Sense and percept

Introduction to
Sensation & Perception
Cleoputri Yusainy, PhD
Sensing the world
 To
study sensation is to study an ageless
question: How does the world out there
get represented in here, inside our heads?
 Sensation is the conversion of energy from
the environment into a pattern of
response by the nervous system  the
registration of information.
 Perception is the interpretation of that
How far do you think
can an ant see?
 Depending
on how far
the light travels.
 Anything that stimulates
the optic nerve is
perceived as light.
In or out?
 “When
we look at someone or something,
does anything such as rays, waves, or
energy go out of our eyes? Into our
 How your eyes work
1. Vision
Light enters the eye through
the pupil. It is focused by the
lens and cornea and
projected onto the retina.
The retina’s visual receptors
(light-sensitive rods and colorsensitive cones) convert the
light energy into neural
Neural impulses are coded by
the retina before traveling
along the optic nerve to the
“If we went to some other planet,
would we see different colors?”
Young-Helmholtz trichromatic (three-color) theory
suggests that the retina contains three types of cones.
Each is most sensitive to the wavelengths of one of the
three primary colors of light (red, green, or blue).
 After
staring at something blue, you get a
yellow afterimage. After staring at yellow,
you see blue; after red, you see green;
after green, you see red; after white,
black; and after black, white → Negative
color afterimage.
 The nervous system codes the colorrelated information from the cones into
pairs of opponent colors → Opponentprocess theory.
2. Hearing
When sound waves strike the
eardrum (a), they cause it to
vibrate three tiny bones
(hammer, anvil, and stirrup)
that convert the sound waves
into stronger vibrations in the
fluid-filled cochlea (b). Those
vibrations create movement
in tiny hair cells, triggering
neural messages to the brain.
3. Touch
 Four
basic skin senses: pressure, warmth, cold,
and pain.
 Pain is an alarm system that draws our
attention to some physical problem.
 A person’s experience of pain can be seen
as the sum of:
Biological influences, ex. nerve fibers sending
messages to the brain;
Psychological influences, ex. the situation and our
past experiences;
Social-cultural influences, ex. cultural expectations
and the presence of observers.
1. Vision
2. Hearing
3. Touch
 Suppose
4. Taste
5. Smell
6. Kinesthesis
you had the godlike power to
create a new species of animal, but you
could equip it with only one sensory system.
Which sense would you give it?
 Now imagine that you have to choose one
of your senses to lose. Which one will it be?
4. Taste
Taste, a chemical sense, is a composite of five basic
sensations: sweet, sour, salty, bitter, and umami.
Taste buds contain
taste receptor cells.
The influence of smell
on our sense of taste is
an example of sensory
5. Smell
 Like
taste, smell is a chemical sense, but there
are no basic sensations for smell.
 For most mammals, olfaction (the sense of
smell) is critical for finding food and mates and
for avoiding dangers.
 An odor’s ability to spontaneously evoke
memories and feelings is due to the close
connections between brain areas that process
smell and those involved in memory storage.
 Why
do we have brains at all?
Plants and sponges survive just
fine without them.
 A sea squirt (a marine
invertebrate) swims and has a
brain during its infant stage, but
when it transforms into an adult,
it becomes a stationary filter
feeder and eats its own brain!
 Ultimately, the purpose of a
brain is to control behaviours,
and behaviours are movements.
6. Kinesthesis
 Organizing
a movement is not something
we do at the end of our thinking. It is
intimately intertwined with all of our sensory
and cognitive processes.
 By means of millions of position and motion
sensors all over our body, our kinesthetic
sense monitors the position and movement
of our individual body parts.
Sensation & perception
 Our
senses detect physical energy from
the environment and encode it as neural
signals → Sensation
 Aided by knowledge and expectations,
our brain perceives meaning in these
signals → Perception
 Is the link between sensation and
perception ever simple?
Visual capture
 Conflict
between visual and other sensory
information is usually resolved with the
mind’s accepting the visual data, a
tendency known as visual capture.
 But can you trust your eyes?
Perception & attention
 The
monkey business
 We selectively attend to, and process, a limited
number of the data bombarding our senses and
block out the others. This focused attention can
result in inattentional or change blindness, and
even choice blindness.