PSYC 212 Chapter 8-13: Perception notes 2nd half of course: Chapter 8 and on

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9 Feb 2016
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Chapter 8 The Visual System: Light,
Optics, and the Eye
VISION is the dominant sensory system for humans.
Allows for the greatest distance of perception out of all sensory systems.
Nearly half of the human brain is dedicated to processing visual information.

Early theory: Particle theory
Due to reflective and bending properties of light.
oIt was believed that light was made up of particles.
Wave-theory (1700-1800s)
Realized diffraction couldn’t be explained by particles, but could be explained to
take on a wave-form.
But what was the medium (waves must travel in a medium)?
Dual-theory of light (current theory)
Albert Einstein brought back the particle theory.
oFound that a light beam can produce an ejection of electrons from an object
under appropriate conditions.
Light travels in (small packets) that have a wave-like quality.
propagation = wave theory + interaction with matter = particle theory
 !"
#$#%a type of moving energy field
that is found everywhere in nature.
Produced by oscillating (motion) of charged particles –
characterized by the flow of photons.
oThis movement of photons through space
produces an oscillating electric and magnetic
field.
oThe two fields are %# to each
other.
oThe fluctuation between the two fields produces
waves.
Wavelength
One full cycle represents a wavelength.
Denoted by &
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Variations in wavelength = different types of electromagnetic radiation.
'()$#$#%
#$##$full range of electromagnetic radiation that can be
produced.
Measured in nanometers.
Shortest wavelength = gamma rays
Longest wavelength = ELF waves
 '( = 400-700 nm
oThe different wavelengths allow us to perceive different colors.
Why is visible light the only type of electromagnetic radiation we can see?
Well, the major source of electromagnetic radiation reaching Earth is the sun
(emission spectrum)
oSpans from 100-4,000 nm.
The transmission properties of the atmosphere are important (transmission
spectrum)
oSimilar profile to the sun’s emission spectrum.
Visible light falls comfortably between the overlap the emission and transmission
spectra (figure).
%
Light travels with amazing speed, allowing it to be our most
distant sense.
“Seeing lightning before hearing thunder” occurs due
to the much faster speed of light than of sound.
%*+,,-.,+/$0
Unlike sound, light does not need to travel through a
medium in order to be seen.
oSpeed slows down somewhat in denser
mediums.

To understand the propagation of light, we must collapse the light source down to an
imaginary point – #.
Wave fronts
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Light waves originate from this point source and spreads out in all directions.
In the immediate vicinity, 12 are very small, and grow larger as they
distance themselves from the source
oRepresented by concentric circles.
The point where the diameter becomes so large that the curvature flattens is called
#3 (6 meters from point source).
oRepresented by horizontal lines.
Light rays
A way of representing light in terms of particles,
rather than waves – .
oThis is the path followed by photons.
Beyond optical infinity, the rays are shown as
parallel vertical lines (#%).
4#%#
Light intensity decreases with increasing distance,
because the total number of photons per unit of area
decreases with increasing distance (become more
spread out).
Inverse square law:*0%+
+5!"6"785
(-9#-%$
When light meets an opaque object, it does one of two things:
(
When the atoms of an object can convert the light energy into vibrational motion,
the light is ((%.
oThe vibrational energy is dissipated in the form of heat (this is why opaque
objects feel warm when exposed to light for extended periods)
9#
When the object’s atoms cannot convert the light energy into vibrational motion, the
light is 9#%.
The atoms re-emit the energy back as reflected light.
When light meets a transparent object:
$
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