Sensation and Perception
Sensation: your window to the world
Perception: interpreting what comes
in your window.
Sensation
• the passive process of bringing information
from the outside world to the body and the
brain
• Process of sensing our environment through
taste, sight sound, touch and smell
• Example:
Perception
• the active process of
selecting, organizing, and
interpreting the
information brought to the
brain by the senses
• Perception is the way we
interpret sensations and
therefore make sense of
everything around us
• Example:
Bottoms-up Processing
• AKA - Feature analysis
• Begins with the sensory
receptors and works its
way up to the brain
• Use the features of the
object itself to process
the information
• Examples:
Top Down Processing
• Processing information from the
senses with higher level mental
processes using our experiences
and expectations
• Using your background
knowledge to fill in the gaps
• Example:
Selective Attention
• Ability to focus our conscious awareness
on a particular stimulus
• Example:
Selective Attention
Cocktail-party phenomenon
• The cocktail party effect
describes the ability to
focus one's listening
attention on a single talker
among a mixture of
conversations and
background noises, ignoring
other conversations.
• Form of selective attention.
• Example:
Selective Inattention
• Change Blindness/Inattentional Blindness Falling to notice changes in the environment
• Example:
– Choice Blindness - failure to notice a switch in a
choice that is made
• Example:
– Change deafness – failure to notice a change in
voices that are speaking
• Example:
• Pop out – stimuli we don’t chose to attend to but
they draw our eyes and demand our attention
• Example:
Psychometrics
• Study of how
physical stimuli are
translated into
psychological
experience.
• Psychologists use
thresholds to
measure these
events
• Example:
Thresholds
• Absolute threshold – minimum
stimulation needed to detect a
stimulus of light, sound pressure,
taste, or odor 50% of the time
• Examples:
Signal Detection Theory
• Predicts how and when we
detect a signal amid
background noise
• Assumes no absolute
threshold
• Detection depends partly
on a person’s experience,
expectations , motivation
and alertness…
alertness…people respond
differently to same stimuli
• Examples:
Subliminal Stimulation
• Subliminal Stimulation –
below one’s absolute
threshold for conscious
awareness
• Example
• Priming – increased
sensitivity to certain
stimuli due to prior
experience outside
conscious awareness
• Example
Do Subliminal Messages work?
• Based on studies, some
people do respond to
stimuli below the
absolute threshold, under
some circumstances.
100
75
Percentage
of correct 50
detections
Subliminal
stimuli
25
0
Low
Medium
Absolute
threshold
Intensity of stimulus
– The problem is people
behave differently at
different levels, so what
could be subliminal (or
below the threshold) for
one person, may be
supraliminal (above the
threshold) for another
person.
Backmasking- More Subliminal
Messaging?
Listing to Songs in Reverse
• There are legends about hidden messages in songs Led Zeppelin's Stairway to Heaven was one of the
first songs to have supposed hidden, satanic
messages.
– http://jeffmilner.com/backmasking.htm
• Why does this seem to work?
Difference Threshold
AKA
• Just Noticeable Difference – the
amount a change needed in a
stimulus (stronger or weaker) for
us to recognize the change has
occurred
• the greater the intensity (ex.,
weight) of a stimulus, the greater
the change needed to produce a
noticeable change.
• Example:
Weber’s Law
• Related to JND
• For people to really
perceive a difference,
the stimuli must differ
by a constant
"proportion" not a
constant "amount".
• Proportion varies
depending on the
stimulus
• Example:
Weber’s Law
• JND = Constant (K) X Intensity
– Pitch = .003 ( if someone sings a little off key, we
will be able to tell)
– Loudness = .10
– Saltiness = .20
– Light = .08
• Example:
Sensory Adaptation
• Diminished
sensitivity as a
consequence of
constant stimulation
• Example
Do you feel your underwear all day?