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