Mechanisms of
Perception
Prepared by: Ace Alvin Lopez
Sensation V.S. Perception
While our sensory receptors are
constantly collecting
information from the
environment, it is ultimately
how we interpret that
information that affects how we
interact with the world.
Sensation and perception
are two separate processes that
are very closely related
•Sensation-input about the
physical world obtained by our
sensory receptors. It is a physical
process
•Perception- the process by which
the brain selects, organizes, and
interprets these sensations. It is a
psychological process
Sensation
• Sensory receptors are
specialized neurons that
respond to specific types of
stimuli.
• When sensory information is
detected by a sensory
receptor, sensation has
occurred
•Transduction- the conversion
from sensory stimulus energy
to action potential
Perception
•Perception- the way sensory
information is organized,
interpreted, and consciously
experienced
•It involves two types of
processing:
•Top-down processing
•Bottom-up processing
•Bottom-up processing-refers to
the fact that perceptions are built
from sensory input
•Top-down processing- how we
interpret those sensations is
influenced by our available
knowledge, our experiences, and
our thoughts
Factors that affect
Perception
•Sensory adaptation
•Attention
•Motivation
• Signal detection theory
•Beliefs, Values,
Prejudices, Expectations
and Life Experiences
• Müller-Lyer illusion
•Personality
Principles of Sensory
System Organization
• The sensory areas of the
cortex are considered to be of
three fundamentally different
types: primary, secondary,
and association.
•Primary sensory cortex- an
area that receives most of its
input directly from the
thalamic relay nuclei
•The interactions among these
three are characterized by
three major principles: (1)
hierarchical organization,
(2) functional segregation,
and (3) parallel processing.
Hierarchical Organization
• Sensory systems are
characterized by hierarchical
organization
• Sensory structures are
organized in a hierarchy on the
basis of the specificity and
complexity of their function.
• Implication of this organization
to the effects of damage to
various levels.
Functional Segregation
• It was once assumed that the
sensory areas of the cortex
were each functionally
homogenous.
• Functional segregation-
each levels of the cerebral
cortex contains functionally
distinct areas that specialize
in different kinds of analysis.
Parallel Processing
• It was once believed that
different levels of sensory
hierarchy were connected in a
serial fashion.
• Parallel systems- systems in
which information flows through
the components over multiple
pathways.
• It features parallel processingthe simultaneous analysis of a
signal in different ways by
multiple parallel pathways of a
neural network.
• There appear to be two
fundamentally different
kinds of parallel streams of
analysis:
1.one is capable of
influencing our behavior
without conscious
awareness
2. one that influences our
behavior by engaging our
conscious awareness.
Summary Model of Sensory
System Organization
•
Sensory systems are
characterized by a division of
labor. Multiple specialized
areas, at multiple levels, are
interconnected by multiple
parallel pathways.
•
Binding Problem
Visual System
The Visual System
• The visual system constructs a
mental representation of the
world around us.
• This contributes to our ability to
successfully navigate through
physical space and interact with
important individuals and
objects in our environments
How does the Visual
System works?
• In the human visual
system, the eye
receives physical
stimuli in the form of
light and sends those
stimuli as electrical
signals to the brain,
which interprets the
signals as images.
Anatomy of the Human Eye
Parts of the Eye
• The sclera- the white part of
• The pupil- an opening where
• The cornea and lens- are like
• The choroid-
• The iris-the colored part of
• The ciliary muscle-
the eye; functions as a
structure where the eye
muscles for movement are
attached
a tag-team as they bend light
(refraction) together, focusing
it on the retina
the eye
light enters; able to dilate (open
wide) in a dim light
environment or constrict
(narrow) in bright light
provide
nourishment to the outer layers
of the retina through blood
vessels
used to
change the shape of the lens
Parts of the Eye
• The retina- the part where
electromagnetic energy is turned into
neural energy; transduction is possible
through photoreceptors
• Cones- light detecting cells; acuity,
spatial resolution, & color perception
• Rods- involved in our vision in dimly lit
environment
• The fovea- tiny pit; provides the clearest
vision of all.
Visual Pathway
•Light enters the Eye and
reach the Retina
• Light reflected in your eyes
are basis for vision
•Light-
waves of
electromagnetic energy
between 380- 760
nanometers in length.
•Properties of light:
wavelengths (color) and
intensity (brightness)
• Light enters the eye through the
opening of the iris which is the
pupil
• Light is focused by the lens
(adjustable) and cornea (not
adjustable) and projected onto
the retina.
