Transcript What we*ll sense and perceive* in this chapter:

What we’ll sense and perceive…
in this chapter:
 Sense:
 especially vision and hearing
 smell, taste, touch, pain, and
awareness of body position
 How do the sense organs and
nervous system handle incoming
sensory information?
 How does the brain turn sensory
information into perceptions?
 Why is our style of creating
perceptions better at perceiving
the real world than at decoding
tricky optical illusions?
Basic Principles of
Sensation and
Perception
Your brain will interpret, perceive
these topics as they enter your
sense organs:
 Sensation vs. Perception, BottomUp vs. Top-Down Processing
 Transduction and Thresholds
 Sensory Adaptation
 Perceptual Set
 Context Effects on perception
 Emotion/Motivation effects
DO NOW
What is the difference between sensation
and perception?
What is the difference between Bottom-up
and Top-down Processing?
Sensation vs. Perception
Sensation
“The process by which our
sensory receptors and
nervous system receive and
represent stimulus energies
from our environment.”
The brain
receives input
from the
sensory organs.
Perception
“The process of organizing
and interpreting sensory
information, enabling us
to recognize meaningful
objects and events.”
The brain makes
sense out of the
input from
sensory organs.
Making sense of the world
What am I
seeing?
Bottom-up
processing:
taking sensory
information and
then assembling
and integrating it
Top-down
processing:
using models,
ideas, and
expectations to
interpret sensory
information
Is that
something I’ve
seen before?
Top-down
Processing
You may start
to see
something in
this picture if
we give your
brain some
concepts to
apply:
“tree”
“sidewalk”
“dog”
“Dalmatian”
From Sensory Organs to the Brain
The process of sensation can
be seen as three steps:
Reception-the stimulation
of sensory
receptor cells by
energy (sound,
light, heat, etc)
Transduction-transforming
this cell
stimulation into
neural impulses
Transmission-delivering this
neural
information to
the brain to be
processed
Thresholds
The absolute threshold: the
minimum level of stimulus
intensity needed to detect a
stimulus half the time.
Anything below this
threshold is considered
“subliminal.”
When Absolute Thresholds
are not Absolute
Signal detection theory
refers to whether or not we
detect a stimulus, especially
amidst background noise.
This depends not just on
intensity of the stimulus but
on psychological factors
such as the person’s
experience, expectations,
motivations, and alertness.
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Subliminal Detection
Subliminal:
below our threshold for
being able to consciously
detect a stimulus
 Although we cannot learn complex
knowledge from subliminal stimuli,
we can be primed, and this will
affect our subsequent choices.
 We may look longer at the side of
the paper which had just showed a
nude image for an instant.
The “Just Noticeable Difference”
 Difference threshold: the minimum difference (in
color, pitch, weight, temperature, etc) for a person to
be able to detect the difference half the time.
 Weber’s law refers to the principle that for two
stimuli to be perceived as different, they must differ
by a minimum percentage:
 2 percent of weight
 8 percent of light intensity
 0.3 percent of sound wave frequency to notice a
difference in pitch.
 Any changes noticeable on this slide?
Sensory Adaptation
 To help detect novelty in our
surroundings, our senses
tune out a constant stimulus,
such as:
 a rock in your shoe
 the ticking of a clock
 If you concentrate on
keeping your eyes in one
spot, you’ll see the effects,
as your eyes adjust to stimuli
 Visual sensory adaptation
will be tested when
discussing opponent-process
theory.
Perceptual Set
Perceptual set is what we expect to see, which influences
what we do see.
Perceptual set is an example of top-down processing .
Loch Ness monster
or a tree branch?
Flying saucers
or clouds?
Perceptual set can be “primed.”
Ambiguous
Old woman
Young woman
Context Effect on Perception
In which picture does the center dot look larger?
Perception of size depends on context.
Spelling test answers:
double pear
payee pair
apple payor
Did context affect which word you wrote?
Effect of Emotion, Physical State, and
Motivation on Perception
Experiments show that:
 destinations seem farther
when you’re tired.
 a target looks farther
when your crossbow is
heavier.
 a hill looks steeper with a
heavy backpack, or after
sad music, or when
walking alone.
 something you desire
looks closer.
Vision, and Perceptual Organization
and Interpretation
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Topics we’ll be looking into:
Vision (Sensation):
Visual Organization:
The Eye
 Form, Depth, and Motion
Perception
From light input to mental
images
 Size, Shape, and Color
Constancy
Retina and Receptors
 Visual Interpretation:
Feature Detection
 Restored Vision
Parallel Processing
 Perceptual Adaptation
Color Vision
And: ESP, Perception without Sensation
Vision:
Energy, Sensation,
and Perception
The
Visible
Spectrum
We encounter waves
of electromagnetic
radiation.
Our eyes respond to
some of these waves.
Our brain turns these
energy wave
sensations into colors.
Color/Hue and
Brightness
We perceive the
wavelength/frequency of
the electromagnetic
waves as color, or hue.
We perceive the
height/amplitude of
these waves as
intensity, or
brightness.
The Eye
 Light from the candle passes through the cornea and the
pupil, and gets focused and inverted by the lens. The
light then lands on the retina, where it begins the
process of transduction into neural impulses to be sent
out through the optic nerve.
 The lens is not rigid; it can perform accommodation by
changing shape to focus on near or far objects.
The Retina
The Blind
Spot
 There is an area of missing information
in our field of vision known as the blind
spot. This occurs because the eye has no
receptor cells at the place where the
optic nerve leaves the eye.
 To test this, walk slowly up to the screen
with one eye closed and the other eye
fixed on the dot, and one of the phones
will disappear.
Photoreceptors: Rods and Cones
 When light reaches the back of the retina, it triggers
chemical changes in two types of receptor cells:
 Rods help us see the black and white actions in our
peripheral view and in the dark.
 Cones help us see sharp colorful details in bright light.
Visual Information Processing
The rods and cones send messages to ganglion and
bipolar cells and on to the optic nerve.
Once neural signals enter the optic nerve, they are sent
through the thalamus to the visual cortex.
The images we
“see” are not
made of light;
they are made of
neural signals
which can be
produced even
by pressure on
the eyeball.