Page 136 - 2024-bfw-MyersAP4e-TE

called accommodation If the lens focuses the image on a point in front of the retina, you see
ENGAGE 1.6-4
(5 minutes) Point out to students that
nearsightedness occurs when the lens
focuses objects in front of the retina.
Farsightedness occurs when the lens
focuses objects behind the retina. To
demonstrate accommodation, use a
document camera (or an overhead
projector). Have students imagine
the screen is the retina. When the
projector is blurred in either direction,
you have to move the projector or the
screen to focus it.
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
TEACH 1.6-5
Enrichment
Ask students if they know why red
eye, that annoying red dot that
appears in people’s eyes in pictures,
occurs. Explain that red eye usually
occurs in pictures where the sur-
rounding illumination is dim, so the
camera’s flash must be used to take
an accurate picture. The flash is so
quick that the iris doesn’t have time
to contract, making the pupil big
enough to see right through to the
red retina! Cameras with “red-eye Copyright © Bedford, Freeman & Worth Publishers.
reduction” features provide a series
of quick flashes that warn the eye that
a picture is about to be taken. The
iris reacts to these light pulses and
shrinks the pupil so that the retina is
protected from the bright flash. Bonus:
To turn this into an ENGAGE activity,
put students in small groups and ask
each group to come up with its own
hypothesis about red eye before you 126
explain the phenomenon.
03_myersAPpsychology4e_28116_ch01_002_163.indd
126 Unit 1 Biological Bases of Behavior
03_HammerTE4e_47547_ch01_2a_163_4pp.indd 126
.
near objects clearly but not distant objects. This nearsightedness — myopia — can be remedied
with glasses, contact lenses, or surgery. (Farsightedness — seeing distant objects better than
near objects — occurs when the lens focuses the image on a point behind the retina.)
For centuries, scientists knew that an image of a candle passing through a small open-
ing will cast an inverted mirror image on a dark wall behind. If the image passing through
,
the pupil casts this sort of upside-down image on the retina, as in F igure 1.6-8 how can we
see the world right-side up? Eventually, the answer became clear: The retina doesn’t “see”
a whole image. Consider the four-tenths of a second a baseball batter takes to respond to a
pitcher’s fastball. The retina’s millions of receptor cells convert the particles of light energy
into neural impulses and forward those to the brain, which reassembles them, right-side up,
into what the batter perceives — incoming fastball! Visual information processing percolates
through progressively more abstract levels, all at astonishing speed.
Figure 1.6-8 Lens Retina
The eye Pupil
Light rays reflected from a candle
pass through the cornea, pupil, Fovea
and lens. The curvature and (point of
thickness of the lens change to
bring nearby or distant objects central focus)
into focus on the retina. Rays from
the top of the candle strike the Pascal Goetgheluck/Science Source
bottom of the retina, and those Iris Optic nerve
from the left side of the candle Cornea to brain’s
strike the right side of the retina.
The candle’s image on the retina Blind spot visual cortex
thus appears upside down and
reversed.
Information Processing in the Eye and Brain
How do the r
1.6-5
ods and cones pr
ocess information, and what is the path
accommodation the process 1.6-5 How do the rods and cones process information, and what is the path
by which the eye’s lens changes
information travels from the eye to the brain?
shape to focus images of near or information travels from the eye to the brain?
far objects on the retina.
rods retinal receptors that How do we make meaning out of the light energy constantly striking this marvelous organ,
detect black, white, and gray, and the eye? Let’s examine how our eyes and our brain work together to enable our visual expe-
rience of the world.
are sensitive to movement. Rods
are necessary for peripheral and
twilight vision, when cones don’t The Eye-to-Brain Pathway
respond.
cones retinal receptors that Imagine that you could follow behind a single light-energy particle after it reached your
retina. First, you would thread your way through the retina’s sparse outer layer of cells. Then,
are concentrated near the
reaching the very back of your eye, you would encounter the retina’s buried photoreceptor
center of the retina and that
function in daylight or in well-lit cells, the rods and cones ( F igure 1.6-9 ). There, you would see the light energy trigger chem-
conditions. Cones detect fine ical changes. That chemical reaction would spark neural signals in nearby bipolar cells. You
could then watch the bipolar cells activate neighboring ganglion cells, whose axons twine
detail and give rise to color
sensations. together like the strands of a rope to form the optic nerve After a momentary stopover at
.
optic nerve the nerve that the thalamus, the information would fly on to its final destination, your visual cortex, in the
carries neural impulses from the
eye to the brain. occipital lobe at the back of your brain.
The optic nerve is an information highway from the eye to the brain. This nerve can send
blind spot the point at which nearly 1 million messages at once through its nearly 1 million ganglion fibers. (The auditory
the optic nerve leaves the eye, nerve, which enables hearing, carries much less information through its mere 30,000 fibers.)
creating a “blind” spot because
,
no receptor cells are located We pay a price for this high-speed connection. Your eye has a blind spot with no receptor
cells, where the optic nerve leaves the eye ( Figure 1.6-10 ). Close one eye. Do you see a black
there.
hole? No — because without seeking your approval, your brain fills in the hole.
Unit 1 Biological Bases of Behavior
126 15/12/23 9:25 AM
07/02/24 5:27 PM