• Light from the left side of the
world strikes the right side of the
retina and vice versa
• Light from above strikes the
bottom half of the retina and vice
versa
•Adjustment of pupil size:
• In response to changes in
illumination
•Sensitivity- ability to detect
the presence of dimly lit
objects
•Acuity-
ability to see the
details of objects.
•Adjustment of lens:
• In response to changes in
distance of an object
•Near objects- lens assumes
natural cylindrical shape;
increases its ability to refract
light
•Far objects- lens is flattened
•Accommodation- process of
adjusting the configuration o
lenses to bring the images into
focus in the retina
•The Retina and Translation of light
into Neural Signals
• After light passes and reaches the
retina, it converts light to neural
signals and conduct them towards the
CNS
•Five layers of the retina:
• Receptors ( rods and cones)
• Horizontal cells (lateral
communication)
• Bipolar cells
• Amacrine cells (lateral communication)
• Retinal ganglion cells
•Retina has an inside-out
arrangement
• Two visual problems:
• Distortion of incoming light
•Blind spot
• Solutions for visual problems:
•Fovea- minimizes the first
visual problem
•Completion - filling in for the
blind spot.
Visual Receptors: Rods and
Cones
• Vertebrae retina contains two
types of receptors
(photoreceptors):
•Rods- abundant in the
periphery of the human
retina; respond to faint light;
not useful in daylight
because it bleaches them.
•Cones-
abundant in and
near the fovea, are less
active in dim light; essential
for color vision
•
Because of the distribution of
rods and cones, you have good
color vision in the fovea but not
in the periphery.
•
Cones provide 90% of the brains
input even if rods outnumber
cones.
•
Reason:
•
Each cone has its own line to
the brain ( fovea)
•
Rods shares a line with tens or
hundreds ( periphery)
Human Foveal and
Peripheral Vision
Characteristic
Foveal Vision
Peripheral Vision
Receptors
Cones
Proportion of Rods
increases toward
periphery
Convergence of input
Each Ganglion cell
excited by a single
cone
Each Ganglion cell
excited by many
receptors
Distinguishes among
Responds well to dim
Brightness sensitivity bright lights; responds
light
poorly to dim light
Sensitivity to detail
Good detail vision
Poor detail vision
Color Vision
Good (many cones)
Poor (few cones)
Color Vision
• Visible light consists of
electromagnetic radiation
within the range of less than
400 nm and more than 700
nm
• We perceive the shortest
visible wavelengths as violet
• Progressively longer
wavelengths are perceived as
blue, green ,yellow,
orange, and red.
Color Vision
•Black is experienced when
there is an absence of light.
•White is produced by an
intense mixture of a wide
range of wavelengths in
roughly equal proportions
•Gray is prodded by the same
mixtures at lower intensities.
•The correct term for colors is
hues.
QUESTION:
What is there about a visual
stimulus that determines the color
we perceive?
ANSWER:
To a large degree, the perception of an object’s
color depends on the wavelengths of light that it
reflects into the eye.
However, outside the laboratory, one never
encounters objects that reflect single
wavelengths.
The Trichromatic (YoungHelmholtz) Theory
• First proposed by Thomas
Young
• He recognized that color
required a biological
explanation
• He proposed that we
perceive color by comparing
the responses across few
types of receptors
• Modified by Hermann von
Helmholtz
The Trichromatic (YoungHelmholtz) Theory
• We perceive color through the
relative rates of response by
three kinds of cones, each one
maximally sensitive to a
different set of wavelengths.
•Trichromatic-
three colors
•Question: How did Helmholtz
decide on number 3?
•Answer: He found out that
people could match any color by
mixing appropriate amounts of
just three wavelengths
The Trichromatic (YoungHelmholtz) Theory
• Three kinds of receptors (cones) are
sufficient to account for human
color vision.
• We discriminate among wavelengths
by the ratio of activity across the
three types of cones.
• The perception depends on the
frequency of response in one cell
relative to the frequency of another
cell.
• Long and medium-wavelength cones
are far more abundant than shortwavelength cones
Let’s have an
activity!
I need six volunteers
The Opponent- Process
Theory
• The trichromatic theory is
incomplete as a theory of color
vision.
• Activity: Do the afterimage
activity
• Proposed by Ewald Hering
• We perceive color in terms of
opposites.
