Sensation
 Approximate Absolute Thresholds
 Subliminal Perception
 Main Senses
 Perception

True or False?
T/F People have five senses.
T/F If we could see waves of light with slightly longer
wavelengths, warm-blooded animals would glow in the dark.
T/F People sometimes hear what they want to hear.
T/F Some people can read other people’s minds.
The brain senses the world indirectly because the sense organs
convert stimulation into the language of the nervous system:
neural impulses.
Phi Phenomenon
Sensation and Perception Defined
Sensation:
 The detection of physical energy emitted or reflected
by physical objects.
 Sense Receptors:
 Specialized cells that convert physical energy in the environment
to chemical and electrical energy in the body.
Perception:
 The process by which the brain organizes and
interprets sensory information.
Transduction:
 Transformation of stimulus information into
nerve impulses (electrical).
Sensation
Absolute Threshold:

Smallest quantity of physical energy that
can be reliably detected by an observer.
Difference Threshold: (Just Noticeable Difference)

Smallest difference between two stimuli that can be reliably
detected by an observer.
Weber’s Law:
 Thresholds increase in proportion to the background.
 When you are in a noisy environment you must shout to be
heard while a whisper works in a quiet room.
Sensation
Signal Detection Theory:
 Divides a sensory signal into two processes:
 Sensory process
 Decision process

After receiving a weak stimulus you will:
 Hit: Detect a signal that was there.
 False Alarm: Says the signal was there when it was not.
 Miss: Fail to detect a signal when it was present.
 Correct Rejection: Correctly say the signal was absent when it
was not there.
Approximate Absolute Thresholds





Vision:
 Candle flame seen from 30 miles on a clear, dark night.
Hearing:
 Tick of a watch from 20 feet in very quiet conditions.
Smell:
 Drop of perfume diffused throughout a three-room
apartment.
Taste:
 .0356 ounce of table salt in 529 quarts of water.
Touch:
 Bee wing falling on your cheek from a height of 1
centimeter.
Sensation

Sensory Adaptation:
 Reduction or disappearance of sensory responsiveness that
occurs when stimulation is unchanging or repetitious.
 Brain responds more readily to new stimuli.

Sensory Deprivation:
 Absence of normal levels of sensory stimulation.
 Selective Attention protects us from sensory overload○ Not capable of fully processing all incoming sensory
information.
○ We focus attention on selected aspects of the environment
and block out others.
Subliminal Perception

Definition: Below threshold.
 We can process some information from stimuli too weak to
recognize.

Effect of Subliminal Stimulation: A subtle, fleeting
effect on thinking.
Does subliminal advertising work?
 No. The goal of using subliminal
advertising is to increase the
likelihood that you will buy a
particular product.
Main Senses
Main Senses: (theoretical)
1.
Visual
2.
Audition
3.
Tactile (touch)
4.
Gustation (taste)
5.
Olfactory
6.
Proprioception (kinesthetic in parietal)
7.
Immunological
Vision
Why are we so dependent on our visual sense? Would we be
as advanced as we are today without it?
Fun Facts:
 More information comes from our eyes than any other
senses.
 Our eyes see through visible light.
 Our eyes pick up these light waves.
 Color itself is not a property of the external world.
 It is derived from the wavelength of visible light.
Colorblindness
Prevalence: One out of twelve men and one out of two hundred
women.
 Protanomaly (one out of 100 males): Red-weakness,
Deuteranomaly (five out of 100 males): Green-weakness,
Dichromasy
 Monochromats: People who are totally colorblind.
 Dichromats: People who are blind to either red-green or
yellow-blue.

Colorblindness
Vision

Humans:
 Lack certain pigments found in
primate eyes. (our sclera is
white)
 Contrast in color between our
facial skin, sclera and irises.

Gorillas:
 Low contrast between their
eyes and facial skin.
Afterimages :
Sensations that linger after the stimulus is removed.
Fix your eyes on the dot in the center of the flag.
Trichromatic Theory
There are three types of cones: red, green, and blue.
 The colors we see are the result of a combination of the differing
amount of light absorbed by the three types of cones.

Rods: Dim light. (better with edges and curves)

Concentrated in the periphery.
Cones: Color vision. (very poor at night)

Concentrated in the fovea.
Ganglion cells:

Neurons in the retina of the eye.

