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Sensation
 Sensation – Raw data of
experiences, including
smells, sights, tastes,
touch, balance and pain.
 The process by which
stimulation of a sensory
receptor produces neural
impulses that the brain
interprets.
 The first series of steps
in processing of
incoming information.
How does stimulation become
sensation?
 Sensory Receptors –
Converts incoming
stimulus information into
electrochemical signals –
neural activity – the only
language the brain
understands.
 Example – Light only
reaches the back of your
eyes, neurons then carry
what your eyes see to your
brain.
How does stimulation become
sensation?
 Transduction –
Transformation of one
form of energy into
another – especially the
transformation of
stimulus information
into nerve signals by the
sense organs.
 Ripe tomatoes would
not appear red without
transduction.
Sensory Adaptation
 Sensory Adaptation – Loss of
responsiveness in receptor cells
after stimulation has remained
unchanged for a while.
 Example – When a
swimmer becomes adapted
to the temperature of the
water.
 Thus, our sense organs are
really just change detectors.
 Example – Feed lots in
Greeley.
Thresholds
 Absolute Threshold – The amount of stimulation
necessary for a stimulus to be detected.
 Varies from one person to another.
 In practice, this means that the presence or absence of a
stimulus is detected correctly half the time over many
trials.
 Example – Dog Whistle, Smell
Thresholds
 Difference Threshold – The smallest amount by which
a stimulus can be changed and the difference detected
half the time.
 Example – Turn up the volume on the TV a very small
amount and your sister says, “You haven’t turned it up
enough.” By “enough,” she is referring to her difference
threshold.
 Example – Frog in hot water.
 Just Noticeable Difference – Same as the difference
threshold.
Thresholds
 Weber’s Law – This
concept says that the size
of the JND is proportional
to the intensity of the
stimulus.
 The JND is large when the
stimulus intensity is high
and is small when the
stimulus intensity is low.
Signal Detection Theory
 Signal Detection Theory – Explains how we detect
“signals,” consisting of stimulation affecting our eyes,
ears, nose, skin, and other sense organs.
 Says that sensation is a judgment the sensory system
makes about incoming stimulation.
 Often, it occurs outside of consciousness.

In contrast, the older theories from psychophysics, signal
detection theory takes observer characteristics into account.
Subliminal Sensations
 Sensations in the outside world that occur outside our
conscious awareness.
 Do they still influence our thinking?
 Example – Pop and Popcorn at a movie.
 Example – Words in the clouds at a Disney movie.
Vision
Vision – Parts of the Eye
 Cornea – Where light enters the eye
 Pupil – Opening in the center of the eye
 Iris – Colored part of the eye
 Lens – Part of the pupil light passes through
 Retina – Light sensitive inner lining of the back of the
eyeball on which light is focused
 Retina then contains the receptor cells responsible for
vision.
 Fovea – Center of the Visual field, area where images
are sharpest.
The Retina
 Retina – The thin, light-
sensitive layer at the back
of the eyeball.
 Contains millions of
photoreceptors and other
nerve cells.
 Photoreceptors – Lightsensitive cells (neurons)
in the retina that convert
light energy to neural
impulses.

This is as far as light gets
into the visual system.
Rods & Cones in the Retina
 Rods – Photoreceptors in
the retina that are
especially sensitive to
dim light but not to
colors.
 Cones – Photoreceptors
in the retina that are
especially sensitive to
colors but not to dim
light.
Fovea
 Fovea - The tiny area of
sharpest vision in the
retina.
 With movements of our
eyeballs, we use the
fovea to scan whatever
interests us visually.
Optic Nerve
 Optic Nerve – The bundle
of neurons that carries
visual information from
the retina to the brain.
Blind Spot
 Blind Spot – The point
where the optic nerve
exits the eye and where
there are no
photoreceptors.
 Any stimulus that falls
on this area cannot be
seen.
Processing Visual Sensation in
the Brain
 We look with our eyes, but we see with the brain.
 Visual images are imported through the optic nerve to
the visual cortex in our brains, which process the
information.
Brightness
 Psychological sensation
caused by the intensity of
light waves.
Color
 Color – Color is not a property of things in the external
world.
 Rather, it is a psychological sensation created in the
brain from information obtained by the eyes from the
wavelengths of visible light.
Color
 Electromagnetic spectrum – The entire range of
electromagnetic energy, including radio waves, X rays,
microwaves, and visible light.
 Visible Spectrum – The tiny part of the electromagnetic
spectrum to which our eyes are sensitive. The visible
spectrum of other creatures may be slightly different
from our own.
Two Ways of Seeing Colors
 Trichromatic Theory – The idea that colors are sensed
by three different types of cones sensitive to light in
the red, blue, and green wavelengths.
 Opponent-Process Theory – The idea that cells in the
visual system process colors in complementary pairs,
such as red or green or as yellow or blue.
Colors
 Afterimages – Sensations
that linger after the
stimulus is removed.
 Most visual afterimages
are negative afterimages,
which appear in reversed
colors.
Colors
 Color Blindness – Typically a genetic disorder
(although sometimes the result of trauma, as in the
case of Jonathan) that prevents an individual from
discriminating certain colors.
 The most common form is red-green color blindness.
Sound and the Ear
The Ear
From Coren, Ward, & Enns. Sensation and Perception 6th ed. John Wiley &
Sons, Inc. 2004
Outer Ear
•Auditory Canal
•Eardrum
Middle Ear
•Hammer, anvil, stirrup
Inner Ear
•Cochlea
Unit IV.
Sensaton
and
Perception
Parts of the Ear
 Tympanic Membrane – The Eardrum.
 Includes 3 tiny bones.