• The brain has a mechanism that
perceives color on a continuum
from red- green; yellow-blue;
white-black
The Opponent- Process
Theory
• After you stare at one color in
one location long enough, you
fatigue that response and tend
to swing to the opposite
• Part of the explanation for this
process pertains to the
connections within the retina.
The Retinex Theory
QUESTION: “ If we
change our light bulbs
into red and blue light,
will the color of our
classroom and
everything in it change
also in color?"
The Retinex Theory
Why do you think colors will stay the same
even if we change the color of the light
source?
•
Color constancy- ability to recognize
colors despite changes in lighting.
•
is an example of subjective constancy
and a feature of the human colour
perception system that ensures that the
perceived colour of objects remains
relatively constant under varying
illumination conditions
The Retinex Theory
Colour is one of the most important
aids for recognition of objects. But
the level and colour of the
illumination may vary widely.
The human vision system is highly
efficient at compensating such
changes and, as a result of this
adaptation, the perceived colour of
the object remains approximately
constant.
The Retinex Theory
• Your brain compares the color of one
object with the color of another, in
effect subtracting a certain amount of
green from each.
• Similarly, we perceive the brightness of
an object by comparing it to other
objects
The Retinex Theory
• Retinex theory of color vision-
accounts for both color and brightness
constancy
• The cortex compares information from
various parts of the retina to
determine the brightness and color for
each area
•
the color of an object is determined
by its reflectance- the proportion of
light of different wavelengths that a
surface reflects
The Retinex Theory
• visual perception requires reasoning
and inference, not just retinal
stimulation.
Color Vision Deficiency
• Color deficiency results when people
with certain genes fail to develop one
type of cone, or develop an abnormal
type of cone
• In red-green color deficiency, the most
common form of color deficiency,
people have trouble distinguishing red
from green because their long- and
medium- wavelength cones have the
same photopigment instead of
different ones.
•From Retina to Primary
Visual Cortex
• Many pathways carry visual
information
•Retina-geniculate-striate
pathways- most thoroughly
studies.
•Conduct signals from each
retina to the primary cortex
via lateral geniculate
nuclei
•About 90% of axons of retinal
ganglion cells become part of
the retina-geniculate-striate
pathways
• All signals from the left visual
field reach the right primary
visual cortex either
ipsilaterally (from the
temporal hemiretina of the
right eye) or contra laterally
(via the optic chiasm from the
nasal hemiretina of the left
eye)
• Each lateral geniculate nucleus
has six layers ( each layer of
each nucleus receives input
from all parts of the
contralateral via field of one
eye)
• Most of the lateral geniculate
neurons that project to the
primary visual cortex terminate
in the lower part of the cortical
layer IV producing stripe or
striation when viewed in
cross section, hence the name
striate cortex.
The M and P Channels
• At least two parallel channels of
communication flow through each
lateral geniculate nucleus
•Parvocellular layers (P layers)-
composed of neurons with small cell
bodies
•Responsive to color, fine
pattern details, stationary or
slow moving objects
•Magnocellular layers (M layers)composed of neurons with large
bodies
•Responsive to movement
• The primary visual cortex is located in the
posterior region of the occipital lobes
• Secondary visual cortex:
• Prestriate cortex
• Inferotemporal cortex
• Association cortex
• Posterior parietal cortex
Damage to Primary Visual Cortex:
Scotomas and Completion
● Damage to an area of the
primary visual cortex produces a
scotoma
● Perimetry test
● Many patients with extensive
scotomas are not consciously
aware of their deficits.
● One of the factors that
contributes to this lack of
awareness is completion.
Damage to Primary Visual Cortex:
Scotomas and Completion
● Conscious awareness
● Blindsight- ability of patients
with scotomas to respond to
visual stimuli in their scotomas
even though they have no
conscious awareness of the
stimuli.
● Of all visual abilities, perception
of motion is most likely to survive
damage to primary visual cortex.
Prosopagnosia
● Is also considered as visual
● agnosia for faces
● Agnosia- is a failure of
recognition that is not
attributable to a sensory deficit or
to verbal or intellectual
impairment
● Visual agnosia is a specific
agnosia for visual stimuli
● It is presumed that damage to an
area of secondary visual cortex
that mediates the recognition of a
particular attribute results to
agnosia
Akinetopsia
● Akinetopsia is a deficiency in
the ability to see movement
progress in a normal smooth
fashion.
● it can be triggered by high doses
of certain antidepressants
● It is often associated with
damage to middle temporal (MT)
area of the cortex. The location
of MT- near the junction of the
temporal, parietal and occipital
lobes.