Gather information from receptor cells.
Path from Eye to Visual Cortex
light
photoreceptors
LGN
bipolar cells
visual
cortex
ganglion
cells
Vision

Cornea



Optic Nerve


Responsible for sharp central vision.
Necessary for reading, TV, driving.
Any activity where visual detail is important.
Pupil



Provides color to the eye.
Fovea




Transports sensory material to optic chiasm.
Iris


Transparent front part of the eye that
covers the iris, pupil, and anterior chamber.
Refracts light and aids in focusing.
Black circular/slit opening in the center of the iris.
Regulates the amount of light that enters the eye.
Retina


Back of eye.
Contains receptors.
Gestalt Principles of Perception
Principles that describe the brain’s organization of sensory information
into meaningful units and patterns.
Proximity:

Things near each other are grouped together.
Closure:

The brain will fill in gaps in order to make a whole.
Similarity:

Things that are alike are perceived as belonging together.
Continuity:

Lines and patterns are perceived as continuing in
time and space.
Gestalt Principles of Perception
Perceptual Set:
 Readiness to detect a particular stimulus in a given context.
Gestalt Principles of Perception




Law of Pragnanz
Figure-Ground Organization
Isomorphism
Laws of Perceptual Grouping
Gestalt Principles of Perception
The Herman Grid
Figure-Ground Distinction


Figure: Entity perceived to stand apart from the
background.
Ground: Background against which a figure
appears.
Perceptual Constancies

Size constancy
 The perception of an object as the same size
regardless of the distance from which it is viewed.

Shape constancy
 Tendency to see an object as the same shape
no matter what angle it is viewed from.

Brightness constancy
 We perceive an object as having a constant lightness
even while its illumination varies.

Color constancy
 An inclination to perceive familiar objects as retaining
their color despite changes in sensory information.
Perceptual Cues
Superposition

Monocular distance cue in which one object,
by partially blocking another, is perceived as being closer.
Linear Perspective:

Two parallel lines appear to converge at the horizon.
Elevation:

The higher on the horizontal plane an object is, the farther away it appears.
Depth Perception (seeing in 3D)
Monocular cues: Depth cues requiring only one eye.
 Binocular cues: Depth cues requiring both eyes.

Hearing
Fun Facts:
 Sense of hearing never turns off at one time or another.
 Cerebellum
 Uses the fluid in the cochlea ( part of the semicircular canals) to aid in
balance.
 Organ of Corti (pronounced: cortee):
 Structure in the cochlea containing hair cells that serve as the receptors for
hearing.
 Sensory receptors called hair cells
turn air pressure changes into
neural signals.
Major Divisions: External, Middle, Inner
Decibel Level for Common Sounds
Auditory Pathway
eardrum
cochlear
middle
ear
oval
window
organ of
Corti
Hearing
If a tree falls in a forest and no one is
around to hear it, does it make a sound?
Tactile
Fun Facts:

We have more pain nerve endings than any other type.

The least sensitive part of your body is the middle of your back.

The most sensitive areas of your body are your Hands, Lips, Face, Neck, Tongue, Fingertips, Feet

Shivering is a way your body has to get warm.

There are approximately 100 touch receptors in your fingertips.
Taste
Fun facts:

Your sense of taste can replace itself.

Single taste bud contains 50-100 taste cells

Each taste cell can represent all 5 taste sensations.

Taste buds are the structures on the tongue that contain taste receptor cells.

An adult has about 10,000 taste buds.

Taste receptors die and are replaced every 7 days.

The number of taste buds decrease with age.
Taste:

The ability to respond to dissolved molecules and ions called tastants.

Detect taste with taste receptors clustered in taste buds.
Taste
Five primary taste sensations:
I.
Salty-helps an animal suffering from Na+ deficiency.
II.
Sour-detects acids in food.
III. Sweet-detects glucose in food.
IV. Bitter-typically defective or rotten compounds.
V.
Umami-glutamic acid salts such as MSG.
Anatomical Pathway
taste
buds
medulla
primary
somatosensory
cortex
thalamus
anteriorinsular
cortex
Olfaction
Olfaction:

Sense of smell
Olfactory bulbs:

Brain sites of olfactory processing
Pheromones:

Chemical signals released by organisms to
communicate with other members of the species.
Detecting Odors:

Odorant binding protein (OBP) makes the detection of odors possible.

A nasal gland coats airborne molecules with OBP to facilitate detection by
the receptors in the olfactory epithelium.
Variations in Odor Sensitivity



Women have a better sense of smell than men.
The ability to smell diminishes with age.
Smell acuity is greatest during early adulthood (ages 20-40).
Pheromones
Pheromones are chemicals produced by an animal that affects the
behavior of another animal through scent.
 Receptors in the vomeronasal organ detect pheromones.

Proprioception
Defined:
 The movement of arms and legs in relation to each other.
Kinesthetic Sense:
 Provides specific information about muscle movement, changes in posture,
and strain on muscles and joints.
 Receptors: stretch receptors and Golgi tendon organs (provide information
about stretching and contraction of individual muscles).
Vestibular Sense
o
The sense of equilibrium and awareness of body position in space.
o
2 types of vestibular senses:
— body rotation
— gravitation and movement
Immunological
Immune System:
 Process in an organism that identifies and removes antigens
by identifying items that are non-self.