Chapter 3
4th Edition
Sensation and
Perception
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3-1
Sensation, Perception and
Psychophysics
• Sensation refers to stimulation or
activation of the receptors.
• Sensations are the basic building blocks of
perception, the process of interpreting or
making sense of our sensory input.
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Sensation, Perception and
Psychophysics
• Receptors for each sensory system respond to
only one type of environmental stimulus.
• Transduction is the process by which the
receptors change the energy they receive into a
form that can be used by the nervous system.
• Adaptation occurs when continued presentation
of the same stimulus results in a loss of
sensitivity.
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Sensation, Perception and
Psychophysics
• Psychophysicists, such as Ernst Weber
and Gustav Fechner, studied the
relationship between the mind and the
body.
• Weber’s law relates the amount of change
in a stimulus and the conscious
experience of change in the stimulus.
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Sensation, Perception and
Psychophysics
• Fechner studied:
– The smallest amount of energy that could be
detected 50% of the time (the absolute
threshold)
– The smallest change that could be detected
50% of the time (the differential threshold or
Just Noticeable Difference (Jnd).
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Sensory Systems
• The visual receptors,
the rods and cones,
respond to a limited
range of light waves,
the visible spectrum.
• Light waves differ in
terms of wavelength
(hue) or color,
amplitude (intensity),
and saturation
(purity).
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Sensory Systems
• The cones have greater acuity, respond to
color, and have a higher threshold for
activation.
• The rods have lower acuity, respond to
black and white and shades of gray, and
have a lower threshold.
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Sensory Systems
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Sensory Systems
• The visual receptors
are located in the
retina at the back of
the eye.
• To reach the
receptors, light waves
pass through several
other structures in the
eye, as well as
several layers of
retinal cells.
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Sensory Systems
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Sensory Systems
• Two theories of color vision have been
formulated.
• The trichromatic theory proposes that
there are three different types of cones;
• The opponent-process theory argues that
color-sensitive cells are arranged in pairs.
• Both theories are supported by research
findings.
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Sensory Systems
• Dichromats lack the ability to see one of
the three primary colors.
• Monochromats are unable to see color.
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Sensory Systems
• Audition, the sense of hearing, is initiated
by the movement of molecules in the air.
• Vibration of the eardrum starts a chain
reaction that results in movement of fluid
in the inner ear and the bending of
specialized hair cells, which are the
receptors for hearing.
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Sensory Systems
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Sensory Systems
• The pitch or
frequency of a sound
wave is determined
by the location of the
hairs that are
activated (Place
theory) and the
rapidity with which the
basilar membrane
vibrates ( theory).
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Sensory Systems
• Hearing disorders can result from damage
to the bones of the middle ear (conduction
deafness), the inner ear, especially the
hair cells (sensodneural deafness), or the
auditory nerve and auditory cortex (central
deafness).
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Perception
• Perception is the process of organizing
and making sense of the stimuli in our
environment.
• Our motives help determine which stimuli
we perceive.
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Perception
• We engage in selective attention because we
cannot process all of the stimuli we encounter.
• Dichotic listening experiments study divided
attention.
• With practice we can learn how to divide our
attention effectively.
• To attract our attention, stimuli should be more
colorful, larger, and louder than other stimuli in
our environment.
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Perception
• The ability to discriminate among shapes and
figures is known as pattern perception.
• The feature analysis theory states that we
perceive the elements of an object and then
combine them to produce our perception of the
object (bottom-up processing).
• Other research has shown that we perceive the
object before we perceive its elements (topdown processing).
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Perception
• We experience perceptual constancies when our
perception of an object does not change, even
though the retinal image.
• The Gestalt psychologists demonstrated that we
actively organize our perceptual world into
meaningful groups or wholes.
• The figure-ground relation is one of the most
basic perceptual organizations.
• Additional principles for the grouping of stimulus
elements are proximity, similarity, good
continuation, and closure.
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Perception
• Perceptual hypotheses are inferences
about the nature of the stimuli we sense.
• Perceptual illusions and ambiguous
figures may cause us to develop incorrect
perceptual hypotheses.
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Perception
• Parallel, as opposed to sequential,
processing appears to characterize much
of our perceptual activity.
• Parallel processing is seen in visual
search, in which a target stimulus must be
distinguished among a group of
distractors.
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Perception
• Perception may be influenced by the
social context.
• For example, the Ebbinghaus illusion is
influenced by the type of social stimuli
used. Which center circle below is larger?
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Ambiguous Figures
Perceptual Set
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Context Effects
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Paranormal Phenomena
• Extrasensory perception (ESP) refers to the
occurrence of experiences or behaviors in the
absence of an adequatestimulus.
• Such occurrences are considered to be
paranormal, or beyond our normal sensory
abilities.
• Clairvoyance, telepathy, precognition, and
psychokinesis are examples of paranormal
phenomena
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