2. Sensations and Perceptions
Sensations - the passive process of
bringing information from the outside
world into the body and to the brain.
Perception - the active process of
selecting, organizing, and interpreting
the information brought to the brain
by the senses
3. What is Sensation?
A stimulus can be measured
in a variety of ways including
it’s size, duration, intensity, or
wavelength.
A Sensation occurs anytime a
stimulus activates one of your
receptors.
The sense organs then detect
any change in energy, such
as light, heat, sound, and
physical pressure.
4. What is Sensation?
Sensation occurs when special receptors
in the sense organs—the eyes, ears,
nose, skin, and taste buds—are activated,
allowing various forms of outside stimuli to
become neural signals in the brain. (This
process of converting outside stimuli, such
as light, into neural activity is called
transduction.)
5. Sensory systems
Transduction - Communication between the
brain & the rest of the body occurs via neuron.
Information goes from the senses to the
thalamus , then to the various areas in the brain.
All senses involve something called receptor
cells. Their job is to transduce (transform or
even “translate”) physical stimulation/physical
energy from the environment into
electrochemical messages that can be
understood by the brain.
6. Psychophysics
This explains how sensation and
perception are related
Psychophysics: The study of the
relationships between sensory
experiences and the physical stimuli that
cause them!
7. So where do vision and hearing
(& the other senses) happen?
The Brain!
The physical energy in
the environment is
detected by the eyes,
ears, etc. but we can’t
see, hear, etc. until the
brain interprets them—
i.e., makes sense of
them. So in a way, we
see, hear, smell, etc. in
our brains!
8.
9. Absolute Threshold
The Absolute Threshold is the level of
stimulus that produces a positive response
of detection 50% of the time.
the lowest level of stimulation that a
person can consciously detect 50 percent
of the time the stimulation is present.
10. The Absolute Thresholds for the “5” senses
in humans are the following:
1. Vision: Seeing a candle flame 30 miles away
on a clear night.
2. Hearing: Hearing a watch ticking 20 feet
away.
3. Taste: Tasting 1 teaspoon of sugar dissolved
into 2 gallons of water.
4. Smell: Smelling one drop of perfume in a 3
room house.
5. Touch: Feeling a bee’s wing falling a
distance of one centimeter onto your cheek.
11. Weber’s law of just noticeable
differences (jnd, or the difference
threshold).
• The difference threshold is the amount of
change needed for us to recognize that a
change has occurred.
• It’s the smallest difference between two
stimuli that is detectable 50 percent of the
time
• Weber's Law states that “The larger or
stronger the stimulus, the larger the
change required for a person to notice that
anything has happened to it.”
12. Example
• Imagine holding a five pound weight and
one pound was added. Most of us would
notice this difference. But what if we were
holding a fifty pound weight? Would we
notice if another pound were added? The
reason many of us would not is because
the change required to detect a difference
has to represent a percentage. In the first
scenario, one pound would increase the
weight by 20%, in the second, that same
weight would add only an additional 2%.
13. Sensory Adaptation
Adaptation (sometimes called habituation) is a part
of everyday experience. It’s a decreased
responsiveness to stimuli due to constant
stimulation.
We are able to respond to the changes in our
environment because our senses have the ability to
adapt, or adjust themselves, to a constant level of
stimulation.
Once your senses get used to a new level of a
stimulation, they respond only to deviations from it.
14. Examples of Adaptation
1. Your eyes eventually adjust to a
darkened movie theatre. At first you
see blackness, but eventually, you can
see what is going on around you.
2. When you first jump into a pool that
“feels cold” your body reacts to the
stimulus. Eventually, your body
adapts to the sensation and you
become “comfortable.”
3. When you first walk into a sports
locker room, the smell is almost
nauseating. After a while, your senses
adjust and you can hardly tell.
15. Visual Sensation
• Vision is the most studied of all of the senses! Our
most dominating sense.
• There are many parts of an eye but the basic ones
are the cornea, iris, retina, optic nerve and pupil.
