CHAPTER 4
SENSATION AND PERCEPTION
Introduction
To consider how psychologists understand
the senses, and more broadly, sensation and perception, we have to first
define:
SENSATION
Sensation
is the activation of sense organ using physical energy that processes the
receiving of stimulus from the external environment.
PERCEPTION
These are
meaningful sensory experiences that result after the brain combines hundreds of
sensations. (Plotnik, et.al, 2008) Perception
is the sorting out, interpretation, analysis and integration of stimuli carried
out by the sense organs and brain (Feldman, 2010).
PSYCHOPHYSICS
This is the study
of the relationship between the physical aspects of stimuli and our
psychological experience of them (Feldman,2010).
In this chapter, we
will discuss six of the major human senses--- vision, hearing, balance
(vestibular system), taste, olfaction (smell) and touch.
Your eyes, ears,
nose, skin and tongue are complex, miniaturized, living senses that
automatically gather information about your environment. These three definitions
will help you understand sensation.
Transduction
It refers to the
process in which a sense organ changes, or transforms, physical energy into
electrical signals that become neural impulses, which may be sent to the brain
for processing
(Plotnik, et al., 2008).
Adaptation
Adaptation refers
to the decreasing response of the sense organs, the more they are exposed to a
continuous level of stimulation (Plotnik, et al., 2008)
THE SCIENCE OF SEEING: Perceptual
Properties of Light (White, 2009)
Light
is a complicated phenomenon. When people experience light, they are really
aware of its dual nature. There are three aspects to the perception of light:
brightness, color, saturation.
A. Brightness
Brightness is
determined by the amplitude of the wave—how high or how low the wave actually
is. The higher the wave, the brighter the light appears to be. Low waves are
dimmer.
B. Color or Hue
It is determined by
the length of the wave. Long wavelengths are found at the red end of the
visible spectrum (the portion of the whole spectrum of the light that is
visible to the human eye) whereas shorter wavelengths are found at the blue
end.
C. Saturation
It refers to the
purity of the color people receive: a highly saturated red, for example, would
contain only red wavelengths, whereas, a less saturated red might contain a
mixture of wavelengths.
For
example, if the child is using the red paint from a set of poster paints, the
paint on the paper will look a pure red, but if the child mixes in some white
paint, it will look pink.
The
hue is still red but it will be less of a saturated red because of the presence
of white wavelengths. Mixture in black or gray would also lessen the
saturation.
THE STRUCTURE OF THE EYE:
Parts of the Eye (Plotnik,et al.,
2008/ White, 2009)
The
surface of the eye is covered in a clear membrane called the cornea. It
is the rounded, transparent covering over the front of your eye. As the light
waves pass through the cornea, its curved surface bends, or focuses the waves
into a narrower beam.
The
next visual layer is a clear, watery fluid called the aqueous humor.
This fluid is continually replenished and supplies nourishment to the eye.
The
light from the visual image then enters the interior of the eye through a hole,
called the pupil in a round muscle called the iris (the colored
part of the eye). The iris controls the amount of light entering the eye.
Behind
the iris, suspended by muscles, is another clear structure called the lens.
The flexible lens finishes the focusing process begun by the cornea and
changes its shape from thick to thin in a process called VISUAL ACCOMODATION,
which allows the eye to focus on objects that are close or far away.
Retina,
located at the very back of the eyeball, is a thin film that contains cells
that are extremely sensitive to light. These light-sensitive cells, called
photoreceptors, begin the process of transduction by absorbing light waves.
Rods
and Cones are the business end of the retina. Rods are receptors of the
retina that are sensitive to light, but they are not very useful for color
vision. Humans have 120 million rods. Cones are receptors of the retina that we
use for color perception. Like the rods, cones are light sensitive.
However,
they require a larger amount of light that the rods do to respond so they
operate best in daylight or under high illumination. There are about 6 million
cone cells in human eyes
(Santrock, 2005).
Because
rods work well in low levels of light, they are also the cells that allow the
eyes to adapt to low light.
Dark
Adaptation occurs as the eye recovers its ability to see when going from a
brightly lit state to a dark state.
Light
Adaptation on the other hand is the recovery of the eye’s sensitivity to visual
stimuli in light after exposure to darkness.
