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=U16J22QsFT8

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

– http://www.youtube.com/watch?v=Ng6hQfGzQig&feature=related

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

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