CHAPTER 4
Sensation & Perception
Lecture Overview
• Introduction to
Sensation & Perception
• Understanding Sensation
• How We See and Hear
• Our Other Senses
• Understanding
Perception
Sensation and Perception
• Sensation
– process of receiving, converting, and transmitting
raw sensory information from the external and
internal environments to the brain
• Perception
– process of selecting, organizing, and interpreting
sensory information
Sensation Versus Perception
• When you stare at the
cube on the left, which
area is the top, bottom,
or back?
• In the figure on the
right, is this a young
woman looking to the
right, or an older
woman with her chin
buried in her jacket?
Sensation Vs. Perception
SENSATION
Processing
• Processing
– sensory organs contain
receptors that receive
sensory information
from the environment
Processing
• Three Types of Processing:
– Transduction:
• Converts sensory stimuli into neural impulses
– Sensory reduction:
• Filters/analyzes incoming sensations before sending to
the brain
– Coding:
• Converts sensory input into a specific sensation sent to
the brain
Processing
• All processing
occurs at the
sensory level and
messages are
then sent on to
the brain.
Thresholds
• Psychophysics: Testing limits and changes
– Absolute Threshold:
• smallest amount of a stimulus we can detect
– Difference Threshold:
• Min. difference needed to detect a stimulus change;
also called the just noticeable difference (JND)
Sensory Thresholds
Vision
A candle flame seen at 30
mi. on a clear, dark night
Hearing
The tick of a watch under
quiet conditions at 20 ft.
Taste
One teaspoon of sugar in 2
gallons of water
Smell
1 drop of perfume diffused
into the entire volume of a 3
room apartment
Touch
The wing of a bee falling on
your cheek from a height of 1
cm
Sensory Thresholds
• Weber’s Law
– to be perceived as different, two stimuli must
differ by a constant minimum percentage (rather
than a constant amount)
• light intensity - 8%
• Weight - 2%
• tone frequency - 0.3%
Thresholds
• Sensory Adaptation:
– decreased sensory response to continuous
stimulation
How We See: Vision
• Light is a form of
electromagnetic
energy that moves in
waves
• Many types of
electromagnetic
waves form the
electromagnetic
spectrum
Electromagnetic Spectrum
Electromagnetic Spectrum
• The flower on the left looks normal to us, whereas the
one on the right was photographed under ultraviolet
light
How We See: Light Waves
• Light waves vary in:
– length (wavelength), which determines frequency
(hue or color)
– height (amplitude), which determines brightness
or intensity
Anatomy of the Eye
• The function of the
eye is to capture light
waves and focus them
on receptors at the
back of the eyeball.
Structures of the Retina
• Receptors for vision are the rods and cones
located in the retina.
Are You Nearsighted or Farsighted?
• Myopia:
– Near sightedness
– Focused in front of retina
• Hyperopia:
– Far sightedness
– Focused behind retina
Optic Nerve, Blind Spot & Fovea
• Optic nerve: Carries neural impulses from the eye to
the brain
• Blind Spot: Point where the optic nerve leaves the eye
because there are no receptor cells located there.
• Fovea: Central point in the retina around which the
eye’s cones cluster.
Photoreceptors
E.R. Lewis, Y.Y. Zeevi, F.S Werblin, 1969
Visual Information Processing
Optic nerves connect to the thalamus in the middle of
the brain, and the thalamus connects to the visual
cortex.
Feature Detection
• Feature Detection:
– Nerve cells in the visual cortex respond to specific
features, such as edges, angles, and movement.
Shape Detection
Specific combinations of temporal lobe activity occur
as people look at shoes, faces, chairs and houses.
How We Hear: Audition
• Sound results from movement of air molecules in a
particular wave pattern.
• Sound waves vary in:
• Length which determines pitch (highness or
lowness).
• Height which determines loudness
How We Hear: Audition
• The loudness of a sound is
measured in decibels.
Constant noise above 90
decibels can cause
permanent nerve damage
to the ear.
How We Hear: Anatomy of the Ear
Receptors for
hearing are hair
cells located in the
cochlea.
Our Other Senses
• Our sense of
smell is called
olfaction.
• Receptors for
smell are
embedded in a
nasal membrane,
the olfactory
epithelium.
Gustation (Sense of Taste)
• Receptors for gustation
are taste buds, located
in the papillae on the
surface of the tongue.
Three Body Senses
•
Skin senses involve three basic
skin sensations
–
–
–
•
Touch (or pressure)
Temperature
Pain
Receptors for these sensations
occur in various concentrations
and depths in the skin.
Three Body Senses
• Vestibular sense (or sense
of balance) involves the
vestibular sacs and
semicircular canals located
in the inner ear.
Three Body Senses
• Kinesthesia provides
the brain with
information about
bodily posture and
bodily movement
• Kinesthetic receptors
are found throughout
the muscles, joints,
and tendons of the
body.
UNDERSTANDING PERCEPTION
Chapter 4
Understanding Perception
• Illusions:
– false or misleading
perceptions help
scientists study the
processes of perception
(e.g., the horizontalvertical illusion)
The Muller-Lyer Illusion
Which vertical line is longer?
Understanding Perception
Do You
See the
Cow?
Understanding Perception
Now Can
You See
the Cow?
Understanding Perception
• Perception’s three basic processes:
– Selection
– Organization
– Interpretation
Selection
• Selection (choosing where to direct
attention) involves these factors:
– Selective Attention
• filtering out and attending only to
important sensory messages (cocktail
party conversations)
– Habituation
• brain’s tendency to ignore environmental
factors that remain constant
Selection
• Kittens raised with
only vertical visual
stimuli fail to develop
the ability to detect
horizontal lines. Can
you explain why?
