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chapter 6
Definitions
Sensation
The detection of physical energy emitted or reflected by
physical objects
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
chapter 6
Sensation and perception
Sensation
• What are the sensory systems?
• Sight, sounds, touch, pain, smell, taste, sensation of
movement
• Why are the sensory systems
important?
• Perception of external world
• Maintains arousal, forms body image, regulates
movement
• Basis for our knowledge about the world and our
surroundings.
Psychophysics
•
Correlates quantitative aspects of
physical stimuli (energy) with the
sensations they evoke
–
4 elementary attributes:
1. Modality
2. Intensity
3. Duration
4. Location
Attributes of Sensation:
Modality
• Quality of a sensation
• Different forms of energy = Different sensations
• 5 major: vision, hearing, touch, taste, smell
– Submodalities:
» Touch – sweet, salty, bitter, sour
» Vision – color, movement
• Law of Specific Energies
• 1826 Johannes Muller
• Each modality = activated by a specific stimulus =
different sensory nerve fiber
Sensory receptors are maximally sensitive to
a specific energy
Modality
Stimulus
Receptor
(energy)
Receptor
Types
Vision
Light
Photoreceptor
Rods, Cones
Audition
(hearing)
Sound
Mechanoreceptor
Hair cells
(cochlear)
Balance
Head motion
Mechanoreceptor
Hair cells
(semicircular
canals)
Somatic
(touch)
Mechanical,
thermal, noxious
(chemical)
Mechanoreceptor, Dorsal root
thermoreceptor,
ganglion neurons
nociceptor,
chemoreceptor
Taste
Chemical
Chemoreceptor
Taste buds
Smell
Chemical
Chemoreceptor
Olfactory sensory
neurons
Adapted from Kandel, Schwartz, and Jessel, 1991
Attributes of Sensation:
Intensity
• Strength of Energy  Amount of sensation
• Frequency of action potentials
– strong stimulus = more action potentials fired
• # of fibers activated
– strong stimulus = more fiber stimulated
• Absolute Threshold
• Smallest amount of energy/stimulation that can reliably
be detected
• Variable
– Influenced by practice, fatigue, context
chapter 6
Absolute thresholds
Vision
A single candle flame from 30 miles on a clear night
Hearing
The tick of a watch from 20 feet in total quiet
Smell
One drop of perfume in a 6-room apartment
Touch
The wing of a bee on the cheek, dropped from 1 cm
Taste
One teaspoon of sugar in 2 gallons of water
Attributes of Sensation:
Intensity
• Strength of Energy  Amount of sensation
• Frequency of action potentials
– strong stimulus = more action potentials fired
• # of fibers activated
– strong stimulus = more fiber stimulated
• Absolute Threshold
• Smallest amount of energy/stimulation that can reliably
be detected
• Variable
– Influenced by practice, fatigue, context
• Difference Threshold
• Smallest difference that can be detected when 2 stimuli
are compared
• Just Noticeable Difference (JND)
chapter 6
Signal-detection theory
A psychophysical theory that divides the detection of a
sensory signal into a sensory process and a decision
process and quantifies the ability to distinguish between
the stimuli and noise
Drugs – Mechanism of Action on
the sensation of pain
• Drugs that elevate the pain threshold
– Morphine
» Reduces detectibility of painful stimuli = raises
threshold
» Elevates criterion used to determine if a stimuli is
painful = creates noise
– Marijuana
» Elevates criterion used to determine if stimuli is
painful = makes noise
Attributes of Sensation:
Duration
• Stimulus intensity and Perceived Intensity
• Adaptation
– The reduction or disappearance of sensory responsiveness
when stimulation is unchanging or repetitious
– Prevents us from having to respond continuously to
unimportant information
• Deprivation
– The absence of normal levels of sensory stimulation
Attributes of Sensation:
Location
• Spatial aspects of sensation:
– Ability to locate origin of sensation
– Ability to distinguish 2 closely spaced stimuli
