Sensation and Perception
Sequence: sensation, transduction, perception
Sensation—activation of the receptors by stimuli in the environment.
Mueller’s Law of Specific Nerve Energies—Each receptor is designed
to receive certain types of stimuli. But, under certain
circumstances, receptors can receive other types of stimuli (touch
Perception—(based on learning and expectations) how we interpret
information. Process of organizing and making sense of sensory
Transduction—taking stimulus and putting it in a form that can travel to the
Adaptation—reduced sensitivity of the receptors. If the outside environment
is not changing, sensory receptors don’t continue to send as much
information. (ex. Perfume--You notice it; they don’t. Food—better at first.
Living near a sewage treatment plant. Dive right in. Ring. Glasses)
Habituation—similar to adaption. But, Habituation occurs in the brain, and
adaption occurs in the receptors. (Elevated train doesn’t wake you, but
baby’s cry does. Lack of elevated train noise could wake you)
Psychophysicist—study the relationship between the mind and the body.
Absolute threshold—smallest amount of stimulation that we can
register 50% of the time.
o Vision: a candle flame at 30 miles on a clear, dark night
o Audition: tick of a watch at 20 feet in a quiet room
o Olfaction: 1 drop of perfume diffused throughout a 3-room
o Gustation—One teaspoon of sugar in two gallons of water
o Touch—the wing of a bee falling on your cheek from 1 cm.
Just notable difference—the amount you must add before a change
can be detected
o Psycophysics—sometimes, we can change the physics but the
human brain can’t detect it (volume increase)
o Weber's law: ΔI/I = K (where I is intensity and K is Weber’s
K) Ex. For brightness, if Weber’s K = 1/60, change from
120 to 121 is undetectable. Change from 120 to 122 is.
Ex. Buying a car, an armani suit, wedding chair covers.
After a large cost, a little more cost doesn’t seem that
Signal Detection Theory—Contention that the threshold varies with
the nature of the stimulus (signal) and with background stimulation
Receiver Operating Characteristics—Likelihood of false negatives
and false positives?
Supraliminal Vs. Sub
` liminal Stimuli
o Supraliminal is above absolute threshold. Subliminal is
below, so you don’t notice you are receiving the stimuli.
o Subliminal messaging is attempted often.
James Vickary (1950s New Jersey) insert ―buy coke‖
―eat popcorn‖ statements into film. Reported ―eat
popcorn‖—popcorn sales increased 58%, coke sales
increased 18%. However, he made this story up to
draw attention to his theatre.
Satanic messages in music. Play song backwards.
Jabberwocky and the 23 psalm.
Subliminal Self Help Tapes—change a bad behavior
o Greenwald Research
Double blind (researchers who have contact with the
subject don’t know what tape the subject is given and
neither do subjects)
Motivated participants (paid)
Pre and Post measures
Two tapes: improving memory and increasing self
Subject given memory and self-esteem pre-test.
Listen to tape once a day for a month (hear ocean and
subliminal message. Some are given tape they want
some are given opposite)
Tapes had no effect on memory or self-esteem; didn’t
matter if they had correct tape or other tape
They believed that they had improved
Illusory Placebo—they believed that it worked even
when there wasn’t even a real placebo effect.
o Priming—might push you in a particular direction
Subjects: Psychology graduate students Task: Generate research ideas
IV: ―shown‖ a smiling face of a familiar colleague
or scowling face of faculty supervisor
DV: Lower rating of own ideas if exposed to
Task: Complete GUI_ _
Likely responses: guide or guile
Subliminal priming can affect outcomes
Subliminally shown ―Direct lead escort‖
Outcome is more likely ―Guide‖
Subliminally shown ―deceit treachery
duplicity‖ Outcome is more likely ―Guile‖
Most people would least like to lose vision. This is the brain’s
answer. More of the brain is devoted to vision than any other sense
The Adequate Stimulus (per Mueller’s law): Electromagnetic energy
o Waves range from long (radio) to short (gamma).
o Visible Spectrum (Roygbiv)–detectable by the human eye.
