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Copyright © Allyn and Bacon 2006
Copyright © Allyn and Bacon 2006
Chapter 4
Sensation and
Perception
Copyright © Allyn and Bacon 2007
Copyright © Allyn and Bacon 2006
Sensation
An early stage of
perception in which
neurons in a receptor
create an internal pattern
of nerve impulses that
represent the conditions
that stimulated it – either
inside or outside the
body
Or simply…
The physical experiences of stimuli
Copyright © Allyn and Bacon 2006
The Basics
• We do not actually experience the world directly, but
instead we experience it through a series of “filters” we
call senses.
• The study of these sense and their effect on our behavior
is called sensory psychology.
Perception
• A process that makes sensory patterns
meaningful and more elaborate
Or simply…
The interpretation
of our sensations
Perception draws heavily on memory, motivation, emotion, and
other psychological processes to give them meaning.
How Does Stimulation
Become Sensation?
The brain senses the world
indirectly because the sense
organs convert stimulation into
the language of the nervous
system: neural impulses
The human mind lacks direct access to the outside world.
All external events are filtered through the sense organs and then
combined with the individual’s unique mix of memories, emotions,
motives, and expectations.
All the senses….
• 1. Transduce stimulus energy into neural
impulses
• 2. Are more sensitive to change that
constant stimulus
• 3. Provide us information about the world
Stimulation  Transduction 
Sensation 
Perception
Transduction
The process that converts physical
energy, (such as light or sound waves,)
into neural messages…the only
language the brain understands
Receptors
Specialized neurons that are activated
by stimulation and transduce (convert) it
into a nerve impulse
Copyright © Allyn and Bacon 2006
Bottom-Up and
Top-Down Processing
• Bottom-Up Processing
Analysis that stress features of the stimulus,
rather than internal concepts
• Example: Noticing a flower in a field
• If your attention is drawn to a flower in a field, it
may be simply that the flower is more visually
outstanding than the surrounding field….you didn’t
have to think about it
Bottom-Up Processing
• In bottom-up
processing, the
resulting percept is
determined by
stimulus features.
• Color, size,
shape…
Bottom-Up and
Top-Down Processing
•
Top-Down Processing
•
--Expectations
--Memories
--Knowledge
--Cultural background
--and other cognitive factors
….influence perception
T0p-Down Processing
•
Top-down processing is also known as
conceptually driven processing.
•
•
Top-down does not emphasize
stimulus features
• Even though the second letter in each word is
ambiguous, top down processing allows for
easy disambiguation based on the context.
Top-Down Processing
•
Your dog has been lost
for three days, and you
cannot stop thinking
about him.
•
When you hear a dog
bark, you assume that
it is your dog.
Figure 6.1
Bottom-Up and
Top-Down Processing
•
Top-Down Processing
•
--Expectations
--Memories
--Knowledge
--Cultural background
--and other cognitive factors
….influence perception
Bottom-Up and
Top-Down Processing
•
Top-Down Processing
•
--Expectations
--Memories
--Knowledge
--Cultural background
--and other cognitive factors
….influence perception
Why Have Attention?
•
Limited resources
•
•
Too much information
Attention:
•
selects important/relevant information
Types of Blindness
•
Inattentional Blindness: Failing to see visible objects
when our attention is directed elsewhere.
•
Change Blindness: Failing to notice change in the
environment around us.
Cocktail Party Effect
• Phenomenon of being able to focus one's
auditory attention on a particular stimulus while
filtering out a range of other stimuli
– a partygoer can focus on a single conversation in a noisy
room.
• Allows most people to "tune into" a single voice and
"tune out" all others.
– also describes why one may immediately detect words of
importance originating from unattended stimuli
• for instance hearing one's name in another conversation