Sensation and Perception
Kyle Kahler and Becky Marx
Introduction
Sensation is the process by which our sensory receptors and nervous system
receive and represent stimulus energies from our environment. Perception
is the process by which we organize and interpret this information. We will
talk about them separately, but know that they are parts of one continuous
process.
Sensation
Vocabulary:
Sensory adaptation: decreasing responsiveness to stimuli due to constant
stimulation
Difference threshold (Just noticeable difference) : the minimum difference
between two stimuli required for detection 50% of the time
Weber’s Law: the principle that, to be perceived as different, two stimuli
must differ by a constant minimum percentage (rather than a constant
amount)
Absolute Threshold: the minimum stimulus needed to detect a particular
stimulus 50% of the time
Signal detection theory: predicts how and when we detect the presence of
a faint stimulus amid background noise. Assumes there is no single
absolute threshold and that detection depends partly on experience,
expectations, motivation, and level of fatigue
Subliminal: below one’s absolute threshold for conscious awareness
Priming: the activation, often unconsciously, of certain associations, this
predisposing one’s perception, memory, or response
•
•
•
•
•
Sensation
Vocabulary Continued
Bottom-up processing: analysis that begins with the sensory receptors and
works up to the brain’s integration of sensory information
Top-down processing: information processing guided by higher-level
mental processes, as when we construct perceptions drawing on our
experience and expectations
Psychophysics: the study of relationships between the physical of stimuli
and our psychological experience of them
Parallel processing: processing several aspects of a problem
simultaneously
Steps of Sensation
1. Acquisition: stimulus is received by sensory organ
2. Transduction: stimulus or energy is converted into neural impulses our
brains can interpret
3. Primary Association: neural impulses are processed
4. Secondary Association: impulses trigger other processes
•
•
•
•
Vision
Stimulus: Light Energy
what strikes our eyes isn’t color but pulses of electromagnetic energy that
our visual system perceives as color
Light’s wavelength - the distance from one wave peak to another determines its hue (the color we experience)
Light’s intensity, the amount of energy in light waves (determined by
wave’s amplitude) influences brightness
•
•
•
Vision
1. Within the eye and Acquisition:
a. reflected light enters the eye through the cornea, which protects the eye and
bends the light for focus
b. passes through the pupil (small adjustable opening) which is regulated by the
iris (colored muscle surrounding pupil) which dilates or constricts in response
to light intensity (or emotions)
c. then the lens focuses the rays into an image on the eye’s light-sensitive back
surface (the retina which contains the rods and cones and neurons). It does this
through accommodation (lens changes curvature for focus)
Vision
2. The Retina and Transduction
a. The first layer of cells in the retina is
directly activated by light. The cells are
cones and rods arranged in a pattern
where the rods outnumber the cones
(around 20 to 1) and are distributed
throughout, and the cones are
concentrated toward the center or fovea
(retina’s area of central focus). Cones are
activated by color and rods respond to
black and white.
b. Light energy striking the rods and cones
produces chemical changes that generate
neural signals that activate bipolar cells
which activate ganglion cells
c. The network of ganglion cells converge
to form an optic nerve that carries
information to the brain where the
Vision
3. Primary Association
a. the thalamus sends the message to the visual cortices in the occipital lobe which
translates impulses into perceptual data
b. feature detector neurons in visual cortex receive information and respond to a
scene’s specific features
4.Secondary Associations
a. Feature detection cells pass information to other areas of the cortex where cells
respond to complex patterns like perceiving faces or houses
Color
Young-Helmholtz trichromatic theory: Three types of cones detect three wavelengths
of light ( blue, green, red).
Opponent- process theory: opposing retinal processes (red-green, yellow-blue) enable
color vision
Hearing
Stimulus: Vibrations/Soundwaves
Frequency - Rate in which a vibration occurs that constitutes a wave.
Loudness - A sound being characterized by the amount of volume and
intensity.
Pitch - The degree of highness or lowness of a tone.
Timbre - The character of quality of a musical sound or voice distinct
from it’s pitch and intensity.
•
•
•
•
Hearing
1. Acquisition
a. Soundwaves are received through the ear canal. First, the outer ear,
which collects and channels sound to the middle ear.
b. The middle ear turns the vibrations into a waves using the eardrum and
3 small bones. The sound vibrates the eardrum at the same frequency and
passes it onto the inner ear.
c. The inner ear turns the waves into nerve impulses through the inner ear
fluid which are then transferred to the brain to be perceived.
Hearing
2. Transduction
a. First transduction of the sound into a nerve signal is in the
cochlea, which is located in the inner ear.
b. In the inner ear, the stapes vibrates the oval window. The perilymph (an
extracellular fluid inside the cochlea), transfers the vibrations to the round
window.
c. The round window bulges when pressure rises and deflates as pressure
decreases. With all of the vibration the membranous labyrinth of the
cochlea encloses the scala media which has the the receptor organ called
the Corti.
Hearing
(Transduction continued, and Association)
d. Inside the Corti lay inner hair cells which are the auditory receptors.
The stereocilia of the hair cells are embedded into the tectorial
membrane.
e. When the stereocilia are pulled in the right direction, the hair
depolarizes; starting the nerve process to the auditory nerve then to the
temporal lobe of the auditory cortex.
f. Primary auditory cortex receives
the vibration info from the thalamus
and identifies pitch and loudness.
The secondary association site is the
frontal lobe.
Touch or Somatosensory
System
Touch is a mix of at least four distinct skin senses: pressure, warmth, cold, and
pain. Within the skin are different types of specialized nerve endings and more
than tactile stimulation is involved. We are more sensitive to an unfamiliar touch
or an unexpected one.