Length measured in nanometers. Between 380 and 760
nm. Determines Hue/color. Red=longest,
Amplitude determines intensity/brightness
Saturation determines purity.
o Radiant light—visible light is emitted directly by an object
(few sources of radiant light. Includes sun and light bulbs)
o Reflected light—light reflected by objects
o If an object absorbs all light waves, it appears black. If it
reflects all light waves, it appears white
o If an object reflects only one wavelength, you perceive pure
color. Degree of purity decreases as the number of
wavelengths reflected increases.
o Weber’s K (just noticeable difference) = 1/60 for brightness
o Anatomy of the eye
Cornea pupil lens retina
Iris—colored section. Basically a muscle. Can contract
or dilate pupil to let in more/less light.
Pupil—opening in eye.
Primary Purpose: Lets light in/adjusts amount of
light let in. Secondary Purpose: Indicator of interest
(Research by Hess showing male college students
playboy centerfolds). Dilates to show interest.
Retina—light-sensitive tissue at the back of the eye.
Contains rods and cones.
Rods—receptors for black and white. ~100
million. Lower threshold (so less light is required
to activate them). Lower acuity (sharpness of
Cones—receptors for color. ~5 million. Higher
threshold. Higher acuity.
When light strikes rods or cones it causes a
chemical reaction, hyperpolarizes rods and
cones, and diminishes their inhibitory
influence on the bipolar cells
Fovea—point in the middle of the retina that
contains the greatest number of cones. (Look
straight ahead to see color because center of eye
(fovea) contains most cones. Peripheral vision is
more black and white)
o Relatively rare in mammals. Some lower animals see color
(Primates, fish, birds, reptiles)
o Trichromatic theory—explains color processing in the cones.
Trichromats see all colors in visibile spectrum (because
it takes 3 types of cones to se all colors).
There are 3 different cones that are each most
sensitive to one of the primary colors. Primary
colors or red, blue, green?
Dichromats have 2 working kinds of cones (has
difficulty distinguishing between 2 colors). Color-
Monochromats see no color. (either don’t have other
types of cones or cones don’t work) Actually color blind.
o Opponent-process theory—explains color processing in bipolar
cells, thalamus, and cortex. Stresses that activation on one
process inhibits another (like red and green).
o Color afterimage—perception of color that is not really
present. Occurs after viewing a complementary color.
o Color Vision Deficiency vs. Color Blindness
Assessment: Ishihara Test for Color Blindness
(misnomer, because it tests Color Vision Deficiency)
Color Blindness: Achromatopsia Causes of Color Deficiency: Diabetes, Glaucoma,
Alzheimer’s, Parkinson’s, Multiple Sclerosis, medications
(high blood pressure, infections, psychological
disorders), aging, chemical exposure (fertilizer, styrene)
May not know they are color deficient.
Color Deficiency: 8% in males, .5% in females (often
females are carriers)
Most common form of CD is Red-Green (has trouble
telling difference between Red and Green)
Less Common: Blue-Yellow
Difficulties: weather maps, traffic lights, clothing,
cooking (raw vs. well done, green tomatoes vs. red
tomatoes, ketchup vs. chocolate syrup)
Adequate Stimulus: Vibrating molecule
o Frequency measured in Hertz: pitch (inversely correlated to
o Timbre (purity)
o Amplitude measured in decibels (50 is normal conversation)
Every time db goes up by 10, it doubles. Measures intensity
o Receptors: hair cells located in inner ear
o We hear sounds between 20 and 20,000 Hz.
Hearing is most accurate ~1,000 Hz. Greater
intensities are required to hear sounds on either end of
Absolute threshold: ticking of a watch at 20 feet
Weber’s K is 1/10 for loudness
o time delay (occurs when