THE BLIND SPOT
This is the area in
the retina where the axons of the three layers of retinal cells exit the eye to
form the optic nerve, insensitive to light.
Nerve
impulses
that are generated in the ganglion cells exit the back of the eye through the optic
nerve, which carries impulses toward the brain. The point where the optic
nerve exits the eye has no receptors and is called the blind spot. At
this point, there are no rods and cones here. You do not notice the blind spot
because your eyes are continually moving.
Color Blindness
It is caused by
defective cones in the retina of the eye.
Kinds of Color Blindness:
- Monochrome Color Blindness- people either have no cones or have cones that are not working at all.
- Red-Green Color Blindness- People with this kind of color blindness, either their red or their green cones are not working. They would see the world in blues, yellow and shades of gray. If blue cones are not working, which is less common, they see reds, greens and shades of gray. (Ciccarelli, et al., 2009)
THE HEARING SENSE: PERCEPTION OF SOUND
Although many of us
think primarily of the outer ear when we speak of the ear, that structure is
only one simple part of the whole. The outer ear acts as reverse megaphone,
designed to collect and bring sounds into the different internal portions of
the ear.
The
location of outer ears on different sides of the head helps with SOUND
LOCALIZATION, the process by which we identify the direction from which a sound
is coming.
Wave
patterns in the ear enter each at a slightly different time, and the brain uses
as discrepancy as a clue to the sound’s point origin. (Feldman, 2010)
TERMS TO REMEMBER: (Ciccarelli et al.,
2009/ Plotnik et al., 2008)
Loudness-It refers to the sounds’ intensity
Pitch- It is the subjective experience of
a sound being high or low, which the brain calculates from specific physical
stimuli.
Decibel- This is the unit to measure
loudness. Our threshold for hearing ranges from 0 decibels, which is absolutely
no sound, to 140 decibels, which can produce pain and permanent hearing loss.
Volume- how soft or loud a sound is
Timbre- richness in the tone of the sound
Hertz (Hz)- cycles or waves per sound, a
measurement of frequency
THE STRUCTURE AND FUNCTIONS OF THE EAR
A. OUTER EAR
The outer ear consists of three
structures: the external ear, the auditory canal and the tympanic membrane. It
consists of PINNA, the outer, visible part of the ear that serves as a kind of
concentrator, funneling the sound waves from the outside into the structure of
the ear.
The pinna is also
the entrance to the AUDITORY CANAL (or ear canal), the short tunnel that runs
down to the TYMPANIC MEMBRANE or eardrum. When the sound waves hit the eardrum,
they cause three tiny bones in the middle ear to vibrate (Ciccarelli, et al.,
2009).
B. MIDDLE EAR
The
middle ear channels the sound through the eardrum, hammer, anvil and stirrup to
the inner ear.
The
middle ear is a tiny bone cavity that is sealed at each end by membranes. It
picks up and increases or amplifies vibrations.
The
three tiny bones are collectively called OSSICLES. When the tympanic membrane
vibrates, so does the hammer. In turn,
the HAMMER sends vibrations to the attached ANVIL, which further sends the
vibrations to the attached STIRRUP. The stirrup makes the connection with the
end membrane, the oval window. The three ossicles act like levers that greatly
amplify vibrations, which in turn, cause the oval window to vibrate. (Plotnik,
et.al. 2008)
C. INNER EAR
The functions of
the inner ear, which includes
the oval window, the cochlea and the
basilar membrane, is to transduce sound waves into neural impulses and send
them to the brain.
·
The
OVAL WINDOW transmits sound waves to the cochlea.
·
The
COCHLEA, is a tubular fluid-filled structure that is coiled up like a snail. It
contains receptors for hearing and its function is transduction—transforming
vibrations into nerve impulses that are sent to the brain for processing into
auditory information.
·
The
BASILAR MEMBRANE lines the inner wall of the cochlea and runs its entire
length. (Santrock, 2005).
THEORIES
OF HEARING
- Place Theory (Herman von Helmholtz, 1863)- states that each frequency produces vibrations at a particular spot on the basilar membrane.
In this theory, the
pitch a person hears depends on where
the hair cells that are stimulated are located in the Organ of Corti.
- Frequency Theory (Ernest Rutherford, 1886)- states that pitch is related to how fast the basilar membrane vibrates.