• Two-Point Threshold
– Minimum distance between 2 stimuli that allows them
to be perceived as distinct
• Function of receptive field of receptor
and sensory neurons
Commonalities of the Senses
• All extract same basic information
• Modality, intensity, duration, location
• Similar organization
• Sensory receptors for specific type of energy
• Receptor transforms energy into electrochemical
signal  action potentials
• Travel up afferent fibers to the brain
• Relay information to Thalamus (except smell)
• Continue on to specific regions in cortex
chapter 6
Vision
Stimuli (energy) = light waves
3 Psychological Aspects of Vision:
Hue
Related to the wavelength of light
Brightness
Related to the amount of light emitted from or reflected by an
object – amplitude of wavelength
Saturation
Related to the complexity of light waves - # of different
wavelengths
Vision
Adapted from Univ. Virginia, Dept of Astronomy
chapter 6
What we see
chapter 6
Anatomy of the Eye
Cornea
Protects eye and bends light
toward lens
Lens
Focuses on objects by changing
shape
Iris
Controls amount of light that gets
into eye
Pupil
Aperture through which light
reaches the retina
chapter 6
Rods and Cones
Retina
Neural tissue lining the back
of the eyeball’s interior
containing the receptors for
vision
Rods
Visual receptors that respond
to dim light
Cones
Visual receptors involved in
color vision
chapter 6
Rods and Cones
chapter 6
Structures of the retina
chapter 6
Your turn
You have a hard time locating your red car at
night, in the poorly lit mall parking lot. Why?
1. Your rods are less sensitive to color in dim light.
2. Your cones, which detect color, do not function well in dim
light.
3. Your ganglion cells receive insufficient overall stimulation to
function.
4. Your rods, which detect color, do not function well in dim light.
chapter 6
The visual system is not
a camera
Visual processing is done in the brain
The visual image that was reflected onto our retina is broken
up into simple and complex features that the brain
perceives, processes and interprets
Simple features - light and dark spots
- Ganglion cells and neurons in Thalamus
Complex features – Lines with specific orientations, bulls-eyes,
spirals, faces)
- Feature-detector cells in the Visual cortex
- Sensitive to specific features in the environment
chapter 6
Visual Cortex Neurons:
Feature-Detector Cells
Respond to lines oriented in a particular direction
and in a particular space in the visual field
Hubel & Wiesel Experiment
chapter 6
Hubel and Wiesel’s
experiment
Simple Cell in Visual Cortex
Hubel DH Sci Amer 209:54-62,1963
How do we see color?
• Two theories:
– Trichromatic theory
– Opponent-process theory
chapter 6
Trichromatic theory
Young-Helmholtz
Theory:
The eye detects 3 primary
colors
Red, blue, and green
Retina has 3 basic cones
detects the 3 primary
colors
All other colors detected by
the combined activity of
these 3 cones
chapter 6
Opponent-process
theory
The visual system treats pairs of colors as
opposing or antagonistic
• 3 opponent channels
– Red-Green
– Blue-Yellow
– Black-White
If opponent-process cells are inhibited by a color
then removal of the color results in a burst of activity
• Many respond in the opposite fashion to red and green,
i.e. fire in response to red and turn off in response to
green
• Negative afterimage
chapter 6
Form Perception:
Gestalt principles
Proximity
Things close to one another are grouped together
Closure
The brain tends to fill in gaps to perceive complete forms
chapter 6
Form Perception:
Gestalt principles cont.
Similarity
Things that are alike are perceived together
Continuity
Seeing continuity in lines that could be interpreted as either
continuous or abruptly shifting in direction.
chapter 6
Your turn
Which Gestalt
principle is illustrated
by the fact that we
see columns of dots
rather than rows in
this diagram?
1.
2.
3.
4.
