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
A Sensation occurs anytime a
stimulus activates one of your
The sense organs then detect
any change in energy, such
as light, heat, sound, and
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
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.
This explains how sensation and
perception are related
Psychophysics: The study of the
relationships between sensory
experiences and the physical stimuli that
8. So where do vision and hearing
(& the other senses) happen?
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
9. Principles of sensation
• Absolute threshold
• Signal detection theory
• Difference threshold
• Weber’s law
• Sensory adaptation
10. 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.
11. 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
3. Taste: Tasting 1 teaspoon of sugar dissolved
into 2 gallons of water.
4. Smell: Smelling one drop of perfume in a 3
5. Touch: Feeling a bee’s wing falling a
distance of one centimeter onto your cheek.
12. Signal detection theory
Signal detection theory is a method of differentiating a
person's ability to discriminate the presence and
absence of a stimulus (or different stimulus intensities)
from the criterion the person uses to make responses to
13. Subliminal stimuli
Subliminal stimulation is sensory stimulation that
is below a person's threshold for perception. It
can't be seen by the naked eye or consciously
14. Weber’s law of just noticeable
differences (jnd, or the difference
• 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
• 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.”
15. Sensory Adaptation
Adaptation (sometimes called habituation) is a part
of everyday experience. It’s a decreased
responsiveness to stimuli due to constant
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
Once your senses get used to a new level of a
stimulation, they respond only to deviations from it.
16. 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
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.
• Our most dominating sense.
• Parts:- cornea, iris, retina, optic nerve and
• Stimulated by various wavelengths of
• The different wavelengths are responsible
for the diversity of colors we see.
• Light is electromagnetic radiation that
travels in the form of waves. Light is
emitted from the sun, stars, fire, and
20. Sensory Receptor Cells
• There are two types of sensory receptor
cells which are located on the retina
• 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
21. 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”!
• 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.
24. Transduction in the ear
Sound waves hit the eardrum then anvil then
hammer then stirrup then oval window.
Everything is just vibrating. Then the
The cochlea is lined with mucus called basilar
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!!!
25. 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.)
• Smell depends on sensory receptors that respond
to airborne chemicals.
• In humans, these chemoreceptors are located
in the olfactory epithelium.
• 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
28. Disorders of olfaction:
• Anosmia – inability to smell
• Cacosmia – things smell like feces
• Dysosmia – things smell different than they
• Hyperosmia – an abnormally acute sense of
• 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
29. Gustatory/Taste Sensation
• Gustation - The sensation of
– We have bumps on our tongue called
– Taste buds are located on the
papillae (they are actually all over
32. Sense of touch/Cutaneous or
• Skin - The largest organ of your
• Our sense of touch is controlled by
a huge network of nerve endings
and touch receptors in the skin
known as the somatosensory
• This system is responsible for all
the sensations we feel - cold, hot,
smooth, rough, pressure, tickle,
itch, pain, vibrations, and more.
• Pain receptors are probably the most important for
your safety because they can protect you by
warning your brain that your body is hurt!
– Motivates us to tend to injuries, to restrict activity, and to
seek medical help
– Teaches us to avoid pain-producing circumstances in the