The Process of Sensation
q Sensation
q Process through which the senses
pick up visual, auditory, and other sensory stimuli and transmit them to the
brain.
q
Perception
q
Process
by which sensory information is actively organized and interpreted by the brain
Absolute Threshold
q Absolute threshold
q The minimum amount of sensory stimulation that can be
detected 50% of the time
Just Noticeable Difference (JND)
q
Smallest
increase or decrease in a physical stimulus required to produce the “just noticeable difference (JND)”
q
The JND
is the smallest change in sensation a person is able to detect 50% of the time
Sensory Receptors
q Highly specialized cells in the sense organs
q Detect and respond to one type of sensory stimuli
q Convert the stimuli into nerve impulses (neural)
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Interesting Afterimage Illusion
Vision The
most studied sense
q
Visible spectrum — the band of electromagnetic waves visible to the human eye.
q
Wavelength — the distance from the peak of a light wave to the
peak of the next wave
The Eye
q Cornea
q Tough, transparent, protective layer
q Covers front of eye
q Bends light rays inward through the pupil
q Lens
q Transparent disk-shaped structure behind the iris
& pupil
q Accommodation — the flattening and bulging of the lens to focus
items on the retina
q Retina
q Contains visual sensory receptors
The Eye
qRods
q Light sensitive receptor cells in the retina
q Allow eye to respond to low light
q Look like slender cylinders
qCones
q Light sensitive receptor cells in the retina
q Enable humans to see color and fine detail
q Function poorly in very dim light
The Eye
q Fovea
q Small center area of the retina
q Provides clearest and sharpest vision
q Largest concentration of cones
q Blind
spot
q Point in each retina with no rods or cones
q Optic
nerve
q Carries visual information from retina to both sides
of the brain
q Primary
visual cortex
q Part of brain which processes visual information
q Feature
detectors
q Neurons that respond to specific visual patterns
Color Vision
qHue
q Specific color perceived
qSaturation
q Purity of the color
q Brightness
q Intensity of the light energy that is perceived
Theories of Color Vision
q Trichromatic theory
q Three types of cones in the retina each make a
maximal chemical response to one of three colors:
q Blue, Green, or Red.
q Each cone is sensitive to one of the colors.
q Opponent-process
theory
q Three kinds of cells respond by increasing or
decreasing their rate of firing when different colors are present
q Types of
cells:
q Red/green – firing increases when red present; green decreases
firing
q Yellow/blue – firing increases when yellow present; blue decreases
firing
q White/black – firing increases when white present; black decreases
firing
Hearing
q Sound
q In order to be heard, sound requires a medium through
which to move
q Air, water, or other solid objects can carry sound
waves
q First demonstrated by Boyle 1660
with a watch in a jar.
q When air was pumped out the sound could not be heard
q Frequency
q Number of cycles completed by a sound wave in one
second
q Determines the pitch of the sound
q Unit of measure is the hertz
q Amplitude
q Loudness of sound
q Unit of measure is the decibel
q
Timbre
q The distinctive qualities of a sound
q Distinguishes it from other sounds of same pitch and
loudness
q
e.g., a
trumpet and a violin sound different when each plays B note
The Hearing Process
q
Sound
waves pass through the auditory canal to the ear drum
q
Ear drum
vibrates
q
Ossicles set in
motion in middle ear
q
Stirrup
pushes on oval window causing vibrations in inner ear
q
Fluid in
cochlea moves back and forth
q
Hair
cells set in motion causing message to be sent to brain via auditory nerve
The Human Ear
q Middle
Ear
q Contains the ossicles
q Connects the ear drum to the oval window
q Amplifies sound waves
q Inner
Ear
q Cochlea
q The fluid-filled snail shaped bony chamber
q Contains the basilar membrane and hair cells
q Hair cells
q Sound receptors inside inner ear
Theories of Hearing
qPlace Theory
q Each individual pitch is determined by the particular
spot or place along the basilar membrane of the cochlea that vibrates the most
qFrequency Theory
q Hair cell receptors vibrate the same number of times
per second as the wave sounds that reach them
Decibel Levels of Various Sounds
q
Loudness
of a sound (amplitude) is measured in decibels
q
Each
increase of 10 decibels makes a sound 10 times louder
q
Normal
conversation at 3 feet measures about 60 decibels (10,000 times louder than a
soft whisper of 20 decibels)
q
Any
exposure to sounds of 130 decibels or higher puts a person at immediate risk
for hearing damage
The Sense of Smell
q Olfaction
q The sense of smell
q Olfactory
epithelium
q Two 1-inch square patches of tissue, at the top of
each nasal cavity
q Contain about 10 million olfactory neurons
q Receptors for smell
q Olfactory
bulbs
q Relays messages to thalamus and orbitofrontal
cortex
q Distinguishes odors and relays information to other
parts of the brain
q
Smell
sensitivities vary for each individual
The Sense of Smell
q Smell
and Memory
q Key connections between smell, emotion, and memory
q Bypass the hippocampus
q Ability to associate smells with memories peak
between 6 and 10 years old
q Olfaction functioning can predict onset of memory
problems