Similarity
Proximity
Closure
Continuity
chapter 6
Depth and distance
perception
Binocular cues
Require both eyes working together
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 right and left eyes
chapter 6
Depth and distance
perception
Monocular cues
For objects over 50 feet away
Does not depend on both eyes
Interposition
Linear Perspective
Light and Shadow
Motion Parallax
Relative Size
Relative Clarity
Texture Gradients
chapter 6
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
Last Class in Review
• Sensation
The detection of physical energy emitted or reflected by physical
objects
• Perception
The process by which the brain organizes and interprets sensory
information
• Psychophysics – attributes of sensation
Modality, Intensity, Duration, Location
• Law of Specific Energies
• Absolute Threshold vs. Difference Threshold (JND)
• Adaption and Deprivation
• Two-Point Threshold
• Vision
– Psychological Attributes – hue, brightness, saturation
– Anatomy – visual receptors = rods and cones; feature detector
cells
– Depth and Distance perceptions: monocular and binocular cues
– Gestalt Principles: proximity, closure, similarity, continuity
chapter 6
Sensation and Perception
Learning Objectives:
1.
What are the 3 main psychological dimensions of hearing?
2.
What are the major structures of the inner ear that contribute to the sense of
hearing?
3.
Understand how the Gestalt principles may apply to other sensations, such as
hearing.
4.
What are the 5 major tastes? Why do people tastes things differently?
5.
What are the basic senses of the skin? How is sensation organized? (hint:
understand somatotopy)
6.
How does gate-control theory account for our perception of pain?
7.
Is there any evidence that some perceptual abilities are present from birth? What
are these abilities and what is the evidence?
8.
What 5 factors can influence our perception?
chapter 6
What we hear (audition)
Stimulus (energy) = wave of pressure caused by
vibrations
3 Psychological Aspects of Sound:
Pitch
Frequency of a pressure wave
Measured in hertz (Hz)
Loudness
Intensity (amplitude) of a pressure wave
Measured in decibels (dB)
Timbre
Complexity of a pressure wave
White noise – all frequencies of the sound spectrum
Psychological Aspects of Sound
From Genetic Science Learning Center, University of Utah,
http://gslc.genetics.utah.edu.
Example of differences in pitch and complexity
chapter 6
Anatomy of the Ear
Gestalt Principles in Audition
• Proximity
– Which sounds go together to form words
• Continuity
– Helps you follow 1 persons voice in a room full of
background noise
• Similarity
– Might also help you follow 1 persons voice in a room full of
background noise
• Closure
– Helps you complete words when the speakers voice trails
off
chapter 6
Auditory localization
Sounds from different
directions are not
identical as they arrive at
left and right ears.
Loudness
Timing
Phase
The brain calculates a
sound’s location by using
these differences.
chapter 6
Taste (Gustation)
Taste buds =
Bundles of taste receptor cells
Taste hairs (microvilli) contain
taste receptors
Taste stimuli (energy) = chemical
Taste receptor cells send signals
to sensory nerves (taste nerves)
Sensory nerves send action
potential to the brain
chapter 6
Five tastes
Five basic tastes
Salty – keeps electrolytes (salt-balance) in check
Sour – detects acidity = rancid food
Bitter – allows sensing of natural poisons
Sweet – energy rich nutrients, presence of sugars
Umami – taste of amino acids (glutamate) = protein rich foods
Why do people have different tastes?
Genetics - supertasters
Culture
Learning
Food attractiveness
chapter 6
Smell (Olfaction)
Smell stimuli (energy) = chemicals
Enter through the nose or mouth and pass into nasal cavity.
Receptors  Olfactory nerve  Olfactory bulb  Pyriform
cortex, hypothalamus, thalamus, frontal cortex, hippocampus
Senses of the Skin
• Basic skin senses:
• Tactition (touch) » stimuli is pressure
» mechanoreceptor
• Thermoception (hot & cold)
» stimuli is thermal
» thermoreceptor
• Nociception (pain)
» stimuli is noxious
» nociceptor
chapter 6
Sensitivity to touch
Somatotopy
Adapted from Sabes Lab - UCSF
chapter 6
The environment within
Kinesthesis
The sense of body position and movement of body parts
Equilibrium
The sense of balance
- Semicircular canals
Sense organs in the inner ear, which contribute to
equilibrium by responding to rotation of the head
chapter 6
Critical period
An important period of
time during development
when the brain is capable
of acquiring a specific
ability
–Environmental stimulation
needed to strengthen hard-wired
innate connections
–If infants miss out on
experiences during a crucial
period of time, perception will be
impaired.
Zebra finches learn their
adult song from a tutor
during a critical period