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Chapter 2

May 15_The Structure of the eye&Basic Visual Neural Processing-Chapter 2.docx


Department
Psychology
Course Code
PSYC 367
Professor
James Hyman
Chapter
2

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I. The structure of the eye
1. A Little Light Physics:
The dual nature of light: to avoid confusion, just treat light as being made up
of waves when it moves around the world, and being made up of
photons(tiny particles that each consist of one quantum of energy)光子 when
it is absorbed.
Wavelengths in the visible spectrum: 380 nm 780 nm (nanometers)
Refraction 折射 occurs when light passes from air into the eyeball.
2. Eyes That See Light:
Structure of the Human Eye:
1) Sclera 巩膜: the tough outer
membrane of the eye that holds the rest
of the structures in; continuous with the
cornea in front, and forms a sheath
around the optic nerve in back; the
“whites of your eyes.”
2) Cornea 角膜: the transparent
window into the eyeball; continuous
with the sclera but clear, is the first eye
structure that light encounters as it is
transmitted into the eye; serves as a
barrier to the outside world and does
much of the focusing and refracting of
light rays as they pass through it; allows
us to see things from behind; a damaged
cornea can be very painful, due to the large
numbers of free nerve endings (pain
detectors) in them. Minor scratches usually
heal on their own.
3) Aqueous Humor 晶状体: a fluid derived from blood, fills the space immediately behind the
cornea, supplying oxygen and nutrients to & removing waste from the cornea and the lens;
function as cerebrospinal fluid in the brain to keep its shape by fluid pressure.

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4) Iris: gives us our distinctive eye color; consists of a muscular diaphragm 光圈 surrounding
the pupil and regulats the light entering the eye by expanding and contracting the pupil
Bright light: iris expense(causing the pupil to shrink); dim light: iris contracts(causing the
pupil to enlarge).
5) Pupil: the opening at the center of the iris, where light enters the eye
6) Lens: the lens inside the eye that enables changing focus
Four structuresthe cornea, aqueous humor, lens, and vitreous humorall
refract light rays and help to focus images on the retina. The cornea is the most
powerful refractor (does more of the focusing); The lens is the only one that can
change its refractive power to bring objects at different distances into focus. The
lens becomes fatter to focus on near objects and returns to its normal, thinner,
shape when viewing far objects, a process called accommodationLens
fatter/rounder: near objects; Lens thinner/flatter: far objects. (Ciliary muscles
are responsible for changing the shape of the lens to bring close objects into
focus.)
All humans experience a gradual stiffening of their lenses with age. This
decreases the ability to focus on near objects, a condition known as presbyopia
老花眼. At about 4050 years old, most adults will need glasses to read. The
glasses compensate for the focusing power that the lens has lost. Lenses can also
form cataracts 白内障 and become opaque 不透明, blocking light from entering
the eye. Treatment of cataracts usually involves removing the natural lens and
replacing it with an artificial one.
7) Vitreous Humor: a jelly-like substance that helps the eye maintain its ball shape and
refracts light rays.
8) Retina 视网膜: A light-sensitive membrane in the back of the eye that contains rods and
cones, which receive an image from the lens and send it to the brain through the optic
nerve.
Optics of the Human Eye:
o Myopia: nearsightedness.
o Hyperopia: farsightedness.
II. Basic visual neural processing
1. The Retina
1) Fovea and Optic Nerve:
o The Fovea:
The retina thins into a dented region directly behind the pupil.
This area is called the fovea (a term derived from a Greek word
meaning “pit,” describing its shape), and is the portion of the

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retina that “sees” the world most clearly. The fovea is packed
with color-sensitive cones and processes images with extremely
high resolution.
o The Optic Nerve:
The axons from ganglion cells in the retina gather together in
the optic nerve for their journey into the brain. The small area
of the retina where the optic nerve emerges contains no
receptor cells, forming a “blind spot” in your visual field. Your
brain automatically fills in the blind spot with information from
surrounding areas.
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