The Nature of Sensation

• Question to consider: How is light or sound converted into a message to the brain?

• The Basic Process• Sensory Thresholds• Subliminal Perception• Extrasensory Perception

The Nature of Sensation

• Sensations– Raw senses, the actual experience– What are your 5 senses?

• Perceptions– Giving meaning to raw data

The Basic Process

• Receptor cell– Specialized cell that responds to energy

• Now for the sensory process…

The Basic Process• Energy (light waves,

sound vibrations, airborne chemicals, etc.) stimulate a receptor cell

• If the energy is strong enough, the message goes to your brain

• Each sensory organ “invades” the brain on a different channel

The Basic Process

• Hard part…• Signals carried by optic nerve NOT

“visual” - we cannot see them• Signals carried by the auditory nerve

are NOT “audible” - we cannot readily hear them

• These signals produce an experience we interpret, or perceive, as visual or audible in the brain

The Basic Process

• Johannes Müller discovered this one-to-one relationship– Stimulating a

specific nerve produces a specific perceptual experience

– He called this the doctrine of specific nerve energies

Stop, Drop, Test it Out!

• Close your eyes. No, I’m not joking!• Now gently press on your eyelids• What did see?!• Perhaps a flash of light?!

• This tells us that the optic nerve carries signals to the brain caused by more than just light waves– The brain interprets pressure as

visual

The Basic Process

• Quick test: How would your brain interpret a stream of water trickling into your ear?– AS SOUND!!!– The auditory nerve would be stimulated

and your brain would hear

Sensory Thresholds

• Absolute threshold– Minimum amount of energy required to

produce a sensation– Point at with people can detect a stimuli

50% of the time

Sensory Thresholds

• The threshold for each sense is LOW!– Taste: 1 gram salt in 500 liters of water– Smell: 1 drop perfume in 3-room apt.– Touch: Wing of beam falling on cheek

from height of 1 cm– Hearing: Tick of a watch 20 ft away

(only when quiet)– Vision: Candle flame from 30 miles

away on a clear night

Sensory Thresholds

• Sensory adaptation– When your sensory threshold changes– Your senses adjust to the amount of

stimulation

• Example: When you walk in a dark room, can you immediately see?– No– But, as you remain in the room your

eyes adjust

Sensory Thresholds

• Difference threshold– Also called the JND– Smallest change in energy that can be

detected 50% of the time

• Example: You are holding 1 lb, 15 lbs are added, will you notice?

• However… You are holding 15 lbs, 1 lb of weight is added, will you notice?

Sensory Thresholds

• The difference threshold is proportional– A 2% change of

weight is necessary to notice a change

– This is called Weber’s law

Subliminal Perception

• Can we respond to stimuli that are below the absolute threshold?

WHAT????

Subliminal Perception

• People CAN be influenced by information they are not consciously aware of– Seen in laboratory studies– Does NOT mean people are

brainwashed by advertisements, music, or self-help tapes

– Outside of labs, subliminal messages seem to be ineffective marketing tools

Subliminal Perception

• Links to try!– http://www.youtube.com/watch?v=U16J2

2QsFT8– http://www.youtube.com/watch?v=PVrOF

t-0-e0&feature=related– http://www.youtube.com/watch?v=Ng6h

QfGzQig&feature=related– http://www.youtube.com/watch?v=2NPK

xhfFQMs

Extrasensory Perception

• You probably know this as ESP– A response to an unknown event not

presented to any known sense• Parasychology

– Field of psychology that analyzes ESP and psychic phenomenon

• Not yet proven to exist

Extrasensory Perception• Clairvoyance

– Aware of an unknown object or event– Example: You just know the missing card

must be under the area rug• Telepathy

– Knowledge of another person’s thought or feelings

• Precognition– Foreknowledge of future events– Example: You are positive that NH

football team will win the homecoming game 14 to 6