scotopic visionBlack and whiteDim lightProvided by rod cellsChemicals synthesized for night vision - slight delay after light is reduced
Scotopic visionBlack and whiteDim lightProvided by rod cellsChemicals synthesized for night vision - slight delay after light is reduced
Light Response CurvesLight Response Curves
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ConesBlue - short wavelength - peak at 420 nm
Green - medium wavelength - peak at 534 nm
Red - long wavelength - peak at 564 nm
RodsPeak sensitivity at 498 nm
ConesBlue - short wavelength - peak at 420 nm
Green - medium wavelength - peak at 534 nm
Red - long wavelength - peak at 564 nm
RodsPeak sensitivity at 498 nm
Peak sensitivities
Distribution of Rods and Cones
Distribution of Rods and Cones
Cones most dense at the center Rods most dense at an angle of 20° away from the center
No rods or cones where optic nerve leaves the back of the eye (blind spot)
Cones most dense at the center Rods most dense at an angle of 20° away from the center
No rods or cones where optic nerve leaves the back of the eye (blind spot)
Variation in Cell Densities
Variation in Cell Densities
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Accommodation - Focusing of the EyeAccommodation -
Focusing of the Eye Eye lens is short and fat for close objects - ciliary muscles are contracted and suspensory ligaments are slack
Lens can be pulled taut and thin - ciliary muscle is relaxed and suspensory ligaments are taut
Relaxed ciliary muscle - lens is thin so eye is focused on infinity
Pupil contracts and expands to control amount of light entering
Eye lens is short and fat for close objects - ciliary muscles are contracted and suspensory ligaments are slack
Lens can be pulled taut and thin - ciliary muscle is relaxed and suspensory ligaments are taut
Relaxed ciliary muscle - lens is thin so eye is focused on infinity
Pupil contracts and expands to control amount of light entering
Perception of ColorPerception of Color
Monochromatic frequencies perceived as different colors (ROYGBIV)
Frequencies can mix to get other colors
Primary colors - red, green, blue
Secondary colors - magenta (purple), cyan, and yellow
Monochromatic frequencies perceived as different colors (ROYGBIV)
Frequencies can mix to get other colors
Primary colors - red, green, blue
Secondary colors - magenta (purple), cyan, and yellow
Color mixingColor mixing
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Filter in front of light source absorbs most frequencies, and allows only certain colors to pass through
Colored surface reflects color seen, absorbs others
Trichromatic Theory - three types of cones are most responsive to S, M, L wavelengths
Filter in front of light source absorbs most frequencies, and allows only certain colors to pass through
Colored surface reflects color seen, absorbs others
Trichromatic Theory - three types of cones are most responsive to S, M, L wavelengths
Color BlindnessColor Blindness
Failure of one or more type of cones to respond
Red-Green most common hereditary problem - more common in males - genes on x chromosome so males have only one copy
Failure of one or more type of cones to respond
Red-Green most common hereditary problem - more common in males - genes on x chromosome so males have only one copy
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Depth PerceptionDepth Perception Brain interprets different images seen by each of our two eyes - stereoscopic vision
“Near point” - closest point that can be focused upon without straining or optical aids - 25 cm
“Far point” - furthest point that can be focused upon - infinity
Brain interprets different images seen by each of our two eyes - stereoscopic vision
“Near point” - closest point that can be focused upon without straining or optical aids - 25 cm
“Far point” - furthest point that can be focused upon - infinity
Light and ShadowLight and Shadow Deep shadow - objects look larger
Colors that spread out beyond boundaries are ignored
Color perception remains constant when light changes from sunlight to artificial light
Deep shadow - objects look larger
Colors that spread out beyond boundaries are ignored
Color perception remains constant when light changes from sunlight to artificial light
Color can provide warmth - blues are perceived as cold
Color can change perceived size - light-colored ceiling give a room height
Color can provide warmth - blues are perceived as cold
Color can change perceived size - light-colored ceiling give a room height