Download 2.8 notes

Unit II Lesson 8
The Science of Seeing
Perceptual Aspects to
Light
• Three aspects of the perception of light
– Brightness
• Determined by amplitude of wave – height of wave
• Higher waves are bright, low waves dimmer
– Color (hue)
• Determined by wavelength
• Visible spectrum
– Portion of spectrum visible to the human eye
• Long wavelengths in red end, shorter wavelengths
found at blue end
– Saturation
• Purity of color
• Less saturated contains larger variety of wavelengths
The Visible Spectrum
Structure of the Eye
• Cornea
–
–
–
–
Clear membrane, covers eye’s surface
Protects eye
Focuses most light coming into the eye
Photoreactive Keratectomy (PRK)/ LaserAssisted keratomileusis (LASIK)
• Vision-improving techniques
• Small incisions in the cornea change focus
• Aqueous humor
– Clear, watery fluid
– Continually replenished
– Supplies nourishment to the eye
Structure of the Eye (2)
• Pupil
– Hole where light from visual image enters interior of
the eye
• Iris
– Colored, round muscle
– Controls light via pupil size
• Lens
– Located behind the iris
– Suspended by muscles
– Finishes focusing process begun by the cornea
Structure of the Eye (3)
• More Lens
– Visual accommodation
• Change in the thickness of lens
• Eye focuses on objects that are far away or close
– Vitreous humor
• Jelly-like fluid
• Nourishes the eye and gives it shape
• Retina
– Final stop for light in the eye
– Contains 3 layers:
• Ganglion cells
• Bipolar cells
Structure of the Eye (4)
• Retina
– Contains 3 layers:
• Photoreceptors
– Respond to various
light waves
– Rods
» Sensitivity to low
levels of light
– Cones
» Color vision, sharpness of vision
The Blind Spot
• “Hole” in retina
• Axons of three layers of retinal
cells exit the eye
• Form the optic nerve
• Insensitive to light
How the Eyes Work
• Retina is divided into halves
• Temporal retinas
– Halves toward the temples of the head
• Nasal retinas
– Halves toward nose
• Axons from temporal halves project to
visual cortex on the same side of brain
• Axons from the nasal halves cross over
to the visual cortex on opposite side of
brain
How the Eyes Work (2)
• Dark adaptation
– Rods work best in low light
– Eyes adapt to low light after exposure
to bright light
• Light adaptation
– Cones adapt to increase
in light rapidly
• 6 million cones in each eye
Theories of Color Vision
• Trichromatic theory
– Proposes three types of
cones:
• Red, blue, and green
– Mixing of direct light is
additive; painting is subtractive
– Afterimage
• Visual sensation persists for a brief time
after original stimulus is removed
• Colors contrast to those initially seen
Theories of Color Vision
(2)
• Opponent-process theory
– Proposes four primary colors with
cones paired:
• Red and green, blue and yellow
– Theory explains colors in afterimage
– Opponent-process cells
are located in Lateral
geniculate nucleus
(LGN) of thalamus
Color Blindness
• Caused by defective cones in the retina
• Color deficient more accurate
description
• Three types:
– Monochrome colorblindness
• Either have no cones or cones not working
– Red-green colorblindness
• Either red or the green cones are not working
– Sex-linked inheritance
• Recessive inheritance pattern