Transcript SENSATION AND PERCEPTION

SENSATION &
PERCEPTION
CHAPTERS 4 & 5
AP PSYCHOLOGY
SENSATION
How do we take in information?
• A sense is a system that translates
information from outside the nervous system
into neural activity.
• Messages from senses are called sensations
– For example, vision is the system through which
the eyes convert light into neural activity. This
tells the brain something about the source of the
light (brightness) or about the objects from which
the light is reflected (round, red, etc).
Elements of a Sensory System
1.
2.
3.
4.
5.
6.
Energy (light, sound waves, etc) contains info about
the world
Accessory Structures (lens, ear, etc) modify energy.
Transduction- the process of converting incoming
energy into neural activity through sensory receptors
Sensory nerves transfer the coded activity to the
Central Nervous System.
Thalamus processes and relays the neural response
(except in smell).
Cortex receives input and produces the sensation and
perception
Figure 4.1: Elements of a
Sensory System
How does physical energy get
converted into neural activity?
CODING - translation of the physical properties of a
stimulus into a pattern of neural activity that specifically
identifies those physical properties.
Doctrine of Specific Nerve Energies - stimulation of a
particular sensory nerve provides codes for that one
sense, no matter how the stimulation takes place
Temporal Code - involves changes in the timing of the
neurons firing. Ex: A bright light will cause some
neurons in the visual system to fire faster than a dim
light.
Spatial Code - the location of the firing neurons provides
information about the stimulus (tells us where the
sensation is coming from).
HEARING
• Sound is a repetitive
fluctuation in the pressure of
a medium, such as air.
• In a place like the
moon, which has
almost no atmospheric
medium, sound cannot
exist
• When you speak, your vocal
cords vibrate, producing
fluctuations in air pressure
that spread as waves. A
wave is a repetitive variation
in pressure that spreads out
in 3 dimensions.
Physical Characteristics of
Sound
1. Amplitude- (intensity) difference in air
pressure from the baseline to the peak of a
wave.
2. Wavelength- the distance from one peak
wave to the next.
3. Frequency- number of complete waves, or
cycles, that pass by a given point in space
every second. Described in a unit called
hertz, (Hz). 1 cycle per second is 1 hertz
Figure 4.2: Sound Waves and
Waveforms
Psychological Dimensions of Sound
What do we actually hear?
1. Loudness- determined by amplitude.
Greater amplitude = Louder sounds
2. Pitch- how high or low a tone sounds.
Determined by frequency.
– High frequency = High Pitch
– Low Frequency = Low Pitch
3. Timbre- (pronounced “tamber”) is the
quality of the sound
The Ear
• Auditory accessory
structures modify sound
waves before information
affects neural signals
Sound Waves 1
– Pinna – crumpled part of ear
that funnels sound through
the ear canal
– Tympanic Membrane –
eardrum – tightly stretched
membrane in the middle ear
where sound waves strike
– Vibrations of the tympanic
membrane are transferred
through 3 tiny bones malleus (hammer), incus
(anvil), stapes (stirrup)
Auditory Transduction
• After sound passes through the oval window, it
enters the inner ear or cochlea - this is where
transduction occurs
• The basilar membrane forms the floor of this long
tube
• Sound waves bend hairs of the organ of Corti – a
group of cells which rest on the membrane
• Hair cells connect with fibers from the auditory
nerve, a bundle of axons that goes into the brain
Figure 4.4:
The Cochlea
Sound
Waves 2
Auditory Pathways
• Auditory nerve  brainstem  thalamus
• The information coded in the activity of
auditory nerve fibers is conveyed to the brain
and processed further
• Information is relayed from the auditory nerve
to an area of the cerebral cortex called the
primary auditory cortex
• Various aspects of sound processed in
different regions of auditory system.
• Certain parts of auditory cortex process
certain types of sounds.
Auditory Transduction
How we hear?
