General Psychology (PY110)
Chapter 3
Sensation and Perception
Windows on the World
Our sensory neurons (receptors) are
constantly bombarded with stimuli
 We understand the world through our
senses, our “windows” on the world
 Our reality, in fact, is dependent upon two
processes:

◦ Sensation: Gathering information
◦ Perception: Interpreting information (a process)
Stimulus – Sensation – Perception
Stimulus
Sensation
Perception
• Anything that can be received
by a receptor
• Awareness of a stimulus
• A simple mental process
• Sensation + Interpretation +
Response
• A complex mental process
Examples of Misperception
Examples of Misperception
Examples of Misperception
Bottom-up Processing and Topdown Processing


Bottom-up processing is
the processing of sensory
information as it enters the
sensory structures and
travels to the brain
Top-down processing is the brain’s use of existing
knowledge, beliefs, and expectations to interpret the
sensory stimulation
◦ Perception is subjective because of top-down processing
◦ Perceptual set occurs when we interpret an ambiguous
stimulus in accordance with our past experiences
◦ A contextual effect occurs when we use the present context
of sensory input to determine its meaning
Perceptual Organization
and Top-down Processing
A Context Effect on Perception
Illusion Vs Hallucination
Perception
Stimulus
Interpretation
Response
Perception
Misinterpretation
Response
Illusion
Response
Hallucination
Illusion
Stimulus
Misinterpretation can be caused by
Hallucination
No Stimulus
Misinterpretation
Perceptual Organization
Gestalt means “organized whole”
◦ Gestalt psychologists believe that the organized whole is
greater than the sum of its individual pieces of sensory
information
◦ The figure-and-ground principle states that the brain
organizes sensory input into a figure (the center of
attention) and a ground (the background)
An Example of
Figure-Ground Ambiguity
An Example of
Figure-Ground Ambiguity
Both purses do the
same job… Right?
So they should cost about
the same… Right?
Gestalt Principles of Organization

Similarity-objects similar are considered a unit

Proximity-because of spacing objects
considered a unit

Closure- the tendency to fill in the gap to
produce a familiar object
Similarity
Does this furniture
go together?
Proximity
What do you see?
Did you interpret the closeness of these two people as
evidence of a relationship?
Closure
What about this?
What is this?
Do you see the white triangle?
An Example of an Organizational
Perceptual Ambiguity
An Example of an Organizational
Perceptual Ambiguity
An Example of an Organizational
Perceptual Ambiguity
Examples of Misperception
Examples of Misperception
Perceptual Constancy

Refers to the perceptual stability of
◦
◦
◦
◦

Size – Football player
Shape - Nickel
Brightness - Coal
Color - Coca-Cola
For familiar objects seen at
◦ Varying distances
◦ Different angles
◦ Different lighting conditions
Perceptual Constancy - Color
Can this
really taste
the same as
this?
Perceptual Constancy - Size
Even though they look like ants from our seats…
We know how big they really are
Perceptual Constancy - Shape
We know that both of these
balls are actually the same shape
because our experience tells us
how a football is shaped
Examples of Misperception
Examples of Misperception
Examples of Misperception
Examples of Misperception
Examples of Misperception
Visual Illusions
In the Ponzo illusion, two
horizontal lines are equal
in length, but one appears
longer than the other
 The convergence of
the two lines (i.e.,
linear perspective)
outside the horizontal
lines normally
indicates increasing
distance
Visual Illusions
In the Müller-Lyer illusion, two vertical line segments are equal
in length, but the one with arrow feather endings appears to be longer

The line with arrow feather endings
has the appearance of a corner that
is receding away from you (the
corners where two walls meet in a
room), while the line with arrowhead
endings has the appearance of a
corner that is jutting out toward you
(the corners where two sides of a
building meet)

Thus, it is our past experience with
corners that leads the brain to believe
that the line with arrow feather
endings is farther away
Examples of a Visual Illusion
Summary of Perception
Senses
• Detects
Brain
• Select
Mind
• Elects
• based on experience