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Introduction to Psychology
Sensation and Perception
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• Sensation is the stimulation of sense organs
• Perception is the selection, organization,
and interpretation of sensory input.
• Sensory receptors are tuned to a particular form
of energy
– Auditory receptors in the ear code for sound
pressure changes, not for light
• Sensory systems require a minimum amount of
energy for activation (absolute threshold)
– Just-noticeable difference (JND): The minimum
difference in stimulation that is just noticeable
• Weber noted that the JND is a fraction of the original
stimulus intensity: the fraction is different for different
© 2002 John Wiley & Sons, Inc.
The Visual System
• The eye detects electromagnetic radiation
– Vision is functional
• Allows for detection of movement (predator or prey?)
• Allows for detection of color (ripe or spoiled?)
• Light detection is useful because:
• Light travels rapidly (no delay, unlike hearing)
• Light travels in straight lines (no distortion)
• Light interacts with the surfaces of objects in the
environment (is reflected or absorbed)
© 2002 John Wiley & Sons, Inc.
Electromagnetic Spectrum
© 2002 John Wiley & Sons, Inc.
Details of the Human Eye
© 2002 John Wiley & Sons, Inc.
Transduction of Light
• Light travels through the retina to impinge on
photoreceptors at the back of the eye
– Light bleaches a pigment contained within the
• Bleaching leads to a graded receptor potential that eventually
produces an action potential in the ganglion cell
– Two types of photoreceptors
• Cones: found in center of retina (fovea) and are sensitive to
fine detail and color
• Rods: found in periphery of retina and are sensitive to
movement but not fine detail
© 2002 John Wiley & Sons, Inc.
Visual Pathways in Brain:
“Where” versus “What”
© 2002 John Wiley & Sons, Inc.
Perception of Color
• Color is a psychological perception
– Three dimensions of color:
• Hue is the apparent color of an object (blue)
• Brightness is the intensity of a color
• Saturation is the purity of the color
– Three different types of cones are found in the eye
• Each is sensitive to different wavelengths of light
– S-cones: blue
– M-cones: green
– L-cones: red
© 2002 John Wiley & Sons, Inc.
Color Vision Theories
• Young-Helmholtz:
– Color is explained by differential activation of 3
color elements in eye
• Could not account for negative color afterimages
• Hering: Opponent-Process Theory
– Colors are derived from activity of 3 antagonistic
• Black-white
• Red-green
• Blue-yellow
© 2002 John Wiley & Sons, Inc.
Negative Color Afterimages
Stare at the globe for 10 seconds
and then look away at a white surface
© 2002 John Wiley & Sons, Inc.
• Sound waves are vibrations of molecules
that travel through air.
• Amplitude - decibels
• Wavelength - frequency (cps or hertz)
• Purity - timbre
The Auditory System
• External ear – pinna, eardrum
• Middle ear – ossicles (hammer, anvil,
• Inner ear – cochlea
• basilar membrane –hair cells
Taste: the Gustatory System
Taste buds
Primary tastes: sweet, sour, bitter, salty
Perception of flavor
Papillae: circumvallate, foliate, & fungiform
Smell: the Olfactory System
• Smell: chemical substances dissolved in
• Olfactory cilia
• Olfactory nerves
• Olfactory bulb
Skin Senses
• Receptors are localized within the skin to
detect physical stimuli in the outside world
• Three classes of skin receptors:
– Touch: physical contact of objects with the skin
– Temperature of objects
– Pain: destruction of skin tissue
© 2002 John Wiley & Sons, Inc.
• Pain is a source of information that relates to
tissue destruction
– Force
– Heat
– Chemical
• Pain is a adaptive to a degree (motivates behaviors
to terminate the source of the pain)
• Pain is influenced by
Cultural beliefs
Emotional states
Exogenous drugs (opiates)
Internal transmitters (endorphins)
© 2002 John Wiley & Sons, Inc.
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