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Sensation and Perception
All is not as it appears!!
Sensation and Perception
 Sensation
– The process by which
our sense organs
respond to and
translate stimuli into
nerve impulses sent to
the brain
 Perception
– Organizing the
stimulus input and
giving it meaning
Sensation and Perception
 Stages of sensation and perception
– Stimuli activate sensory receptors
– Sensory receptors translate information into
nerve impulses
– Specialized neurons analyze stimuli features
– Stimulus pieces are reconstructed and
compared to stimuli in memory
– Perception is then consciously experienced
Psychophysics: Studies of
Sensitivity to Stimuli
 Absolute limits of
sensitivity
– Dimmest light in
which we can see
objects
– Softest sound we can
hear
 Recognizing
differences between
stimuli
– Smallest difference in
brightness detectable
– Recognizing
differences between
tones
Stimulus Detection
 The Absolute Threshold
– The lowest intensity at which a
stimulus can be detected 50% of
the time
Signal Detection Theory
 Decision criterion: A personal standard of
certainty before a person will say that they
detect a stimulus
– Affected by:
• Conservativeness or boldness
• Increasing rewards for hits or costs for misses
Subliminal Perception
 A subliminal stimulus cannot be perceived
consciously but do register in the nervous
system
– “subliminal perception”
Subliminal Perception:
Research Results
 Stimuli above threshold influence behavior
much more than subliminal stimuli
 Subliminal stimuli have stronger effects on
attitudes
 Effects may be due to placebo effects
The Difference Threshold
 The difference threshold (just noticeable
difference or JND) is the smallest
difference between two stimuli that people
can perceive 50% of the time
– Weber’s Law: the JND is directly proportional
to the magnitude of the stimulus with which
the comparison is made (e.g 1/50 for weight)
Sensory Adaptation
(Habituation)
 Sensory neurons respond to a
constant stimulus by decreasing
their activity
The Sensory Systems: Vision
 Lens:
– Becomes thinner to
focus on distant
objects and thicker to
focus on closer ones
 Rods: Black and
white receptors
 Cones: Color
receptors
The Sensory Systems: Vision
 Transduction
– Absorption of light by photopigments
produces a chemical reaction changing the rate
of neurotransmitter release at the receptor’s
synapse
– The greater the change in release, the stronger
the signal passed into the optic nerve
The Sensory Systems: Vision
 Dark Adaptation
– Photopigment molecules are regenerated,
increasing receptor sensitivity
– Cones reach maximum sensitivity in 5 minutes;
rods take 1/2 hour
The Sensory Systems: Vision
 Young-Helmholtz
trichromatic theory
– Individual cones are
most sensitive to
wavelengths
corresponding to:
• Blue
• Green
• Red
 Opponent Process
Theory (Hering, 1870)
– Three cone types
respond to two different
wavelengths
Red/Green
Blue/Yellow
Black/White
The Sensory Systems: Vision
 Dual-Process Theory
– Trichromatic theory
confirmed
– Opponent processes
occur in the ganglion
cells of the retina
rather than the cones
The Sensory Systems:Color
Blindness
 Dichromat
– Blind in Red - Green
or Yellow - Blue
systems or both
 Monochromat
– Sensitive only to the
Black - White system
The Sensory Systems: Audition
 Characteristics of sound waves
– Frequency: the number of sound waves, or
cycles, per second (measured in Hz)
– Amplitude: the vertical size of the sound
waves (measured in dB)
The Sensory Systems: Auditory
Transduction
1. Sound waves strike
eardrum, setting
cochlear fluid into
motion
2. Fluid waves vibrate
the basilar
membrane, bending
the hair cells in the
organ of Corti
3. Neurotransmitters
are released into the
synapse, resulting in
a nerve impulse
Audition: Theories of Pitch
 Frequency Theory
– Nerve impulses sent to
the brain match the
frequency of the sound
wave
 Place Theory
– There is a specific
point in the cochlea
where the fluid wave
peaks and most
strongly bends the hair
cells
The Sensory Systems: Audition
 Sound localization
– Sounds arrive first at the ear closest to the sound
– Judgments of sound intensity also affect
localization
The Sensory Systems: Audition
 Types of Deafness
– Conduction
• Caused by problems transmitting sound waves to cochlea
– Nerve deafness
• Caused by damaged receptors in inner ear or damaged
auditory nerve
The Sensory Systems: Gustation
 A “taste”
results from
complex
patterns of
neural activity
produced by the
four types of
taste receptors
The Sensory Systems: Olfaction
 Humans have
about 40 million
olfactory
receptors.
The Sensory Systems: Olfaction
 Menstrual Synchrony
– The tendency of women who live together or
are close friends to become similar in their
menstrual cycles
– May be due to pheromones (Preti et al., 1986),
but synchrony was not found in cohabiting
lesbian couples (Weller & Weller, 1997, 1998)
The Sensory Systems:
The
Tactile Sensations
 Humans are sensitive to:
– Pressure (touch)
– Pain
– Warmth
– Cold
The Sensory Systems:
Body Senses
 Kinesthesis
– Provides us with feedback about our
muscles and joints’ positions and
movements
The
Perception: The Creation
Experience
 Bottom-up
processing
– Taking individual
elements of a stimulus
and combining them
into a perception
 Top-down
processing
– Using existing
knowledge in
perception
of
 Attention:
– Focusing on certain
stimuli
– Filtering out other
information
Perception: The Creation
Experience
 Stimulus factors in
attention
– !!!Intensity!!!
– Novelty
–
Movement
–Contrast
– Repetition Repetition
of
 Personal factors in
attention
– Motives
– Interests
Gestalt Principles of Perceptual
Organization
Gestalt Principles of Perceptual
Organization
Gestalt Principles of Perceptual
Organization
 FigureGround
Relations
Perception: The Creation
Experience
of
 Perceptual schemata: allow us to classify
sensory input in a top-down fashion
 Perceptual set: A readiness to perceive
stimuli in a particular way
 Perceptual constancies: Allow us to
recognize familiar stimuli under varying
conditions
Depth Perception
 Monocular cues
–
–
–
–
–
–
–
–
Light and shadow
Linear perspective
Interposition
Height in the
horizontal plane
Texture
Clarity
Relative size
Motion parallax
 Binocular cues
– Binocular disparity
– Convergence
Perception: The Creation
Experience
 Illusions are false perceptions
of
Understanding Pain
 Endorphins: Natural opiates inhibit the
release of neurotransmitters involved in
pain perception
 Stress-induced analgesia: A reduction in
perceived pain that occurs under stressful
conditions
– Adaptive for functioning so that a person can
deal with the stressful stimulus
Psychology and Pain
Can psychology help people
suffering from pain?
http://www.crha-health.ab.ca/clin/adultpsy/features/chronic.htm