• http://www.youtube.com/watch?v=CSO76
5hyxrc&feature=related
Sensing Pitch
• Different people may experience the
“same” sound as different pitches.
• Pitch-recognition abilities influenced by
genetics.
– Cultural factors are also partly responsible
for the way in which a pitch is sensed.
Locating Sounds
• Determined partly
by the very slight
difference in when
sound arrives at
each ear.
• The brain also uses
information about
the difference in
sound intensity at
each ear.
Coding Intensity and Frequency
• The more intense the sound, the more
rapid the firing of a given neuron.
• Frequency appears to be coded in two
ways: place theory and frequencymatching theory
Coding Frequency: Place Theory
• Sounds produce waves
that move down the
basilar membrane.
– Where the wave peaks
depends on the
frequency of the sound.
• Hair cells at a particular
place on the membrane
respond most to a
particular frequency.
Coding Frequency: Frequency
Matching Theory
• Firing rate of an auditory nerve
matches a sound wave’s frequency.
• Sometimes called the “volley theory” of
frequency coding.
Vision
• Light – electromagnetic radiation
• Visible light has a wavelength from just under 400
nanometers to 750 nanometers
• Light intensity –
– How much energy the light contains
– Determines the brightness of light
• Light Wavelength –
– The difference between peaks in light waves
– Determines what color we see
Figure 4.7: Spectrum of
Electromagnetic Energy
The spectrum of electromagnetic
energy
Physical Properties of Light
Waves
Short wavelength=high frequency
(bluish colors, high-pitched sounds)
Great amplitude
(bright colors, loud sounds)
Long wavelength=low frequency
(reddish colors, low-pitched sounds)
Small amplitude
(dull colors, soft sounds)
Accessory Structures of the Eye
• Cornea – curved, transparent layer through
which light rays enter the eye
• Pupil – opening in the eye through which light
passes
• Iris – colorful part of the eye which adjusts the
amount of light entering the eye
• Lens – bends rays, focusing them on the retina
• Retina – Surfaces at back of the eye onto which
the lens focuses light rays
Figure 4.8: Major Structures of
the Eye
Vision
• Accommodation- the process by which the
eye’s lens changes shape to help focus near
or far objects on the retina
 Acuity- the sharpness of vision
 Nearsightedness- condition in which nearby
objects are seen more clearly than distant objects
because distant objects in front of retina
 Farsightedness- condition in which faraway
objects are seen more clearly than near objects
because the image of near objects is focused
behind retina
How Light enters the eye
• http://www.youtube.com/watch?v=15P8q3
5vNHw
Vision
Normal Vision
Nearsighted
Farsighted
Converting Light into Images
• Visual transduction
is the conversion of
light energy into
neural activity.
• Conversion done by
photoreceptors in
the retina.
• Two main types of
photoreceptors:
Rods and cones.
Rods and Cones
 Rods
 peripheral retina
 detect black, white
and gray
 twilight or low light
 Cones
 near center of retina
 fine detail and color
vision
 daylight or well-lit
conditions
Interactions in the Retina
• Photoreceptor cells connect to bipolar
cells and then to ganglion cells
• Axons of the ganglion cells form the
optic nerve, which extends out of the
eye and into the brain
• Each neuron of a sensory system has a
receptive field – part of the retina and
the region of the environment to which
that cell responds
Figure 4.11: Center-Surround
Receptive Fields of Ganglion
Cells
Figure 4.12: The Hermann Grid
The cell whose receptive field includes the space at the intersection has
more whiteness shining on its inhibitory surround than the cell whose
receptive field is just to the right of the intersection. The output of the
intersection cell will be lower than that of the one on the right, creating the
impression of a shadow.
