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Sensation and Perception
Sensation and Perception
• Sensation: The detection of physical
energy emitted or reflected by physical
objects; it occurs when energy in the
external environment or the body
stimulates receptors in the sense
organs.
• Perception: The process by which the
brain organizes and interprets sensory
information.
Ambiguous Figure
• Colored surface can
be either the outside
front surface or the
inside back surface
– Cannot
simultaneously be
both
• Brain can interpret
the ambiguous cues
two different ways
The Riddle of Separate
Sensations
• Sense Receptors: Specialized neurons that
convert physical energy from the environment
or the body into electrical energy that can be
transmitted as nerve impulses to the brain.
• Doctrine of Specific Nerve Energies: Different
sensory modalities exist because signals
received by the sense organs stimulate
different nerve pathways leading to different
areas of the brain.
Measuring the Senses
• Absolute Threshold
– The smallest quantity of physical energy that
can be reliably detected by an observer
• Difference Threshold
– The smallest difference in stimulation that
can be reliably detected by an observer
when two stimuli are compared; also called
Just Noticeable Difference (JND).
Signal Detection Theory
• Holds that responses in a detection task depend on a
sensory process and a decision process.
• These may vary with a person’s motivation, alertness,
and expectations
Present
Detection
No
Detection
Hit
Miss
Not
Present
False
Alarm
Correct
Rejection
Absolute Sensory Thresholds
• Vision: A single candle flame from 30 miles on
a dark, clear night
• Hearing: The tick of a watch from 20 feet in
total quiet
• Smell: 1 drop of perfume in a 3-room
apartment
• Touch: The wing of a bee on your cheek,
dropped from 1 cm
• Taste: 1 tsp. Sugar in 2 gal. water
Absolute Sensory Thresholds
• Despite our impressive sensory skills, our senses
are tuned to a narrow band of physical energies.
• Other species can detect signals that we cannot.
Sensory Adaptations
• Sensory Adaptation: The reduction or
disappearance of sensory
responsiveness that occurs when
stimulation is unchanging or repetitious.
• Sensory Deprivation: The absence of
normal levels of sensory stimulation.
Sensory Overload
• Selective Attention: The focusing of
attention on selected aspects of the
environment and the blocking out of
others.
– Protects us from being overwhelmed
Vision
•
•
•
•
•
What We See
An Eye on the World
Why the Visual System is Not a Camera
How We See Colors
Constructing the Visual World
What We See
• Hue: The dimension of visual experience
specified by color names and related to the
wavelength of light.
• Saturation: Vividness or purity of color; the
dimension of visual experience related to the
complexity of light waves.
• Brightness: Lightness and luminance; the
dimension of visual experience related to the
amount of light emitted from or reflected by an
object (height of wave).
An Eye on the World
• Retina: Neural tissue lining the back of the
eyeball’s interior, which contains the receptors
for vision.
• Rods: Visual receptors that respond to dim
light.
• Cones: Visual receptors involved in color vision.
Most humans have 3 types of cones.
• Dark Adaptation: The process by which visual
receptors become maximally sensitive to light.
Structures of the Human
Eye
Retinal Image
Structures of the Retina
The Visual System is Not a
Camera
• Much visual processing is done in the brain.
– Some cortical cells respond to lines in
specific orientations (e.g. horizontal)
– Other cells in the cortex respond to other
shapes (e.g., bulls-eyes, spirals, faces)
• Feature-detectors: Cells in the visual cortex
that are sensitive to specific features of the
environment.
How We See Colors
• Trichromatic Theory
• Opponent Process Theory
Trichromatic Theory
• T. Young (1802) & H. von Helmholtz (1852) both
proposed that the eye detects 3 primary colors
– Red, blue, & green
• All other colors can be derived by combining these three
Opponent-Process Theory
• A competing theory of color vision,
which assumes that the visual system
treats pairs of colors as opposing or
antagonistic.
• Opponent-Process cells are inhibited by
a color, and have a burst of activity
when it is removed.
