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Chapter 4
Sensation & Perception
These power point slides are to only be used as a means to take notes
during Mrs. Bartolotti’s lecture. They are not to be reproduced in any
way without the permission of the teacher. Also, the slides presented
here are not to be the only means of studying for the chapter test. You
will still need to read and take notes for both the reading and the lecture.
Finally, please note, not all of the slides from Mrs. Bartolotti’s lecture are
included in these slides; hey, some things have to be a surprise!
Sensation and Perception
Sensation –
An early stage of perception in which
neurons in a receptor create an internal
pattern of nerve impulses that represent
the conditions that stimulated it – either
inside or outside the body
Perception –
A process that makes sensory patterns
meaningful and more elaborate
How Does Stimulation
Become Sensation?
The brain senses the world
indirectly because the sense
organs convert stimulation
into the language of the
nervous system: neural
impulses
Transduction
Transduction –
Transformation of one form of energy into
another – especially the transformation of
stimulus information into nerve impulses
Receptors –
Specialized neurons that are activated by
stimulation and transduce (convert) it into
a nerve impulse
Stimulation
Transduction
Sensation
Perception
Transduction
Sensory pathway –
Bundles of neurons that carry information
from the sense organs to the brain
Sensory Adaptation
Sensory adaptation –
Loss of responsiveness in receptor cells
after stimulation has remained
unchanged for a while
Thresholds
Absolute threshold – p.114 table 4.1
The minimum amount of stimulation
required in order for a stimulus to be
detected.
Difference threshold –
Smallest amount by which a stimulus can
be changed and the difference be
detected 50 percent of the time (also
called just noticeable difference – JND)
Thresholds
Weber’s law – (Ernest Weber) (ever notice how commercials are
always louder than the show you were just watching?)
The principle that, to perceive their difference, two stimuli
must differ by a constant % (rather than by a constant
amount)
• The size of the JND is proportional to the intensity of the
stimulus – so, the JND is large when the stimulus intensity is
high, and the JND is small when the stimulus intensity is low.
• 2 lights must differ by 8% in intensity
• 2 objects by 2% in intensity
• 2 tones by .03%
Thresholds – Weber’s In Real Life
• This also parallels some of our life experiences.
If the price of a .50 cent candy bar goes up .05
cents, shoppers would probably notice it;
similarly, if the cost of a $50,000 Mercedes
goes up $5,000, potential buyers would raise an
eyebrow. In both cases, the price went up by
10%; our thresholds for detecting differences
are a roughly constant proportion of the original
stimulus.
Signal Detection Theory
Signal detection theory – Assumes there is no
single absolute threshold and that detection
depends on perceptual judgment as a
combination of sensation and decision-making
processes.
Noise in the dark
Stimulus event
RAS alerts your
brain – NOISE!
Neural activity
Have I heard that
before?
It’s a cat on the
roof; no need to get
up.
Comparison with
personal standard
Action (or no action)
Subliminal Persuasion
Studies have found that subliminal words
flashed briefly on a screen can “prime” a
person’s later responses
No controlled research has ever shown
that subliminal messages delivered to a
mass audience can influence people’s
buying habits
How Are the Senses Alike?
How Are They Different?
The senses all operate in
much the same way, but each
extracts different information
and sends it to its own
specialized processing region
in the brain
The Anatomy of Visual Sensation
Retina –
Light-sensitive layer at the back of the eyeball
Photoreceptors – Light-sensitive cells in the retina
that convert light energy to neural impulses
Rods – Sensitive to dim
light but not colors
Cones – Sensitive to
colors but not dim light
Fovea –
Area of sharpest
vision in the retina
Afterimages – What happens when retina is
fatigued?
• If you fatigue the cells in the retina, it will cause an effect known
as an “afterimage.” These are sensations that linger after the
stimulus is removed.
• Positive afterimages are caused by a continuation of the
receptor and neural processes following stimulation (e.g. seeing
the flash of a light bulb after it goes off; sparklers on 4th of July.
• Negative afterimages are caused by the opposite or the reverse
of the original stimulus. This is best explained by the Opponent
Process Theory of Color.
• Opponent Process Theory of Color states that when you are
seeing one color, you are suppressing or inhibiting the opposite
color from being seen (e.g. sensing red, not sensing green;
sensing blue, not sensing yellow; sensing black, not sensing
white). Colors come in OPPOSITE pairs.
The Anatomy of Visual Sensation
Optic nerve –
Bundle of neurons that carries visual
information from the retina to the brain
Blind spot –
Point where the
optic nerve exits
the eye and
where there are
no photoreceptors
Transduction of Light in the Retina
The Anatomy of Visual Sensation
Visual cortex –
Part of the brain – the occipital cortex –
where visual sensations are processed
Color –
Psychological sensation derived from the
wavelength of visible light – color, itself, is
not a property of the external world
Neural Pathways in the Human Visual
System
How the Visual System Creates Color
Electromagnetic spectrum –
Entire range of electromagnetic energy,
including radio waves, X-rays,
microwaves, and visible light
Visible spectrum –
Tiny part of the electromagnetic spectrum
to which our eyes are sensitive
How the Visual System Creates Color
Copyright © Allyn and Bacon 2006
The Ways of Sensing Colors
•Trichromatic Theory: The
earliest stage of color
sensation that states that
colors are sensed by three
different types of cones
sensitive to light in the red,
blue, and green
wavelengths.