The faster this
membrane vibrates, the higher the pitch;
the slower it vibrates, the lower the pitch. (CIccarelli, et al., 2009)
TYPES OF HEARING IMPAIRMENTS (CIccarelli,
et al., 2009)
- Conduction Hearing Impairment- means that sound vibrations cannot be passed from eardrum to the cochlea. The caused might be a damaged eardrum or damage to the bones of the middle ear (usually from an infection).
In this kind of
impairment, hearing aids maybe of some
use in restoring hearing.
- Nerve Hearing Impairment- the problem lies either in the inner ear or in the auditory pathways and cortical areas of the brain.
Normal aging causes
loss of hair cells in the cochlea and
exposure to loud noises which can damage hair cells. TINNITUS
refers for an extremely annoying ringing in one’s
ears, and it can also be caused by infections
or loud noises.
CHEMICAL SENSES: It Tastes Good, It Smells
Terrible
A. Gustation
TASTE BUDS (name
for taste receptors) are specialized kinds of neurons found in the mouth that
are responsible for the sense of taste or gestation.
Each
taste bud has about 20 receptors that are very similar to the receptor sites on
receiving neurons at the synapse.
THE FIVE BASIC TASTES
- Sweet
- Sour
- Salty
- Bitter
- Umami (glutamate)
Glutamate not only exists in chicken soup,
tuna, cheese, etc., but also in human breast milk.
The
five taste sensations work together, along with the sense of smell and the
texture, temperature and “heat” of foods, to produce thousands of taste
sensations (CIccarelli, et al., 2009).
Taste is often called as a CHEMICAL
SENSE because it works with the molecules of foods people eat in the same
way the neural receptors work with neurotransmitters.
THE SENSE OF SCENTS: OLFACTION
Olfaction
is called a chemical sense because its stimuli are various chemicals that are
carriedby the air. The upper part of the nose has a small area that contains
receptor cells for olfaction.
The
function of olfactory receptors is transduction, to transform chemical
reactions into nerve impulses (Plotnik, et. al., 2008).
OLFACTORY
RECEPTOR CELLS
These cells have
about a half dozen to dozen little “hairs” that project into the cavity. These
hairs are called CILIA.
Olfactory receptors
also have to be replaced as they naturally die off, every 5 to 8 weeks. Unlike
the taste buds, there are more than 5 types of olfactory receptors. In fact,
there are at least 1,000 of them (CIccarelli, et al., 2009).
THE
OLFACTORY BULB
These
are located right on top of the sinus cavity on each side of the brain directly
beneath the frontal lobes.
The
olfactory receptors send their neural signals directly up to these bulbs, by
passing the entire lower brain and its selective attention filter, the
reticular formation.
SOMETHETIC SENSES (“soma”-body/“esthetic”-
feeling)
(CIccarelli, et al., 2009)
A. The Skin Senses: Touch, Pressure and
Temperature
Skin
is the body’s largest organ. It receives and transmits information from the
outside world to the central nervous system.
Sensory Receptors in the Skin
There are about
half a dozen different receptors in the layers of the skin.
1. Pacinian Corpuscles
These
can be found beneath the skin and respond to pressure only.
2. Free Nerve Endings
They
are located just beneath the uppermost layer of the skin that responds to
changes in temperature and to pressure and to pain.
Types
of Pain:
- Visceral Pain- The receptors that detect pain (and pressure) in the organs
- Somatic Pain- Large nerve fibers that carry pain sensations in the skin, muscles, and tendons. Somatic pain is the body’s warning system that something is being damaged.
GATE-CONTROL THEORY OF PAIN (Melzack
,1960/Wall ,1965) – states that the spinal column contains a neural gate that
can be opened (allowing the perception of pain) or closed (blocking the
perception of pain).
B. The Kinesthetic Sense
This is processed by
a proprioceptive receptors in skin, joints, muscles and tendons. Kinesthesia
comes from the Greek words kenein (to move) and aesthesis (sensation).
When
you close your eyes and raise your hand above your head, you know where your
hand is because the proprioceptors tell you about the changes in pressure
within the muscles (CIccarelli, et. al., 2009).
C. The Vestibular Sense (from the Latin word
meaning
“entrance”
or “chamber”)
This
is processed by vestibular organs that convey information about movement and
body position. There are two kinds of vestibular organs: (1) the otolith organs
and the (2) semicircular canals.
