Option A - Sight and Wave Phemonena Option A - Sight and Wave Phemonena The Eye and Sight

 The human eye

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 Cones  Photopic vision  Color vision  Normal light levels  Provided by 3 different cone cells with peak sensitivity in short, medium and long wavelengths (S, M, L)  Photopic vision  Color vision  Normal light levels  Provided by 3 different cone cells with peak sensitivity in short, medium and long wavelengths (S, M, L)

 Scotopic vision  Black and white  Dim light  Provided by rod cells  Chemicals synthesized for night vision - slight delay after light is reduced  Scotopic vision  Black and white  Dim light  Provided by rod cells  Chemicals synthesized for night vision - slight delay after light is reduced

Light Response Curves

 Cones  Blue - short wavelength - peak at 420 nm  Green - medium wavelength - peak at 534 nm  Red - long wavelength - peak at 564 nm  Rods  Peak sensitivity at 498 nm  Cones  Blue - short wavelength - peak at 420 nm  Green - medium wavelength - peak at 534 nm  Red - long wavelength - peak at 564 nm  Rods  Peak sensitivity at 498 nm Peak sensitivities

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

Accommodation - 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 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 mixing

 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 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

Depth 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 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