1. Acquisition: the epidermis is a barrier. The dermis holds blood vessels and the
nerves that give us our sense of touch. There are several types of receptors for
pain or temperature or others. A stimulus comes in contact with skin and
receptors are triggered
2. Transduction: a specific sensory neuron is triggered and the information is sent
to the part of the brain associated with that stimulus. This is different for pain or
pressure or other feelings.
3. Primary Association: Processing primarily occurs in the primary somatosensory
area in the parietal lobe of the cerebral cortex
Information is sent from the receptors via sensory nerves, through tracts in the
spinal cord and finally into the brain.
Touch or Somatosensory
System
Names
Function
Pacinian Corpuscle
(Mechanoreceptor)
Vibration Pressure
Receptor
Meissner’s
Corpuscle
(Mechanoreceptor)
Heavy Pressure
Receptor
Krause Corpuscle
(Thermoreceptor)
Cold Receptor
Ruffini Corpuscle
(Mechanoreceptor)
Skin Stretch/Heat
Receptor
Merkel Disks
(Mechanoreceptor)
Light Touch
Receptor
Pain
•
•
•
•
•
Alarm system that draws our attention to a physical problem
Biological, Psychological, and sociocultural influences on pain
Phantom limb sensations - brain can misinterpret nervous system activity
that occurs in the absence of normal sensory imput
Gate- control theory: spinal cord contains a neurological gate that blocks
pain signals or allows them to pass on to the brain. The gate is opened by
the activity of pain signals traveling up small nerve fibers and is closed by
activity in larger fibers or by information coming from the brain.
where body meets mind - treatable physically and psychologically
Taste
Stimulus: Food molecules
Fungiform papillae - large bumps on the tongue, receptor for taste.
The five acknowledged tastes are sweet, sour, salty, bitter, and umami.
Olfactory plays a large part in taste. What we perceive as taste is a
complex interplay of smelling and taste receptors on our tongue.
Olfactory - Sense of smell
It is a myth that different parts
of your tongue taste each
of the types of tastes.
•
•
•
•
•
Taste
1. Acquisition
a. From the taste buds in which you put the food, three nerves gather
information about the taste: the facial nerve, the hypoglossal nerve, and
the glossopharyngeal nerve.
b. At the same time, the molecules of the food is being processed by the
olfactory system (which we will get to in a minute).
2. Transduction and Association
a. The nerves transfer the data to the thalamus and on to the specific
area
on the cerebral cortex.
b. That in combination with the olfactory transduction and association
process makes up what we perceive as taste.
Smell
Stimulus: Odor Molecules
Olfactory Epithelium - Tissues within the nasal cavity that are responsible
for detecting odors.
Olfactory Receptors - Detects the odor and sends a nerve impulse to the
brain.
Olfactory Bulb - Structure found within the forebrain, helps with
perception of odor.
Nasal Cavity - Inside middle of your nose, lined with mucus.
Cilia - Moves with mucus up and down the nasal trap and collects dust
from the air.
•
•
•
•
•
Smell
1. Acquisition
a. Molecules of an odor enter through the nasal cavity when you breath.
the olfactory epithelium extends along the upper wall of the nasal
cavity
to the nasal septum while the epithelium dissolves odors with mucus.
b. Odors bind with proteins that are on the receptors in the nasal cavity.
Smell
2. Transduction and Association
a. From there, the proteins will cause the olfactory cell to generate a
nerve impulse which is sent to the olfactory bulb where the information
gathered from the receptors.
b. The information is then sent to the olfactory cortex in the temporal lobe
(more specifically the uncus, entorhinal areas). The olfactory bulb is
connected to the amygdala and the hippocampus.
Perception
Vocabulary:
Illusions - something that is/is likely to be wrongly perceived by the
senses.
Perceptual Adaptation - in vision, the ability to adjust to an artificially
displaced or even inverted visual field.
Perceptual Set - a mental predisposition to perceive one thing and not
another.
Extrasensory perception - reception of data not gained through the
recognized physical sense but with the mind itself.
•
•
•
•
Perceptual Organization
Early 20th century, a group of german psychologists noticed that when given
a cluster of sensations, we tend to organize them into a gestalt (whole,
form).
When seen alone, each circle simply looks like there are some random white
lines in them. But when seeing the
whole image you can see a cube, or
a “whole” or a “form”.
Sensation is not simply a bottom-up
process and perception is not simply
a top-down process. Sensation and
perception blend into a continuous
process.
Perceptual Interpretation
Perceptual adaptation: ability to adjust based on differences that the subject may
witness, particularly alterations in the visual field. For example, if an individual's
visual field is altered forty five degrees left, the brain accounts for the difference
allowing the individual to function normally.
Perceptual set: a mental predisposition to perceive one thing and not another. For
example, we are more likely to perceive two people as looking alike if we are
previously told that they are related.
Context also affects perception. Lew Kulechov showed this in his experiment on how
film evokes emotion. He created three short films with one of three contexts
followed by an actor with neutral expression. The audience was struck by the actor’s
sadness in the film where a woman died. When the actor was eating, they thought
the actor seemed thoughtful. When the actor was playing with children, they
perceived him as happy.
Extrasensory Perception?
Denotes psychic abilities such as telepathy, clairaudience, and clairvoyance.
Also referred to as “the sixth sense”. The study of ESP and other psychic
phenomena is called parapsychology. Because of lack of evidence, theory,
and experimental techniques that can provide reliable results, ESP is
considered a pseudoscience.