SENSATION AND PERCEPTION
6-8% of the AP Psychology Exam
TWO STORIES ABOUT DOGS…
SENSATION AND PERCEPTION
 Sensation- process by which sensory receptors receive energy
from the external environment and transform it into neural
energy
 Perception- the process of organizing and interpreting sensory
information
PROCESSING
 Bottom-up processing
 Begins with sensation and works up to the brain
 The type of processing used when we have no prior knowledge
 Top-down processing
 Begins with cognition
 We construct perceptions drawing on experience and expectation
 Uses prior knowledge
SENSORY RECEPTION
Signal
Transduction
• External stimuli picked
up by sensory
receptors
• Photoreceptors
• Mechanoreceptors
• Chemoreceptors
• Energy is transformed
into action potential
• Strength of the
stimulus is represented
by the frequency of
action potentials
Response
• The brain
processes
information
(perception)
• Signals the
body to
respond if
necessary
THRESHOLDS- RECEIVING A SENSATION
 Absolute threshold- the minimum amount of stimulus energy
that a person can detect
 Difference threshold- the degree of difference that must exist
between two stimuli before a difference can be detected
 Weber’s Law: difference threshold must differ by a constant
minimum percentage rather than a minimum amount
PERCEPTION
 Subliminal Perception- The detection of information below the
level of conscious awareness
 Example: thirsty words study
 Signal Detection Theory- Theory of perception that focuses on
decision making (top-down processing) about stimuli in the
presence of uncertainty
SENSATION VS. PERCEPTION
WHAT DO YOU SEE?
SELECTIVE ATTENTION
 Selective Attention- the focusing of conscious
awareness on a particular stimulus
 Cocktail Party Effect- being able to focus on one conversation,
or one voice, in a room full of people
FAILURES OF SELECTIVE ATTENTION
 Inattentional Blindness:
 failing to see visible objects when our attention is focused
elsewhere
 Closely related to change blindness- the inability to notice
change when not focused on a specific aspect of a scene
SELECTIVE ATTENTION
SELECTIVE ATTENTION
FAILURES OF SELECTIVE ATTENTION
 Google: “The Stroop Effect Online” – First Link
 The Stroop Effect: represents failure of selective attention
 Pop-Out Phenomena: powerful or strikingly distinct stimuli that
cannot be ignored
FAILURES OF SELECTIVE ATTENTION
 Page 107 in your book.
 Perceptual Set: a predisposition or readiness to perceive
something in a particular way; a result of top-down processing
SENSORY ADAPTATION
 A change in the responsiveness due to constant exposure to a
stimulus
EXTRASENSORY PERCEPTION (ESP)
 Known in the psychology community as parapsychology
 It is NOT real
 Science depends on three things: evidence, valid conclusions,
reproducibility
 While it has been studied over the past 75 years, no scientific
evidence supports the existence of ESP