Color Blindness
Color blindness –
Vision disorder that prevents an
individual from discriminating certain
colors
Hearing: If a Tree Falls in the
Forest...
The Physics of Sound
Frequency –
Number of cycles completed by a wave in a
given amount of time
Low Frequency
High Frequency
Hearing: If a Tree Falls in the
Forest...
The Physics of Sound
Amplitude –
Physical strength of a wave
High Amplitude
Low Amplitude
How Sound Waves Become Auditory
Sensations
Tympanic membrane –
The eardrum
How Sound Waves Become Auditory
Sensations
Cochlea –
Where sound
waves are
transduced
How Sound Waves Become Auditory
Sensations
Cochlea
Basilar membrane –
Thin strip of tissue
sensitive to
vibrations
How Sound Waves Become Auditory
Sensations
Auditory nerve –
Neural pathway
connecting the ear
and the brain
How Sound Waves Become Auditory
Sensations
Auditory cortex –
Portion of the temporal lobe that
processes sounds
The Psychology of Pitch,
Loudness, and Timbre
Pitch –
Sensory characteristic of sound produced by
the frequency of the sound wave (place theory
and frequency theory)
Loudness –
Sensory characteristic of sound produced by
the amplitude (intensity) of the sound wave
Timbre –
The quality of the sound wave that comes from
both pitch and loudness (mom’s voice vs. Mrs.
B’s voice).
Deafness
Conduction deafness –
An inability to hear resulting from damage to
structures of the middle or inner ear
Nerve deafness –
An inability to hear, linked to a deficit in the
body’s ability to transmit impulses from the
cochlea to the brain, usually involving the
auditory nerve or higher auditory processing
centers
Position and Movement
Vestibular sense –
Sense of body orientation with
respect to gravity
Kinesthetic sense –
Sense of body position and
movement of body parts relative to
each other
How Do You Smell? (haha)
Olfaction –
Sense of smell
Olfactory bulbs –
Brain sites of olfactory
processing
Pheromones –
Chemical signals
released by organisms
to communicate with
other members of the
species
Taste
Gustation – The sense of taste
Taste buds –
Receptors for taste
(primarily on the
upper side of the
tongue)
The Skin Senses
• Touch
• Warmth
• Cold
• All skin senses
are registered in
the
somatosensory
cortex of the
parietal lobe.
Pain
•Pain is psychological, not
physical!
•Gate Control Theory –
Close the gate on the
sensation that gets to the
brain that way I won’t feel
the pain!
Placebos –
Substances that appear to
be drugs but are not
Placebo effect –
A response to a placebo
caused by subjects’ belief
that they are taking real
drugs
What is the Relationship
Between Perception
and Sensation?
Perception brings meaning
to sensation, so perception
produces an interpretation of
the external world, not a
perfect representation of it
The Machinery of Perceptual Processing
Percept –
Meaningful product of a
perception
Feature detectors –
Cells in the cortex that
specialize in extracting certain
features of a stimulus
Binding problem –
A major unsolved mystery in
cognitive psychology,
concerning the physical
processes used by the brain to
combine many aspects of
sensation to a single percept
Bottom-Up and
Top-Down Processing
Bottom-up processing –
Analysis that emphasizes characteristics
of the stimulus, rather than internal
concepts
Top-down processing –
Emphasizes perceiver's expectations,
memories, and other cognitive factors
Perceptual Constancies
Perceptual constancy –
Ability to recognize the same object
under different conditions, such as
changes in illumination, distance, or
location
Perceptual Ambiguity and Distortion
Illusions –
Demonstrably incorrect experience of a
stimulus pattern, shared by others in the
same perceptual environment
Ambiguous figures –
Images that are capable of more than
one interpretation
Perceptual Illusions
Do you see
or
?
Perceptual Illusions
The Herman Grid
Do you see small gray squares between
the black squares?
Theoretical Explanations for
Perception
Learning-based inference –
View that perception is primarily shaped
by learning, rather than innate factors
Perceptual set –
Readiness to detect a particular stimulus
in a given context
Some illusions are learned!
Here is what you are seeing
The Gestalt Approach
Gestalt psychology –
View that much of perception is shaped
by innate factors built into the brain
Figure –
Part of a pattern that commands attention
Ground –
Part of a pattern that does not command
attention; the background
The Gestalt Approach
Subjective contours –
Boundaries that are perceived but do not
appear in the stimulus pattern
Copyright © Allyn and Bacon 2006
The Gestalt Approach
Closure –
Tendency to fill in gaps in figures and see
incomplete figures as complete
The Gestalt Laws of Perceptual
Grouping
Similarity
Proximity
Continuity
Common fate
Prägnanz
Law of Prägnanz
A
BIRD
IN THE
THE HAND
How do we perceive depth?
The Visual Cliff
How do we perceive depth?
Monocular Cues – Depth cues that do not
depend on having two eyes.
Binocular Cues – Depth cues that depend
on having both eyes.
End of Chapter 4