Organization
• Organization: assembling of information into patterns
that help us understand the world
• We organize sensory information in terms of:
– Form
– Consistency
– Depth
– Color
Form Perception
• Gestalt psychologists developed laws explaining
how people perceive form according to:
– Figure and ground
• Ground is always seen as farther away
than the figure
– Proximity
• Objects that are physically close together are grouped
together
Form Perception
• Gestalt laws cont’d
– Continuity
• Objects that continue a pattern
are grouped together
– Closure
• The tendency to see a finished
unit from an incomplete stimulus
– Similarity
• Similar objects are grouped
together
Grouping Principles
The Gestalt
Grouping
Principles
are in use
here
Form Perception
Form Perception:
Can You Explain These Impossible Figures?
Organization
• Perceptual Constancy:
– Tendency to perceive the environment as
remaining the same even with changes in sensory
input.
• Four best-known constancies:
– Size
– Shape
– Color
– Brightness
Organization
Can You
Identify the
Size, Shape,
Color, and
Brightness
Constancies?
The Ames Room Illusion
Interpretation
Depth Perception
• Depth Perception:
– ability to perceive three
dimensional space and
accurately judge
distance
Depth Perception
The Visual Cliff
Depth Perception
• Depth Perception involves both binocular
(two eyes) and monocular (one eye) cues.
• Two Binocular Cues for Depth:
– Retinal disparity
• separation of the eyes causes different images to fall
on each retina
– Convergence
• the closer the object the more the eyes turn inward
Depth Perception
Binocular Cues
Retinal Disparity
(left)
Convergence
(right)
Depth Perception
• Monocular Cues
– relative size
• smaller image is more distant
– interposition
• closer object blocks distant object
– relative clarity
• hazy object seen as more distant
– texture
• coarse = close
• fine = distant
Depth Perception
Relative Size
Depth Perception
Interposition
Depth Perception
• Monocular Cues (cont.)
– relative height
• higher objects seen as more distant
– relative motion
• closer objects seem to move faster
– linear perspective
• parallel lines converge with distance
– relative brightness
• closer objects appear brighter
Depth Perception
Relative Height
Depth Perception
Six Monocular Depth Cues: Can You Find Them?
1.
2.
3.
4.
5.
6.
linear perspective
interposition
relative size
texture gradient
aerial perspective
light and shadow
Colour Perception
Two main theories:
• 1. Trichromatic:
– color perception
results from mixing
three distinct color
systems (red,
green, and blue)
Colour Perception
2. Opponent-process:
• color perception results from three systems of color
opposites (blue-yellow, red-green, and black-white)
“ON”
“OFF”
red
green
green
red
blue
yellow
yellow blue
black
white
white
black
Colour Perception
• After-Image effect
– Complimentary colours don’t exist together (no
bluish-yellow or reddish-green)
– After images appear in complimentary colours
Interpretation
• Interpretation
– How we explain perception
– 4 factors
•
•
•
•
Perceptual adaptation
Perceptual set
Frame of reference
Bottom-Up or Top-Down Processing
Four Factors in Interpretation
• 1. Perceptual
adaptation
– Brain adapts to
changed environments
Four Factors in Interpretation
• 2. Perceptual set
– Readiness to perceive in a
particular manner, based on
expectations
– Past experiences, motives,
contexts, or suggestions
Perceptual Set
Flying saucers or clouds
Four Factors in Interpretation
• Another example of
perceptual set.
• Do you notice
anything wrong with
these photos?
Four Factors in Interpretation
• 3. Frame of reference:
– based on the context of the situation
– Internal standards for judging stimuli
Four Factors in Interpretation
•
4. Bottom-Up Processing:
– Analyzing information starting at the bottom
(small units) and going up to form a complete
perception
•
4. Top-Down Processing:
– Pre-existing knowledge that is used to rapidly
organize features into a meaningful whole
•
drawing on our experience and expectations
Perception & Memory
• The ability to accurately perceive stimuli in
the environment is highly correlated with the
ability to correctly remember that same
stimuli
– i.e. the better you are at perceiving, the more
accurate you will be at remembering
Extrasensory Perception
• Extrasensory perception (ESP):
– supposed ability to perceive things that go beyond the 5
normal senses
– ESP research is criticized due to lack of experimental
control and replicability.
Extrasensory Perception (ESP)
• Parapsychology: Study of ESP and other psi
phenomena (events that seem to defy accepted
scientific laws)
– Clairvoyance: Purported ability to perceive events
unaffected by distance or physical barriers
– Telepathy: Purported ability to read minds
– Precognition: Purported ability to accurately predict the
future (“Minority Report” and the “Pre-Cogs,” like
Agatha)
– Psychokinesis (Mind Over Matter): Purported ability to
influence physical objects by willpower
ESP continued
• Run of Luck: Statistically unusual outcome that could
occur by chance alone (e.g., getting five heads in a
row, two jackpots within six pulls of a slot machine)
• Stage ESP: Simulation of ESP for entertainment
purposes
• Conclusion: Existence of ESP has NOT been
scientifically demonstrated; positive results are
usually inconclusive and easily criticized
• In sum: Be skeptical! If it seems too good to be true, it
probably is!
Problems with Believing in Subliminal
Perception and ESP
• Subliminal perception
may occur, but there is
little or no evidence of
subliminal persuasion