Auditory System
Physics and Psychology of
Sound
•Sound waves- are periodic compressions of
air, water, or other media.
•Varies in amplitude and frequency
•Amplitude- is the sound wave’s intensity
(loudness)
•Frequency- the number of compressions per
second (pitch)
•Sound is measured in Hertz. Humans hear a
range from 20 Hz to 20, 000 Hz.
• Children hear higher frequencies than adults because
the ability to perceive high frequencies decreases with
age and exposure to loud noises.
•Timbre- means the tone quality or tone
complexity
• Makes a particular musical sound different from
another
• People communicate emotion by alterations in pitch,
loudness, and timbre.
•Prosody- conveying emotions information by tone of
voice.
“That was interesting”
Structure of the Ear
• Three parts of the ear:
•Outer Ear
•Middle Ear
•Inner Ear
Outer Ear
•Pinna- structure of flesh and
cartilage attached to each side
of the head
•Helps us locate the source of
sound ( reflector and
attenuator)
•Auditory canal- passage way
•Tympanic membrane-
vibrates at the same frequency
as the sound waves that strike
it.
Middle Ear
• Composed of three small
bones (ossicles)
• Connects tympanic membrane
to oval window
•Hammer ( malleus)
•Anvil (Incus)
•Stirrup (Stapes)
Inner Ear
•Liquid filled. That is why a conversion
of low pressure to higher pressure is
needed.
•Cochlea-
a snail-shaped structure.
•Where sound waves are transformed
to electrical signals ( transduction)
•Contains three long fluid-filled
tunnels: (a) scala vestibuli; (b)
scala media; (c) scala tympani
•Organ of Corti-
composed of hair cells
( transduction). It forms the auditory
nerve.
•Auditory nerve (hearing)
& vestibular
nerve (balance) forms the
Vestibulocochlear nerve
Pitch Perception
• Your ability to understand
speech or enjoy music
depends on your ability to
differentiate among
sounds of different
frequencies
•“How do you do it?”
•Place theory- the basilar
membranes resembles the
strings of a piano. Each area
along the membrane is tuned
to a specific frequency.
•Each frequency activates the
hair cells at only one place
along the basilar membrane
•Nervous system distinguishes
among frequencies based on
which neurons respond.
•Frequency theory- the basilar
membrane vibrates in synchrony
with a sound, causing auditory nerve
to produce action potentials at the
same frequency
•Example: a sound at 50 Hz would
cause 50 action potentials per
second in the auditory nerve
•Downfalls of both theories:
• place theory- various parts of the
basilar membrane are bound
together too tightly for any part to
resonate like a piano
• Frequency theory- the refractory
period of a neuron is typically about
1/1000 second so the maximum
firing rate of a neuron is 1000 Hz.
• The current theory is a
modification of both theories
• In low-frequency sounds (up
to 100 Hz) , the basilar membrane
vibrate in synchrony with the
sound waves ( frequency theory)
• As sound exceed 100 Hz, it
becomes harder for a neuron to
continue firing in synchrony with
the waves.
• Each wave of a high-frequency
tone excites at least a few
auditory neurons.
•Volley principle of pitch
discrimination- groups of
neurons respond to a sound by
firing AP slightly out of phase with
one another so when combined, a
greater frequency can be encoded
and analyzed
•auditory nerve as a whole produces
volleys if impulses for sounds up to
about 4000 per second.
•Most human hearing takes place
below 4000 Hz ( e.g. highest C
octave in the piano)
• When we hear higher
frequencies, we use a
mechanism similar to the place
theory
• Basilar membrane varies from
stiff at its base and apex at
the end of the cochlea.
• Hair cells along the basilar
membrane have different
properties based on their
location
•Amusia (tone deafness)- impaired
detection of frequency changes
•Although not entirely tone-deaf, they
generally do not detect a change in
sound ( e.g C vs. C sharp)
•Have a hard time recognizing tunes,
singing off-key, “wrong” note in a
melody
•Have trouble gauging people’s mood
from tone of voice.
•Have no trouble imitating one’s
intonation.
•Reason: Pitch information reaches
some parts of the brain but not in
others
• Amusia has a genetic basis.
• People with amuse have a
thicker than average auditory
cortex in the right hemisphere
but fewer than average
connection from it to the
frontal cortex
• When they here two tones that
slightly differ, the brain’s initial
response is the same with
other people but they fail to
process the information further
•Absolute pitch (perfect pitch)-
ability to hear a note and identify
it.