q Pheromones
q Chemicals excreted can have powerful effect on
behavior
The Sense of Taste
q Gustation
q The sense of taste
q Taste sensations:
qSweet
qSour
qSalty
qBitter
qUmami
q Papillae
q small bumps on the tongue containing the taste buds
q Taste buds lie alongside some of the papillae
The Skin Senses
q Touch
q Tactile – pertaining to the sense of touch
q
Information
is carried to the brain when an object touches and depresses the skin
q
Skin is
largest sense organ
q
Distinct nerve receptors in skin
are stimulated sending messages through nerves, spinal cord, through the
brainstem, midbrain, to the somatosensory cortex
qSomatosensory cortex allows
sensation of where and how hard you have been touched
qTwo-point threshold
qHow far
apart two touch points so they can be felt as two distinct touches
Pain
Cross-Cultural Variations in Pain
Balance and Movement
qKinesthetic sense
q Provides information about the position of body parts
in relation to each other
q The movement of the entire body or its parts
qVestibular sense
q Detects movement and the body’s orientation in space
qSemicircular canals
q Three fluid filled tubular canals in the inner ear
q
Sense
the rotation of the head
Principles of Perception
Gestalt
q A German word that refers to the whole form, pattern, or
configuration a person perceives
q Figure-ground
qWhen viewing the world, some object (the figure)
often seems to stand out from the background (the ground)
Gestalt Principles of Grouping
Perceptual Constancies
Allows perceived objects to maintain stable
properties (size, shape, brightness) despite differences in distance, viewing
angle, and lighting:
q Size
constancy – as objects move away they seem to maintain same size
q Brightness
constancy – objects seem to maintain a constant level of
brightness regardless of differences in lighting conditions
q Shape
constancy – objects are perceived as having an unchanging shape
regardless of viewing angle changes that alter the retinal image
Perceptual Constancies
The door projects very different images on the retina
when viewed from different angles, but because of shape constancy, you continue
to perceive the door as a rectangle.
Depth Perception
The ability to perceive the visual world in three
dimensions and to judge distances accurately
ØBinocular
depth cues
Ø
Visual
depth cues that depend on both eyes working together
Monocular Depth Cues
q Interposition
q When one object partly blocks your view of another, you perceive the partially blocked
object as farther away
q Linear
perspective
q Parallel lines that are known to be the same distance
apart appear to grow closer together, or converge, as they recede into the
distance
q Relative
Size
q Larger objects are perceived as being closer to the
viewer, and smaller objects as being farther away
q Texture
gradient
q Near objects appear to have sharply defined textures,
while similar objects appear progressively smoother and fuzzier as they recede
into the distance
q Atmospheric
perspective
q Objects in the distance have a bluish tint and appear
more blurred than objects close at hand
Monocular Depth Cues
q
Shadow or shading
q When light falls on objects, they cast shadows
q You can distinguish bulges from indentations by the shadows they cast
q
Motion parallax
q When riding in a moving vehicle and look out the side
window, the objects you see outside appear to be moving in the opposite
direction
q The objects also seem to be moving at different
speeds — those
closest to you appear to be moving faster than those at a distance
q Objects very far away, such as the moon and the sun,
appear to move in the same direction as the viewer
Motion Perception
q Real
motion
q Perceptions of motion tied to movements of real
objects through space
q Apparent
motion
q Psychologically constructed perceptions of motion
in response to
various kinds of
stimuli
Motion Perception
q Phi
phenomenon
q Apparent motion that occurs when several stationary
lights in a dark room are flashed on and off in sequence
q Perception is that a single light is moving from one
spot to another
q Autokinetic illusion
q Apparent motion caused by movement of the eyes rather
than the objects being moved
Puzzling Perceptions
Puzzling Perceptions
Influences on Perception
q
Prior knowledge
q Enhances or leads to perceptual errors
q Bottom-up
processing
q
Received
stimulus are combined with prior knowledge to make inferences about received
patterns
q Top-down
processing
q Previous experience and conceptual knowledge are used
to recognize stimuli and logically deduce individual components of that whole
q Perceptual
set
q Expectation of what will be perceived
q
Can
affect what actually is perceived
Influences on Perception
Attention
q Process of sorting through sensations and selecting
some for further processing
q Some sensations are automatic requiring minimal
mental effort
q Inattentional blindness
q Focus is shifted from one object to another
q Changes in objects not receiving direct attention are
not noticed
q Cocktail
party phenomenon
q When you hear your name, focus follows due to
assumption that other meaningful information will follow
q Focus
q Information that receives focus is remembered while
other stimulation received at same time is lost
q Hearing words spoken into both ears at same time;
only words that receive focus of attention are recalled