• Our eye is stimulated by various wavelengths of
light. The different wavelengths are responsible for
the diversity of colors we see. There are many
other types of waves that our eye cannot detect.
• Light is electromagnetic radiation that travels in
the form of waves. Light is emitted from the sun,
stars, fire, and lightbulbs. Most other objects just
reflect light.
16. People experience light as having three features: color,
brightness, and saturation. The color or hue of light
depends on its wavelength, the distance between the
peaks of its waves.
• The brightness of light is related to intensity or the amount
of light an object emits or reflects. Brightness depends on
light wave amplitude, the height of light waves.
Brightness is also somewhat influenced by wavelength.
Yellow light tends to look brighter than reds or blues.
• Saturation or colorfulness depends on light complexity,
the range of wavelengths in light. The color of a single
wavelength is pure spectral color. Such lights are called
fully saturated. Outside a laboratory, light is rarely pure or
of a single wavelength. Light is usually a mixture of several
different wavelengths. The greater number of spectral
colors in a light, the lower the saturation. Light of mixed
wavelengths looks duller or paler than pure light.
• Wavelength ——> ColorAmplitude ——>
BrightnessComplexity ——> Saturation
18. How does vision occur?
• 1. Light waves enter the eye through the cornea,
a transparent protective structure at the front of
the eye. Behind the cornea is the pupil, The
opening in the iris that regulates the amount of
light entering the eye.
• 2. Light then reaches the lens: A flexible, elastic,
transparent, structure in the eye that changes its
shape to focus light on the retina.
• 3. Light then hits the retina: The innermost
coating of the back of the eye, containing the
light-sensitive receptor cells. The fovea is the
most sensitive area of the retina because it has
the greatest concentration of cones. Rods and
cones are the photoreceptors.
• 4. This light energy is then turned into “neuronal
impulses,” which are sent down the optic nerve:
The nerve that carries impulses from the retina to
the brain.
19. Sensory Receptor Cells
• There are two types of sensory receptor
cells which are located on the retina
– Rods
– Cones
• Rods enable us to see black and white, are
more sensitive to light, and there are 100
million in each eye
• Cones enable us to see color, they work
best in bright light, there are 6.5 million in
each eye and they are located mostly at
the center of the eye
20. Sensory Receptor Cells
• These cells transform light energy into
neural impulses that are sent to various
areas in the brain through the bundle of
neurons called the optic nerve.
• What is the place called in which the optic
nerve leaves the eye?
– The blind spot
• Why is it called “the blind spot”?
– Because there are no rods & cones on this area
(there are neurons instead), images that fall
on this area of the retina are not “seen”!
21. Light/Brightness and Dark
Adaptation
• Dark adaptation occurs as the eye recovers its
ability to see when going from a brightly lit state
to a dark state. (The light-sensitive pigments that
allow us to see are able to regenerate or
“recharge” in the dark.) The brighter the light
was, the longer it takes the rods to adapt to the
new lower levels of light
• When going from a darkened room to one that is
brightly lit, the opposite process occurs. The
cones have to adapt to the increased level of
light, and they accomplish this light adaptation
much more quickly than the rods adapt to
darkness—it takes a few seconds at most (Hood,
1998).
22. Common Visual defects
• Hyperopia/farsight • Color blindness
edness - Totally color blind
• Presbyopia - Partially color blind
• Myopia/nearsighted
ness
• Astigmatism
• Tunnel vision
• Diplopia
• Scotoma
24. Hearing
• Hearing depends on vibrations in the air
called sound waves.
• Sound waves from the air pass through
various bones until they reach the inner
ear, which contains tiny hair like cells that
move back and forth.
• These hair cells change sound vibrations
into neuronal signals that travel through
the auditory nerve to the brain.
25. We hear sound WAVES
• The height of the wave gives us the amplitude of the
sound.
• The frequency of the wave gives us the pitch if the sound.
26. Three parts:
• External or outer ear – Function: Gathering sound
energy and amplification of sound pressure.