•Factors that contributes to
absolute pitch:
•Genetic predisposition
•Early musical training
•Absolute pitch is also more
common among people who
speak tonal languages ( e.g.
Vietnamese and Mandarin
Chinese)
The Auditory Cortex
• Information from the auditory system
passes through subcortical areas, axons
cross over in the midbrain to enable each
hemisphere of the forebrain to get most
of its input from the opposite ear
•Superior temporal cortexauditory cortex (A1)
primary
• Auditory system has a “what”
pathway (anterior temporal
cortex) sensitive to patterns
of sounds; “where”
pathway (posterior temporal
and parietal cortex) sensitive
to sound location
• Damage in parts of the
superior temporal cortex
become motion deaf
• A1 responds to imagined
sounds as well as real ones.
• Development of the auditory
system depends on experience.
• Damage to area A1 does not
produce deafness
• People with damage to A1 have
trouble with speech and music
but they identify and localize
single sounds reasonably well.
• The cortex is not necessary for
hearing, just for processing the
information.
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Hearing Loss
• Although few people are
totally insensitive to all
sounds, man people have
enough impairment to reduce
or prevent speech
comprehension.
•Conductive deafness
(middle-ear deafness)- caused
by diseases, infections, or
tumorous bone growth by
preventing the middle ear from
transmitting sound waves to
the cochlea.
•Nerve deafness (inner-ear
deafness)- results from
damage to the cochlea, hair
cells or the auditory nerve.
•It can be inherited, result from
diseases or exposure to loud
noises
•Tinnitusthe ears.
frequent ringing in
Somatosensory
System
Somatosensory System:
Touch and Pain
• Sensation from your body are
referred to as somatosensations.
• Mediates bodily sensations
• Three separate interacting systems:
•Exteroceptive system- senses
external stimuli applied to skins
•Proprioceptive system-
monitors information about
position of the body
•Interoceptive system-
provides general information
about conditions within the body
Somatosensory System:
Touch and Pain
• This discussion deals most
exclusively with the
exteroceptive system
• Three divisions:
•Mechanical stimuli
(touch)
•Thermal stimuli
(temperature)
•Nociceptive stimuli (pain)
Cutaneous Receptors
Receptor
Location
Responds to
Free nerve ending
Near base of hair and
elsewhere in skin
Pain, warmth, cold
Hair-follicle receptors
Hair-covered skin
Movement of hairs
Hairless areas
Sudden displacement of skin;
low-frequency vibration
Pacinian corpuscles
Both hairy and hairless skin
Sudden displacement of skin;
high-frequency vibration
Merkel’s disks
Both hairy and hairless skin
Light touch
Ruffini endings
Both hairy and hairless skin
Stretch of skin
Krause end bulbs
Mostly or entirely hairless
areas (including genitals)
Uncertain
Meissnner’s
corpuscles
Dermatomes
• Neural fibers that carry information from cutaneous
receptors and other somatosensory receptors gather
together in nerves and enter the spinal cord via the
dorsal roots.
• Dermatome- area of the body that is innervated by
the left and right dorsal roots of a given segment of
the spinal cord
• Considerable overlap between adjacent dermatomesdamage produces little somatosensory loss.
Two Major Somatosensory
Pathways
•Dorsal-column medial-leminiscus
system- tends to carry information about
touch and proprioception
•Anterolateral system- tends to carry
information about pain and temperature
•The key words in the preceding sentence
are “tends to”
• Implications of damage on these areas
• If both ascending somatosensory paths are completely
transected by a spinal injury, the patient can feel no
body sensation from below the level of cut.
• When it comes to spinal injury, lower is better.
• Research by Mark, Ervin, and Yakolev (1962) on
“effects of lesions to the thalamus on chronic
pain of patients in advanced stages of cancer”
• Results:(1) lesions to the ventral posterior nuclei
produced loss of cutaneous sensitivity ( touch,
temperature and sharp pain) but not to deep
chronic pain; (2) lesions to parafascicular and
intralaminar nuclei reduced deep, chronic pain
without disrupting cutaneous sensitivity.
Cortical Areas of
Somatosensation
• Penfield and colleagues ( 1937) mapped the
primary somatosensory cortex of patients during
neurosurgery. (electrical stimulation to cortical
surface)
• When stimulation was applied to the post central
gyrus, the patients reported somatosensory
sensations in parts of their bodies
•Somatosensory homunculus
Cortical Areas of
Somatosensation
• Somatosensory homunculus is distorted
• The greatest proportion of SI is dedicated to
receiving input from the body that we use to make
tactile discriminations (e.g., hands, lips, and
tongue)
• Only small areas of SI receive input from large
areas of the body (e.g., back) which are not used to
make somatosensory discriminations.