Visual Pathways
• Axons from ganglion cells converge as a bundle
of fibers called the optic nerve and exit the
eyeball at one spot
• The exit point has no photoreceptors and is
insensitive to light creating a blind spot
• About ½ the fibers of the optic nerve cross over
to the opposite side of the brain at the optic
chiasm (part of the bottom surface of the brain)
Visual Pathways con’t
• Axons from most of ganglion cells in
retina form synapses in the thalamus,
in a specific region called the lateral
geniculate nucleus (LGN)
• Neurons in the LGN relay the visual
input to the primary visual cortex,
located in the occipital lobes in the
back of the brain
Pathways from the Eyes to the
Visual Cortex
Visual Representations
• Receptive fields of neurons are characterized
by parallel processing and hierarchical
processing
– Parallel Processing of visual properties: Brain conducts separate
kinds of analysis simultaneously on the same information.
– The “what” system
– The “where” system
– Hierarchical Processing of visual properties:
• Individual cells in the visual cortex receive input from several
LGN neurons.
• Cortical cells respond to specific features of objects in the
visual field – Feature detectors
Light Conversion
Seeing Color
• Hue – color determined by the
dominant wavelength in the mixture of
the light (excludes black, white, gray)
• Saturation – purity of a color
• Brightness – overall intensity of the
wavelengths that make up light
Visual Information
Processing
 Trichromatic (three color) Theory
 Young and Helmholtz
 three different retinal color receptors
Trichromatic Theory of Color
• Any color can be produced by mixing
pure lights of blue, green, and red.
• There are three types of cones, each
most sensitive to particular
wavelengths.
• Ratio of the activities of the three types
of cones indicates what color is
sensed.
Opponent-Process Theory
• Ewald Hering
• Each of the three color sensitive
elements are organized as pairs, where
each pair member opposes, or inhibits,
the other
– Red-Green
– Blue-Yellow
– Black-White
Trichromatic and OpponentProcess Theories
Opponent-Process Theory
Figure 4.20: Color Coding and
Ganglion Cells
The Chemical Senses
• Olfaction detects airborne chemicals
– Our sense of smell
• Gustation detects chemicals in solution
that come into contact with receptors
inside the mouth
– Our sense of taste
Figure 4.23: The Olfactory
System
Olfactory System
• Employs about 1,000 different types of
receptors.
• Only sense that does not send its
messages through the thalamus.
• Processing in several brain regions
including frontal lobe and amygdala
• Strong relationship between olfaction
and emotional memory
Olfactory System (cont’d.)
• Only sense that does not send its
messages through the thalamus.
• Pathways from olfactory bulb sends
information on for further processing in
several brain regions.
– Including frontal lobe and amygdala.
• Strong relationship between olfaction
and emotional memory.
Pheromones
• Chemicals released
by one animal, and
when detected by
another, can shape
the second animal’s
behavior or
physiology.
• Role of pheromones
in humans not clear
Age, Sex and Sense of Smell
Number
of correct
answers
Women and young adults
have best sense of smell
4
Women
3
Men
2
0
10-19
20-29
30-39
40-49
50-59
60-69
Age Group
70-79
80-89 90-99
Smell, Taste, and Flavor
• Smell and taste act together to form
system known as flavor.
• Tastes and odors can prompt strong
emotional responses.
• Nutritional state can affect taste and
flavor of food and motivation to eat
particular foods.
• Flavor includes other characteristics of
food.
Somatic Senses and the
Vestibular System
• Somatosensory systems are spread
throughout the body
• Somatic senses include:
– Skin senses of touch, temperature, and
pain
– Kinesthesia
• Vestibular system tells the brain about
the position and movement of the head
Touch
• Energy detected is physical pressure
on tissue.
• Many nerve endings in the skin act as
touch receptors.
• Touch is both an active and passive
sense.
• Changes in touch provide most
important sensory information.
Coding of Touch Information
• Intensity of the stimulus is coded by:
– Firing rate of individual neurons and
– The number of neurons stimulated.
• Location is coded by the location of the
neurons responding to the touch.
Temperature
• Some of the skin’s
sensory neurons
respond to a change in
temperature.
– “Warm” and “cold” fibers
• Sensations of touch
and temperature
sometimes interact.