-pinna, external meatus, eardrum/tympanic
membrane
• Middle ear Function: Transmission of acoustic
energy from air to the cochlea.
- Hammer, anvil, stirrup
• Inner ear Function: Transformation of mechanical
waves (sound) into electric signals (neural
signals).
– vestibular portion, cochlea, basilar membrane
27. Transduction in the ear
• Sound waves hit the eardrum
then anvil then hammer then
stirrup then oval window.
• Everything is just vibrating.
• Then the cochlea vibrates.
• The cochlea is lined with mucus
called basilar membrane.
• In basilar membrane there are
hair cells.
• When hair cells vibrate they turn
vibrations into neural impulses
which are called organ of Corti.
• Sent then to thalamus up auditory It is all about the vibrations!!!
nerve.
28. Auditory defects =Deafness
• There are 2 types of deafness:
– 1. Conduction Deafness: occurs when
anything hinders physical motion through the
outer or middle ear or when the bones of the
middle ear become rigid and cannot carry
sounds inward. (Can be helped with a
conventional hearing aid.)
– 2. Sensorineural Deafness: Occurs from
damage to the Cochlea, the hair cells, or the
auditory neurons. (Complete Sensorineural
deafness cannot be helped by a hearing aid.)
30. Olfactory/Smelling
Sensation
• Smell depends on sensory receptors that respond
to airborne chemicals.
• In humans, these chemoreceptors are located
in the olfactory epithelium — a patch of tissue
about the size of a postage stamp located high in
the nasal cavity. The olfactory epithelium is made
up of three kinds of cells:
-sensory neurons each with a primary cilium
-supporting cells between them
-basal cells that divide regularly producing a fresh
crop of sensory neurons to replace those that die
32. Disorders of olfaction:
• Anosmia – inability to smell
• Cacosmia – things smell like feces
• Dysosmia – things smell different than they
should
• Hyperosmia – an abnormally acute sense of
smell.
• Hyposmia – decreased ability to smell
• Olfactory Reference Syndrome – psychological
disorder which causes the patient to imagine he
or she has strong body odor
• Parosmia – things smell worse than they should
• Phantosmia – "hallucinated smell," often
unpleasant in nature
33. Gustatory/Taste Sensation
• Gustation - The sensation of taste
– We have bumps on our tongue called papillae.
– Taste buds are located on the papillae (they are actually all
over the mouth).
• Your tongue and the roof of your mouth are
covered with thousands of tiny taste buds. When
you eat something, the saliva in your mouth
helps break down your food. This causes the
receptor cells located in your tastes buds to send
messages through sensory nerves to your brain.
Your brain then tells you what flavors you are
tasting.
36. Sense of touch/Cutaneous or
skin sensation
• Skin - The largest organ of your body
– Performs many important biological functions while also
providing much of what is known as sensual pleasure
• Our sense of touch is controlled by a huge network of
nerve endings and touch receptors in the skin known as
the somatosensory system. This system is responsible for
all the sensations we feel - cold, hot, smooth, rough,
pressure, tickle, itch, pain, vibrations, and more.
3 layers:
– Epidermis - outer layer
– Dermis - intermediate layer
– Deep layers of subcutaneous adipose tissue
38. Pain
• Pain receptors are probably the most important
for your safety because they can protect you by
warning your brain that your body is hurt!
• Pain
– Motivates us to tend to injuries, to restrict activity, and
to seek medical help
– Teaches us to avoid pain-producing circumstances in the
future
• Chronic pain
– Pain that persists for three months or more
– Three common types
• Low-back
• Headache
• Arthritis
39. Skin Senses
• Melzack and Wall
– Gate-control theory
• Contend that there is an area in the spinal cord that
can act like a “gate” and either inhibit pain
messages or transmit them to the brain
• You feel pain when pain messages carried by the
small, slow-conducting nerve fibers reach the gate
and cause it to open
• Contend that messages from the brain to the spinal
cord can inhibit the transmission of pain messages
at the spinal gate and thereby affect the perception
of pain