Effects of Damage to the
Primary Somatosensory Cortex
• Effects of damage to the primary
somatosensory cortex are often
remarkably mild- because of
numerous parallel pathways.
• Research: “ the somatosensory abilities
of epileptic patients before and after a
unilateral excision that included SI”
• Results: minor deficits; reduced ability to
detect light touch and identify objects by
touch.
Somatosensory Agnosias
• Two major types of
somatosensory agnosia:
•Astereognosia-
inability to
recognize the objects by touch
•Asomatognosia-
failure to
recognize parts of one’ own
body.
Pain
•Pain,
the experience evoked
by a harmful stimulus, directs
your attention toward a
danger.
•The prefrontal cortex
(attention) typically responds
only brief to any new light,
sound or touch
•With pain, it continues
responding as long as the pain
lasts.
Stimuli and Spinal Cord
Paths
• Pain sensation begins with
the least specialized receptors
(bare nerve ending)
• Axons carrying pain
information have little or no
myelin ( slow conduction; 2
to 20 m/s)
•Thicker and faster axons
convey sharp pain
•Thinner ones convey dull
pain (post-surgical pain)
• Motor responses to pain are
faster than motor responses
to touch stimuli.
•Mild pain releases the
neurotransmitter glutamate
•Stronger pain releases
several neuropeptides
including substance P and
CGRP ( calcitonin generelated peptide
Emotional Pain
• Pain stimuli also activate a
path that goes through the
reticular formation of the
medulla then to several of the
central nuclei of the thalamus,
amygdala, hippocampus,
prefrontal cortex and cingulate
cortex
• These areas react not to
sensation but to its
emotional associations
• If you watch someone in pain, you experience sympathetic pain
• A hypnotic suggestion to feel no pain decreases the
responses in the cingulate cortex without much effect on
the somatosensory cortex
• Hurt feelings do resemble physical pain
• Research : “Virtual-ball tossing game”
• Results: People’s brain activity increased in the cingulate cortex
(emotional aspects of pain)
• More intense hurt feelings increases activity in both emotional
areas ( especially cingulate cortex) and sensory areas
( responsive to physical pain)
• Hurt feelings are like real pain in another way: you can receive
it with pain-relieving drugs
Ways of Relieving Pain
•
Insensitivity to pain is
dangerous
•
People with a gene that
inactivates pain axons suffer
repeated injuries and generally
fail to learn to avoid dangers
•Opioids and endorphins
•
After pain alerts you to a danger, continuing pain messages are
unnecessary
•Opioid mechanismssimilar chemicals
systems that respond to opiate drugs and
•The discovery was important:
•Opiates act on the NS rather than the injured tissue
•It implies the that the NS has its own opiate-type chemicals
•Endorphins- relieve different types of pain (pain from cut v.s. burn);
released during sex or when listening to thrilling music
•Gate theory- spinal cord neurons that receive messages from pain
receptors also receive input from touch receptors and from axons
descending from the brain; these other inputs can close the “gates”
for pain messages
•Placebos
• A drug or other procedure with no pharmacological effects
• People who receive placebos do not jut say the pain
decreased, scans of the brain and spinal cords also show a
decreased response.
• Conversely, if someone is told to expect pain to increase ,
the spinal cord response to a painful stimulus does increase
•Cannabinoids and capsaicin
•Cannabinoids- chemicals related to marijuana also blocks
certain kinds of pain; act mainly on the periphery of the
body.
•Capsaicin-
a chemical in jalapeños and similar peppers
that stimulates receptors for heat.
Itch
• Have you ever wondered “
What is itch anyway?”
• It is a separate sensation
(special receptors and special
spinal cord paths)
• Itch pathways are slow to
respond
• Itch is useful because it directs
you to strict the itchy area ad
remove whatever is irritating
your skin
Active Touch
• Your sense of touch operates
over time. Your brain is sensitive
to overall patterns of cutaneous
input that may be quite complex.
When you rub your fingertips
(which are particularly rich in
cutaneous receptors) over a
surface like cloth, plastic, or
wood, the distinct texture of the
surface depends on activity from
thousands of touch receptors
firing in sequence and in
combination. This is
called active touch and is used,
for example, in reading Braille.
Let’s have an activity!