1. Otolith Organs- tiny sacs found
above the cochlea. These sacs contain gelatin-like fluid within which tiny
crystals are suspended. The head moves and the crystals cause the fluid to
vibrate, setting off some tiny hairlike receptors on the inner surface of the
sac, telling the person that he or she is moving forward, backward, sideways,
up or down.
2. Semicircular Canals- circular tubes
that are filled with fluid and stimulate hairlike receptors when rotated. These
are located in the inner ear; contains the sensory receptors that detect head
motion.
PERCEPTUAL ORGANIZATION
Psychologists
distinguish between bottom-up and top-down processing in sensation and
perception
A. Bottom-Up Processing
The
sensory receptors register information about the external environment and send
it up to the brain for analysis and interpretation. Bottom-up processing is
initiated by stimulus input.
B. Top-Down Processing
It
starts out with cognitive processing at the higher levels of the brain. These
cognitive processes include knowledge, beliefs and expectations. Thus, top-down
processing does not start with the detection of stimulus, as bottom-up
processing does.
Absolute Thresholds
This is the
smallest intensity of a stimulus that must be present for it to be detected.
Our senses are extremely responsive to stimuli. For example, our sense of touch is so sensitive that we can feel
a bee’s wing falling on our cheeks when it is dropped from a distance of one
centimeter (Feldman, 2010).
Differential Thresholds
It is the smallest
level of added (or reduced) stimulation required to sense that a change in
stimulation has occurred. Thus, the differential threshold is the minimum
change in stimulation required to detect the difference between two stimuli and
so it is also called as JUST NOTICEABLE DIFFERENCE (JND).
The
stimulus value that constitutes a just noticeable difference depends on the
initial intensity of stimulus. The relationship changes in the original value
of a stimulus and the degree to which the stimulus will be noticed forms one of
the basic laws of psychophysics: Weber’s Law (with Weber pronounced as
“vay-ber”) states that a just noticeabale difference is in a CONSTANT
PROPORTION of the intensity of an initial stimulus (Feldman, 2010).
THE CONSTANCIES: SIZE, SHAPE AND BRIGHTNESS
A. PERCEPTUAL
CONSTANCY (Ciccarelli, et al.,
2009)
Perceptual
constancy is a phenomenon in which physical objects are perceived as unvarying
and consistent despite changes in their appearance or in the physical
environment.
One
good example for this involves the rising moon.
This type of constancy applies not just to size but to shape and color as
well (Feldman, 2010).
- Size constancy- the tendency to interpret an object as always being the same actual size regardless of its distance.
- Shape constancy- The tendency to interpret the shape of an object as being constant, even when its shape changes on the retina.
- Brightness constancy- The tendency to perceive the apparent brightness of an object as the same even when the light conditions change.
THE GESTALT PRINCIPLES
1. Figure-Ground Relationships
It
refers to the tendency to perceive objects or figures as existing on a
background.
2. Proximity
This
is the tendency to perceive objects that are close to each other as part of the
same grouping.
3. Similarity
It
refers to the tendency to perceive things that look similar as being part of
the same group.
4. Closure
This
is the tendency to complete figures that are incomplete.
5. Continuity
The
principle of continuity is easier to see than it is to explain in words. It
refers to the tendency to perceive things as simply as possible with a
continuous pattern rather than with a complex, broken-up pattern.
6. Contiguity
This
is the tendency to perceive two things that happen close together in time as
being related. Usually, the first occurring event is seen as causing the second
event.
There
are various cues for perceiving depth in the world. Some require the use of
only one eye (MONOCULAR CUES) and some are a result of the slightly different
visual patterns that exist when the visual fields of both eyes are used
(BINOCULAR CUES) (Ciccarelli, et al., 2009).
A. MONOCULAR CUES
Monocular
cues are often referred to as PICTORIAL DEPTH CUES because artists can use
these cues to give illusion of depth to paintings and drawings.
1. Linear Perspective
This
tendency for lines that is actually parallel to seem to converge on each other.
It works in picture, as in real life, the converging lines indicate that the
“end” of the lines are a great distance away from where the people are as they
view them.
