1. Chapter 3
Sensation and Perception
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2. Chapter 3 Overview
 The process of sensation
 Hearing
 Smell and taste
 The skin senses
 Influences on perception
 Principles of perception
 Unusual perceptual experiences
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3. The Process of Sensation
 Sensation is the process through
which the senses pick up visual,
auditory, and other sensory stimuli and
transmit them to the brain
 Perception is the process by which
the brain actively organizes and
interprets sensory information
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4. What is the difference between
the absolute threshold and the
difference threshold?
 What is the softest sound you can hear and
the dimmest light you can see?
 How much must the volume be turned up or
down for you to notice a difference in the
loudness of music?
 Researchers in sensory psychology have
performed many experiments to answer
these kinds of questions
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5. Absolute threshold
 The minimum
amount of sensory
stimulation that can
be detected 50% of
the time
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6. Difference threshold
 The smallest increase or decrease in a
physical stimulus required to produce a
difference in sensation that is noticeable
50% of the time
 Just noticeable difference (JND) is the
smallest change in sensation that a person
is able to detect 50% of the time
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7. How does transduction enable the
brain to receive sensory
information?
 Sensory receptors are highly specialized cells in
the sense organs that detect and respond to one
type of sensory stimuli and transduce (convert) the
stimuli into neural impulses
 Transduction is the process through which
sensory receptors convert sensory stimulation into
neural impulses
 Sensory adaptation is the process in which
sensory receptors grow accustomed to constant,
unchanging levels of stimuli over time
– e.g., Smokers grow accustomed to smell of cigarettes
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8. Hearing
 Sound requires a medium, such as air
or water, through which to move
 First demonstrated by Robert Boyle in
1660
– Watch in a jar experiment
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9. What determines the pitch and
loudness of sound, and how is each
quality measured?
 Frequency
– The number of cycles completed by a sound wave in one
second
– Determines the pitch of a sound
– Frequency is measured in hertz (Hz)
 Amplitude
– The loudness of sound
– Amplitude is measured in decibels (dB)
 Timbre
– The distinctive quality of a sound that distinguishes it from
other sounds of the same pitch and loudness
– Example: A piano and guitar sound different when playing
the same note 9

10. Decibel levels of various sounds
Figure 3.5
The loudness of a sound (its
amplitude) is measured in
decibels. Each increase of 10
decibels makes a sound 10
times louder. A normal
conversation at 3 feet
measures
about 60 decibels, which is
10,000 times louder than a soft
whisper of 20 decibels. Any
exposure to sounds of 130
decibels or higher puts a
person at immediate risk for
hearing damage, but levels as
low as 90 decibels can cause
hearing loss if one is exposed
to them over long periods of
time.
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11. What are the primary taste
sensations, and how are they
detected?
 Traditionally, four primary taste sensations
have been recognized
– Sweet
– Sour
– Salty
– Bitter
 Recent research suggests that there is a
fifth taste sensation
– Umami
– This sensation is triggered by glutamate
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12. What are the primary taste
sensations, and how are they
detected?
 Taste sensations are detected by receptor cells in the taste
buds
 Specialized receptors are activated by each flavor (sweet,
sour, etc.)
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– These receptors send separate messages to the brain

13. The Skin Senses
 Include the senses of touch and pain
 These senses are critical for survival
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14. How does the skin provide
sensory information?
 When an object touches and depresses the
skin it stimulates receptors in the skin
 These receptors send messages through
nerve connections to the spinal cord,
through the brainstem and midbrain, and to
the somatosensory cortex
 Areas on the skin vary in sensitivity to
touch, as measured by the two-point
threshold
– Areas with greater sensitivity are more densely
packed with touch receptors
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15. What is the function of pain, and how is
pain influenced by psychological factors,
culture, and endorphins?
 Pain serves as an early warning system for many
potentially deadly situations
 Pain can be influenced by several psychological
factors
– Focusing attention elsewhere reduces pain
– Placebo effect reduces pain
– Negative thoughts increase pain
– Some cultures encourage individuals to suppress, or
exaggerate, emotional reaction to pain
 Endorphins are the body’s natural painkillers
– They block pain and produce a sense of well-being
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16. Influences on Perception
 Perception is the process through
which the brain assigns meaning to
sensations
 Perception is influenced by a number
of factors, including
– Attention
– Prior knowledge
– Cross-modal perception
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17. What is gained and what is lost
in the process of attention?
 Attention is the process of sorting through
sensations and selecting some of them for further
processing
 When attention is focused on some sensations,
others are missed altogether or misperceived
– Inattentional blindness occurs when attention is
shifted from one object to another and we fail to notice
changes in objects not receiving direct attention
– The cocktail party phenomenon shows that we focus
attention on information that is personally meaningful
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18. How does prior knowledge
influence perception?
 Bottom-up processing
– Information processing in which individual bits of
data are combined until a complete perception is
formed
 Top-down processing
– Information processing in which previous
experience and knowledge are applied to
recognize the whole of a perception
– Perceptual set is an expectation of what will
be perceived that can affect what is perceived
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19. Principles of Perception
 A few principles govern perceptions in
all humans
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20. What are the principles that govern
perceptual organization?
 Gestalt principles of perceptual organization
– Similarity: Objects that have similar characteristics are perceived as a
unit
– Proximity: Objects that are close together are perceived as belonging
together
– Continuity: Figures or objects are perceived as belonging together if
they appear to form a continuous pattern 20
– Closure: Figures with gaps in them are perceived as complete

21. How does the brain perceive
motion?
 The brain perceives real motion by
comparing the movement of images
across the retina to reference points
that it assumes to be stable
 Autokinetic illusion
– An unmoving light in a dark room appears
to move
 Your eyes are moving, not the light
 In the dark, the brain has no stable reference
point to determine what is moving 21

22. What are three types of
puzzling perceptions?
 Ambiguous figures
– The perceptual system tries to resolve the uncertainty by
seeing the figure first one way and then another
 Impossible figures
– May not seem unusual until you examine them closely and
see the impossibility 22

23. What are three types of
puzzling perceptions?
 Illusions
– False perceptions or misperceptions of an actual stimulus
in the environment
 Figure c shows the Müller-Lyer illusion
 Figure d shows the Ponzo illusion 23

24. Unusual Perceptual
Experiences
 Subliminal perception
– The capacity to perceive and respond to
stimuli that are presented below the
threshold of awareness
 Extrasensory perception (ESP)
– Gaining information about objects,
events, or another person’s thoughts
through means other than known sensory
channels
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25. In what ways does subliminal
perception influence behavior?
 Research suggests that subliminal
information can influence behavior to
some degree
– But it appears to be ineffective at
persuading people to buy products or
vote in certain ways
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26. What have studies of ESP
shown?
 Some studies have suggested that ESP
exists
 But, in almost all cases, attempts to
replicate these studies have failed
– So most psychologists remain skeptical
about existence of ESP
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