Hammer
Anvil
Stirrup
 These bones pass vibrations to the primary organ of hearing,
the cochlea.
Parts of the Ear
 Cochlea – The primary
organ of hearing.
 A coiled tube in the
inner ear, where sound
waves are transduced
into nerve messages.

Cochlea then focuses
vibrations on the basilar
membrane.
Parts of the Ear
 The Basilar Membrane – A thin strip of tissue sensitive
to vibrations in the cochlea.
 Contains hair cells connected to Neurons.
 When a sound wave causes the hairs cells to vibrate, the
associated neurons become excited.

As a result, the sound waves are converted into nerve activity
and carried to the brain (the auditory cortex).
Sensations of Sound
 Pitch – Sensory characteristic of sound produced by
the frequency of the sound wave.
 Loudness – Sensory characteristic of sound produced
by the amplitude (intensity) of the sound wave
 Timbre – The quality of a sound wave that derives from
the wave’s complexity.
 Table 4.3 page 127
Deafness
 Conduction Deafness –
An inability to hear
resulting from damage to
structures of the middle
or inner ear.
Deafness
 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.
Hearing / Parts of the ear
 Eardrum – Hearing begins when sound waves strike
the eardrum and cause it to vibrate.
 Hammer, Anvil, and Stirrup – Three tiny bones that hit
one another, allowing the vibrations of the eardrum to
be carried to the inner ear.
 Vibrations then travel to the Oval Window, Cochlea,
and Basilar Membrane before they reach the receptor
cells in the Organ of Corti and finally reach the brain.
Taste
 Gustation – The sense of
taste – from the same
word root as “gusto” – also
called the gustatory sense
Taste
 Evolves throughout life
 Babies – Enjoy bland food
 Adults – Like novelties (pickles, mustard, ice cream are
all acquired tastes).
 Flavor vs. Taste
 Flavor – Combination of smell and taste.
 Taste – Sweet, sour, salty, and bitter.

Can still get taste without smell, but can’t get flavor.
Taste
 Taste Buds – Located on the tip, sides, and back of the
tongue, they are the receptor cells for the sense of
taste.
 Adults – 10,000 taste buds
 Number of taste buds decreases with age, explaining
why some elderly people lose interest in food.
 Papillae – Bumps on your tongue that house the taste
buds.
The Nose and Smell
 Olfaction – The sense of smell
 Olfactory Epithelium – Area of the nose that receives
airborne molecules high in each nasal cavity.
 Receptor Cells in O.E. then send smell to Olfactory Bulb.
 Olfactory Bulb – Receives information from the O.E.
and sends it to the temporal lobes of the brain where
we then become aware of smells.
The Nose and Smell
 Smell sensitivity is related to gender and age:
 Women more sensitive to smell than men.
 Young adults have the most sensitive sense of smell.
 The older you get the less sensitive you become to smell.
 Pheromones!

Humans???
Vestibular and Kinesthetic
Sense
 Vestibular – The sense of body orientation with
respect to gravity.
 Closely associated with the inner ear and, in fact, is
carried to the brain on a branch of the auditory nerve.
 Kinesthetic – The sense of body position and
movement of body parts relative to each other.
Skin Senses
 Sensory systems for
processing touch,
warmth, cold, texture,
and pain.
 Gate Control Theory –
Proposes that we have a
neural “gate” that can, at
times, block incoming
pain signals.
Pain
 Serves as a warning signal, telling us that we have been
injured or that something is wrong.
 Comes from nerve endings
 No pains / Phantom limb pains
 Individuals have different thresholds and tolerances
for pain.