Transcript Class 6 - Vision and Perception

Psychology 001
Introduction to Psychology
Christopher Gade, PhD
Office: 621 Heafey
Office hours: F 3-6 and by apt.
Email: [email protected]
Class WF 7:00-8:30 Heafey 650
Sensation and Perception
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Sensation: the conversion of energy from
the environment into a pattern of
responses by that nervous system.
Perception: the interpretation of that
information.
In order to understand our perception of
information, we first need to understand
how we are sensing that information.
What Exactly Do We See?
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Light is composed of
pulses of
electromagnetic
energy that vary in
both wavelength and
amplitude.
The amplitude of the
electromagnetic wave
is what determines
the intensity
(brightness) of the
light.
What Exactly Do We See (cont.)?
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The wavelength (i.e. frequency) of the
light pulse is what determines the hue
(color) of the light wave.
• Humans are able to see light on a range
of 400 to 700 nanometers (nm). Other
animals have sensitivity at different
wavelength ranges.
The Path of Vision (After the Eye)
And…
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The fact that many of our areas are
arranged very intricately
• Layering and columns (related to brain
structures and the paths to those
structures)
• Specialization of
function
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Location receptors
Orientation receptors
Ocular information
receptors
Color receptors
Color Sensation
The Young-Helmholtz/trichromatic theory.
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Proposes that our receptors respond to three primary colors: blue,
green and red.
“Color vision depends on the relative rate of response by the three
types of cones.”, I.e. the combination of different levels of firing in
each type of cone gives rise to the broad spectrum of colors
perceived.
Visual Sensation
Color:
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What about yellow, white, and black?
What about negative afterimages?
The Opponent Process Theory:
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We sense color not in terms of
separate categories but rather in a
system of paired opposites: red
vs. green, blue vs. yellow and
black vs. white.
“ON”
red
green
blue
yellow
black
white
“OFF”
green
red
yellow
blue
white
black
The Interpretation of Colors and Patterns
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The Brightness Contrast
• Method of determining the colors of objects (going beyond
just the frequency of the electromagnetic waves).
• The brightness of surrounding objects influences our
perception of the color and brightness of an object.
Visual Sensation
The Retinex Theory:
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The Cerebral Cortex also plays a role in how we experience
color, I.e. color constancy, by comparing different patterns
of light from different areas of the retina.
Perception and Gestalt Psychology
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Knowing the visual
system is great if
we want to know
about the basics of
vision.
But what about
interpretation?
How do we make
sense of
ambiguous stimuli?
Gestalt and
perception
psychology address
this problem.
Gestalt Psychology (cont.)
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Gestalt psychology is
a field that focuses on
our ability to perceive
overall patterns.
“The whole is
different (and often
greater) than the sum
of its parts”.
Our perception is
based on our
attempts to create
semblance out of the
mess of stimuli that
we are presented
with.
Tricks to Determining
Distance/Depth
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Binocular Cues (two eyes)
• Retinal disparity: the
position of an object is
determined by the
different signals received
by the two eyes.
• Convergence: the
distance of an object is
determined by the
amount of eye
movement required to
focus on an object.
Monocular Cues (two eyes are not required)
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Object size (relative
size): nearer objects
look bigger.
Accommodation: Our
brains can detect how
much the lens of the
eye needed to shift in
order to focus on an
object.
Detail (relative clarity):
more detail signifies a
closer object.
Visual Illusions
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So we interpret stimuli in our world
to make sense of it… great. Is there
any situations where this comes at a
cost?
Most of the time, this translation of
information is very useful for our
interaction with the real world.
But sometimes, there are situations
that trick the mind.
The Muller-Lyer Illusion
Depth Perception Illusions
The Ponso Illusion
The
Moon
Illusion
The Ames Room