Chapter 8
Sensation and
Perception
Section 1: Sensation
• Sensation and perception are needed to
gather and interpret information in our
surroundings.
• Any aspect of or change in the environment
to which an organism responds is called a
stimulus.
– A sensation occurs anytime a stimulus activates
one of your receptors.
– The sense organs detect physical changes in
energy such as heat, light, sound, and physical
pressure.
• A sensation may be combined with other
sensations and your past experience to yield
a perception.
• Psychologists are interested in the
relationship between physical stimuli and
sensory experiences.
– This study is called psychophysics.
– The goal is to understand how stimuli from the
world affect the sensory experiences.
• In order to establish laws about how people
sense the external world, psychologists first
try to determine how much of a stimulus is
necessary for a person to sense it at all. This
is called the threshold.
– Absolute threshold: the weakest amount of a
stimulus required to produce a sensation.
• In humans, the absolute threshold in the five
senses are:
– Vision: seeing a candle flame 30 miles away on a
clear night
– Hearing: hearing a watch ticking 20 feet away
– Taste: tasting 1 teaspoon of sugar dissolved in 2
gallons of water
– Smell: smelling I drop of perfume in a 3 room
house
– Touch: feeling a bee’s wing falling a distance of 1
centimeter onto your cheek
** Humans sense a somewhat limited range of the physical phenomena in the everyday world.
• Weber’s Law: the larger or stronger a
stimulus, the larger the change required for a
person to notice that anything has happened.
– Backpack example
• Senses are most responsive to increases and
decreases, and to new events rather than to
ongoing, unchanging stimulation.
– Movie theater example
Section 2: The Senses
• Vision
– Is the most studied of all the senses
– Provides us with a great deal of information about
our environment
– It works by:
• Light entering the eye through the pupil where it reaches
the lens that focuses the light onto the retina
• The photoreceptor cells (rods and cones) change the
light energy into impulses that travel to the brain by way
of the optic nerve
– When a person’s cones do not work properly, he/she is
said to be color-deficient (color blind)
– Binocular vision
• Because we have two eyes, we see two images that
combine to produce one complete image (binocular
fusion)
• Difference between the images is called retinal disparity
– Essential for depth perception
» The greater the difference, the closer the object
• Hearing
– Depends on the vibrations of the air, called sound
waves, which passes through various bones until
they reach the inner ear where hair like cells
change the sound vibrations into signals that
travel to the brain through the auditory nerve
– 2 Types of Deafness
• Conduction – something hinders the motion through the
outer or middle ear or when the bones become rigid and
can not carry sounds – can be helped with hearing aids
• Sensorineural – damage to the cochlea, hair cells, or the
auditory neurons – can be helped with cochlear implants
• Smell and Taste
– Known as chemical senses because they are
sensitive to chemical molecules
– Gaseous molecules travel up the nose to the
receptors that send messages to the brain through
the olfactory nerve
– Liquid chemicals stimulate receptors in the taste
buds, sending information to the brain
• Four primary sensory experiences are sour, salty, sweet,
and bitter
– The combination of taste, smell, and tactile
sensations is known as flavor
• Touch (skin senses)
– Receptors in the skin provide the brain with at
least four kinds of information about the
environment : pressure, warmth, cold, and pain
– Gate control theory of pain
• We can lessen some pains by shifting our attention away
from the pain impulses or by sending other signals to
compete with the pain signals
Section 3: Perception
• Perception: brain receives information from
the senses and organizes & interprets it into
meaningful experiences
• The brain makes sense of the world by
creating whole structures out of bits and
pieces of information – each whole created
by the brain is called a Gestalt.
– The principles that people use in organizing such
patterns are:
• Proximity – group together elements that are close
together
• Continuity – see smooth, continuous contours
• Similarity – group together elements that are similar in
appearance
• Simplicity – perceive a pattern in the simplest form
• Closure - group according to enclosed or completed
figures
• Perceiving is something that people learn to
do.
• Experiments show that active involvement in
one’s environment is important for accurate
perception.
• Learning to perceive is influenced by our
needs, beliefs, and expectations.
– “When we want to see something, we are more
likely to see it.”
• Hungry people experiment
• Constancy
– When we have learned to perceive certain objects
in our environment, we tend to see them in the
same way, regardless of changing conditions.
• Illusions
– Incorrect perceptions created when perceptual
cues are distorted so that our brains cannot
correctly interpret space, size, and depth cues.
• Extrasensory perception (ESP)
– Receiving information about the world through
channels other than the normal senses
– Four types of ESP
• 1) clairvoyance – perceiving objects or information
without sensory input
• 2) telepathy – reading someone else’s mind or
transferring one’s thoughts
• 3) psychokinesis – moving objects through purely mental
effort
• 4) precognition – ability to foretell events
– Scientists have been investigating ESP since the
1900’s.
– Most people claiming to have ESP have been
proven to be frauds.