• Stimulation of the touch
sense can have
psychological and
physiological effects.
Pain
• Pain provides information about impact
of world on body.
• Information-carrying aspect of pain
very similar to that of touch and
temperature.
• Two types of nerve fibers carry pain
signals from skin to the spinal chord.
• Cerebral cortex plays role in the
experience of pain.
Figure 4.25: Pain Pathways
Modulating Pain
• Gate Control Theory
 theory that the spinal cord contains a
neurological “gate” that blocks pain signals or
allows them to pass on to the brain
 “gate” opened by the activity of pain signals
traveling up small nerve fibers
 “gate” closed by activity in larger fibers or by
information coming from the brain
• Natural Analgesics
– Serotonin
– Endorphins
Proprioceptive Senses
• Sensory systems that provide
information to the brain about:
– The position of the body.
– What each of part of the body is doing.
• Vestibular sense indicates the position
of the head in space and its general
movements.
– Sense of balance.
Vestibular Sense
• Organs:
– Vestibular sacs
– Otoliths
– Semicircular canals
• Neural connections to:
– The cerebellum
– The autonomic nervous system
– The eye muscles
Kinesthesia
• Sense that indicates
where the parts of the
body are with respect to
one another.
– Necessary guide for
movement.
• Kinesthetic information
comes primarily from
the joints as well as
muscles.
PERCEPTION
Three Approaches to Perception
• Computational – tries to determine the
computations that a machine would
have to solve perceptual problems
• Constructivist – reality is constructed
from fragments of sensory information
• Ecological – environment contains
most of the information needed to form
perceptions
Psychophysics
• Describes the relationship between the
physical energy in the environment and
the psychological experience of that
energy
• Absolute Threshold – the minimum
detectable amount of environmental
energy a sensory system can detect
Absolute Thresholds
Table 5.1
Signal-Detection Theory
• Sensitivity – a person’s ability to pick out a
particular stimulus or signal
• Response Criterion – a person’s willingness
or reluctance to say that a stimulus is
present
• Signal-Detection Theory – model of our
personal sensitivity and response criterion
combined to determine whether or not a
near-threshold stimulus has occurred
Figure 5.4: Signal Detection
Judging Differences Between
Stimuli
• Difference Threshold or JustNoticeable Difference (JND)
• JND determined by two factors:
– How much of a stimulus was there to
begin with?
– Which sense is being stimulated?
Click the link below to see how JND impacts the consumer world:
http://www.psfk.com/2009/03/media-arts-mondays-just-noticeabledifference.html
Weber’s Law
• Weber’s Constant
• Law States That JND = KI
– K is the Weber’s constant for a particular
sense.
– I is the amount, or intensity, of the
stimulus.
• The smaller K is, the more sensitive a sense is
to stimulus differences
Magnitude Estimation
• Magnitude estimation is how our
perception of stimulus intensity is
related to actual stimuli strength
• Fechner’s Law
– Constant increases in physical energy will
produce smaller increases in perceived
magnitude
• Steven’s Power Law
– Describes a wider range of sensations
Perceptual Illusions
• Illusion – incorrect perception of a
stimulus
• Delusion – a false belief
• Hallucination – a perception in the
absence of a stimulus
Figure 5.5: Length Illusions
Figure 5.6: Organize This!