2. Relative Size
This
is the perception that occurs when objects that a person expects to be of a
certain size appear to be small and are, therefore assumed to be much farther
away.
3. Overlap (Interposition)
The
assumption that an object appears to be blocking part of another object is in
front of the second object and closer to the viewer.
4. Aerial (atmospheric) perspective
The
haziness that surrounds objects that is farther away from the viewer, causing
the distance to be perceived as greater.
5. Texture gradient
This
is the tendency for texture surfaces to appear to become smaller and finer as
distance from the viewer increases. This is another trick used by artists to
give illusion of depth in painting.
6.
Motion Parallax
This
is the perception of motion of objects in which close objects appear to move
more quickly than objects that is farther away.
7. Accommodation
As
a monocular cue, the brain’s use of information about the changing thickness of
the lens of the eye in response to looking at objects that are close or far
away.
B. BINOCULAR CUES
1. Convergence
It
refers to the rotation of the two eyes in their sockets to focus on a single
object. If the object is close, the convergence is pretty great. If the object
is far, the convergence is much less.
2. Binocular Disparity
This
is the scientific way of saying that because the eyes are a few inches apart,
they don’t see exactly the same image.
This
is also the difference in images between the two eyes, which is greater for
objects that are close and smaller for distant objects.
PERCEPTUAL ILLUSIONS: THE DECEPTIONS OF
PERCEPTIONS
ILLUSION- this is a perception that does
not correspond to reality; visual stimuli that “fool” the eye.
1. Visual Illusions
These
are physical stimuli that consistently produce errors in perception.
A. Muller- Lyer Illusion
This
is the most common type of visual illusion where the eye movements are greater
when the arrow tips point inward, making us perceive the line as longer than it
is when the arrow tips face outward (Feldman, 2010).
B. The Moon Illusion
In
which the moon in the horizon appears to be much larger than the moon in the
sky with no cues for depth surrounding it (Ciccarelli, et al., 2009).
THINKING CRITICALLY ABOUT ESP
Extra
Sensory Perception (ESP) is defined as a claim of perception that occurs
without the use of normal sensory channels such as sight, hearing, taste, touch
or smell.
PARAPSYCHOLOGY
It is the
scientific study of ESP, ghosts and all things that do not normally fall into
the realm of ordinary psychology (Ciccarelli, et al., 2009).
KINDS OF ESP
1. Telepathy (“distant feeling”)
This
is commonly used to refer to the claimed ability to read another person’s
thoughts, or mind reading
2. Clairvoyance (“clear sight”)
This
is the supposed ability to “see” things that are not actually present.
3. Precognition
This
is the supposed ability to know something in advance of its occurrence or to
predict future events.
4.
Psychokinesis
This is the ability
to affect the physical world purely through thought.
5.
Astral Projection
The astral body
leaves the physical.
These are physical stimuli that
consistently produce errors in perception.
- MULLER- LYER ILLUSION
The most common type of visual
illusion where the eye movements are greater when the arrow tips point inward,
making us perceive the line as longer than it is when the arrow tips face
outward. (Feldman, 2010)
- THE MOON ILLUSION
In which the moon in the horizon
appears to be much larger than the moon in the sky with no cues for depth
surrounding it. (Ciccarelli, et.al. 2009)
- ILLUSION OF MOTION (Ciccarelli, et.al. 2009)
Sometimes people perceive that the
object is moving when it is really still.
- Auto-kinetic effect
- Stroboscopic motion
- Phi phenomenon
THINKING
CRITICALLY ABOUT ESP
Extra Sensory Perception (ESP) is defined as a claim of perception
that occurs without the use of normal sensory channels such as sight, hearing,
taste, touch or smell.
PARAPSYCHOLOGY
It is the
scientific study of ESP, ghosts and all things that do not normally fall into
the realm of ordinary psychology. (Ciccarelli, et.al. 2009)
KINDS OF ESP
1. Telepathy (“distant feeling”)
Commonly used to refer to the
claimed ability to read another person’s thoughts, or mind reading
2. Clairvoyance (“clear sight”)
The supposed ability to “see”
things that are not actually present
3. Precognition
The supposed ability to know
something in advance of its occurrence or to predict future events
4.
Psychokinesis
This is the ability
to affect the physical world purely through thought.
5.
Astral Projection
The astral body
leaves the physical.