Constructing the Visual
World
• Form Perception
• Depth and Distance Perception
• Visual Constancies: When Seeing is
Believing
• Visual Illusions: When Seeing is
Misleading
Gestalt Principles
• Gestalt principles
describe the brain’s
organization of
sensory building
blocks into
meaningful units and
patterns.
– Proximity
– Closure
– Similarity
– Continuity
Depth and Distance
Perception
• Binocular Cues: Visual cues to depth or
distance that require the use of both eyes.
– Convergence: Turning inward of the eyes,
which occurs when they focus on a nearby
object
– Retinal Disparity: The slight difference in
lateral separation between two objects as
seen by the left eye and the right eye.
• Monocular Cues: Visual cues to depth or
distance that can be used by one eye alone.
Visual Constancies
• The accurate perception of objects as
stable or unchanged despite changes in
the sensory patterns they produce.
– Shape constancy
– Location constancy
– Size constancy
– Brightness constancy
– Color constancy
Visual Illusions
• Illusions are valuable in understanding perception
because they are systematic errors.
– Illusions provide hints about perceptual strategies
• In the Muller-Lyer illusion (above) we tend to perceive
the line on the right as slightly longer than the one on
the left.
Fooling the Eye
• The cats in (a) are the
same size
• The diagonal lines in
(b) are parallel
• You can create a
“floating fingertip
frankfurter” by holding
hands as shown, 5-10”
in front of face.
See Chapter 6 Fun Slides
Hearing
• What We Hear
• An Ear on the World
• Constructing the Auditory World
What We Hear
• Loudness: The dimension of auditory
experience related to the intensity of a
pressure wave.
• Pitch: The dimension of auditory
experience related to the frequency of a
pressure wave.
• Timbre (pronounced “TAM-bur”): The
distinguishing quality of sound; the
dimension of auditory experience related
to the complexity of the pressure wave.
Other Senses
•
•
•
•
•
Taste: Savory Sensations
Smell: The Sense of Scents
Senses of the Skin
The Mystery of Pain
The Environment Within
Taste: Savory Sensations
• Papillae: Knoblike elevations on the tongue,
containing the taste buds (Singular: papilla).
• Taste buds: Nests of taste-receptor cells.
Smell: The Sense of Scents
• Airborne chemical molecules enter the nose
and circulate through the nasal cavity.
– Vapors can also enter through the mouth
and pass into nasal cavity.
• Receptors on the roof of the nasal cavity detect
these molecules.
Smell: The Sense of Scents
• Red bars show the
people who could
identify a substance
dropped on the
tongue when they
were able to smell it
Smell: The Sense of Scents
• The Blue bars show
the people who could
identify the
substance when they
were not able to
smell it
Senses of the Skin
• The skin senses include:
– Touch
– Warmth
– Cold
– Pain
– Various others (itch and tickle)
Gate-Control Theory of Pain
• Experience of pain
depends (in part) on
whether the pain
impulse gets past
neurological “gate” in
the spinal cord and
thus reaches the
brain.
Neuromatrix Theory of Pain
• Theory that the
matrix of neurons in
the brain is capable
of generating pain
(and other
sensations) in the
absence of signals
from sensory nerves.
The Environment Within
• Kinesthesis: The sense of body position
and movement of body parts; also called
kinesthesia.
• Equilibrium: The sense of balance.
• Semicircular Canals: Sense organs in the
inner ear, which contribute to equilibrium
by responding to rotation of the head.
Psychological and Cultural
Influences on Perception
• Needs
• Emotions
• Expectations
– Perceptual Set: A habitual way of perceiving,
based on expectations.
• Beliefs
Puzzles of Perception
• Subliminal Perception
• Extrasensory Perception: Reality or
Illusion?
Extrasensory Perception
• Extrasensory Perception (ESP):
– The ability to perceive something without
ordinary sensory information
– This has not been scientifically demonstrated
• Three types of ESP:
– Telepathy – Mind-to-mind communication
– Clairvoyance – Perception of remote events
– Precognition – Ability to see future events