Perceptual Illusions
Ames room
Perceptual Illusions
Ames room
Basic Processes in Perceptual
Organization
• Figure-Ground Organization
– Perceptual apparatus picks out some objects to be figures,
while others are less relevant in the background
• Grouping
– Inherent properties of the stimulus environment lead people
to group them together
 Grouping Principles





Proximity--group nearby figures together
Similarity--group figures that are similar
Continuity--perceive continuous patterns
Closure--fill in gaps
Connectedness--spots, lines, and areas are seen as unit when
connected
 Synchrony – occur at the same time
 Common region – located within some boundary
 Connectedness – connected by other elements
Figure 5.7: Reversible Images
Figure-Ground
Figure 5.8: Gestalt Principles of
Perceptual Grouping
More Grouping Principles
Perceptual Organization
• Likelihood Principle
– We perceive objects in the way that
experience tells us is the most likely
physical arrangement (consistent with
Constructivism)
• Simplicity Principle
– We organize stimulus elements in a way
that gives us the simplest possible
perception
Figure 5.9: Impossible Objects
Perception of Location and
Distance
• Two-Dimensional Location – uses an
equation that takes information about
where an image strikes the retina and
adjusts it based on information about
movement of your eyes and head
– Visual dominance – bias toward using
visual information when it conflicts with
information from other senses
Depth Perception
•
Our ability to perceive distance, allowing people to
experience the world in three-dimensions
1. Interposition – closer objects block the view of
things further away
2. Relative Size – the object producing a larger
image on the retina is perceived as closer
3. Height in the Visual Field – more distant objects
are higher in the visual field
4. Texture Gradient – graduated change in texture –
less detailed as distance increases
5. Linear Perspective – the closer together 2
converging lines are, the greater the perceived
distance
6. Clarity, Color, Shadow – distant objects appear
hazier
7. Motion Parallax – objects closer appear to move
rapidly, while those distant appear motionless
Figure 5.10: Stimulus Cues for
Depth Perception
Cues Based on Physiology
• Accommodation – muscles surrounding
the lens either tighten (to focus on close
objects) or relax (to focus on distant
objects)
• Convergence – each eye rotates inward to
see closer objects
• Binocular Disparity – the difference
between the two retinal images of an
object provides distance cues
Perceptual Organization: Depth
Perception
Visual Cliff
Perceptual Organization: Depth
Perception
Relative Size
Perceptual Organization: Depth
Perception
Interposition
Perceptual Organization: Depth
Perception
Perception of Motion
• Looming – a rapid expansion in the size
of an image so that it fills the retina and
is perceived as an approaching object
• Stroboscopic Motion – our tendency to
perceive motion through a series of
flashing rapid light
Perceptual Constancy
• The perception of objects as constant in size,
shape and color
• Size Constancy – occurs as objects move
closer or farther away
• Shape Constancy – occurs as an object
appears the same, even though the shape of
its retinal image changes
• Brightness Constancy – occurs so that no
matter how the amount of light striking an
object changes, its perceived brightness
remains constant
Figure 5.12: A Size Illusion
Perceptual Organization: MullerLyer Illusion
Figure 5.13: Brightness Contrast
Recognizing the Perceptual
World
• The brain analyzes the incoming pattern of
the stimulus and compares that pattern to
information stored in the memory
– Top-down processing – guided by knowledge and
expectations
• Our experiences create schemas, or mental
representations of what we know about the world
– Bottom-up processing – relies on specific,
detailed information from sensory receptors that
are integrated and assembled into a whole
Parallel Distributed Processing
Models (PDP)
• Units in a network
operate
parallelsimultaneously
• Each element is
connected to all other
computational elements
• Recognition occurs as
a result of the
simultaneous operation
of connected units
Attention
• The process of
directing and
focusing certain
psychological
resources to
enhance perception,
performance, and
mental experience
Articles
• http://www.hhmi.org/senses/
Illusions
• http://psylux.psych.tudresden.de/i1/kaw/diverses%20Material/w
ww.illusionworks.com/index.html
Blind Spot Demonstration
• http://serendip.brynmawr.edu/bb/blind
spot1.html
Jeopardy
• http://www.uni.edu/walsh/jeopardy.html
More Information on Sensation
and Perception
• http://www.muhlenberg.edu/depts/psychol
ogy/lsnodgrass/sp/dem_links.html
References
• http://college.cengage.com/psychology/ber
nstein/psychology/7e/instructors/index.htm
l
• http://www.lbusd.k12.ca.us/millikan/Teach
er_folder/HawkinsS/AdPlPsychology2.htm